SU671519A1 - Scintillation gamma-chamber - Google Patents

Description

The invention relates to medical technology, namely to scintillation gamma cameras and can be used in therapeutic, prophylactic and scientific research facilities in diagnostics and research of internal organs and systems of a person using radioactive isotopes.

A known scintilla ion gamma camera l, consisting of a collimator, a rotating crystal, a set of photomultipliers optically conjugated through a flat optical fiber from a transparent material with a scintillating crystal, linear preamplifiers, the shapy of coordinate and SHEvgetic signals, amplitudes, outgoing pulses corresponding to the photopic region of the radiation spectrum of the radioactive isotope used, linear transmitters of coordinate signals ops for Komantsev height analyzer, and an imaging device associated with the linear amplitude and anal propuskatelem; 1zatorom so that each scintillation incorporated in the crystal corresponds vsgadshka screen imaging device.

But in the specified gamma camera due to the absence of. the gamma camera of an analog computing device, the coordinate signals depend on random fluctuations of the energy signal, a change in the intensity of scenes leads to a proportional change in the coordinate signal, which in turn degrades the spatial resolution, reduces the accuracy of detection of pathological foci, reduces the accuracy and accuracy of the information obtained; Due to the lack of threshold devices in the gamma camera, the photomultiplier signals are the most distant. From scintillation appearance points,

The crystal emission component is completely determined in the crystal and in the fiber multiply and does not carry 367 information about the coordinates of the gamma quang interaction point with the crystal substance, while the static fluctuation is proportional to the amplitude of the pulse, therefore, the photomultipliers most remote from locations of scintillation degrading the spatial resolution, which in turn reduces the accuracy of the selection of pathological foci, reliability and diagnostic value of the information obtained; Also known is guide to the prototype opisyyaemogo technical solution stsingill-translational gamma camera 2, comprising a collimator, a scintillation crystal, a light guide fogoumyozhiteli, before the amplifiers, the threshold device summagory coordinate and energy signals Vp {5gy analyzer linear propuskageli, analog calculator Noe and a visualization device, in which the computing device consists of ds}) of the effective amplifiers and the scheme of dividing the coordinate signals on the amplification signal used to; and the energy dependence of the CCW} dinatnyh signals, and visualizing device associated with analog vychislichrelnym device such that each scintillation crystal to flash on the screen of the imaging yc-p royztva. But in this gamma camera, the execution of threshold devices with a constant threshold value predetermines the energy dependence of the coordinate signals and introduces additional heterogeneity of characteristics over the crystal area, which limits the spatial resolution of the gamma camera and the accuracy of detection of the pathological foci; Sequential switching on of the threshold devices and the amplitude analyzer leads to deterioration of the energy resolution of the gamma camera, since this is equivalent to incomplete collection of light from scintillations. The chain of the present invention is to eliminate these drawbacks, to improve the accuracy of detection of pathological foci; by improving the spatial and energy resolution, reducing the heterogeneity of the characteristics of the gamma camera crystal area. The goal is achieved by the fact that the threshold devices are made with variable thresholds, the inputs of the energy signal adder are connected to the outputs of the preamplifiers, and the outputs of the adder are connected to the control input of the threshold devices and an amplitude analyzer. The essence of the proposal is explained in the drawing, which shows a block diagram of a gamma camera. The gamma camera consists of collimator 1, scintillation crystal 2, light guide 3, photomultipliers 4, preamps; 5, threshold devices 6, made as terminal stages of preamplifiers, adders 7 energy signal & la, adders 8 coordinate signals, amplitude analyzer 9, linear transmitters 10, analog computing device 11, visualizing device 12. Threshold devices 6 are made with a variable threshold proportional instantaneous values of the pulses of the adder 7 of the energy signal, and connected to the output of the latter in parallel to the amplitude analysis; the gate 9. The input circuits of the adder 7 of the energy A signal is connected between preamplifiers 5 and threshold devices 6. The gamma camera operates as follows. A patient who received the required amount of radioactive drug-. This is placed in front of the collimator 1 of the gamma camera. Gamma quanta pass through the apertures of collimator 1, enter scintillation crystal 2, interact with the latter and form a flashlight, KOTOpbie illuminates the photodiode of photomultipliers 4 optical connected to crystal 2 through a light guide 3. Photomultipliers 4 convert light energy electrical pulses, the amplitude of which depends on the distance between each photomultiplier 4 and the place of origin of the scintillation and on the energy of the gamma quantum that caused this scintillation. The pulses of photomultipliers 4, linearly amplified by preamplifiers 5, arrive at the threshold devices 6. In addition, signals from preamplifiers 5, min threshold devices b, arrive at the adder 7 of the energy signal. From the output of the energy signal adder 7, the pulses proportional to the energies of each scintillation are sent to the threshold devices 6 and the threshold value is instantly set in proportion to its own amplitude. At the same time, the magnitude of the signals arriving at the threshold devices 6 from the preamplifiers 5 is reduced by the threshold value. Amplitude Analyzer

9, turned on at the output of the power 7 adder, generates an output signal only if the output pulses correspond to the photopic of the radiation of the isotope used. From the output of the threshold devices 6, the signals arrive at the adders of 8 coordinate signals, where pulses are formed that are proportional to the coordinates of the scintillation in crystal 2. The linear transmitters 10 are triggered by the command of the amplitude analyzer 9 and pass impulses from the adders to 8 coordinate signals for further processing to an analog computing device 11. Analog (google computing device 11 performs the division of each coordinate signal by the total value of these slips to eliminate the energy dependence Coordinate signals from an analog computing device: TWA 11 are fed to a visualization device 12, on the screen of which are displayed. With coordinates that are proportional to these signals. The result of the study is recorded by photographing light flashes from the screen of the visualizing device 12.

Due to the fact that the thresholds of the device 6 are connected to the output circuits of the adder 7 of the energy signal that are controlled by them and the thresholds are proportional to the instantaneous value of the output signal (pulse) of the sum, the mat 7, and its input circuits are connected between the preamps 5 and by threshold devices 6, the sharpness of the detection of pathological foci is increased by improving the spatial and energy resolution, reducing the inhomogeneity of characteristics over the area of the crystal 2.

Improving the intrinsic spatial resolution of a gamma camera. Compared with the prototype, this is due to a decrease in the dispersion of the coordinate signal. The coordinate signal at the output of an analog digital device is described by the expression and) and where. - the attenuation coefficients of the US resistor matrix; - the total number of photomultipliers; Uz is the instantaneous value of energy. tic signal; (1 is the instantaneous value of the signal after the threshold device i, associated with the vth photomultiplier;

(Hell-1C, if (2) il Osli A.

D the instantaneous value of the signal at the input .1 th threshold device;

It g threshold value. Taking into account (2), expression (l) can be represented as

x-U I / iAj-I K, (3)

where the summation is performed only over those photomultipliers whose signals, after amplification of the trans, multiply the threshold value. Since the instantaneous value of the energy signal U and the signal at the input of the jth threshold, the devices are random, the dispersion of the coordinate signal is equal

, 6., G, (4) /

: where e, C | - respectively, the variance of the first and second terms in the expression &(III); K - correlation coefficient between them.

According to the invention, the threshold values are proportional to the instantaneous value of the energy signal. (ft-SUz. where is the proportion ratio,

In this case, the expression (3) is converted to the following form

- QC

 Ux l where the second term is actually; is no longer random and the dispersion of the coordinate signal is equal to the cisperia of the first term

yy2

Claims (2)

(5) From comparison (5) and (4) it follows that the described technical solution reduces the dispersion of the coordinate signal, and, consequently, its own spatial resolution before comparison with the prototype .. In accordance with the calculations, its own spatial resolution gamma 7: 671 cameras with The 19th photomultiplier of the PMT-110 type is improved by 1 mm (from 9 to 8 Mvi). This means that the size of the minimum focus located at a depth of 10 mm, which can be detected and localized using a gamma camera, will decrease from 5 to 4 mm when using the Tc isotope (140 keV. The energy resolution of gamma and measure is improved compared to due to the fact that the summation of the energy signal is carried out in addition to the threshold devices, the mean value of the energy signal increases, and its relative fluctuation decreases, the calculations and measurements show that The high resolution is improved from 21% to 15% with the use of the Tc isotope and an average threshold value equal to 10% of the maximum signal. The indicated narrowing of the energy signal spectrum reduces the mixing of the photo-peak spectrum beyond the window, ampli fi cation of the analyzer, which means that the inhomogeneity decreases images in the crystal area from 1O to 8% with a window width of 20% and from 15 to 10% with a window width of 5%. By narrowing the spectrum of the energy signal at a constant window width of the amplitude analyzer, the efficiency of selection of gamma rays n Energy, which reduces the background of the radiation scattered in the patient's gel, and increases the intensity of the focus image. As a result, according to the phantom test, the diameter of the minimally distinguishable focus, located at a depth of 50 mm, is reduced for the indicated isotope with an amplitude analysis window of a torus 20% from 12–13 mm to 8–9 mm. The technical implementation of the invention eliminates the need for a unit for adjusting threshold devices associated with an isotope energy switch, since this adjustment is automatically performed when the isotope changes. Thus, the described invention allows to detect and localize smaller pathological foci located at different depths in the patient’s body, and reduces the maximizing effect of image heterogeneity, THAT makes it possible to diagnose earlier and, consequently, increases the efficiency of liver cancer and cardiovascular diseases. vascular diseases of the population. Claims. Scintillation gamma camera containing collimator, scintillation crystal with light guide, photomultipliers, Preamps, threshold devices, combiners of coordinate and energy signals, amplitude analyzer, l & Non-new transmitters, analog computing and visualizing devices, characterized in that, in order to improve the detection of pathological foci by improving the spatial and energy resolution to reduce the heterogeneity of the characteristics of the crystal area, the threshold, the devices are made with variable thresholds, the inputs of the energy controller the signal is connected to the outputs of the amplifiers, and the outputs of the adder are connected to the control input of the yorog devices and the amplitude analyzer. . Sources of information taken into account in the examination 1. US patent number 3.011.057, cl. G 01 T 1/20, publ., 1972. 2. US patent number 3.732.419, cl. 71.5, published 1976. 671519 1 g