High dynamic range light sensor

1. A dual-mode light sensor for an imaging system detector, including:

an array of photodiodes coupled to one or more scintillation crystals that convert received rays into light; and

a controller that monitors a signal-to-noise ratio (SNR) of signals output by the photodiodes and switches the photodiodes between two modes of operation, including a Geiger mode and a linear mode, based on the monitored signal-to-noise ratio.

2. The sensor according to claim 1 , further including:

an externally programmable lookup table that the controller accesses when selecting the mode of operation.

3. The sensor according to claim 1 , wherein the controller places the photodiodes in the Geiger mode when the signal-to-noise ratio (SNR) is above a predetermined threshold level.

4. The sensor according to claim 3 , further including:

a bias voltage generator that increases a bias voltage applied to the photodiodes to a level that causes the photodiodes to operate in the Geiger mode.

5. The sensor according to claim 1 , wherein the controller places the photodiodes in the linear mode when a signal-to-noise ratio (SNR) of detected rays is at or below a predetermined threshold level.

6. The sensor according to claim 5 , further including:

a bias voltage generator that decreases a bias voltage applied to the photodiodes to a level that causes the photodiodes to operate in the linear mode.

7. The sensor according to claim 1 , wherein the photodiodes are arranged in columns and further including:

an analog to digital converter (ADC) coupled to each column of photodiodes that converts detected gamma ray information from analog format into digital format; and

an adder that adds the voltage levels corresponding to a charge of the respective photodiodes to generate cumulative voltage information.

8. The sensor according to claim 7 , further including;

a Schmidt trigger coupled to each column that determines whether the column of photodiodes is at “0” (ground) or “1” (V excess ); and

a concentrator that converts an N-bit input vector into an M-bit binary value that contains the number of “1s” representing columns of pixels at V excess in the N-bit input vector.

9. The sensor according to claim 8 , further including:

an accumulator that receives the M-bit binary value and the cumulative voltage information and outputs information related to scintillation events detected in the one or more scintillation crystals.

10. The sensor according to claim 7 , wherein the photodiodes define pixels that are arranged in rows and further including:

a row decoder that reads each row of the photodiodes; and

an offset and corrections lookup table that is accessed by a processor that performs dark current subtractions on read-out pixel data and provides correction information to the ADCs.

11. A diagnostic imaging system detector having a plurality of the sensors of claim 1 disposed thereon in a tiled arrangement, each sensor being removably coupled to the detector and coupled to a one or a scintillation crystal and an array of scintillation crystals.

12. The sensor according to claim 1 , wherein each photodiode corresponds to a pixel.

13. A method of extending sensing range for a gamma ray sensor, including:

measuring ambient light conditions at the sensor, including a signal-to-noise ratio (SNR) for rays detected at the sensor;

determining whether the measured SNR is greater than or equal to a predetermined threshold SNR;

applying a first bias voltage to the sensor to cause photodiodes therein to operate in a Geiger mode if the measured SNR is greater than or equal to the predetermined threshold SNR; and

applying a second bias voltage to the sensor to cause photodiodes therein to operate in a linear mode if the measured SNR is less than the predetermined threshold SNR.

14. The method according to claim 13 , further including:

switching the sensor between the Geiger mode and the linear mode as a function of the measured SNR.

15. The method according to claim 14 , further including:

switching the sensor from the Geiger mode to the linear mode when the measured SNR falls below the predetermined threshold SNR.

16. The method according to claim 14 , further including:

switching the sensor from the linear mode to the Geiger mode when the measured SNR equals or rises above the predetermined threshold SNR.

17. A non-transitory computer-readable medium having stored thereon computer-executable instructions for performing the method according to claim 13 .

18. A gamma ray sensor comprising:

an array of photodiodes;

a biasing circuit which is controlled to bias the photodiodes to a Geiger mode or to a linear mode;

a signal-to-noise detector which detects a signal-to-noise ratio of output signals from the photodetectors;

a controller which controls the biasing circuit to bias the photodiodes to the Geiger mode in response to the detected signal-to-noise ratio being above a threshold and to bias the photodiodes to the linear mode in response to the signal-to-noise ratio being at or below the threshold.

19. A gamma ray sensor according to claim 18 , further including:

one or more scintillation crystals that convert received gamma rays into light;

each photodiode coupled to the one or more scintillation crystals and to a sensing transistor and a reset transistor;

a readout transistor coupled to the sensing transistor, that reads a voltage drop across the photodiode;

wherein the photodiode is charged V ex volts over its breakdown voltage by closing the reset transistor and thereafter operates in the Geiger mode to sense single photons; and

wherein the readout transistor senses a voltage drop of V ex volts across the photodiode when a photon is received by the photodiode.

20. The sensor according to claim 19 , further including:

a protection diode that clips a peak voltage at a gate of the readout transistor to protect the readout transistor from breakdown.

21. An imaging system including a plurality of sensors according to claim 19 .