High energy photon detection using pulse width modulation

1. A method of processing an analog signal that is generated by a high energy photon detector in response to a high energy photon interaction, the method comprising:

receiving the analog signal;

generating a digital edge representing the time of the interaction from the analog signal along a first path;

encoding the energy of the interaction as a delay from the digital edge from the analog signal along a second path;

wherein said generated digital edge and said delay encode the time and energy of the analog signal using pulse width modulation;

wherein said encoding the energy comprises:

converting the analog signal to a converted signal having a first edge and a falling signal edge with constant slope decay from a peak, wherein the peak is proportional to an integral of a charge of the analog signal:

determining a length of time for the converted signal to decay to zero from the peak; and

encoding said determined length of time as the delay from the digital edge.

2. The method of claim 1 , wherein said generating a digital edge comprises:

employing an amplitude-independent timing circuit to encode a time of the interaction as the digital edge.

3. The method of claim 1 , wherein the high energy photon interaction is one of a pair of coincident interactions of high energy photons with a high energy photon detector generated from a positron-electron annihilation event.

4. The method of claim 1 , further comprising:

digitally encoding at least one of the spatial location of the high energy photon interaction and an identification of the detector using pulse width modulation.

5. The method of claim 4 , further comprising:

providing a combined signal comprising said digital edge, said encoded energy, and said digitally encoded at least one of spatial location and said digitally encoded identification;

transmitting said provided digital signal on a multiplexed output line.

6. The method of claim 5 , wherein said output line is at least one of electrical and optical in nature.

7. The method of claim 1 ,

wherein said determining a length of time is conducted on a first channel having the converted signal as an input.

8. The method of claim 7 , wherein said determining a length of time comprises:

detecting the peak of the converted signal;

providing a delay for the converted signal that is dependent on an amplitude of the detected peak;

determining the length of time based on said provided delay.

9. The method of claim 1 , further comprising:

providing a multi-detector combined signal for a detection system comprising a plurality of high energy photon detectors;

wherein said providing comprises, for each of the high energy photon detectors, providing a generated digital edge representing the time of a high energy photon interaction and an encoded energy of the interaction as a delay from the digital edge;

wherein the generated digital edge and the delay encode the time and energy of the analog signal using pulse width modulation.

10. The method of any of claim 1 , further comprising:

decoding said generated digital edge and delay using a time-to-digital converter.

11. A front-end device for processing an analog signal that is generated by a high energy photon detector in response to a high energy photon interaction, the front-end device comprising:

a time encoding circuit along a first path that generates a digital edge representing the time of the interaction;

an energy encoding circuit along a second path that encodes the energy of the interaction as a delay from the digital edge;

wherein said time encoding circuit and said energy encoding circuit encode the time and energy of the analog signal using pulse width modulation;

wherein said encoding the energy comprises:

converting the analog signal to a converted signal having a first edge and a falling signal edge with constant slope decay from a peak, wherein the peak is proportional to an integral of a charge of the analog signal;

determining a length of time for the converted signal to decay to zero from the peak;

encoding said determined length of time as the delay from the digital edge.

12. The front-end device of claim 11 , further comprising:

a preamplifier for receiving the analog signal and integrating the analog signal.

13. The front-end device of claim 12 , wherein said energy encoding circuit is coupled to said preamplifier to receive said integrated signal along the first path.

14. The front-end device of claim 13 , wherein said time encoding circuit is coupled to said preamplifier to receive said integrated signal along the second path.

15. The front-end device of claim 14 , wherein said preamplifier comprises a charge sensitive preamplifier.

16. The front-end device of claim 14 , wherein said time encoding circuit comprises a timing discriminator.

17. The front-end device of claim 14 , wherein said energy encoding circuit comprises:

a peak detector for converting the integrated signal and detecting the peak of the converted signal;

a delay circuit for providing a delay dependent on an amplitude of the converted signal.

18. The front-end device of claim 17 , wherein said peak detector further comprises:

a comparator for determining when the falling signal edge of the converted signal reaches a threshold.

19. The front-end device of claim 17 , wherein said peak detector further comprises:

a shaper for shaping the integrated signal and providing the converted signal, the converted signal having a falling signal edge with a constant slope.

20. A front end for an imaging system, comprising:

at least one high-energy photon detector comprising at least one detector channel; and

the front-end device of claim 11 .

21. An imaging system comprising:

the front end of claim 20 ; and

a readout system coupled to said front end.

22. The imaging system of claim 21 , wherein said readout system comprises a time-to-digital converter.

23. The imaging system of claim 21 , wherein said front end comprises a digital bus.

24. An imaging system comprising:

a front-end device for processing an analog signal that is generated by a high energy photon detector in response to a high energy photon interaction; and a readout system coupled to said front-end device; wherein the front-end device comprises:

a time encoding circuit along a first path that generates a digital edge representing the time of the interaction; and

an energy encoding circuit along a second path that encodes the energy of the interaction as a delay from the digital edge;

wherein said time encoding circuit and said energy encoding circuit encode the time and energy of the analog signal using pulse width modulation;

wherein said front-end device is disposed within a magnetic resonance imaging (MRI) system;

wherein said front-end device is coupled to said readout system via an optical coupling to reduce interference between said front-end device and said MRI system.