Signal processing method for gamma-ray semiconductor sensor

• US 5,825,033 A
• Filed: 10/31/1996
• Issued: 10/20/1998
• Est. Priority Date: 10/31/1996
• Status: Expired due to Fees

• Current Assignee: Arizona Board of Regents (University of Arizona)
• Original Assignee: Arizona Board of Regents (University of Arizona)
• Inventors: Barber, H. Bradford, Marks, Daniel G., Eskin, Joshua D., Barrett, Harrison H.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US08/742,252
• Time in Patent Office: 719 Days
• Field of Search: 250/370.1, 250/370.09, 250/371, 250/369
• US Class Current: 250/370.1
• CPC Class Codes: H01L 27/14658 X-ray, gamma-ray or corpuscular radiation imagers measuring X-, gamma- or corpuscular radiation G01T1/00

Abstract

A CdZnTe detector array with pixel electrodes indium-bump-bonded to a multiplexer readout circuit. The pixel size is selected so as to minimize the effect of hole trapping while ensuring that all interacting electrons deposit their energy in a designated central pixel. The readout is carried out either when a gamma-ray interaction event occurs or at time intervals likely to produce no more than one event of photon interaction at any given pixel. The readout signal for each pixel is compared to a corresponding threshold signal to identify clusters of adjacent pixels having an above-threshold signal. Then, a central pixel is designated for each cluster, the signals from a predetermined number of pixels in and/or neighboring the cluster are added to produce a cumulative signal, and the cumulative signal is assigned to the designated central pixel. The cumulative signals so produced and the positions of corresponding central pixels are then processed to generate an image of the gamma-ray emitting source. According to other embodiments of the invention, the signals from a predetermined number of pixels in and/or neighboring the clusters are used to estimate spatial coordinates and energy of each interaction event or to estimate the spatial and energy distribution of the fluence of events of gamma-ray interaction with the detector.

Claims

1. A method of estimating spatial and energy parameters of gamma rays interacting with a semiconductor detector, wherein a slab of semiconductor material is positioned in a field of view of an aperture imaging system to receive gamma rays from a gamma-ray emitting source, said semiconductor material being capable of absorbing incident gamma rays;

wherein said slab of semiconductor material is subjected to an electric field between an electrode attached to a side of the slab exposed to radiation and a plurality of electrodes attached to another side of the slab, whereby the slab is partitioned into a corresponding plurality of sensor-cell pixels individually capable of producing an electric current pulse when a gamma ray is absorbed within a pixel;

wherein a monolithic multiplexer is coupled to said plurality of electrodes for the read-out of electric pulses generated in each of said pixels as a result of gamma-ray absorption events; and

wherein the current-pulse output of each pixel is integrated during each step of operation of said monolithic multiplexer by accumulation in a corresponding capacitor means that is discharged at predetermined times producing a voltage signal through a single-output channel of the multiplexer and that is then reset for charging during a next step of operation;

said method comprising the following steps;

(a) comparing said voltage signal for each pixel to a corresponding predetermined threshold signal and identifying all pixels having an above-threshold voltage signal;

(b) identifying clusters of adjacent pixels having above-threshold voltage signals and selecting a pixel within each cluster as a central pixel for the cluster;

(c) summing all voltage signals of adjacent pixels within a predetermined range of said central pixel to produce a cumulative voltage signal for the cluster and assigning said cumulative voltage signal to the central pixel of the cluster; and

(d) processing the cumulative voltage signal generated in step (c) for each cluster as an output signal associated with a spatial coordinate of said corresponding central pixel for constructing an image of the gamma-ray emitting source.

2. The method described in claim 1, wherein said predetermined range includes pixels having a voltage signal below said threshold signal.

3. The method described in claim 1, wherein said voltage signal for each pixel is read out at predetermined time intervals.

4. The method described in claim 1, wherein said voltage signal for each pixel is read out each time a gamma-ray interaction event occurs.

5. The method described in claim 1, wherein said electrode attached to a side of the slab of semiconductor material exposed to radiation consists of plurality of electrodes, whereby pixel arrays exist on both sides of the slab.

6. A method of estimating spatial-coordinate and energy parameters of gamma rays interacting with a semiconductor detector for which a probability distribution is known relating spatial and energy parameters of each interaction event, wherein a slab of semiconductor material is positioned in a field of view of an aperture imaging system to receive gamma rays from a gamma-ray emitting source, said semiconductor material being capable of absorbing incident gamma rays;

wherein said slab of semiconductor material is subjected to an electric field between an electrode attached to a side of the slab exposed to radiation and a plurality of electrodes attached to another side of the slab, whereby the slab is partitioned into a corresponding plurality of sensor-cell pixels individually capable of producing an electric current pulse when a gamma ray is absorbed within a pixel;

wherein a monolithic multiplexer is coupled to said plurality of electrodes for the read-out of electric pulses generated in each of said pixels as a result of gamma-ray absorption events; and

wherein the current-pulse output of each pixel is integrated during each step of operation of said monolithic multiplexer by accumulation in a corresponding capacitor means that is discharged at predetermined times producing a voltage signal through a single-output channel of the multiplexer and that is then reset for charging during a next step of operation;

said method comprising the following steps;

(a) comparing said voltage signal for each pixel to a corresponding predetermined threshold signal and identifying all pixels having an above-threshold voltage signal;

(b) identifying clusters of adjacent pixels having above-threshold voltage signals; and

, for each such cluster, recording the voltage signal and coordinate position of a predetermined number of adjacent pixels within a predetermined range of pixels intersecting said cluster;

(c) utilizing said probability distribution for gamma rays interacting with the semiconductor detector to calculate a maximum-likelihood estimate of a spatial coordinate and an energy level for each gamma-ray interaction event recorded within each cluster; and

(d) processing the spatial coordinate and energy level for each recorded gamma-ray interaction event generated in step (c) for each cluster as output signals for constructing an image of the gamma-ray emitting source.

7. The method described in claim 6, wherein said predetermined range includes pixels having a voltage signal below said threshold signal.

8. The method described in claim 6, wherein said voltage signal for each pixel is read out at predetermined time intervals.

9. The method described in claim 6, wherein said voltage signal for each pixel is read out each time a gamma-ray interaction event occurs.

10. The method described in claim 6, wherein said probability distribution consists of a theoretical model with parameters fitted to data obtained from detector measurements.

11. The method described in claim 6, wherein said electrode attached to a side of the slab of semiconductor material exposed to radiation consists of plurality of electrodes, whereby pixel arrays exist on both sides of the slab.

12. A method of estimating a spatial and an energy distribution of a fluence of gamma rays interacting with a semiconductor detector when a probability distribution is known relating spatial and energy parameters of each interaction event, wherein a slab of semiconductor material is positioned in a field of view of an aperture imaging system to receive gamma rays from a gamma-ray emitting source, said semiconductor material being capable of absorbing incident gamma rays;

wherein said slab of semiconductor material is subjected to an electric field between an electrode attached to a side of the slab exposed to radiation and a plurality of electrodes attached to another side of the slab, whereby the slab is partitioned into a corresponding plurality of sensor-cell pixels individually capable of producing an electric current pulse when a gamma ray is absorbed within a pixel;

wherein a monolithic multiplexer is coupled to said plurality of electrodes for the read-out of electric pulses generated in each of said pixels as a result of gamma-ray absorption events; and

wherein the current-pulse output of each pixel is integrated during each step of operation of said monolithic multiplexer by accumulation in a corresponding capacitor means that is discharged at predetermined times producing a voltage signal through a single-output channel of the multiplexer and that is then reset for charging during a next step of operation;

said method comprising the following steps;

(a) comparing said voltage signal for each pixel to a corresponding predetermined threshold signal and identifying all pixels having an above-threshold voltage signal;

(b) identifying clusters of adjacent pixels having above-threshold voltage signals and recording the voltage signal and coordinate position of a predetermined number of adjacent pixels within a predetermined range of pixels intersecting said cluster;

(c) utilizing said probability distribution for gamma rays interacting with the semiconductor detector to calculate a maximum-likelihood estimate of a spatial distribution and an energy distribution of a fluence of recorded gamma-ray interaction events; and

(d) processing said spatial distribution and energy distribution of a fluence of recorded gamma-ray interaction events generated in step (c) for constructing an image of the gamma-ray emitting source.

13. The method described in claim 12, wherein said predetermined range includes pixels having a voltage signal below said threshold signal.

14. The method described in claim 12, wherein said voltage signal for each pixel is read out at predetermined time intervals.

15. The method described in claim 12, wherein said voltage signal for each pixel is read out each time a gamma-ray interaction event occurs.

16. The method described in claim 12, wherein said probability distribution consists of a theoretical model with parameters fitted to data obtained from detector measurements.

17. The method described in claim 12, wherein said electrode attached to a side of the slab of semiconductor material exposed to radiation consists of plurality of electrodes, whereby pixel arrays exist on both sides of the slab.