RU2151552C1 - Gamma-chamber with rectangular vision field - Google Patents

Abstract

FIELD: medical engineering. SUBSTANCE: device has collimator unit, scintillation crystal, optically bound light guide, photodetector, as well as summing amplifier, analog-to-digital converters, summer, pulse detector, group signal processing units, devices for collecting and processing data and visualization unit. EFFECT: enhanced spatial resolution; improved diagnostic characteristics. 7 dwg

Description

 The invention relates to medical equipment, namely to medical diagnostic gamma cameras intended for the early diagnosis of malignant tumors and other human diseases by visualizing the distribution of radioactive drugs introduced into the body for diagnostic purposes. The invention may find application in medical, prophylactic and research institutions.

 Known gamma camera described in US patent N 3011057, CL. G 01 T 1/20, containing a collimator, a scintillation crystal, a light guide, photodetectors, amplifiers, a coordinate matrix, X and Y correctors, an information collection and processing system, and a visualization device.

This gamma camera can have both round and rectangular field of view, however, in any case, it has the following disadvantages:
- the presence of regular nonlinear distortions of the resulting images, as a consequence of the nonlinear dependence of the amplitude of the photodetector signal on the distance to the scintillation point;
- poor spatial resolution, because the weighted average algorithm that is implemented in this gamma camera to determine the coordinates of the scintillation point does not fully use the information contained in the totality of the photodetector signals.

 These disadvantages are partially eliminated in the device described in US patent N 4228515, G 01 T 1/20, containing a collimator, a scintillation crystal, a fiber, photodetectors located in the form of a rectangular assembly, amplifiers, analog-to-digital converters according to the number of photodetectors, two coordinates , a device for collecting and processing information and a visualization device, each of the coordinate determinants includes a normalization device, a multi-input comparator with the number of inputs by the number of photodetectors, a subtracting device property, detector, switching device, memory blocks according to the number of photodetectors, two summing devices, division device.

 The disadvantage of this device is the poor spatial resolution due to the fact that the scintillation coordinate determination algorithm implemented in this device does not fully use the information contained in the set of photodetector signals.

 This invention solves the problem of improving the spatial resolution of the gamma camera.

 The solution to this problem is achieved by the fact that a gamma camera containing a collimator, optically coupled scintillation crystals, a fiber and photodetectors located in the form of a rectangular assembly, analog-to-digital converters, the number of which is equal to the sum of the rows and columns in the photodetector assembly, is an information collection and processing device and the imaging device according to the present invention is provided with two groups of summing amplifiers (group (X) and group (Y)). The number of summing amplifiers of group (X) is equal to the number of columns, and the number of summing amplifiers of group (Y) is equal to the number of rows in the assembly of photodetectors, and the input of each summing amplifier of group (X) is connected to the outputs of all photodetectors of only one of the columns, and the input of each summing amplifier group (Y) is connected to the outputs of all photodetectors of only one row. The outputs of the summing amplifiers of the group (X) are connected to the signal inputs of the analog-to-digital converters of the group (X), and the outputs of the summing amplifiers of the group (Y) are connected to the signal inputs of the analog-to-digital converters of the group (Y). The gamma camera is also equipped with an adder, the input of which is connected to the outputs of the summing amplifiers of the group (Y), and a pulse detector, the input of which is connected to the output of the adder, and the output - to the start inputs of all analog-to-digital converters; a group (X) signal processing unit, the data bus of which is connected to the data outputs and the “ADC Ready” outputs of the analog-to-digital converters of the group (X) and to the input “X” of the information collection and processing device; control outputs - to the read inputs of the analog-to-digital converters of group (X) and to one of the inputs of the start of the device for collecting and processing information; the signal processing unit of the group (Y), the data bus of which is connected to the data outputs and the “ADC ready” outputs of the analog-to-digital converters of the group (Y), and to the input “Y” of the data acquisition and processing device, the control outputs to the analogue digital converters group (Y) and to the second input of the start of the device for collecting and processing information.

 Thus, the essence of the present invention lies in the fact that thanks to the proposed technical solution, it became possible to implement the optimal algorithm for determining the coordinates of scintillations, which can significantly improve the spatial resolution of the gamma camera, which increases the diagnostic capabilities of the device.

The aforesaid is confirmed by the following. Thanks to the supply of the gamma camera with summing amplifiers and the summation of the photodetector signals separately for rows and columns, it became possible to use each row or column of photodetectors as an independent element for estimating scintillation coordinates. This means that knowing the dependence of the amplitude of the total signal of a number of photodetectors on the distance between the middle line of the series and the scintillation point, we can determine the y-coordinate of the scintillation point of the ith photodetector series as:
Y _i = y _i + r _i δ _i , (1)
where Y _i is the estimate of the y-coordinate of scintillation by the ith row of photodetectors;
y _i -y - coordinate of the i-th row in the assembly;
r _i is the distance from the i-th row to the scintillation point;
δ _i - coefficient taking the value +1 or -1 depending on whether scintillation occurred above or below the i-th row.

, (2)
где B_i - соответствующим образом подобранный весовой коэффициент;
k - число рядов в сборке.The optimal estimate of the Y coordinate of the scintillation (i.e., unbiased with minimal dispersion) can be obtained according to the expression:

, (2)
where B _i - appropriately selected weight coefficient;
k is the number of rows in the assembly.

 The proof of assertion (2) can be found, for example, in the book by Brownley KA (Brownlee K.A.) Statistical Theory and Methodology in Science and Engineering, John Wiley & Sons, New York, 1965. (Russian translation): Statistical theory and methodology in science and technology, M., "Science", 1977).

, (3)
здесь m - число колонн фотоприемников в сборке;
δ_j - коэффициент, принимающий значения +1 или -1, в зависимости от того, слева или справа от j-й колонны произошла сцинтилляция.All of the above is true, of course, for estimating the X coordinate
X _j = x _j + r _j δ _j

, (3)
here m is the number of columns of photodetectors in the assembly;
δ _j - coefficient taking values +1 or -1, depending on whether scintillation occurred to the left or right of the jth column.

 The estimates of the X and Y scintillation coordinates obtained according to expressions (2) and (3) are unbiased estimates with minimal dispersion, which means obtaining the best spatial resolution, since the latter is directly related to the variances of the coordinate estimates.

 The invention is illustrated by a specific example of its implementation and the drawings, where in FIG. 1 shows a block diagram of the proposed gamma camera and a block diagram of a signal processing unit, FIG. 2 - assembly of photodetectors with signal adders, in FIG. 3 is a flow chart of a group (Y) signal processing unit, FIG. 4 is a flowchart of the operation of the signal processing unit of group (X), in FIG. 5 is a distance-signal relationship, in FIG. 6 shows a weight-signal relationship, FIG. 7 - peak distribution of signals by amplitudes.

 The gamma camera (see Fig. 1) consists of a collimator 1 mounted close to the scintillation crystal 2, which is optically coupled to the optical fiber 3, which, in turn, is optically coupled to a rectangular array of photodetectors 4 (Fig. 2). The outputs of each row of photodetectors 4 are interconnected and connected to the input of one of the summing amplifiers 5, which form a group (X), in the same way, the outputs of each column of photodetectors 4 are combined and connected to the input of one of the summing amplifiers 5 of the group (Y). The outputs of the summing amplifiers of group 5 (X) are connected to the signal inputs of the analog-to-digital converters of group (X) 6 (ADC), and the outputs of the summing amplifiers of the 5th group (X) are connected to the signal inputs of the analog-to-digital converters of group (X) 6 (ADC) . The outputs of the summing amplifiers of group (Y) are also connected to the input of the adder 7, the output of which is connected to the input of the pulse detector 8. The output of the pulse detector 8 is connected to the start inputs of all ADCs 6. The data outputs and the “readiness of the ADC” ADCs of group 6 (Y) are connected to the data bus of the signal processing unit of group (Y) 9 (BOCY), the data outputs and the “ADC availability” of the ADC of group 6 (X) are connected to the data bus of the signal processing unit of the group (X) 10 (BOSX), the read-in inputs of the ADC of group 6 (X) ) are connected to the outputs of the control BOSX 10, one of the outputs of the control BOSX 10 under It is connected to the first input of the start of the device for collecting and processing information 11 (USOI), the outputs of which are connected to the inputs of the visualization device 12 (HC), and the data bus BOSX 10 is also connected to the input "X" of the USOI 11. ADC readings of group 6 (Y) connected to the control outputs of BOCY 9, one of the control outputs of BOCY 9 is connected to the second trigger input of USOI 11, and the data bus BOCY 9 is also connected to input "Y" of USOI 11.

 The collimator 1 is a honeycomb structure made of a material with a high absorption coefficient for gamma radiation (usually lead or its alloys). It transmits only those gamma rays that fall normally to the surface of scintillation crystal 2 (see, for example, drawing tA5.176.063).

 Scintillation crystal 2 is used to convert the energy of the gamma quantum into the energy of light photons of scintillation (see, for example, TU6-09-26-650-90).

 The light guide 3 serves to form the light flux and transmit light from scintillation to photodetectors (see, for example, drawing tA7.220.050).

 The photodetector 4 is used to convert the light flux into an electrical signal. A rectangular cross-section photomultiplier can be used as a photodetector, for example, the R5900U photomultiplier (see Hamamatsu catalog "Photomultiplier Tubes and Assemblies for Scintillation Counting and High Energy Physics" May 1998).

 The summing amplifier 5 is a differential amplifier in discrete or integrated design, for example, the K544UD2 chip in inverse switching.

 As an analog-to-digital converter 6, any at least 10-bit ADC with a third state and conversion time of no more than 1 μs can be used, for example, an ADC based on a Burr-Brown DSP102 chip (see drawing UKEU.411618.002).

 The adder 7 is used to determine the total signal proportional to the energy of scintillations. Structurally, the adder 7 can be made completely identical to the summing amplifiers 5.

 The pulse detector 8 is designed to record an act of scintillation. It can be performed, for example, using the K554CA3 microcircuit, on one of the inputs of which the signal of the adder 7 is supplied, and on the other a constant voltage corresponding to the noise level of this assembly of photodetectors. When setting the gamma camera, this voltage is set as the minimum voltage at which the pulse detector 8 does not operate in the absence of an external gamma radiation stream.

 The signal processing unit of group (Y) BOCY 9, the block diagram of which is shown in FIG. 1, is intended to calculate an estimate of the Y coordinate of the scintillation y coordinate. It consists of three memory blocks: BP 13, BP 14 and BP 15, as well as the arithmetic device AU 16.

 The memory unit 13 (BP 13) is a read-only memory (ROM), in the memory of which the coordinates of the middle lines of the rows of photodetectors must be pre-recorded. The amount of memory is 2xk bytes, where k is the number of horizontal rows in the assembly of photodetectors (usually no more than 10).

 The memory block 14 (BP 14) is a ROM, the memory of which stores the distance between the center line of the row and the scintillation point, as a function of the amplitude of the total signal of the row, normalized to the total signal of all photodetectors 4. These values are determined by preliminary calibration. The size of the memory is at least 512 values, the depth is 2 bytes.

 The memory block 15 (BP 15) is a ROM, the memory of which stores the values of the weight coefficients as a function of the amplitude of the total signal of the series normalized to the total signal of all photodetectors 4. The memory size is at least 512 values, depth - 2 bytes. Structurally, PSU 15 is equivalent to PSU 14.

 As BP 13, BP 14 and BP 15 are used the corresponding amount of memory areas of the media on the hard disk, which is part of USOI 11.

 The arithmetic device 16 (AU 16) reads the data of the ADC 6, controls the operation of the BOSY 9, performs all the necessary mathematical operations for pre-calibration and calculation of the estimate Y and transmits the data to the input "Y" of USOI 11. As such a device can be used, for example , signal processor POS-116 UKEU 467459.002 TO based on the TMS320 / 25 microprocessor.

The signal processing unit of group (X) 10 (BOSX 10) is designed to calculate the estimate of the X coordinate of the "x" scintillation. BOSX 10 is arranged similarly to BOSY 9, except that the number of inputs of BOSX 10 is equal to the number of columns of the photodetector assembly 4, in the memory block 17 (BP 17), the coordinates of the middle lines of the columns of the photodetector assembly 4 should be recorded in the memory block 18 (BP 18 ) the distance between the center line of the column and the scintillation point is stored, as a function of the amplitude of the column signal normalized to the total signal of all photodetectors 4, the weight coefficients A _j are stored in memory block 19 (BP 19) as a function of the amplitude of the column signal, normal specified on the total signal of all photodetectors 4. Arithmetic device 20 (AU20) in its purpose and device is completely identical to AU16.

 The device for collecting and processing information 11 (USOI 11) perceives the coordinate signals X and Y and increments by 1 unit element of the image matrix with the corresponding coordinates. As a result, after a sufficiently long exposure, an image of a radiating object, i.e., any patient's organ, in which the radioactive drug has accumulated, will be formed in the matrix. USOI 11 also processes the obtained images (smoothing, etc.) to facilitate diagnosis. As such a device can be used, for example, "System for the automated collection and processing of radio diagnostic information from gamma cameras" SCINTI-116 EVNK 941351.001 TO.

 The visualization device 12 (UV12) is used to visualize the received information. As such a device, any IBM-compatible display can be used, for example, SUPER VGA COLOR MONITOR Mode = 1439SV.

Pre-calibration
Pre-calibration is a necessary step and is performed by the manufacturer when setting up the gamma camera. Initially, the x and y coordinates of the midlines of all rows and columns of photodetectors 4 are entered into the memory blocks BP 13 and BP 17 4. For further calibration, a linear gamma radiation source is required, the length of which must be not less than the maximum size of the gamma camera's field of view .

The calibration task is to create data arrays in which the distance between the center line of the row or column of photodetectors 4 and the scintillation point is recorded as a function of the normalized signal of the row or column. These data are subsequently stored in the memory units BP 14 and BP 18. In addition, the calibration task is to create data arrays in which the values of the weight coefficients A _j , B _i are written as a function of the normalized signal of a row or column.

 To obtain these dependences, the linear source of gamma radiation moves sequentially along the X and Y axes of the field of view with a step of 1 mm. In each position of the source, the peak of the distribution of signals of the selected row or column of photodetectors 4 is measured and recorded in the operational memory of AU 16 or AU 20 (Fig. 7). After at least 1000 samples accumulate at the peak maximum, data accumulation ceases and the average amplitude and width of the distribution peak at half its height are determined. Based on these data, the dependence of the distance from the midline of the row (column) to the scintillation point averaged for all rows (columns) is constructed. These dependencies in the form of tables of values are then recorded in BP 14 and BP 18.

, (4)
где ΔN_i,ΔN_j - ширина пиков распределения на середине высоты.After you determine the averaged curves "distance-signal" for rows and columns (Fig. 5), the weighting coefficients A _j and B _{i are} calculated by the formulas:

, (4)
where ΔN _i , ΔN _j is the width of the distribution peaks in the middle of the height.

The derivatives dN _i / dr, dN _j / dr are determined from the curve of FIG. 5 as relations of finite differences.

Tables of values of A _i and B _j (Fig. 6) are then recorded in PSU 15 and PSU 19. At this point, the calibration step is completed and the gamma camera is ready for operation.

Mode of operation
The gamma camera operates as follows. A patient whose body is preliminarily injected with a pharmaceutical labeled with a radioactive nuclide is placed in front of the entrance window of collimator 1. Gamma rays generated during the decay of the nuclei of a radioactive nuclide and entering through scintillator 1 into scintillation crystal 2, excite light flashes in it - scintillation. The light of each scintillation is perceived by photodetectors 4 and converted by them into electrical pulses, which are summed in rows and columns using summing amplifiers 5. At the output of adder 7, a signal appears equal to the sum of the signals of all photodetectors, the amplitude of which is proportional to the scintillation energy. If the signal amplitude of the adder 7 exceeds the total noise level of the photodetectors 4, then a trigger gate appears at the output of the pulse detector 8, which is fed to the input inputs of the ADC 6, after which the ADC 6 converts the analog signals received at their inputs into a digital code. After the conversion by each of the ADC 6s, at its output “ADC Ready”, a signal appears that goes to the data bus BOSX 10 or BOSY 9. After the signals “ADC Ready” appear at the outputs of all ADCs of group 6 (X), BOSX 10 starts step-by-step polling and reading the contents of ADC buffers of group 6 (X). Similarly, after the signals “readiness of the ADC” appear at the outputs of all ADCs of group 6 (Y), BOSY 9 starts a step-by-step poll and reads the contents of all the ADCs buffers of group 6 (Y). Next, BOSX 10 and BOSY 10 calculate estimates of the scintillation coordinates X and Y in accordance with the algorithms, block diagrams of which are presented in FIG. 3 and 4. When triggering signals occur at the inputs “1” and “2” of the USOI 11 trigger, the cell of the image matrix is incremented, the address of which corresponds to the estimates of X and Y of the scintillation point.

 Further, the cycle described above is repeated until enough readings are accumulated in USOI 11 to obtain a statistically reliable image.

 As shown by the results of mathematical modeling of the gamma camera, the implementation of the proposed scheme and algorithm of the gamma camera improves the resolution of the gamma camera from 5.0 mm to 3.5 mm compared to the prototype. This will allow you to recognize smaller foci of pathology, which will increase the diagnostic capabilities of the device.

Claims (1)

 A gamma camera with a rectangular field of view, containing a collimator, optically coupled scintillation crystals, a fiber and photodetectors located on the surface of a fiber in the form of a rectangular assembly, analog-to-digital converters, the number of which is equal to the sum of the rows and columns in the photodetector assembly, an information collection and processing device and a visualization device, characterized in that it is equipped with two groups of summing amplifiers (group X) and group (Y)), a signal processing unit of group (X), a signal processing unit group (Y), an adder and a pulse detector, and the input of each summing amplifier of group (X) is connected to the outputs of all photodetectors of only one of the columns, and the input of each summing amplifier of group (Y) is connected to the outputs of all photodetectors of only one row, the outputs of summing the amplifiers of the group (X) are connected to the signal inputs of the analog-to-digital converters of the group (X), the input of the adder is connected to the outputs of the summing amplifiers of the group (Y), and the output is connected to the input of the pulse detector, the output of which is connected to the start inputs of all tax-to-digital converters, the data bus of the signal processing unit of the group (X) is connected to the data outputs and the readiness outputs of the analog-to-digital converters of the group (X) and to the input X of the data acquisition and processing device, the control outputs are connected to the read inputs of the analog-to-digital converters group (X) and to the 1st input of the start of the device for collecting and processing information, the data bus of the signal processing unit of the group (Y) is connected to the data outputs and the readiness outputs of the analog-to-digital converters of group (Y) and the input Y of the device In order to collect and process information, the control outputs are connected to the read inputs of the analog-to-digital converters of group (Y) and to the 2nd input of the start of the device for collecting and processing information.

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