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A PET scanner (8) includes a ring of detector modules (10) encircling an imaging region (12). Each of the detector modules includes at least one detector pixel (24,34). Each detector pixel includes a scintillator (20, 30) optically coupled to one or more sensor APDs (54) that are biased in a breakdo

A PET scanner (8) includes a ring of detector modules (10) encircling an imaging region (12). Each of the detector modules includes at least one detector pixel (24,34). Each detector pixel includes a scintillator (20, 30) optically coupled to one or more sensor APDs (54) that are biased in a breakdown region in a Geiger mode. The sensor APDs output a pulse in response to the light from the scintillator corresponding to a single incident radiation photon. A reference APD (26, 36) also biased in a break-down down region in a Geiger mode is optically shielded from light and outputs a temperature dependent signal. At least one temperature compensation circuit (40) adjusts a bias voltage applied to the sensor APDs based on the temperature dependent signal.

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1. A radiation detector module for use in diagnostic imaging, the detector module comprising: at least one detector pixel, each detector pixel including a scintillator optically coupled to one or more sensor APDs that are biased in a breakdown region in a Geiger-mode, the sensor APDs being configure

1. A radiation detector module for use in diagnostic imaging, the detector module comprising: at least one detector pixel, each detector pixel including a scintillator optically coupled to one or more sensor APDs that are biased in a breakdown region in a Geiger-mode, the sensor APDs being configured to output a current pulse in response to light from the scintillator corresponding to a single incident radiation photon;at least one reference detector configured to output a temperature dependent signal, the reference detector including: at least one reference APD biased in a breakdown region in the Geiger mode and configured to output a current pulse in response to each breakdown event triggered by a thermal generation of an electron-hole pair;at least one temperature compensation circuit configured to adjust a voltage bias applied to the sensor APDs based on the temperature dependent signal. 2. The radiation detector according to claim 1, wherein the at least one reference APD is optically isolated such that the output of the at least one APD is independent of light output by the scintillator. 3. The radiation detector module according to claim 2, further including: an active or passive quenching circuit coupled with the at least one reference APD which quenches the at least one reference APD after each breakdown event such that the at least one reference APD outputs a series of pulses at a rate which is indicative of temperature. 4. The radiation detector module according to claim 3, wherein the temperature compensation circuit further includes: a gated counter connected to at least one corresponding reference APD to receive output pulses therefrom and configured to output a dark current count rate for the at least one corresponding reference APD;a controller configured to output a control signal based on the dark count rate;a variable voltage source configured to adjust the voltage bias applied to corresponding sensor APDs; andwherein the reference APD is statically biased. 5. The radiation detector module according to claim 4, wherein the controller outputs a digital control signal which is (i) determined from an algorithm that incorporates the dark count rate in a formulation, or (ii) determined from a look-up table that associates the dark count rate with a corresponding output and further including: an analog-to-digital converter which converts the digital signal to an analog control signal that is applied to the variable voltage source. 6. The radiation detector module according to claim 2, wherein each reference APD is disposed in a gap between adjoining pixels. 7. The radiation detector module according to claim 2, wherein the sensor APDs, the reference APDs, and the at least one temperature compensation circuit are disposed monolithically on a common silicon substrate. 8. A plurality of the detector modules according to claim 1, in which the modules are mounted in a close-packed array. 9. The plurality of detector modules according to claim 8, wherein each module is rectangular and the modules are mounted in a rectangular array. 10. A PET scanner including: a plurality of the radiation detection modules according to claim 2, geometrically arranged about an imaging region;a coincidence detector which detects pairs of detected radiation events and determines lines of response corresponding to the coincident pairs; anda reconstruction processor which reconstructs the lines of response into an image representation. 11. The PET scanner according to claim 10, wherein the sensor APDs of each detector module further includes a time stamp circuit which associates a time stamp(s) with the pulses from the pixels and wherein the temperature compensation circuit is further configured to temporally adjust the time stamp circuit based on the temperature dependent signal. 12. A method of compensating for temperature changes of a radiation detector module used in diagnostic imaging, the method comprising: generating output pulses from pixels, each pixel including at least one sensor APD which is biased in a breakdown region in a Geiger mode in response to light from an associated scintillator causing one or more of the sensor APDs to break down:with a reference APD biased in a breakdown region in the Geiger mode and shielded from light, generating a temperature dependent dark current based on thermally generated electron hole pairs;adjusting a bias voltage applied to the sensor APDs based on the temperature dependent dark current. 13. The method according to claim 12, further including: periodically quenching the reference APD; andcounting a pulse rate of the dark current. 14. The method according to claim 13, further including: converting the counted pulse rate into a bias voltage;applying the bias voltage to the sensor APDs. 15. A method of making a radiation detector module comprising: forming an array of APDs;optically coupling sensor APDs with scintillators;optically shielding at least one reference APD;mounting the optically shielded at least one reference APD to the scintillator, the at least one reference APD being optically shielded from the scintillator;biasing the sensor and reference APDs to a breakdown region in a Gieger mode such that the sensor APDs breakdown in response to light from the scintillators and the at least one reference APD breaks down in response to a thermal generation of an electron-hole pair;quenching the sensor and reference APDs which break down such that the sensor APD generates a series of pulses indicative of light received from the scintillators and the least one reference APD generates a series of pulses indicative of temperature;connecting the optically shielded reference APD with a temperature compensation circuit which adjusts a bias voltage applied to the sensor APDs based on the series of pulses from the at least one reference APD. 16. The method according to claim 15, wherein the array of sensor APDs are formed with a gap between pixels and the at least one reference APD is formed in the gap. 17. The method according to claim 15, wherein a plurality of the optically shielded reference APDs are defined among the APDs which are coupled to the scintillators. 18. A radiation detector module for use in radiation emission tomography, the detector module comprising: at least one monolithically disposed detector pixel, each detector pixel including a scintillator optically coupled to one or more sensor APDs that are biased in a breakdown region in a Geiger-mode and connected with quenching circuits, the sensor APDs being optically coupled to the scintillator and configured to output a current pulse in response to light from the scintillator corresponding to a single incident radiation photon;at least one monolithically disposed reference APD optically isolated from the scintillator, statically biased in a breakdown region in the Geiger mode, and configured with at least one quenching circuit to output a current pulse in response to each breakdown event triggered by a thermal generation of an electron-hole pair;at least one monolithically disposed temperature compensation circuit configured to determine a corrected voltage bias based on a rate of the thermally generated break down events; andat least one monolithically disposed variable voltage source configured to adjust the voltage bias applied to sensor APDs to apply the corrected voltage bias determined by the temperature compensation circuit.