Device and method for determining the assumed position of a phenomenon relative to a set of photodetectors, and application to gamma-cameras

• US 6,326,624 B1
• Filed: 06/15/1999
• Issued: 12/04/2001
• Est. Priority Date: 11/08/1996
• Status: Expired due to Fees

• Current Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission)
• Original Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission)
• Inventors: Chapuis, Alain, Tararine, Michel, Mestais, Corinne, Janin, Claude
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): HANIG, RICHARD E
• Application Number:
  US09/284,977
• Time in Patent Office: 903 Days
• Field of Search: 250/369, 250/363.02, 250/363.09, 250/370.11, 250/370.12, 250/390.11, 702/150
• US Class Current: 250/369
• CPC Class Codes: G01T 1/1647 Processing of scintigraphic data not related to a particular imaging system G01T1/2992
• CPC Class Codes: G01T 1/208 Circuits specially adapted for scintillation detectors, e.g. for the photo-multiplier section
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof

Abstract

Method and apparatus for determining a position of an event. The system processes signals from an assembly of N photodetectors and includes a signal generator for producing a signal representing the value of the maximum, or the energy, of a pulse delivered by the photodetector and is digitized. It also includes a signal generator for producing a threshold-exceeded signal for each photodetector when the amplitude of the signal representing the value of the maximum, or the energy, of the digitized pulse is greater than the threshold. It also includes a signal generator common to the photodetectors, for delivering a signal representing a position of an event as a function of the threshold-exceed signals. This device can be used with gamma cameras.

Claims

1. A device for processing signals from an assembly of N photodetectors having:

a) means, associated with each photodetector, for producing a signal representing the value of one of a group consisting of the maximum, or the energy, of a pulse delivered by the photodetector and digitized;

b) means for producing a signal of exceeding of a threshold for each photodetector when the amplitude of the signal representing the value of one of the group consisting of the maximum, or the energy, of the pulse is greater than the said threshold; and

c) means, common to the photodetectors, for delivering a signal representing a position of an event as a function of the threshold-exceeded signals, these means constituting means for delivering;

1) a first signal, representing a first position, if a single threshold-exceeded signal is delivered, coming from any first photodetector among the N photodetectors;

2) a second signal, representing a second position, if a single threshold-exceeded signal is delivered, coming from a second photodetector, a neighbor of the photodetector; and

3) a third signal, representing a third position, different from the first and second positions, if two threshold-exceeded signals corresponding to the first and second neighboring photodetectors are issued.

2. A device according to claim 1, also having means, associated with each photodetector, for detecting the timewise position of the maximum of the digitized pulse and for delaying the issuing of the threshold-exceeded signal for a certain duration from the said timewise position.

3. A device according to claim 1, further having:

means for forming a total analog signal, equal to the sum of the analog signals delivered by N₁ photodetectors (N₁≦

N);

means for delivering a signal representing the timewise position of the maximum of the total analog signal; and

means for delaying the delivery of the signal representing the position of an event for a certain time interval running from the timewise position of the maximum of the total analog signal.

4. A device according to claim 1, the means for delivering a signal representing the position of an event being such that the said signal depends only on threshold-exceeded signals produced inside a time slot whose instant of origin is fixed with a shift with respect to each event.

5. A device according to claim 1, the means for delivering a signal representing a position being such that such a signal is issued only if all the threshold-exceeded signals produced correspond to neighboring photodetectors.

6. A device according to claim 1, further having, for each photodetector, means of digitizing a pulse delivered by the photodetector, the digitizing being performed with a duration p.

7. A device according to claim 6, each threshold-exceeded signal being issued for a duration greater than or equal to 3 p.

8. A device for detecting events including a device according to claim 1, having:

a two-dimensional array of N photodetectors, defining a map;

digitization means, associated with each photodetector;

the device according to claim 1.

9. A device according to claim 8, the signal representing a position of an event having a first component and a second component, each component corresponding to a coordinate of the event located in the map of the two-dimensional photodetector array.

10. A device according to claim 8, the photodetectors being disposed in a square array.

11. A device according to claim 10, the photodetectors having a square cross-section.

12. A device according to claim 8, the photodetectors being disposed in a hexagonally symmetrical array.

13. A device according to claim 12, the photodetectors having a hexagonal or circular cross-section.

14. A device according to claim 1, the means for delivering a signal representing a position of an event not delivering any position signal when two threshold-exceeded signals are issued by non-neighboring photodetectors.

15. A device for processing signals from an assembly of N photodetectors, having:

a) N digital coding units;

b) one of a group consisting of digital summation means or maximum amplitude detection means, associated with each digital coding unit;

c) means of comparing an output signal from the one of the group consisting of the digital summation means or the maximum amplitude detection means, with a predetermined value; and

d) at least one read-only memory, addressed by the outputs of the comparing means, and configured to deliver;

1) a first signal, representing a first position, if a single threshold-exceeded signal is delivered, coming from any first photodetector among the N photodetectors;

2) a second signal, representing a second position, if a single threshold-exceeded signal is delivered, coming from a second photodetector, a neighbor of the first photodetector; and

3) a third signal, representing a third position, different from the first and second positions, if two threshold-exceeded signals corresponding to the first and second neighboring photodetectors are issued.

16. A device according to claim 15, further having, associated with each digital coding unit:

means of detecting the timewise position of the maximum of a digitized pulse, these means being controlled by the corresponding digital coding unit;

a shift register; and

an AND gate controlled by the output of the comparing means and the output of the shift register.

17. A device according to claim 15, further having:

analog summation means intended to receive, at the input, the outputs of the N photodetectors;

means of detecting a maximum of an analog signal, controlled by the analog summation means;

a shift register controlled by the maximum detecting means; and

a register controlled by the read-only memory and by the previous shift register.

18. A device according to claim 15, having two read-only memories.

19. A device for detecting events including a device according to claim 15, having:

a two-dimensional array of N photodetectors; and

the device according to claim 15.

20. A camera having a device according to claim 19, the photodetectors being photomultipliers.

21. A gamma radiation imaging device, having a camera according to claim 20.

22. A method of processing signals produced by an assembly of N photodetectors, in response to an event, this method including:

a) for each photodetector, producing a signal representing the value of the maximum, or the energy, of a pulse delivered by the photodetector and digitized;

b) producing a signal of exceeding of a threshold, for each photodetector, when the amplitude of the signal representing the value of one of a group consisting of the maximum, or the energy, of the digitized pulse, is greater than the said threshold; and

c) forming a signal representing a position of an event as a function of the threshold-exceeded signals, the forming step constituting;

1) forming a first signal, representing a first position, if a single threshold-exceeded signal is delivered, coming from any first photodetector among the N photodetectors;

2) forming a second signal, representing a second position, if a single threshold-exceeded signal is delivered, coming from a second photodetector, a neighbor of the first photodetector; and

3) forming a third signal, representing a third position, different from the first and second positions, if two threshold-exceeded signals corresponding to the first and second neighboring photodetectors are issued.

23. A method according to claim 22, further including, for each photodetector, detection of the timewise position of the maximum of the digitized pulse, and delaying of the issuing of the threshold-exceeded signal for a certain duration from the said timewise position.

24. A method according to claim 22, further including:

forming a total analog signal, equal to the sum of the analog signals delivered by N₁ photodetectors (N₁≦

N);

delivering a signal representing the timewise position of the maximum of the total analog signal; and

delaying the delivery of the signal representing the position of an event for a time interval running from the timewise position of the maximum of the total analog signal.

25. A method according to claim 22, the forming of a signal representing the position of an event being such that the said signal depends only on threshold-exceeded signals produced inside a time slot whose instant of origin is fixed with a shift with respect to each event.

26. A method according to claim 22, the forming of a signal representing a position being such that a signal is issued only if all the threshold-exceeded signals produced correspond to neighboring or related photodetectors.

27. A method according to claim 22, further including, for each photodetector, a step of digitizing a pulse delivered by the photodetector, the digitizing being performed with a certain duration p.

28. A method according to claim 27, each threshold-exceeded signal being issued for a duration greater than or equal to 3 p.

29. A method for detecting events in relation to a two-dimensional array of photodetectors, defining a map, digitization means being associated with each photodetector, this method including a signal processing method to according to claim 22.

30. A method according to claim 29, the signal representing a position of an event having a first component and a second component, each component corresponding to a coordinate of the event located in the map of the two-dimensional photodetector array.

31. A method according to claim 22, the forming of a signal representing a position of an event being such that no position signal is formed or delivered when two threshold-exceeded signals are issued by non-neighboring photodetectors.

32. A method according to claim 22, the photodetectors being photomultipliers of a gamma camera.

33. An attenuation equalization by transmission imaging method, implementing the method according to claim 32.

34. A coincidence PET imaging method, implementing the method according to claim 32.