RU2349932C2 - Method of defining radioactive medicine distribution inside examined object, and device for method implementation - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: method involves measurement of radiation intensity of radionuclide inside object through multifissure collimator 7 by strip detector 9 mounted beside collimator output, with collimator input oriented towards object 12, at various angular positions of collimator-detector system 11 against object, and obtainment of radiation intensity data set similar to computer tomography, with further application of reconstruction algorithm to data set and visualisation of reconstruction result. Device includes fissure collimator 7 with input oriented toward object 12 under examination, radiation intensity strip detector 9 mounted at collimator output, first rotation device 15 for detector-collimator system rotation around longitudinal axis 14 of object under examination, second rotation device 16 for detector-collimator system 11 rotation around axis 25 perpendicular to longitudinal axis of object under examination, measurement device 18 for output signals of radiation intensity strip detector, measurement data storage and processing device (22, 20) and processing result visualisation device 21.

EFFECT: enhanced precision of reconstruction of radioactive source distribution inside examined object, or reduced examination time or inserted radionuclide.

8 cl, 15 dwg

Description

The invention relates to methods and devices for determining the distribution of a radioactive drug inside a test object and can be used in medical diagnostics and non-destructive testing methods. Both for visualization of two-dimensional (on the plane of the detector), and three-dimensional distribution of a radioactive preparation inside the studied object.

The aim of the invention is to reduce the cost of the device and improve the accuracy of determining the distribution of the radioactive drug inside the test object.

A known method for determining the distribution of a radioactive preparation within the studied as an image of this distribution according to US patent 3,684,886 (publ. 1972.08.15) [2], US patent 4,090,080 (publ. 1978.05.16) [3], US patent 4,563,583 (publ. 1986.01 .07) [4], US patent 6,627,893 B1 (publ. 2003.09.30) [5], US patent 6,631,285 B2 (publ. 2003.10.07) [6]. The method consists in measuring the radiation intensity of the drug through the slotted collimators with a coordinate sensitive detector located at the outputs of the slotted collimators, the inputs of which are directed towards the object under study. Measurements are made for various angular positions of the collimator-detector system, obtaining a data set similar to computed tomography, to which some processing algorithm is applied (for example, the inverse Radon transform [3]), and an image of the distribution of the radioactive preparation inside the object is obtained.

The advantage of this measurement method relative to the classical method of measurement through a narrowly directed collimator [1] is the high efficiency of gamma quanta registration through slotted collimators. The disadvantage, as in [1], is the need to use coordinate sensitive detectors in devices for implementing the method (for example, in the form of an Angers camera [2] or strip detector [3]), the manufacture of which is of a certain complexity and leads to an increase in the cost of the device.

Implementations of the method of a strip detector based on a scintillator and a photomultiplier connected to it through an optical coordinator are not effective, as indicated in [3] and [4], and the use of cadmium telluride [4] when implementing the method leads to a rise in the cost of the detector in these devices.

To reduce the cost of the device when implementing the method, it was proposed to use short strips [5] and [6] on cadmium telluride instead of long strips, but this leads to a decrease in the efficiency of radionuclide radiation registration, since the strip area is significantly reduced.

A cardinal solution to reduce the cost of a device that implements the method would be to use an inexpensive strip detector or reject a coordinate-sensitive detector in general, since a coordinate-insensitive detector is much cheaper than coordinate-sensitive. However, no such technical solution was proposed.

In addition, when implementing the method for obtaining images with high spatial resolution, a strip detector of high spatial resolution and a slit collimator with a small pitch between the slots are required. The production of strips of equal sensitivity and collimators with transparency identical for all slots seems problematic, and apparently, no technology will allow to produce absolutely identical slits and strips, which will lead to the appearance of ring artifacts in the resulting image of the radionuclide. The occurrence of ring artifacts associated with inaccuracy of strips and slots of the collimator is also not mentioned in the indicated technical solutions [3-6]. In this regard, in the known technical solutions [3-6] there are no methods for eliminating artifacts associated with different transparency of cracks and sensitivity of strips. No methods have been proposed for measuring the transparency of the collimator slits and strip sensitivity.

However, in the known technical solutions [3-6], it is proposed to compensate for other distortions of the result of three-dimensional reconstruction, for example, associated with the 1 / r weight function, by tilting the plates of the multi-slit collimator, or by algorithmic methods. An analysis of these solutions [3-6] suggests that they are not the only possible ways to compensate for these distortions associated with 1 / r. When using other collimators or other measurement methods, it is apparently possible to compensate for these distortions by other approaches.

This assumption is based on the fact that the use of a collimator in the form of a set of plates is not the only possible for the indicated measurement method and devices implementing it.

To eliminate these drawbacks, it is necessary to modify the measurement method, collimators, device design and measurement data processing algorithms.

The size of the strip detector in the known technical solutions [3-6] is smaller than the size of the investigated object. When reconstructing a two-dimensional image, a problem arises, known in computed tomography as an incomplete data set. The presence of an incomplete data set distorts the result of reconstruction, especially at the edges of the studied area.

Known technical solutions [3-6] do not propose methods to compensate or reduce distortions associated with an incomplete data set at the edges of the studied area when obtaining two-dimensional images.

In well-known technical solutions [3-6], data processing uses an increment of a function to evaluate its derivative. Using increment instead of derivative reduces reconstruction accuracy. Using a more accurate method for estimating the derivative, especially in noise, would improve the accuracy of the final result.

The proposed technical solution proposes a number of approaches to address these shortcomings.

Figure 1 shows a device that implements various approaches to address these disadvantages.

Improvements regarding the detector-collimator system and the collimator proper are shown in FIG. 2 - FIG. 10. To reduce the cost of the device when implementing the method, it is proposed to use a set of scintillation fibers (Figure 2, position A) of the desired cross-section and length, to the ends of which are attached highly sensitive PIN photodiodes or simply photodiodes of the required area, or a line of photodiodes.

The use of a line of photodiodes for constructing a strip detector is known [3], however, in the known technical solution, they are attached not to the ends, but to the side of the scintillator through an optical matching device, which reduces the efficiency of the detector and increases its height. When creating a large area detector, the height may be unacceptably large.

In the known technical solution [4], many thin optical fibers were used to transmit light flashes from scintillator strips to photomultipliers. However, the optical fibers themselves are not scintillation. The use of scintillation fibers is not considered.

In the proposed solution, individual thin scintillation fibers are laid so that the thickness of the scintillator is formed, which is necessary for the effective absorption of radiation of a given energy. The width of the set is arranged so as to obtain the spatial resolution and width of the detector of the desired value (Figure 2, position A).

Similar designs of structured scintillators are used in modern digital x-ray detectors. However, the scintillator length in these devices usually does not exceed a fraction of a centimeter and is determined by the absorption efficiency of the radiation. In the proposed technical solution, the length of scintillation fibers (columns) can be tens of centimeters and meters and is determined by the required length of the strip. The absorption efficiency of radiation is determined by the thickness of the set of scintillation fibers. In addition, the radiation on the structured scintillator in known technical solutions acts from the end of the fiber, while in the proposed technical solution, the radiation falls across the fiber in order to implement the strip detector mode (Fig. 2, positions A and B).

In the proposed solution, it is also possible to use one long scintillator (for example, from cesium iodide CsI) of the required cross section and length for each strip, instead of a set of tables of micron section, which will not affect the operability of the proposed technical solution. The walls of the scintillator in this case should have either a mirror or a diffuse reflector. To the ends of the scintillator should be attached, as before, photodiodes (Figure 2, position B).

Other options for structured scintillation strips are possible, for example, through the use of a capillary filled with a liquid scintillator or a set of capillaries (polycapillary). In any case, in order to implement the strip detector mode, the ratio of length to thickness of such a structured scintillator must be much larger than in the known structured scintillators.

Thus, a distinctive feature of the present invention under this item is the use of a structured scintillator, the ratio of the length of which to its thickness is much greater than unity.

To compensate for the attenuation of light flashes inside a long scintillator, the well-known attenuation compensation scheme in the scintillator material [13] can be applied (for example, by multiplying the signal from two photodiodes mounted on opposite ends of the scintillator), which allows for high energy resolution, and if necessary ( if, in addition to the multiplier, you use a divider, the output signal of which characterizes the coordinate of the flash) provides some spatial resolution along the sc ntillyatora [13]. If the properties of the scintillator are such that the attenuation of light flashes in the scintillator material is negligible, then the attenuation compensation scheme can be dispensed with.

Using the proposed technical solution, it is possible to create a strip detector of a large area, small thickness and low cost, compared, for example, with a detector based on cadmium telluride. Since the line of photodiodes and scintillators based on cesium iodide or plastic scintillators are quite cheap materials. The length of the strips can be very large (tens of centimeters and meters). In contrast to technical solutions [3] using a line of small-area cadmium telluride detectors, the proposed detector will have a large area and, therefore, high radiation detection efficiency.

The ability to create a detector with high detection efficiency is very important in medical applications, since it allows either to reduce the time of the study or to reduce the amount of radionuclide administered.

In addition, such a detector can be made small in thickness and uncooled, which is important when building the device.

A more radical way to reduce the cost of the device is to use a coordinate-insensitive detector as a strip detector (Figure 3). In this case, a large area scintillator is used, equal in area to the strip detector, and a large area photodetector (photomultiplier), connected together and forming a large area radionuclide radiation detector. Between this coordinate-insensitive large-area detector and a multi-slit collimator, a screen of material is placed whose transparency for radionuclide emission is inhomogeneous along the direction perpendicular to the collimator slits. This screen is connected to a means ensuring its linear movement along a direction perpendicular to the slots of the collimator.

As a result of the screen movement, a signal arises at the output of a large-area detector, which is determined by the operation of mathematical convolution of the desired signal (planar integral) and the distribution of inhomogeneity in the screen. To obtain the required initial undistorted signal (planar integral), it is necessary to perform the operation of inverse mathematical convolution. This mathematical problem was solved by academician Tikhonov and belongs to the class of inverse incorrect problems [9].

In practice, measurements are made at discrete points in time, and the inverse problem must be solved in a discrete form. The time interval through which measurements are taken determines the spatial resolution that this strip detector will have, since all measurements are made in time when the screen moves.

This approach allows the use of a coordinate-insensitive detector as a strip detector.

Despite the fact that with this approach it is possible to use almost any heterogeneity in the screen, it is important to maximize the signal-to-noise ratio under noise and discrete measurements. The solution to this problem under discrete measurement conditions is known on the basis of arrays with flat side lobes and one maximum in the autocorrelation function - URA arrays [10].

These arrays consist of ones and zeros, such as 10100111001 ... Their implementation in practice requires only making holes in a screen that is opaque to radionuclide radiation, which can be made of a material with a high atomic number (lead, tungsten, etc.). Such material is heavy in weight, and the means for its linear movement must be powerful enough.

Figure 4 shows a strip detector based on a scintillator and a large area photodetector, between which there is an optical screen containing an inhomogeneity for optical radiation (scintillator radiation) with inhomogeneity properties similar to a screen for radionuclide radiation. In this case, the weight of the optical screen can be minimal, since it can be made, for example, from black thick paper, foil and plastic. It is possible to use other materials, which is not fundamental. The optical screen, as before, must be connected to a means of moving it.

Figure 5 shows a strip detector based on a scintillator and a large area photodetector, between which there is an optical moving screen in the form of a flexible ring enclosing the scintillator. The screen moves constantly in one direction (like a conveyor belt), reciprocating movements are excluded. The device is as simple and light as possible. The optical screen, as before, is connected to a means of moving it.

However, optical spatio-temporal modulators, for example based on liquid crystals, are currently known. Using them, you can eliminate the mechanical movement of the screen. The optical transparency of the modulator should change in time in such a way as to produce a result similar to the motion of the optical screen, i.e., the signal at the output of the photodetector should be determined as the result of mathematical convolution of the desired signal (plane integral) and screen inhomogeneity.

Figure 6 shows a strip detector based on a scintillator and a large area photodetector, between which there is an optical spatio-temporal modulator. As a spatio-temporal optical modulator, you can use liquid crystal optical modulators used in projection televisions, or large-area liquid crystal optical modulators used in flat passive computer monitors. The spatio-temporal modulator is connected to its control means.

If it is required to coordinate the size of the scintillator and the coordinate-insensitive photodetector, an optical coordinator (focon) can be installed between them. In this case, the spatial optical modulator should be installed before or after the optical matching device, in accordance with the dimensions of the modulator (the optical matching device is not shown in FIG. 6).

The specified technical solution can be used both with a parallel arrangement of the plates in the collimator, and with convergent and divergent. If we restrict ourselves to a divergent collimator, the technical solution can be further simplified and, accordingly, the device can be even cheaper. In the divergent case, it is possible to use a radionuclide radiation detector in the form of a single strip and a moving screen, without using a multi-slot collimator.

7 shows a strip detector for a divergent case based on one strip and a moving screen. The screen is connected to a means of moving it.

The registration efficiency will be similar to the case of using a large-area detector and the moving screen indicated earlier. This is explained by the fact that the scintillator acts as an integrator of flashes coming from all directions (as in the case of a large-area detector). Moreover, the integrator in the divergence case can be made in the form of a single strip. In this case, the device is simpler and therefore cheaper compared to a large area detector. The nature of the signal at the output of such a detector will be similar to the signal described earlier, that is, it is the operation of mathematical convolution of the desired signal (planar integral) and the distribution of the inhomogeneity in the screen. To obtain the desired signal (planar integral), it is necessary to perform the operation of inverse mathematical convolution [9].

When the length of the strip is minimal (for example, equal to its width and height), the device is very cheap. In this case, a small piece of scintillator attached to the photodiode is actually used. However, if a strip of short length is used, then the efficiency of detecting radiation will be low. Therefore, despite the fundamental possibility of using a short strip, it is advisable to use a long strip. A short strip can be used when the radiation intensity of the radionuclide is high enough.

In that case, if you use a rotating drum as a screen, inside of which one strip is coaxially located. The drum is connected to its rotation means. The device becomes as simple as possible (Fig. 8).

As before, you can use a short strip. Despite the fundamental possibility of using a short strip, it is advisable to use a long strip. A short strip can be used when the radiation intensity of the radionuclide is high enough.

For efficient detection of high energy gamma quanta (more than 100 keV), the scintillator cross section in strip detectors (Fig. 7 and Fig. 8) should be sufficiently large. However, with a large cross section of the scintillator, the spatial resolution in the reconstructed image decreases. To ensure both high detection efficiency and high spatial resolution, the indicated strip detectors use a scintillator of the required cross section (for efficient registration of quanta of the required energy) and a lead “shirt” around the scintillator with a longitudinal slit of the required width.

Fig. 9 (positions A and B) shows a cross-section of a scintillator combined with a "jacket" of protection for a strip detector based on one strip. The width of the slit in the "shirt" determines the required spatial resolution, and the opening angle of the slit determines the area of the object covered by the detector. In position A, the opening angle of the gap is smaller than in position B, while the width of the gap is the same in both positions.

The use of such a technical solution, in addition to the main purpose, can dramatically reduce the weight of the protective "shirt", which can be significant when creating mobile devices. This is true for the technical solution shown in Fig.7, and Fig.8.

However, the use of a protective "shirt" is necessary in all the previously mentioned technical solutions, but the place of its position and purpose are well known, therefore, it is not shown in the figures explaining other technical solutions. Protection is shown where its position and purpose is not well known.

To eliminate the influence of factor 1 / r on the reconstruction result, the strip is shifted relative to the axis of rotation of the detector-collimator system by an angle δ proportional to the required spatial resolution in the reconstructed image and ranging from 0 to 5 degrees.

Both of these technical solutions based on Fig. 7 and Fig. 8, in addition to reducing the cost of the device and eliminating the influence of factor 1 / r, also solve the problem of the influence of the transparency of the slits of the multi-slit collimator on the final reconstruction result, since the multi-slit collimator is simply missing.

However, the influence of a multi-slit collimator can be avoided for the divergent case by using a detector consisting of many strips, without using a moving screen, by eliminating the multi-slit collimator itself.

In order to eliminate the influence of different transparency of the slits of the multi-slit collimator for the divergent case, it is proposed to use the collimator in the form of a separate long slit parallel to the strips of the detector and made in an opaque screen installed at some distance in front of the detector (Figure 10). In this case, the slit itself is shifted relative to the axis of rotation of the detector-collimator system by an angle proportional to the required angular resolution, ranging from 0 to 5 degrees. This allows us to solve the problem of eliminating the influence of 1 / r distortion simultaneously with eliminating the influence of transparency of the collimator slits.

It should be noted that the use of a plurality of fixed slots displaced relative to the axis of the object under study together with strip detectors is known [12], but they are located at a distance relative to the axis of rotation of the collimator-detector system, which is much higher than 5 degrees, and this value does not proportional to the required spatial resolution. This bias is determined by the desire to simultaneously measure multiple projections, rather than compensate for distortions of the multi-slit collimator and type 1 / r distortions in the resulting image. In addition, slots and detectors are stationary relative to the object under study.

In the proposed technical solution, the detector-collimator system is connected to means for moving (rotating) it around its axis.

The use of a single slit and the absence of a multi-slot collimator, in addition to the indicated advantages, can also reduce the cost of the device, since the cost of its manufacture is much less than the multi-slot.

The specified single-slot collimator can also be used when implementing a strip detector based on a coordinate-insensitive large-area detector and a moving screen (Fig. 3, Fig. 4, Fig. 5, Fig. 6). Its location in this case relative to the axis of rotation and orientation are similar to those previously indicated.

The meaning of the well-known mathematical concepts used is explained below:

"Convolution" (direct aperiodic convolution).

In direct aperiodic convolution, instead of the value of the aperiodic function I (x) at the point x, its weighted average value C (x) is used in the range from minus to plus infinity, and another function H (x) is used as the “weight”. In analog form, such a convolution is described by the convolution integral, in a discrete form, such convolution is described by the sum.

"Reverse convolution" (inverse aperiodic convolution).

In reverse aperiodic convolution, instead of the value of the aperiodic function C (x) at point x, its weighted average value I (x) is used in the range from minus to plus infinity, and another function H ^-1 (x) is used as the “weight”.

The function H ^-1 (x) is chosen in such a way as to compensate for the effect of direct aperiodic convolution, that is, to obtain an undistorted value of the function. In analog form, such a convolution is described by the convolution integral, in a discrete form, such convolution is described by the sum. Such a procedure is also called deconvolution.

"Cycle convolution"

In cyclic convolution, instead of the value of the cyclic (periodic) function I (x) at point x, its weighted average value C (x) is used in the range of the repetition period, while another cyclic function with the same repetition period is used as the "weight".

"Reverse loop convolution."

In the reverse cyclic convolution, instead of the value of the cyclic function C (x) at the point x, its weighted average value I (x) is used in the range of the repetition period, and another function H ^-1 (x) is used as the “weight”.

The function H ^-1 (x) is chosen in such a way as to compensate for the effect of direct cyclic convolution, that is, to obtain an undistorted value of the function. In analog form, such a convolution is described by the convolution integral, in a discrete form, such convolution is described by the sum.

"Direct Radon Transformation."

The direct Radon transform is reduced to the translation of the function I (x, y) from the Cartesian coordinate system to the coordinate system of the angular projections of this function P (Q, s), where Q is the angle at which the projection of the function is obtained, s is the coordinate along the projection.

In analog form, such a transformation is described by the integral equation, in discrete form by the sum.

A clear example of the direct Radon transform is the acquisition of x-ray images of an object from different directions around the object.

"The inverse Radon transform."

The inverse Radon transform reduces to the translation of the function P (Q, s) from the coordinate system of the angular projections into the Cartesian coordinate system I (x, y). In analog form, such a transformation is described by a complex integral equation, in discrete form - by a specific sum.

A good example of the inverse Radon transform is the acquisition of a tomographic image of a patient in medical computed tomography based on a set of X-ray projections obtained from various angles.

The mathematical foundations of the invention

1. Elimination of the influence of factor 1 / r in three-dimensional reconstruction.

The mathematical relations given in the three-dimensional reconstruction are valid both for the case of using a separate slit as a collimator, and for the case of a single strip and a moving screen. In both cases, a geometry equivalent to the divergent collimator arises. However, in the first case, the signal at the output of each strip represents directly a planar integral, and in the second case, the planar integral is obtained only after the reverse convolution operation.

We assume that the value of the planar integral is already measured in one way or another. We show how the distortions of type 1 / r in the reconstructed image are compensated for when the focal point of the “collimator” deviates from the rotation axis 25 by an angle δ.

On figa shows the projection of the integration planes on a plane parallel to the axis of rotation 25, for the rotation angle θ and rotation angle θ + 180 ° of the detector-collimator system 11. The letter a denotes the integration plane for the "extreme strip", the letter b denotes the integration plane for "n-th strip." The integration plane without shifting the focal point is indicated by 50, the integration plane by shifting the focal point by δ is indicated by 51, the integration plane by shifting the focal point by -δ is indicated by 52.

11B shows an isometry of the integration planes for the “n-th strip”.

For a divergent collimator, the value of the planar integral g (δ), in the local coordinate system tied to the "n-th" strip (Fig. 11B), when the focal point deviates from the axis of rotation of the detector-collimator system by an angle δ is equal to δ

where f () is the function of the three-dimensional distribution of the radionuclide 42 inside the investigated object 12.

The value of the planar integral g (-δ), when the focal point deviates from the axis of rotation in the other direction by an angle -δ in the local coordinate system, is

If the difference between these two values g (δ) and g (-δ) is multiplied by a constant

determined by the angle δ of the deviation of the focal point from the axis, we obtain the following relation

which can be rewritten as

The difference

can be interpreted as an approximation of the partial derivative of the function f (), with respect to the variable δ multiplied by a constant equal to

at the same time considering that

Then, taking into account the fact that in the Cartesian coordinate system the partial derivative can be taken out from under the integral sign

the difference for two planar integrals at opposite angles δ can be rewritten as

whence it is clear that this difference does not contain a term proportional to 1 / r and approximates the first derivative of the direct Radon transform of the function ∫∫f (r, α, ω)) rdrdα. At the same time, it is known [10] that in order to obtain the inverse Radon transform it is necessary to carry out the operation of “inverse” projection of the second derivative of the plane integral

to the area of three-dimensional reconstruction.

Thus, calculating the difference of planar integrals for two opposite angles of deviation of the focal point from the axis of rotation, we obtain the first derivative, free from the influence of the factor 1 / r.

After calculating the difference of the planar integrals, we recompute the data into parallel geometry [4], then we calculate the second derivative from the first derivative and perform the “back projection” operation, as a result of which we obtain a three-dimensional reconstruction of the desired value, free from the influence of the 1 / r factor.

In conclusion, we add that:

but. the focus for the single-slot (pinhole) collimator from the mathematical point of view is where the slot is located,

at. the focus for one strip and a moving inhomogeneous screen from the mathematical point of view is where the strip is located.

Therefore, in order to eliminate the influence of factor 1 / r in three-dimensional reconstruction, in the first case it is necessary to shift the gap, and in the second case the strip itself relative to the axis of rotation of the detector-collimator system by angle δ.

1. Accurate calculation of derivatives

An analysis of expression (10) to eliminate the distorting factor 1 / r shows that the increment of the function is used as an estimate of the derivative. But this also leads to certain distortions. The most obvious nature of the distortion can be seen in the frequency domain (Fig).

Using the increment of a function as its derivative leads to a “blockage” of low frequencies in the estimation of the derivative and, as a result, to a distortion of the reconstruction result. This is clearly seen in Fig. 12, which shows the amplitude-frequency characteristics of the increment operator - Fig. 12 (A) and the differentiation operator - Fig. 12 (B).

To eliminate the difference between the increment operator and the differentiation operator, it is necessary to multiply the Fourier image of the increment function by the Fourier image of the correction function in the frequency domain

where f '() is the desired first derivative of the function,

F ^-1 [] - the operator of the inverse Fourier transform,

F [] is the direct Fourier transform operator,

Δf () is the increment function obtained by subtracting measurements for two opposite focal point offsets,

K (Ω) - Fourier image of the correction function.

where D (Ω) is the Fourier transform of the differentiation operator,

K (Ω) is the Fourier transform of the increment operator.

Moreover, as the Fourier transform of the differentiation operator D (ω), it is not necessary to use the “pure” differentiation shown in Fig. 12 (B). It is possible to use various "regularizing" options [6] to improve the accuracy of reconstruction - Fig. 12 (C), the essence of which is reduced to some smoothing of the reconstruction result.

The first derivative obtained in this way will allow reconstruction to be performed with the elimination of the 1 / r factor and without “blocking” the low frequencies in the reconstructed image.

Similarly, after rearranging the data from fan geometry to parallel [4], the second derivative should be calculated using not the increment, but the differentiation operator.

Moreover, as the differentiation operator, it is also possible to use not pure differentiation — FIG. 12B, but various regularization options — FIG. 12C, as in the calculation of the first derivative. Evaluation of the second derivative, especially in noise, will become more accurate, the reconstruction accuracy will improve.

3. Two-dimensional reconstruction

In the proposed technical solution, in addition to three-dimensional reconstruction, it is possible to carry out two-dimensional reconstruction of the three-dimensional distribution of the radionuclide on the plane of the detector for all variants of the technical solution. In this case, the plane integrals are projected onto the detector plane in the form of lines, and the reconstruction from plane integrals proceeds to the reconstruction of linear integrals. In this case, the reconstruction is performed for the inverse Radon transform for linear integrals and "parallel geometry". The term "parallel geometry" is well-established and is widely used in transaxial tomography.

In our case (Fig. 1), this transformation is reduced to obtaining a set of projections R _θ (x ') of plane integrals on the plane of the detector for various angles θ of rotation of the detector-collimator system

where I (x, y) is the projection of the three-dimensional distribution of the radionuclide on the plane of the detector.

The axes x 'and y' are defined by turning the angle θ counterclockwise in the plane of the detector perpendicular to axis 25:

with subsequent restoration of the image of the projection of the three-dimensional distribution of the radionuclide on the plane of the detector from the set of projections, that is, obtaining the inverse R ^-1 Radon transform [6], which in the operator form can be written as

where D _y is the partial derivative operator with respect to the first variable;

H _y is the Hilbert transform operator;

B is the back projection operator.

For a more detailed description of the direct and inverse Radon transforms for linear integrals with parallel geometry, refer to the source indicated earlier [6]. There you can find several discrete options for the implementation of the inverse Radon transform for parallel geometry, usually called reconstruction algorithms [6] and used in digital computers.

It is important to note here that planar integrals (and their linear projections) contain a distorting factor proportional to 1 / r, so the resulting two-dimensional reconstructed image will also contain this factor. You can put up with this, believing that for the two-dimensional case this is unprincipled, since all layers of the three-dimensional distribution are stacked "in one pile" as in an x-ray. The only difference from the X-ray image is that the “contribution” of each layer depends on the distance at which the layer is from the plane of the detector. But you can not put up, believing that two-dimensional reconstruction can be used further in obtaining a three-dimensional restoration result. In this case, the influence of factor 1 / r must be eliminated. After eliminating the 1 / r factor, two-dimensional reconstruction will be similar to a conventional x-ray, where there is no 1 / r effect.

This problem can also be solved as for the three-dimensional case, using the difference of two measurements (increment of the function), carried out at different angles of bias of the focus of the collimator. However, for the two-dimensional case, the first derivative is required, and not the second, which follows from the analysis of the inverse Radon transform for linear integrals.

Using the function as the first derivative will lead to a “blockage” of low frequencies in the reconstructed image, which was noted in the section concerning the calculation of derivatives. Therefore, in order to eliminate distortions of the “blockage” type of high frequencies, one should use the techniques described in the section on calculating derivatives.

4. Reduced distortion associated with an incomplete data set.

In addition to the 1 / r factor indicated earlier, another distorting factor may arise in the reconstruction, due to the fact that the strip detector cannot “capture” the entire object, the edges of the object do not fall into the field of view of the detector. Such a situation arises when the strip detector is smaller than the size of the object, or when a convergent collimator is used [3-6]. From a mathematical point of view, such a situation is known as nonzero boundary conditions in the projection or an incomplete data set [6]. The resulting distortions in the reconstructed image are mainly associated with the “jump” of the derivative in those places where the data breaks off.

It is fundamentally impossible to completely eliminate the effect of lack of data on the reconstruction result. However, the effect of distortion can be reduced. You can reduce distortion by adding data. This technical solution proposes to supplement the missing data with a smoothly changing function of the type sin () or cos (). The data is supplemented by an algorithmic method, as follows

where M is the number of strips in the detector,

K is the number of samples in the complete data set,

i is the number of additions lying in the range from 1 to K - M,

I (1) - the measured values of the radiation intensity for the 1st strip,

I (M) - the measured values of the radiation intensity for the M-th strip,

I _D (M + i) - supplemented values of the radiation intensity.

Moreover, it is believed that the data are not available only "to the right" of the measured values. If the data are not available both “to the right” and “to the left” of the measured values, then the resulting set of “complete” data is shifted cyclically (as in the computer register) by the required value.

This approach is based on the fact that the calculation of derivatives with the elimination of distorting factors is conveniently performed in the frequency domain, as noted earlier. The fast discrete Fourier transform - FFT is used. Using this transformation assumes that the function to which it is applied is periodic. Therefore, the proposed approach is reduced to supplementing the data in such a way that there is no gap at the ends of the periodic function.

Using the above approach to supplement the data is not optimal, however, in many practical cases, it allows to increase the accuracy of reconstruction associated with a jump in the derivative in those places where the data breaks off, especially during two-dimensional reconstruction.

5. Calibration of the measured data - elimination of an unknown factor.

The calibration procedure is required for all variants of the proposed technical solution, since the measured values of the radiation intensity contain distortions caused by various reasons.

When using a multi-slit collimator, the transparency of individual slits cannot be made absolutely identical. It is also impossible to make absolutely identical the gain in each strip of the strip detector. When using a single-slot collimator (pinhole), distortions occur due to the different remoteness of the parts of the object to the detector. Similar distortions arise when using a single strip and a moving inhomogeneous screen as a strip detector.

All of these distortions are multiplicative, that is, distortions caused by multiplying the measured quantity (radiation intensity) by some unknown factor. If this unknown factor is measured and the measured values divided by its value, then the distortions disappear. If the distortions are not eliminated, then ring artifacts will appear in the reconstructed image. In known technical solutions [3, 4] this problem was not considered.

In this technical solution, as in Angers gamma cameras, it is proposed to solve this problem by measuring the radiation intensity from a homogeneous phantom. The measurement feature for this technical solution consists in the absence of rotation of the detector-collimator system, necessary when examining the object, and in the special form of a homogeneous phantom.

After the measurements are carried out, the calibration is carried out in accordance with the following ratio

where i is the number of the strip in the detector,

I (i) is the calibrated value of the measurement of radiation intensity [imp / sec],

A (i) is the measured value of the radiation intensity [imp / sec],

C (i) - measured maximum normalized radiation intensity from a homogeneous phantom [dimensionless from 0 to 1].

Details of the organization of measuring the intensity of radiation from a homogeneous phantom and a description of the phantom are given in the corresponding section.

6. Forward and reverse convolution

The convolution mathematical relations given below are valid both for the case of using a coordinate-insensitive large-area detector and for the case of using a single strip as a detector. In this case, when using a large-area detector, they are valid both for the case with a screen located between the detector and the collimator (screen for radionuclide radiation), and for the case with the screen located between the scintillator and photodetector (screen in the form of a moving or spatial optical modulator).

In all these cases, the signal C (x ') recorded by the detector will be the result of the convolution (convolution) integral of the desired plane integral of the object under study and the distribution function of the screen inhomogeneity along its direction of motion

where I (x ') is the desired plane integral;

H (x ') is the distribution of heterogeneity along the movement of the screen;

C (x ') is the signal recorded by the detector.

Moreover, taking into account the fact that the screen moves (scans), the signal recorded by the detector is a function of time

where V is the scanning speed;

t is the scan time.

To obtain the desired value of the plane integral, it is necessary to perform the operation of reverse convolution (deconvolution) over the signal detected by the detector

where H ^-1 (x ') is the restoring function for H (x').

An analysis of expressions (13) and (14) shows that if the function H (x ') is a delta function, which corresponds to a screen inhomogeneity in the form of a narrow gap, then recovery is not required, since the signal recorded by the detector exactly corresponds to the planar integral of the object under study . If the function H (x ') is constant, which corresponds to the complete absence of heterogeneity, then recovery is generally impossible. Thus, the fundamental requirement for the distribution function of the screen heterogeneity is the requirement that the screen heterogeneity function is different from the constant. If this requirement is met, then a direct and inverse transformation can be carried out with varying degrees of certainty.

From a mathematical point of view, this problem belongs to the so-called class of incorrect inverse problems, the solution of which was developed by academician Tikhonov [4] and is based on regularization. The essence of these decisions based on regularization is most easily stated using the frequency approach.

If F [C (x ')] is the Fourier image of the plane integral, and F [H (x')] is the Fourier image of the distribution of the screen inhomogeneity, then the Fourier image of the desired plane integral F [I (x ')] is

where λ is the regularization coefficient.

And the plane integral itself is equal to

where F- ¹ [...] is the inverse frequency conversion operator.

That is, the Fourier image of the recovery function F [H ^-1 (x ')] is equal to

and the recovery function itself is equal to

Therefore, the essence of the regularization coefficient λ is to protect against dividing by small quantities. Its specific value is selected depending on the nature of the function F [H (x ')].

The above description of the essence of regularization is a particular one and for a more detailed explanation, refer to [4].

In a practical implementation using digital computer technology, the signal recorded by the detector is sampled in time. Continuous integration is converted to a summation of discretized quantities.

The signal registered by the detector is

the desired discrete values of the planar integral are equal

In this case, the discrete recovery functions H ^-1 (...) can be found based on the knowledge of the discrete distributions of the screen inhomogeneity H (...) and the regularizing approach described earlier [4], together with the discrete Fourier transform.

However, in addition to using aperiodic convolution, it is possible to use cyclic convolution. In this case, the data can be presented arranged cyclically with a repetition period of N.

In the case of using cyclic convolution, the ratios take on a slightly different form:

where mod [..., N] means the calculation of the value modulo N of the specified value.

At the same time, the higher the sampling rate of the signal measured by the detector, the greater the spatial resolution will be the image of the studied object after reconstruction.

That is, with this approach, the spatial resolution (to a first approximation) is determined by the sampling rate of the signal measured by the detector. If the distribution function of the screen inhomogeneity is known, then to obtain a higher resolution image, you just need to increase the sampling frequency of the signal without changing the distribution of the radiation intensity in the beam cross section.

The number of strips M, the length of the screen S, its speed V and the sampling interval Δt are related by the following relation

In the presence of noise, which corresponds to the real practical situation, the choice of an arbitrary convolution function (arbitrary distribution of screen inhomogeneity), apparently, will not be a practical solution to the problem. In the presence of noise, a more practical option would be to choose a convolution function that, for a given sampling rate, maximizes, according to some criterion, the signal-to-noise ratio in the image of the subject under study. For example, by the criterion of the maximum signal-to-noise ratio for each individual image element. In this case, the solution of the problem in discrete form is known based on the use of arrays having flat side lobes in cyclic autocorrelation functions, the so-called URA arrays [5]. These arrays are based on the use of Walsh functions, that is, on the basis of 0 and 1. For these arrays, the restoring functions H ^-1 (...) [5] are known, which will consist of -1 and +1. In addition, it is known that the maximum signal-to-noise ratio in each individual element of the reconstructed image is achieved for URA arrays having an effective transparency with respect to penetrating radiation of 50% (i.e., the number of units is 50% of the total length of the array). The use of URA arrays with a different transparency coefficient (greater than or less than 50%) does not interfere with operability, but lowers the signal-to-noise ratio in the resulting image.

Making heterogeneous screens based on URA arrays is also very simple, since it comes down to making holes in the screen.

Using other optimization criteria may lead to the use of other convolution functions, but will not change the method of solving the problem.

Thus, the global conclusion that follows from the proposed consideration is that, with the proper choice of the convolution function (distribution of screen inhomogeneity), it is possible not only to obtain high spatial resolution, but also to efficiently record radionuclide radiation.

At the same time, if we do not consider the task of measuring the planar integrals as efficiently as possible, then almost any function can be used as a convolution function (distribution of screen inhomogeneity), even under noise conditions. In this case, the final resolution in the resulting image will be determined only by the sampling frequency of the measured data, and the form of the convolution function will affect the signal-to-noise ratio in the desired image. In this case, the image restoration problem can be solved on the basis of discrete versions of the previously mentioned regularization methods proposed by Academician Tikhonov [4] (in the time or frequency domain).

The invention is illustrated by drawings, on which:

Figure 1 - General diagram of a device for implementing the method.

Figure 2 - Strip detector based on a structured scintillator.

Figure 3 - Strip detector based on a coordinate-insensitive detector of a large area and located in front of it a movable variable screen along the movement of the transparency screen.

Figure 4 - Strip detector based on a scintillator, coordinate-insensitive photodetector of a large area and a movable light screen variable along the movement of the transparency screen located between them.

Figure 5 - Strip detector based on a scintillator, coordinate-insensitive photodetector of a large area and a flexible flexible light screen of variable transparency, covering the scintillator.

6 - Strip detector based on a scintillator, a coordinate-insensitive large area photodetector and a spatio-temporal optical modulator located between them.

7 - Strip detector based on one strip and moving non-uniform along the movement for radiation of the radionuclide of the screen.

Fig. 8 shows a strip detector based on one strip and a coaxial rotating screen non-uniform for radiation of a radionuclide.

Figure 9 - Location of lead protection on a strip detector, consisting of one strip.

Figure 10 - Collimator in the form of a single slit in the screen.

11 - Geometric ratios in the compensation of distortion 1 / r for the divergent collimator.

Fig - Fourier images of the operator of the increment and differentiation.

Fig - The relative location of the homogeneous phantom and the detector-collimator system during calibration measurements.

Fig - Appearance of a prototype gamma camera with a removed decorative casing.

Fig - Comparative scintigrams of the thyroid gland of two patients, obtained on a standard gamma camera from GE Millennium for 10 minutes from a distance of 10 cm and obtained on a prototype gamma camera from a distance of 10 cm, with a slit collimator 50 mm deep, step 1 , 6 mm and a study time of 15 minutes

Figure 1 shows a device that implements various approaches to address the disadvantages of existing technical solutions.

The device consists of a collimator 7 (convergent, divergent or routine), located in front of the strip detector 9 and directed by the inlet towards the object 12, located on the base 13. The collimator 7 and detector 9 together form a collimator-detector system 11, which is connected to the system its positioning 17, comprising means 15 for rotating the system 17 around the longitudinal axis 14 of the object 12 and connected to it means 16 for rotating the system 11 around the axis 25 perpendicular to the longitudinal axis of the object 12. Signal output stri The p-detector 9 is connected to the input of the data acquisition system 18, which is connected at the output to the data processing processor 22, which in turn is connected to the computer 20. Moreover, the computer 20 itself is also connected to the scanning control means 19 and the visualization result of the data processing 21 The scanning control means 19 is connected to the control inputs of the strip detector 9 and positioning system 17. Numbers 47 and 3 denote: the radionuclide inside the object and its radiation, respectively.

The device shown in figure 1, operates as follows. The computer 20 through the scanning control means 19 supplies the initial setting signals to the strip detector 9 and the positioning system 17. As a result, the positioning system 17 and the means 15 and 16 included in it come to their initial position in the positioning angle relative to the axes 14 and 25. At this at the same time (or later or earlier, which is not critical), the detector 9 also comes into operation. For example, it sets the operating amplifiers of the preamplifiers, operating voltages, and so on. After that, the signal from the scanning control means 19 is supplied to the system 17. As a result, the system 11 begins to rotate from the means 16, which is part of the system 17, around the axis 25 by a predetermined rotation angle θ (for example, 360 degrees). After the system 11 is rotated by a predetermined angle around axis 25, the tool 15 included in the system 17 rotates the system 11 by a small predetermined angle Δφ about axis 14 (for example, 360 / N, where N is the total number of rotations about axis 14). After that, the rotation of the system 11 around the axis 25 from the means 16, but in the opposite direction, is repeated. All signals in the system 17 during the rotation of the system 11 are received from the control means 19. Further, the indicated actions for rotation around the axes 25 and 14 of the system 11 are repeated until a scan is made around the axis 14 by a predetermined angle.

In the process of these actions, a signal about the magnitude of the planar integrals from the output of the strip detector 9 is fed to the input of the data acquisition system 18. After the scan is completed, the data acquisition system 18 contains the data set necessary for three-dimensional reconstruction, which is transmitted to the data processing processor 22, s the output of which enters the computer 20 and the visualization tool 21.

If necessary, the measured data, or the result of processing, can be transmitted to third-party consumers via data transmission lines (not shown).

In the event that three-dimensional reconstruction is not required, but only two-dimensional, then full rotation around axis 14 of system 11 is not required, and scanning ends after rotation of system 11 by a predetermined angle θ around axis 25. In this case, data from the data acquisition system 18 is received also to the input of the data processing processor 22, where two-dimensional reconstruction of the projection of the three-dimensional distribution of the radionuclide in the object 12 onto the plane of the detector 9 is performed. The reconstruction result, as before, is visualized or transmitted to third-party consumers .

Other drawings show improvements regarding various parts of the described device.

2, positions A and B show a strip detector based on a structured scintillator 40 and photodiode arrays 2. The end face of the structured scintillator is shown at positions C and D.

The detector of Fig. 2, position A consists of a structured scintillator 40 and photodiode arrays 2a and 2b. The signal outputs of the photodiode arrays 2a and 2b are connected to the inputs of the pre-amplifier - multiplier - amplitude discriminator 28, and the control inputs of the lines 2a and 2b are connected to the output of the control unit 29. The outputs of the pre-amplifier - multiplier - amplitude discriminator 28 and the control unit 29 are connected to the inputs of the means data collection 18 and controls 19.

The length of the scintillation fibers 41 of the scintillator 40 is much greater than their thickness. The thickness of the fibers 41 is much less than the width of the scintillator 40, determined along the direction 35. The direction 35 and the axis 25 are perpendicular.

That is, many fibers 41 are used to set the desired thickness and width of the scintillator 40. The width of the photodiodes, in the highly sensitive photodiode arrays 2a and 2b, attached (glued) to the ends of the structured scintillator 40, is approximately equal to the thickness of the scintillator 40.

If the thickness of the scintillator 40 and the thickness of the lines 2a and 2b are very different, then they are connected (glued) through an optical coordinator (focon), which is not shown in figure 2, position A.

The detector 2 position B differs from position A in that the thickness of the scintillation fibers (columns) 1 is equal to the thickness of the structured scintillator 40, that is, the thickness of the scintillator 40 is determined by the thickness of one row of scintillation fibers (columns) 1.

The width of the fibers (columns) 1 is approximately equal to the width of the photodiodes in the lines 2A and 2B. It approximately means that a slight deviation is possible due to differences in the sizes of photodiodes and scintillation fibers (columns). If the thickness of the scintillator 40 and the thickness of the lines 2a and 2b are very different, then they are connected (glued) through an optical coordinator (focon), which is not shown in figure 2, position A. The width of the scintillator 40 is determined along the direction 35, perpendicular to the direction of orientation of the fibers (columns) 1. The direction 35 and the axis 25 are perpendicular.

The use of highly sensitive photodiode arrays 2 is not mandatory in the device of Figure 2, instead of them you can use, for example, multi-channel slot PMTs (for example, the Japanese company Hamamatsu), which will not interfere with the operability of the device, but slightly increase its size.

In the proposed solution of FIG. 2, position C, individual thin scintillation fibers are laid so that the thickness of the scintillator is formed, which is necessary for the effective absorption of radiation of a given energy. The width of the set is arranged so as to obtain the spatial resolution and width of the strip detector of the desired value. The manufacturing technology of structured scintillators is similar to that used in modern digital x-ray detectors. The scintillator length in these detectors usually does not exceed a fraction of a centimeter and is determined by the efficiency of radiation absorption. In the proposed technical solution, the length of the scintillation fibers (columns) is significantly larger and can be tens of centimeters, and is determined by the required length of the strip.

As scintillation material, you can use both plastic scintillators and mineral scintillators, for example, based on cesium iodide CsI. The walls of the scintillator must have either a mirror or a diffuse reflector. Mirror reflector is applied by spraying, for example aluminum. The diffuse reflector is applied by painting, for example with white diffuse paint.

Other variants of structured scintillation strips are possible, for example, implemented based on the use of a capillary with filling it with a liquid scintillator (for position 2, position B) or a set of small capillaries (Figure 2 position A). In any case, in order to implement the strip detector mode, the ratio of length to thickness of such a structured scintillator must be much larger than in the known structured scintillators.

Thus, a distinctive feature of the present invention under this item is the use of a structured scintillator in the strip detector, the ratio of the length of which to its thickness is much greater than unity.

The use of amplifiers — multipliers — of an amplitude discriminator 28 and two lines of photodiodes 2a and 2b in the detector of FIG. 2 is determined by the need to compensate for the attenuation of light flashes inside a long scintillator 41 or 1. If the properties of the scintillator 41 or 1 are such that the attenuation of light flashes in the scintillator material is negligible, it is possible to dispense with the attenuation compensation circuit. In this case, you can use only one line of photodiodes, for example, 2a, and instead of an amplifier — a multiplier — an amplitude discriminator 18, simply use an amplifier — an amplitude discriminator, which does not affect the operability of the device in this case.

With a weak attenuation of light flashes in the scintillator material, instead of an amplifier — a multiplier — amplitude discriminator 18, it is also possible to use an amplifier — adder — amplitude discriminator for two inputs (for each strip).

The strip detector shown in FIG. 2 (option A or B) operates as follows. The detector is placed relative to the collimator 7 so that the direction of the scintillation fibers is parallel to the slots of the collimator 7 - Fig. 1 (direction 35 perpendicular to the slots of the collimator 7). From the control means 19, a signal is sent to the control unit 29 at the beginning of the measurement. Light flashes arising in the scintillator 41 or 1, under the action of radiation 3, propagate along the scintillator until it hits the photodiode arrays 2a and 2b. The generated electrical signal from the lines 2a and 2b is fed to the inputs of the amplifier - multiplier - amplitude discriminator 28, where it is amplified and multiplied. The result of multiplication and discrimination is fed to the input of the data collection means 18. Next, the processing of the measured data is carried out in accordance with the approach described in the operation of the entire device shown in FIG. 1.

Since the line of photodiodes and scintillators based on cesium iodide or plastic scintillators are quite cheap components, using the proposed technical solution, it is possible to create a strip detector of large area, small thickness and low cost, compared, for example, with a detector based on cadmium telluride. In contrast to technical solutions [3] using a line of small-area cadmium telluride detectors, the proposed detector will have a large area and, therefore, high radiation detection efficiency.

The ability to create a detector with high detection efficiency is very important in medical applications, since it allows either to reduce the time of the study or to reduce the amount of radionuclide administered.

In addition, such a detector can be made small in thickness and uncooled, which is important when building the device.

A more radical way to reduce the cost of the device is to use a coordinate-insensitive detector as a strip detector.

Figure 3 shows a strip detector built on the basis of a coordinate-insensitive detector. The strip detector contains a large-area scintillator 4 and a large-area photodetector (photomultiplier) 5 connected to it, forming a coordinate-insensitive large-area radiation detector of a radionuclide (in FIG. 3, detector parts 4 and 5 are specially separated for greater clarity). A screen 6 is placed in front of this radiation detector, connected to its linear displacement means 23. Moreover, the screen 6 is made in such a way that its transparency for radionuclide emission is periodically inhomogeneous along the direction of its movement 8. The repetition period of the inhomogeneity of the screen 23 is equal to the width of the detector. The input of the moving means 23 of the screen 6 is connected to the control means 19, and the output of the detector 5 is connected to the input of the amplifier - amplitude discriminator 49, the output of which is connected to the input of the data acquisition system 18.

Such a strip detector works as follows. The detector is placed relative to the collimator 7 so that the direction of movement 8 of the screen 6 is perpendicular to the slots of the collimator 7 - Fig.1. Moreover, the direction 8 is parallel to the direction 35, which determines the width of the strip detector 9 - Fig.2. From the control means 19, a signal is sent to the means 23 at the beginning of the linear movement of the screen 6. As a result of the linear movement of the screen 6 at the output of the large area photodetector 5, a signal arises that is determined by the mathematical convolution of the desired signal (plane integral) and the distribution of the inhomogeneity in the screen (see mathematical basics) . The signal from the output of the photodetector 5 is fed to the input of an amplifier, an amplitude discriminator 49, the output of which is fed to the input of the data acquisition system 18, from the output of which it is transmitted to the input of the data processing processor 22, where the reverse cyclic convolution operation is performed [9] (see mathematical basics) . This mathematical problem was solved by academician Tikhonov and belongs to the class of inverse incorrect problems [9]. The measurements at the output of the amplifier — the amplitude discriminator 49 — are performed at discrete time instants, and the inverse problem is solved in the processor 22 in a discrete form. The time interval Δt through which measurements are taken determines the spatial resolution that this strip detector will have. The number of strips N, the length of the screen S, its speed V and the sampling interval Δt are related by (23).

The purpose of the amplifier - amplitude discriminator 49 is standard - it is a preliminary amplification to the required signal level and its amplitude analysis. Therefore, this amplifier - amplitude discriminator 49 can be performed according to any standard scheme used, for example, in nuclear physics.

Despite the fact that with this approach, it is possible to use almost any periodic inhomogeneity in the screen, it is important to maximize the signal-to-noise ratio under noise and discrete measurements. The solution to this problem under discrete measurement conditions is known on the basis of arrays with flat side lobes and one maximum in the autocorrelation function - URA arrays [10].

These arrays consist of ones and zeros, such as 10100111001 ... Their implementation in practice requires only making holes in a screen that is opaque to radionuclide radiation, which can be made of a material with a high atomic number (lead, tungsten, etc.). Such a material is heavy in weight, and the means for linearly moving it 23 must be powerful enough.

Further improvement of the strip detector device is possible by eliminating the heavy non-uniform screen 6 and using a light non-uniform optical screen.

Figure 4 shows a strip detector 9 based on a scintillator 4 and a large area photodetector 5, between which there is a light optical screen 10 connected to its moving means 24. Moreover, the screen 10 is made so that it is periodically inhomogeneous for optical radiation (radiation scintillator) in the direction of its motion 8. The period of heterogeneity of the screen 10 is equal to the width of the detector 9. In this case, the weight of the optical screen 10 can be minimal, since it can be made, for example, from black thick paper, foil and plastic . It is possible to use other materials, which is not fundamental.

Such a strip detector works as follows. The detector is placed relative to the collimator 7 so that the direction of motion 8 of the screen 10 is perpendicular to the slots of the collimator 7 - Fig.1. Moreover, the direction 8 is parallel to the direction 35, which determines the width of the strip detector 9 - Fig.2. From the control means 19, a signal is sent to the means 24 at the beginning of the linear movement of the screen 10. As a result of the linear movement of the screen 10 at the output of a large-area photodetector 5, a signal arises that is determined by the operation of mathematical convolution of the desired signal (planar integral) and the distribution of periodic inhomogeneity in the screen (see mathematical basis ) The signal from the output of the photodetector 5 is fed to the input of an amplifier, an amplitude discriminator 49, the output of which goes to the input of the data acquisition system 18, from the output of which it is transmitted to the input of the data processing processor 22, where the reverse cyclic convolution operation is performed [9]. This mathematical problem was solved by academician Tikhonov and belongs to the class of inverse incorrect problems [9]. The measurements at the output of the amplifier — the amplitude discriminator 49 — are performed at discrete time instants, and the inverse problem is solved in the processor 22 in a discrete form. The time interval Δt through which measurements are taken determines the spatial resolution that this strip detector will have. The number of strips N, the length of the screen S, its speed V and the sampling interval Δt are related by (23).

The purpose of the amplifier - amplitude discriminator 49 is standard - it is a preliminary amplification to the required signal level and its amplitude analysis. Therefore, this amplifier - amplitude discriminator 49 can be performed according to any standard scheme used, for example, in nuclear physics.

It is possible to further improve the strip detector device by eliminating the reciprocating motion of a non-uniform optical screen and using continuous motion of a non-uniform optical screen.

Figure 5 shows a strip detector 9 based on a scintillator 4 and a large area photodetector 5, between which there is a light optical screen 34 connected to its moving means 30. The screen 34 is made in the form of a flexible ring so that it is periodically inhomogeneous for optical radiation (radiation of the scintillator) in the direction of its movement 48. In this case, the weight of the optical screen can be minimal, since it can be made, for example, from black thick paper, foil and plastic. It is possible to use other materials, which is not fundamental.

As the means of movement 30, any means providing the movement of the screen 34, similar to the movement of the conveyor belt used, for example, during construction, can be used.

Such a strip detector works as follows. The detector is placed relative to the collimator 7 so that the direction of motion 48 of the screen 34 is perpendicular to the slots of the collimator 7 - Figure 1. While the direction 48 is parallel to the direction 35, which determines the width of the strip detector 9 - Fig.2. From the control means 19, a signal is sent to the means 30 at the beginning of the movement of the screen 34. As a result of the movement of the screen 34 at the output of a large area photodetector 5, a signal arises that is determined by the operation of mathematical convolution of the desired signal (planar integral) and the distribution of heterogeneity in the screen (see mathematical basics). The signal from the output of the photodetector 5 is fed to the input of an amplifier, an amplitude discriminator 49, from the output of which to the input of the data acquisition system 18, from the output of which is transmitted to the input of the data processing processor 22, where the operation of reverse cyclic convolution is performed [9]. This mathematical problem was solved by academician Tikhonov and belongs to the class of inverse incorrect problems [9]. The measurements at the output of the amplifier — the amplitude discriminator 49 — are performed at discrete time instants, and the inverse problem is solved in the processor 22 in a discrete form. The time interval Δt through which measurements are taken determines the spatial resolution that this strip detector will have. The number of strips N, the length of the screen S, its speed V and the sampling interval Δt are related by (23).

The purpose of the amplifier - amplitude discriminator 49 is standard - it is a preliminary amplification to the required signal level and its amplitude analysis. Therefore, this amplifier - amplitude discriminator 49 can be performed according to any standard scheme used, for example, in nuclear physics

Perhaps further improvement of the strip detector device by eliminating the mechanical movement of the optical screen.

Currently known optical spatio-temporal modulators, for example, based on liquid crystals, used in projection televisions or displays. With this in mind, the proposed technical solution can be slightly modified by eliminating the movement of the optical screen, using instead of it a spatio-temporal optical modulator connected to its control means.

FIG. 6 shows a strip detector 9 comprising a scintillator 4 and a large area photodetector 5, between which there is an optical spatio-temporal modulator 26 connected to its control means 27.

As a spatio-temporal optical modulator, a liquid crystal optical modulator used in projection televisions or a large-area liquid crystal optical spatio-temporal modulator used in flat passive computer monitors is used.

It is allowed to use other known types of spatio-temporal optical modulators, for example, discrete digital mirrors [7], which does not affect the operability of the device.

If it is necessary to coordinate the size of the scintillator 4 and the coordinate-insensitive photodetector 5, an optical coordinator (focon) can be installed between them. In this case, the spatio-temporal optical modulator 26 should be installed before or after the optical matching device, in accordance with the dimensions of the modulator. 6, an optical coordinator (focon) is not shown.

The optical transparency of the modulator should change in time so as to produce a result similar to the movement of the optical screen, i.e., the signal at the output of the photodetector 5 should be determined as the result of mathematical convolution of the desired signal (planar integral) and screen inhomogeneity (see mathematical basics).

Such a strip detector works as follows. The detector is positioned relative to the collimator 7 so that the direction of change in the transparency of the modulator 26 is perpendicular to the slots of the collimator 7 - Figure 1, that is, parallel to the direction 35, which determines the width of the strip detector 9 - Figure 2. From the control means 19, a signal is sent to the means 27 to establish the initial distribution of the transparency of the modulator 26. As a result of a change in the transparency of the modulator over time by commands from the control 19 at the output of the large area photodetector 5, a signal is determined by the operation of mathematical convolution of the desired signal (plane integral) and distribution heterogeneities in the screen (see mathematical fundamentals). The signal from the output of the amplifier - amplitude discriminator 49 is fed to the input of the data acquisition system 18, the output of which is transmitted to the input of the data processor 22, where the operation of the reverse cyclic convolution is performed [9]. This mathematical problem was solved by academician Tikhonov and belongs to the class of inverse incorrect problems [9]. The measurements at the output of the detector 5 are made at discrete time instants and the inverse problem is solved in the processor 22 in a discrete form. The time interval Δt through which measurements are taken determines the spatial resolution that this strip detector will have. The number of strips N, the length of the screen S, its speed V and the sampling interval Δt are related by (23).

The purpose of the amplifier - amplitude discriminator 49 is standard - it is a preliminary amplification to the required signal level and its amplitude analysis. Therefore, this amplifier - amplitude discriminator 49 can be performed according to any standard scheme used, for example, in nuclear physics.

The specified technical solution can be used both with a parallel arrangement of the plates in the collimator, and with convergent and divergent. If we restrict ourselves to a divergent collimator, the technical solution can be further simplified and, accordingly, cheaper the device even more, leaving only one strip in the strip detector.

In the divergent case, leaving only one strip instead of many strips and using a moving inhomogeneous screen to radiate a radionuclide, you can create a device without using a multi-slot collimator.

7 shows a strip detector 9 for divergence geometry, containing one strip scintillator 1, to the end of which a photodiode 2 is attached (glued). The output of the photodiode 2 (a ruler consisting of one element) is connected to the input of the amplifier - amplitude discriminator 31, the output which is connected to the data collection means 18. In this case, between the strip scintillator 1 and the radiation 3 (from the radionuclide 47 of the object 12) there is a screen 6, periodically inhomogeneous in the direction of its movement 8 for the radiation of the radionuclide 47. The screen 6 is connected to its means ynogo movement 23, whose input is connected to the control means 19.

Such a strip detector works as follows. The detector is placed relative to the radiation 3 so that the direction of motion 8 of the screen 6 is perpendicular to the radiation 3. The direction 8 is parallel to the direction 35, which determines the width of the scintillator 40 - Figure 2. From the control means 19, a signal is sent to the means 23 at the beginning of the linear movement of the screen 6. As a result of the linear movement of the screen 6 at the output of the large area photodetector 5, a signal arises that is determined by the mathematical convolution of the desired signal (plane integral) and the distribution of the inhomogeneity in the screen (see mathematical basics) . The signal from the output of the photo detector 5 is fed to the input of the amplifier, the amplitude discriminator 31, from the output of which to the data acquisition system 18, from the output of which it is transmitted to the input of the data processor 22, where the reverse cyclic convolution operation is performed [9]. This mathematical problem was solved by academician Tikhonov and belongs to the class of inverse incorrect problems [9]. The measurements at the output of the amplifier - the amplitude discriminator 31 are carried out at discrete time instants and the inverse problem is solved in the processor 22 in a discrete form. The time interval Δt through which measurements are taken determines the spatial resolution that this strip detector will have. The number of strips N, the length of the screen S, its speed V and the sampling interval Δt are related by (23).

The purpose of the amplifier - amplitude discriminator 31 is standard - it is a preliminary amplification to the required signal level and its amplitude analysis. Therefore, this amplifier - amplitude discriminator 31 can be performed according to any standard scheme used, for example, in nuclear physics. The difference 31 from 49 is that input 31 is designed for connection to a photodiode, input 49 for connection to a PMT.

The efficiency of detecting radiation in the described strip detector will be similar to the case of using a large-area detector and the moving screen indicated earlier. This is explained by the fact that the scintillator acts as an integrator of flashes coming from all directions (as in the case of a large-area detector). Moreover, the integrator in the divergence case can be made in the form of a single strip. In this case, the device is simpler and therefore cheaper. The nature of the signal at the output of such a detector will be similar to the signal described earlier, that is, it is the operation of mathematical convolution of the desired signal (planar integral) and the distribution of the inhomogeneity in the screen. To obtain the desired signal (planar integral), it is necessary to perform the operation of inverse mathematical convolution [9].

If the length of the strip is minimal (for example, equal to its width and height) - Fig.7, the device is very cheap. In this case, a small piece of scintillator attached to the photodiode is actually used. However, if a strip of short length is used, then the efficiency of detecting radiation will be low. Therefore, despite the fundamental possibility of using a short strip, it is advisable to use a long strip. A short strip can be used when the radiation intensity of the radionuclide is high enough.

If the attenuation of optical flashes in the material of a long scintillator is large, then an attenuation correction scheme should be used based on two photodiodes located at opposite ends of the scintillator and an amplifier — multiplier — amplitude discriminator, which was described earlier for FIG. 2.

For the divergent case, it is possible to further improve the strip detector by eliminating the reciprocating motion of the inhomogeneous screen and using an inhomogeneous rotating drum instead.

On Fig shows a strip detector 9 for divergence geometry, containing one strip scintillator 1, to the end of which is attached (glued) a photodiode 2, the output of which is connected to the input of the amplifier - amplitude discriminator 31, the output of which is connected to the data collection means 18. When this around the strip of the scintillator 1, coaxially with it, there is a rotating drum 32, inhomogeneous in the direction of its rotation 33 for emitting the radionuclide 47. The drum 33 is connected to its rotation means 30, the input of which is connected to the control means 19.

Such a strip detector works as follows. The detector is positioned relative to the radiation 3 so that the direction of rotation 33 of the drum 32 is perpendicular to the radiation 3. That is, the axis of rotation of the drum 32 is perpendicular to the direction 35, which determines the width of the scintillator 40 - FIG. 2. From the control means 19, a signal is sent to the means 30 at the beginning of the rotation of the drum 32. As a result of the rotation of the drum 32 at the output of a large-area photodetector 5, a signal arises that is determined by the operation of mathematical convolution of the desired signal (planar integral) and the distribution of inhomogeneity in the screen (see the mathematical basis). The signal from the output of the photodetector 5 is fed to the input of an amplifier, an amplitude discriminator 31, from the output of which to the input of the data acquisition system 18, from the output of which it is transmitted to the input of the data processing processor 22, where the reverse convolution operation is performed [9]. This mathematical problem was solved by academician Tikhonov and belongs to the class of inverse incorrect problems [9]. The measurements at the output of the detector 5 are made at discrete time instants and the inverse problem is solved in the processor 22 in a discrete form. The time interval Δt through which measurements are taken determines the spatial resolution that this strip detector will have. The number of strips N, the length of the screen S, its speed V and the sampling interval Δt are related by (23).

The purpose of the amplifier - amplitude discriminator 31 is standard - it is a preliminary amplification to the required signal level and its amplitude analysis. Therefore, this amplifier - amplitude discriminator 31 can be performed according to any standard scheme used, for example, in nuclear physics. The difference 31 from 49 is that input 31 is designed for connection to a photodiode, input 49 for connection to a PMT.

When the length of the strip is minimal (for example, equal to its width and height) - Fig. 8, the device is as cheap as possible. In this case, a small piece of scintillator attached to the photodiode is actually used. However, if a strip of short length is used, then the efficiency of detecting radiation will be low. Therefore, despite the fundamental possibility of using a short strip, it is desirable to use a long strip. A short strip can be used when the radiation intensity of the radionuclide is high enough.

If the attenuation of optical flashes in the material of a long scintillator is large, then an attenuation correction scheme should be used based on two photodiodes located at opposite ends of the scintillator and an amplifier — multiplier — amplitude discriminator, which was described earlier for FIG. 2.

For efficient detection of high energy gamma quanta (more than 100 keV), the scintillator cross section in the technical solutions of Fig. 7 and Fig. 8 should be large enough. However, with a large cross section of the scintillator, the spatial resolution in the reconstructed image decreases (due to the large width of the strip). To ensure both high detection efficiency and high spatial resolution, it is necessary to use a scintillator of the required cross section (for efficient registration of quanta of the required energy) and a lead “shirt” around the scintillator with a longitudinal slit of the required width along the scintillator - Fig. 9.

In Fig. 9, positions A and B show a cross-section of a scintillator aligned with a protection jacket. The width of the slit in the “shirt” determines the required spatial resolution, and the opening angle ψ defines the region of the object covered by the detector. The angle ψ should be no more than the repetition period of the heterogeneity in the drum 32 - Fig. 8.

In position A - Fig. 9, the opening angle ψ of the gap is less than in position B, while the width of the gap is the same in both positions.

The use of such a technical solution, in addition to the main purpose, can dramatically reduce the weight of the protective "shirt", which can be significant when creating mobile devices. This is true for the technical solution shown in Fig.7, and Fig.8.

The use of a protective “shirt” is necessary in all proposed technical solutions, but the place of its position and purpose are well known, therefore, it is not shown in the figures explaining other technical solutions. Protection is shown where its position and purpose is not well known.

The proposed technical solutions can be further improved by using a different type of collimator instead of a multi-slit collimator.

Instead of a multi-slit collimator 7 for technical solutions based on FIG. 2, FIG. 3, FIG. 4, FIG. 5 and FIG. 6, a single-slot collimator can be used.

Figure 10 shows a single-slot collimator, for technical solutions of Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6, made in the form of a flat screen with one slit - position A, and in the form of a screen of complex shape with one slit - position B.

In figure 10, position A shows a single-slot collimator, consisting of a flat screen 37 that is not transparent to radionuclide radiation, in which a slit 39 is made, the length of which is equal to the length of the slits in the multi-slit collimator, and the width is proportional to the required spatial resolution in the reconstructed image. One side of the screen 37 is facing the strip detector 9, and the other is directed toward the radiation 3. The slot 39 is parallel to the strip of the strip detector 9.

Figure 10, position B shows a single-slot collimator consisting of a screen 38, in shape corresponding to a prism with one open side. Opposite the open side of the screen 38, there is one slit 39 in the edge of the prism, the length of which is equal to the length of the slits in the multi-slit collimator, and the width is proportional to the required spatial resolution in the reconstructed image of the radionuclide. The open side of the screen 38 is directed towards the strip detector 9, and by the slit 39 towards the radiation 3. The slit 39 is parallel to the strip of the strip detector 9.

The complex shape of the screen 38 is given in order to eliminate the influence of extraneous radiation coming from the lateral directions.

This collimator Figure 10 positions A and B in their functions is similar to a pinhole collimator in gamma cameras such as Angers. The distance d at which the slit 39 is located from the strip detector 9, and the distance at which the slit 39 is located from the object 12 determine the geometric increase β of the investigated object according to the well-known formula:

To eliminate the influence of factor 1 / r on the reconstruction result, the slit 39 is shifted relative to the axis of rotation of the detector-collimator system 25 by an angle δ proportional to the required spatial resolution in the reconstructed image and ranging from 0 to 5 degrees (see mathematical basis).

The use of a single slit and the absence of a multi-slit collimator, in addition to the above advantages, can reduce the cost of the device and obtain images of the desired geometric magnification.

On Fig shows the layout of a homogeneous phantom 42 and the detector-collimator system 11 during calibration measurements.

The calibration procedure is required for all variants of the proposed technical solution, since the measured values of the radiation intensity contain distortions caused by various reasons.

When using a multi-slit collimator, the transparency of individual slits cannot be made absolutely identical. It is also impossible to make absolutely identical the gain in each strip of the strip detector. When using a single-slot collimator (pinhole), distortions occur due to the different remoteness of the parts of the object to the detector. Similar distortions arise when using a single strip and a moving inhomogeneous screen as a strip detector.

All of these distortions are multiplicative, that is, distortions caused by multiplying the measured quantity (radiation intensity) by some unknown factor. If this unknown factor is measured and the measured values divided by its value, then the distortions disappear. If the distortions are not eliminated, then ring artifacts will appear in the reconstructed image. In known technical solutions [3, 4] this problem was not considered.

In this technical solution, as in Angers gamma cameras, it is proposed to solve this problem by measuring the radiation intensity from a homogeneous phantom 42.

Calibration measurements - Fig. 13 is carried out without rotation of the detector-collimator system 11 around axis 25.

The length 45 of the homogeneous phantom 42 should exceed the diameter of the studied area of the object 14 by at least 50%, and the width 46 is approximately equal to the diameter of the studied area of the object 14, when the detector-collimator system 11 is located from the object 14 at a distance 44, similar to the distance used for real examination of the object 14. The thickness of the phantom 42 should be as small as possible, for example about 5-10 mm, so as not to introduce additional distortions in the calibration process associated with the thickness.

In order to carry out calibration measurements, a homogeneous phantom 42 is placed on a stand or table (not shown) so that the long axis 43 of the phantom 42 is parallel to the direction 35, which determines the width of the strip detector 9. The easiest way to do this is to pre-orient the axis 11 in the horizontal plane then it is enough to place the phantom 42 on a horizontal plane and rotate it so that the axis 43 occupies a position parallel to direction 35. The accuracy of the orientation of the axes relative to each other should be no worse than one degree sa.

After phantom 42 is oriented properly, measurements are made without rotation about axis 25. The number of quanta measured by each strip during calibration (directly or after de-convolution, which depends on the implementation of the strip detector) must be at least 10 ⁶ so that the error measurements were no more than 10 ^-3 . In this case, the phantom 42 is positioned relative to the detector-collimator system 11 at a distance 44, similar to the distance used in a real study of object 14.

After calibration measurements are carried out, the radiation intensity values are normalized to the maximum, that is, they lead to unity. After normalization, calibration is carried out according to the formula (19) (see mathematical basis).

Calibration, as noted, allows you to eliminate ring artifacts in the reconstructed image of the object.

On Fig presents an experimental device for testing the health of one proposed technical solutions, shown in Figure 3. The device implements a variant of a strip detector built on the basis of a large area scintillator and photodetector, between which a movable screen is inhomogeneous for the radionuclide radiation in the direction of its movement, located between the multi-slit collimator.

The multi-slit collimator is made on the basis of a set of parallel plates. The collimator plates are made on the basis of bronze foil 100 microns thick with glued lead plates 200 microns thick. The width of the slits in the multi-slot collimator is 1.6 mm, the number of slots is 63, the length of the slits is 100.8 mm, and the height of the collimator plates is 50 mm.

The screen is made of a Rose alloy (bismuth - 58%, lead - 30%, tin - 12%) 5 mm thick and contains heterogeneity in the form of a URA array of 63 elements repeated twice to realize cyclic convolution. Holes correspond to 1 in the URA array, screen material corresponds to 0 in the URA array. The width of the holes is 1.6 mm, the length of the holes is 100.8 mm.

An FEU-125 photomultiplier with an input window diameter of 150 mm was used as a photodetector. CsI CsI iodide, 8 mm thick and 150 mm in diameter, attached to the input window of the photomultiplier using adhesive tape was used as a scintillator. To improve the optical contact between the scintillator and the photomultiplier, their contacting surfaces are lubricated with liquid petroleum jelly.

To simplify the design of the entire experimental device, a scanning mode corresponding to a two-dimensional reconstruction was implemented. The size of the reconstructed image matrix is 63 × 63 elements. The number of samples in the "projection" is 63, the number of "projections" is 64.

We used the procedure for calibrating the measured data based on a homogeneous phantom according to the previously described method and the procedure for supplementing data based on the cosine function.

The measurements were made in clinical conditions, on real patients undergoing thyroid examination using radioisotope methods using a pharmaceutical product containing the technetium Tc ^99m radionuclide. The total activity of the drug administered to each patient was 3 milliecurie.

The measurement results for two different patients with thyroid pathology are shown in Fig. 14, positions A and B, respectively, in comparison with the results of examination of the same patients with a standard Millennium gamma camera of the Angers type, manufactured by General Electric. The results obtained on standard equipment are shown in the upper row, the results obtained on experimental equipment are shown in the lower row.

The examination time on the Angers gamma camera was 10 minutes, on the experimental sample 15 minutes. At the same time, Angers' own gamma camera resolution was 6 mm, and that of the experimental sample was 1.6 mm.

Analysis of the results of experimental measurements allows us to conclude that the proposed technical solutions are correct and that devices can be built on the principles outlined.

Information sources

1. US patent 3,011,057, publ. 1961.10.28.

2. US Patent 3,684,886, publ. 08.28.15.

3. US patent 3,936,639, publ. February 2, 1976

4. US Patent 4,090,080, publ. 1978.05.16.

5. US patent 4,563,583, publ. 1986.01.07.

6. US patent 6,353,227 B1, publ. 2002.03.05.

7. US patent 6,627,893 B1, publ. September 2003.

8. US Patent 6,631,285 B2, publ. 2003.10.07.

9. A.N. Tikhonov, V.Ya. Arsenin "Methods for solving ill-posed problems", M., "Science", 1986.

10. A. Busbom, H. Elders-Boll, and H. D. Schotten, "Uniformly Redundant Arrays", Experimental Astronomy 8: 97-123, 1998.

11. G. Hermen "Image restoration from projections. Fundamentals of reconstructive tomography", translation from English by L.V. Barabin and A. B. Meshcheryakov, ed. L. M. Soroko, M., "World", 1983.

12. N. de Beaucoudrey, L. Garnero, J.P. Hugonin, "Improved tomographic X-ray microimaging of laser plasma by double multislit coding cameras", SPIE Vol. 1140 X-Ray Instrumentation (1989) / 149.

Claims (8)

1. A method of obtaining an image of the distribution of a radioactive drug inside an object under study, including measuring the intensity of radiation from a radionuclide inside an object through a multi-slot collimator with a strip detector installed at the output of the collimator, the input of which is directed toward the object, at different angular positions of the collimator-detector system relative to the object and obtaining a data set of radiation intensity similar to computed tomography, followed by applying the reconstruction algorithm to the data set Function and visualization of the result of the reconstruction. 2. The method according to claim 1, characterized in that the distortion of the reconstruction result caused by the inhomogeneity of the transparency of the collimator slots is additionally eliminated, for which the transparency of the collimator slits is preliminarily measured and the measurement results are used in the reconstruction algorithm, while the radiation intensity is measured to measure the transparency of the collimator slits from a homogeneous phantom without changing the angular position of the collimator-detector system and normalize the results of measurements of radiation intensity from object under the following algorithm:
I (i) = A (i) / C (i),
where i is the number of the strip in the detector,
I (i) is the calibrated value of the measurement of radiation intensity [imp / s],
A (i) is the measured value of the radiation intensity [imp / s],
C (i) - measured maximum normalized radiation intensity from a homogeneous phantom [dimensionless from 0 to 1]. 3. The method according to claim 1, characterized in that in order to eliminate the heterogeneity of the transparency of the slots of the collimator, the radiation intensity of the radionuclide is measured through a single slot made in a screen that is opaque to the radiation of the radionuclide and oriented parallel to the strip detector strips with an offset of an angle δ from the axis of rotation of the detector, proportional to the required spatial resolution in the reconstructed image of the investigated object, and the slit itself is placed between the object and the detector at a distance D, determined as follows general ratio:

where β is the required increase in the measurement [dimensionless from 0 to infinity],
d is the distance from the screen to the plane of the detector [mm],
D is the distance from the screen to the object (the distance to the plane inside the object parallel to the screen, relative to which they want to have the desired increase) [mm]. 4. The method according to claim 3, characterized in that the angle of displacement of the slit δ relative to the axis of rotation is set to not more than 5 °. 5. The method according to claim 3, characterized in that the width of the slit is set constant over its entire length and proportional to the required spatial resolution in the reconstructed image of the object under study. 6. The method according to claim 1 or 2, characterized in that it additionally eliminates the distortion of the reconstruction caused by an incomplete set of data on the radiation intensity, the data is supplemented algorithmically as follows:

where M is the number of strips in the detector;
K is the number of samples in the complete data set;
i is the number of additions lying in the range from 1 to K-M;
I (1) - the measured values of the radiation intensity for the 1st strip;
I (M) - measured values of the radiation intensity for the M-th strip;
I _D (M + i) - supplemented values of the radiation intensity. 7. A device for acquiring an image of the distribution of a radioactive drug inside an object under study, containing a slit collimator, the input of which is directed towards the object being studied, a strip detector of radiation intensity installed at the output of the collimator, the first means of rotation designed to rotate the detector-collimator system around a longitudinal axis investigated object, the second means of rotation, designed to rotate the detector-collimator system around an axis perpendicular to the longitudinal axis og object, a means of measuring the output signals of a strip detector of radiation intensity, a means of storing and processing the measured data and a means of visualizing the processing results. 8. The device according to claim 7, characterized in that as a strip detector of radiation intensity, it contains a structured scintillator in the form of a set of scintillation fibers, to the ends of which photodetectors are connected in the form of a line of photodiodes.

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