JP2004061122A - High-voltage power distribution system for czt array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect the generation of radiation and reduce noise in a large bias voltage in a nucleus imaging apparatus. <P>SOLUTION: The nucleus imaging apparatus comprises a detector 18 for detecting gamma-ray radiation and generating an electric signal by responding to the detection of the gamma-ray radiation; Faraday boxes 68, 92 for shielding the detector 18, an electronic component 64 for processing the electric signal, and a reconfiguration processor 46 for processing the electric signal for image display. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to nuclear camera technology.
[0002]
[Prior art]
The present invention finds particular use in conjunction with electronics used in SPECT (single photon emission computed tomography) cameras and describes certain implications therefor. However, it should be recognized that the present invention may find use in PET (positron emission tomography) cameras and other radiation detection devices where a high voltage bias is applied to the detector array.
[0003]
Nuclear imaging uses a radioactive source to image the anatomy of a subject. Typically, a radiopharmaceutical is injected into the patient. This source contains atoms that decay at a predictable rate. Each time one atom decays, gamma rays are emitted. These gamma rays are detected, and the display of the inside of the object is reconstructed from information such as the position and energy.
[0004]
In general, nuclear cameras have one, two or three detector heads. Each head has a large scintillator sheet that converts incident radiation, such as doped sodium iodide, into scintillation, or flash of light. An array of photomultiplier tubes is located behind the scintillator to monitor the flash of light. The output of the photomultiplier tube and associated circuitry indicates the coordinates of each scintillation with respect to the sodium iodide crystal and its energy. Unfortunately, there is a great deal of non-uniformity and inaccuracy when using large scintillator crystals and arrays of photomultipliers.
[0005]
Rather than using a single large scintillator and photomultiplier, it has been proposed to use an array of small scintillations, each of which is a photodiode or other photodiode that detects scintillation in a separate scintillation crystal. Related to optoelectronic devices. Other types of individual solid state detectors have also been proposed.
[0006]
Solid state radiation detectors detect radiation using the photoelectric effect. That is, the received emitted photons liberate electrons from orbits around atoms of the target material. The electrons are detected as electric signals. The electrons emitted by one photon generally produce a weak signal that is amplified. Generally, a high bias voltage is applied across the sensing material to promote the photoelectron phenomenon. These voltages are typically several hundred volts. With such a high bias, those systems are sensitive to ambient photoemission and electrical noise, such as visible light. Due to this sensitivity, the bias or stray light / radiation can be mistaken for the event that the detector is trying to detect.
[0007]
[Problems to be solved by the invention]
The present invention provides a new and improved method and apparatus that overcomes the above-referenced problems and others.
[0008]
[Means for Solving the Problems]
According to one aspect of the present invention, a nuclear imaging device is provided. The detection device detects the γ-ray and generates an electric signal in response. The Faraday box shields the detection device. Downstream electronics process the electrical signals generated by the detector and a reconstruction processor reconstructs the electrical signals into an image display.
[0009]
According to another aspect of the present invention, a nuclear camera is provided. The plurality of solid-state arrays respond to incident gamma radiation by emitting electrons. The conductive strips provide a bias to the array. The conductive pad is located opposite the conductive strip. A voltage source supplies power to the conductive strip to create an electric field and attract electrons to the conductive pad. The signal processing circuit provides information about the movement of the electrons to a reconstruction processor that processes the data into an image display.
[0010]
According to yet another aspect of the present invention, a radiation detector assembly is provided. The array of detectors that detect high energy radiation is biased by a bias circuit that applies a high voltage potential between opposing faces of the detector array. An electrical insulating layer and a ground layer are mounted on the radiation receiving surface of the bias circuit. High-z metal vanes collimate radiation from above.
[0011]
According to yet another aspect of the present invention, there is provided a method of nuclear imaging. A bias voltage is applied to the solid state detector array and filtered to remove noise. By generating a current pulse, the response is transmitted to incident radiation. The current pulses are processed and reconstructed into an image display.
[0012]
One advantage of the present invention is that it allows for accurate detection of the generation of radiation.
[0013]
Another advantage of the present invention is that it reduces noise at large bias voltages.
[0014]
Yet another advantage of the present invention is that it reduces the chance that the device will be affected by ambient photoemission.
[0015]
Yet another advantage of the present invention is the ease of assembly of the detection device and the ease of disassembly during maintenance of the device.
[0016]
Other advantages and advantages of the present invention will become apparent to those skilled in the art from a reading and understanding of the preferred embodiments.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention can employ various components and configurations of components, and can employ various steps and configurations of steps. The drawings are shown for purposes of illustrating preferred embodiments only, and should not be construed as limiting the invention.
[0018]
Referring to FIG. 1, a subject 10 defines an imaging area 12. In a preferred embodiment, the radiopharmaceutical 14 is injected near the area of the subject to be imaged. For example, if a physician wants to observe an occlusion of the aorta, an isotope is injected into the bloodstream from upstream of the occlusion. Image data is collected as radiopharmaceutical movements that move with the blood to image the circulatory system. In another embodiment, the radiopharmaceutical is injected into the circulatory system and is selectively absorbed by the tissue of interest. After the absorption period, image data is collected to image the tissue of interest and to measure the rate of absorption.
[0019]
As quantum physics predicts, radioisotope nuclei decay over time. Upon decay, energy is emitted in the form of emitted photons, and more particularly in the form of characteristic γ-ray energy.
[0020]
Many of the γ-rays generated during imaging propagate in useless directions. However, in the preferred embodiment, a large amount of gamma rays pass through a thin tungsten collimator collimator 16 and reach a detector array 18. Occasionally, such a large amount of γ-rays arrive in a short period of time to detect duplicate events. In a preferred embodiment, referring to FIG. 2, the detector array 18 comprises a 4 × 24 array of cadmium zinc telluride (CZT) crystal arrays 20, each array having 4 × 8 individual detectors. 22. When gamma rays reach the CZT crystal, electrons are emitted in a small avalanche. The freed electrons are attracted to one side of the electrode or CZT crystal forming a current pulse or spike.
[0021]
In the preferred embodiment, detector array 18 and collimator 16 are provided on a mechanized drive 30 that moves the detector array with the detector head. The array preferably moves with a mechanism of laterally rotating components, although various trajectories are expected. In some applications, the detector array is fixedly mounted in the head. The detector head is mounted on a slowly rotating movable gantry, pointing around the area of interest.
[0022]
In the preferred embodiment, the detector head is mounted on a rotating gantry 32 that completely surrounds the subject 10. The motor control 34 selects the working range of the detector array 18 stepwise or continuously around the imaging area within the range of rotation of the rotating gantry and the gantry 32, if any. I do.
[0023]
In SPECT imaging, the collimator 16 is directed to a detector array 18 for radiation that follows a designated path or trajectory substantially parallel to the collimator vanes, preferably a trajectory approximately perpendicular to the horizontal plane of the detector array 18. Restrict access to In this way, the occurrence of each radiation determines the trajectory that intersects the gamma source, ie, the source of the event. If the movable gantry 32 remains fixed, the detector determines a projected image of the radioisotope distribution in the region of interest. The event analyzer 42 determines where each event reaches the detector array, i.e., where the detector receives the event, and determines the amount of energy in the radiated event. Radiation events collected at each fixed location of the detector array are stored in an archive 44. If the rotating gantry 32 rotates to different angular positions around the object, multiple projection images from different angular directions are collected. The reconstruction processor 46 rear projects or reconstructs data from the archive memory 44 into a volume image display stored in the volume image memory 48. A video processor 50 under the control of the operator selectively extracts a portion of the volumetric image display and converts it to a form suitable for display on a video monitor 52 or other human readable monitor 52. .
[0024]
With reference to FIGS. 1-3, received gamma rays are detected and their energy is measured by electronics mounted on the detector array 18. In the preferred CZT embodiment, a potential difference of -600 volts is applied across the detector array by a plurality of bias strips 80, a high voltage busbar 82, a bias power supply 84 and a resistor 92. The second power supply 61 supplies power to the amplifier P-ASIC 60 disposed on the circuit board 62.
[0025]
Each time a gamma ray reaches one of the detectors, the avalanche effect emits electrons that generate an output electrical pulse. Associated electronics 64, powered by voltage regulator 66, spread the pulse, measure the area under the influence of the pulse, convert the area to digital output, process the received radiation data, The digital data is multiplexed into a series of outputs for a portion of the operable event analyzer.
[0026]
Referring to FIG. 4, in the preferred embodiment, the circuit 64 or the remote control portion of the event analyzer 42 is normally in a standby state (step 70) and is waiting for an electrical signal. When the event analyzer 42 receives the electrical signal, it compares it to a threshold (step 72). If the signal is below the threshold, it is ignored as noise and the analyzer 42 returns to the standby state. If the signal is greater than the threshold, the analyzer classifies it as an event (step 74) and records the energy of the signal and the location of the detector 22 that sent the signal (step 76). Next, the analyzer 42 communicates this information to the event archive 44 where it is maintained for reconstruction processing (step 78). After this transmission, the analyzer 42 returns to the standby state and waits for the next event. In the preferred embodiment, once the analyzer 42 leaves the wait state in the next clock cycle, it looks for another event until the analyzer 42 returns to the wait state (preferably within 20 ns). In the case of a true event, the process is complete and the analyzer returns to standby within 2 μs. In the event of an erroneous event, the analyzer 42 includes a timeout feature that allows only a true determination of the event for a set time. In the case of noise, the analyzer waits to determine if the threshold has been reached, but returns to a standby state within 2 μs after detecting the noise. Circuit 62 has a plurality of parallel channels, and in the preferred embodiment there is one channel in each half of each array 20. If two or more simultaneous events (within 20 ns of each other) are incident on the same half of the detector array, both events are preferably discarded as hard to separate.
[0027]
Referring to FIGS. 2, 3 and 5, each column of the four detector arrays 20 has a common upper electrical connection or conductive strip 80. In the preferred embodiment, conductive strip 80 is a thin layer of copper supported on a sheet 81 of mylar or other flexible insulator. The copper strip 80 evenly covers the top surface of each detector array so that a uniform negative bias voltage is applied over all surfaces. The bias promotes the propagation of electrons through the detector array. The conductive strip 80 is connected by a resistor 92 to a high voltage power busbar 82 also provided on the mylar sheet 81. In the preferred embodiment, the high voltage busbar is also connected to a power supply 84 that biases the busbar 82 and conductive strip 80 to -600 VDC. The other of the power supplies is connected to the ground plane of the circuit board 62. The bus bar 82 is connected at one end thereof to a contact pin 88 that facilitates electrical connection with a power supply 84. Making electrical contact by pressure to the pins 88 obviates the need for physical wiring, simplicity of assembly and disassembly for repair. The opposite surface of each detector of each array 20 is electrically connected to a conductive pad 86 held at a virtual ground. The conductive pads 86 are connected to electrical connectors or pins housed in sockets 90 on the circuit board 62. As electrons are emitted within one of the crystals, the bias causes the emitted electrons to be attracted to electrical pad 86. Electrical pads 86 are connected to amplifiers and other processing circuits 64. In the preferred embodiment, each circuit board 62 includes four P-ASICs 60 or other low-level amplifiers that provide the necessary amplification to analyze the electrical signals generated by detector array 18. .
[0028]
The conductors 80 are preferably connected to the bus bar 82 by a plurality of resistors 92, with each of the conductive strips 80 being separated from the other conductive strips. Capacitor 68 is connected between the conductive strip 80 of each Faraday box and the ground connection of the amplifier to form a noise filter. In the preferred embodiment, capacitor 68 is sized relative to other circuit components to form a low pass filter.
[0029]
In a preferred embodiment, the mylar sheet 81, together with the conductive strips 80, is located adjacent to the four aligned CZT arrays and opposite the contacts 94 on the circuit board. The bus bar strip 82 is adjacent to the contact 96 and the power receiving pin 88 on the circuit board. The resistor 92 is connected via contacts 94 and 96, and the capacitor 68 is connected to the contact 94. By placing the capacitors 68 and the resistors 92 on the circuit board 62, the high voltage distribution busbar 82 and the bias strip 80 can be implemented by a single removable sheet 80, 81, 82.
[0030]
The conductive strip 80 and the ground plane (the conductive layer in each circuit slope) define a Faraday box. Because the rows of the detector array are adjacent to each other without any sources of stray light noise, the central Faraday box can be opened at the sides. A grounded metal end plate 98 of the housing closes the Faraday box at the end of the array.
[0031]
A collimator 16, mainly made of tungsten, is connected to the system ground. Specifically, the collimator 16 is mechanically pressed against an aluminum foil, a screen, or another conductive sheet 100 connected to the system ground. The ground sheet 100 rests on a layer of foam insulation 102 that separates the ground layer 100 from the -600 VDC bias strip 80 by a mylar layer. The conductive sheet 100 performs a Faraday shielding function.
[0032]
The resilient foam insulator 102 not only insulates the ground layer 100 from the conductive strip 80, but also provides good electrical connection between the conductive strip 80 and the contacts 94, and between the bias strip 82 and the contacts 88, 96. Apply sufficient pressure to ensure contact.
[0033]
The P-ASIC 60 along with the voltage regulator 66 and other circuit elements 64 jointly generate a large amount of heat during operation. If all components placed on the circuit board operate in parallel with the detector, sufficient heat will be generated to damage or destroy those components. In a preferred embodiment, the pattern of connections on the crystal substrate is staggered so that the circuit board 62 can be placed back-to-back at right angles to the detector array 18 which is equipped with a large volume for heat dissipation. Has become. Referring to FIG. 5, in a preferred embodiment, a set of fans 110 provided on one or both sides of the device exhaust air traversing the circuit board 62 to the outside, and are disposed on the circuit board. Cool the parts.
[0034]
When such a high bias voltage is applied to the detector array 18, the CZT crystal becomes susceptible to various radiations, including visible light, that readily enter through the fan openings. To solve this problem, an opaque foam is used to construct the heat and light shield for the detector array 18. The opaque foam has also been extended into open areas around the detector array, providing light protection without relying on relatively space-consuming light baffles around fans or other openings. This, in addition to blocking light, isolates substrate heat from the CZT crystal and facilitates cooling, as the spacing between the circuit boards 62 can be used to cool the circuit boards 62 through the device. I do.
[0035]
In an alternative embodiment, the radioactive source is mounted and fixed on the opposite side of the object facing the detector array. In this way, gamma rays emitted outside the subject, either from a point source or source of radioactive material or a low power X-ray tube, pass through the patient.
[Brief description of the drawings]
FIG. 1 is a schematic view of a nuclear imaging apparatus according to the present invention.
FIG. 2 is a perspective view of a detector array and a circuit board.
FIG. 3 is a perspective view of one of a circuit board and a detector array.
FIG. 4 is a flowchart of an event cycle according to the present invention.
FIG. 5 is a perspective view of a detector array, a circuit board, and a bias grid.
FIG. 6 is an enlarged view showing a detector array, an electric connection part, and a collimator mounting arrangement.
[Explanation of symbols]
10 Patient 14 Radioisotope 16 Collimator collimator 18 Detector array 68 Capacitive filter 80 Bias strip 81 Flexible circuit 82 Common bus bar 86 Electrical pad 92 Resistor 100 Ground layer 102 Foam plastic layer

Claims (22)

a detection device for detecting gamma radiation and generating an electrical signal in response thereto;
A Faraday box for shielding the detection device,
An electronic component that processes the electric signal;
A nuclear imaging apparatus comprising: a reconstruction processor that processes the electric signal to display an image. The nuclear imaging device according to claim 1, wherein the detection device comprises a multi-channel cadmium zinc telluride array. The detection device,
A segmented array of solid state detectors;
A light shield to prevent visible electromagnetic radiation from reaching the array of detectors;
3. A nuclear imaging apparatus according to claim 1 or claim 2, comprising a bias grid for applying a voltage bias to the array of detectors. The bias grid is
A plurality of conductive strips arranged parallel to each other,
The nuclear imaging apparatus according to claim 3, further comprising a power supply strip that supplies a voltage to the conductive strip. The nuclear imaging apparatus according to claim 4, wherein at least one of the conductive strip and the power supply strip is attached to a flexible insulating sheet. 6. The system of claim 4, further comprising at least one capacitor connected between the conductive strip and ground to form a Faraday box, for reducing primary electrical noise generated by the bias grid. A nuclear imaging device according to item 1. The nuclear imaging apparatus according to claim 4 or 5, further comprising a low-frequency filter connected between each bias strip and ground. A plurality of detector arrays are grouped, and one of the conductive strips is connected to and covers a radiation receiving surface of all detectors of one of the groups. The nuclear imaging device according to any one of claims 4 to 7, wherein 9. The power supply strip of claim 4, wherein each of the conductive strips is connected to a power supply strip by a resistive connection separating the conductive strips and defining a plurality of Faraday boxes. Item 6. A nuclear imaging device according to Item 1. The nuclear imaging apparatus according to any one of claims 1 to 9, further comprising a tungsten plate arranged parallel to each other and collimating γ-rays in one dimension. The detection device,
A high-z metal collimating plate arranged parallel to each other to collimate incoming radiation,
10. The nuclear imaging apparatus according to claim 3, further comprising an insulating cushion disposed between the bias grid and the metal collimating plate. A conductive grounding sheet on the surface of the insulating cushion adjacent to the metal collimating plate,
11. The nuclear imaging device of claim 10, further comprising an opaque foam that prevents light and heat from reaching the array of detectors. 13. The device according to claim 1, wherein the detection device has a plurality of detector arrays, and the plurality of detector arrays are shielded by a plurality of Faraday boxes. Nuclear imaging device. The nuclear imaging apparatus according to any one of claims 1 to 13, further comprising a low-frequency filter connected to each of the Faraday boxes. The electronic component has a plurality of event analyzers for determining event information,
15. The event information according to claim 1, wherein the event information includes a logic true of the event that occurred, a position of the detector when the event occurred, and an energy of the event that occurred. A nuclear imaging apparatus according to claim 1. The detection device,
An array of radiation-sensitive detectors;
A bias circuit for applying a high voltage potential between the radiation receiving surface and the opposing surface of the detector array,
An electrically insulating layer disposed on a radiation receiving surface of the bias circuit;
A ground layer provided on the radiation receiving surface of the insulating layer;
The nuclear imaging apparatus according to claim 1, further comprising a high-z metal collimating plate provided in connection with the ground layer and collimating incident radiation. 17. The nuclear imaging apparatus according to claim 16, wherein the detector array includes a plurality of cadmium zinc telluride crystal elements. The bias circuit is
A conductive layer on the radiation receiving surface of the array biased to a negative potential;
18. The nuclear imaging apparatus according to claim 16 or 17, further comprising a capacitor connected between a conductive layer and ground and filtering an electric signal generated by the array of detectors. The array of detectors includes a plurality of detector arrays;
Each group is connected to a separate conductive layer on its radiation receiving surface,
The capacitor may further include a plurality of resistive elements connected between each of the conductive layers and a ground to electrically separate each of the conductive layers to determine a plurality of Faraday boxes. 19. The nuclear imaging device according to 18. A plurality of arrays of solid state radiation detectors, each detector responding to gamma ray reception by emitting electrons; and
A bias strip covering all detectors of at least one said array;
A plurality of conductive pads electrically connected to a detector surface facing the conductive strip;
A voltage source connected between the conductive strip and the conductive pad for applying a bias voltage for attracting free electrons to the conductive pad;
A signal processing circuit connected to the conductive pad and converting free electrons biased to the conductive pad into electronic data;
A nuclear imaging apparatus, comprising: a reconstruction processor connected to the processing circuit and reconstructing the electronic data into an image display. A radiation detector assembly for use with a nuclear imaging device, comprising:
An array of radiation-sensitive detectors;
A bias circuit for applying a high voltage potential between the radiation receiving surface and the opposing surface of the detector array,
An electrically insulating layer disposed on a radiation receiving surface of the bias circuit;
A ground layer provided on the radiation receiving surface of the insulating layer;
A high-z metal collimation plate provided in connection with the ground layer for collimating incident radiation. Applying a bias voltage between the radiation receiving surface and an opposing surface of the array of solid state radiation detectors;
Filtering the bias voltage to remove noise;
Responsive to incident radiation passing through the solid state detector by a current pulse;
A nuclear imaging method comprising the steps of processing and reconstructing the current pulse to display an image.

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