Advanced temperature compensation and control circuit for single photon counters

Patent metadata

Field	Value
Publication number	US-11079501-B2
Application number	US-201916239609-A
Country	US
Kind code	B2
Filing date	Jan 4, 2019
Priority date	Mar 6, 2009
Publication date	Aug 3, 2021
Grant date	Aug 3, 2021

Abstract

A PET scanner includes a ring of detector modules encircling an imaging region. Each of the detector modules includes one or more sensor avalanche photodiodes (APDs) that are biased in a breakdown region in a Geiger mode. The sensor APDs output pulses in response to light from a scintillator corresponding to incident photons. A reference APD also biased in a breakdown region in a Geiger mode is optically shielded from light and outputs a voltage that is measured by an analog to digital converter. Based on the measurement, a bias control feedback loop directs a variable voltage generator to adjust a bias voltage applied to the APDs such that a difference between a voltage of a breakdown pulse and a preselected logic voltage level is minimized.

First claim

The invention claimed is:

1. A radiation detector for use in imaging comprising:
a plurality of avalanche photodiodes including (1) at least one reference avalanche photodiode which is shielded from light and (2) a plurality of non-shielded avalanche photodiodes configured to receive light photons to be counted;
a biasing circuit configured to bias the plurality of avalanche photodiodes to operate in a Geiger mode in which the at least one reference avalanche photodiode breaks down in response to dark currents and the non-shielded avalanche photodiodes breakdown in response to the dark currents and to receive light photons generating output pulses wherein the biasing circuit is configured to bias each of the plurality of avalanche photodiodes back to the Geiger mode after each breakdown;
a first cooling element thermally coupled to the plurality of avalanche photodiodes and configured to remove heat from the plurality of avalanche photodiodes;
a control circuit configured to count the output pulses generated by the at least one reference avalanche photodiode in response to the dark currents and control the first cooling element in accordance with a rate at which the output pulses from the shielded reference avalanche photodiode are counted.

2. The radiation detector as set forth in claim 1 , wherein the control circuit is further configured to measure a breakdown voltage across at least the at least one reference avalanche photodiode and adjust the bias voltage of the plurality of avalanche photodiodes to a predetermined characteristic logic voltage level.

3. The radiation detector as set forth in claim 1 , wherein the first cooling element includes a Peltier cooling element which is electrically controlled by the controller and further including:
a second cooling element which transfers heat from the Peltier cooling element to ambient surroundings.

4. An imaging apparatus comprising:
a gantry defining an imaging region;
a subject support configured to support a subject in the imaging region;
a detector array that includes a plurality of radiation detectors as set forth in claim 1 ;
an event verification processor configured to analyze detected radiation to determine whether the detected radiation originated from valid events;
a reconstruction processor configured to reconstruct the valid events into an image representation.

5. The radiation detector as set forth in claim 1 , wherein a cathode of each of the plurality of avalanche photodiodes is pinned to a bias voltage and an anode of each of the plurality of avalanche photodiodes is floating, and during a breakdown, current flows from the cathode to the anode of the avalanche photodiode which broke down raising a voltage at the anode until the voltage at the anode reaches the bias voltage, and
wherein in response to reaching the bias voltage, the biasing circuit is configured to bias the avalanche photodiode which broke down back to the Geiger mode.

6. The radiation detector as set forth in claim 5 , wherein the breakdown raises the voltage at the anode to the bias voltage and biases the avalanche photodiode which broke down to zero such that the output pulse in response to each breakdown is of a selected common voltage.

7. The radiation detector as set forth in claim 1 , wherein the control circuit includes two feedback paths, a first feedback path configured to control the bias voltage to bring the output voltage pulses of the reference and the non-shielded avalanche photodiodes to a preselected voltage level and a second feedback path configured to control the first cooling element.

8. The radiation detector as set forth in claim 1 , wherein:
the non-shielded avalanche photodiodes are configured to be connected with a scintillator configured to emit the light photons received by the non-shielded avalanche photodiodes, the non-shielded avalanche photodiodes generating output pulses in response to the light photons and dark currents; and
the at least one shielded reference avalanche photodiode is configured to generate the output pulses in response to dark currents while the non-shielded avalanche photodiodes are generating the output pulses in response to the light photons and the dark currents.

9. The radiation detector as set forth in claim 1 , wherein the control circuit includes two feedback paths, a first feedback path configured to control a magnitude of the output pulse to an amplitude indicative of a logic 1 and a second feedback path configured to control the cooling element to control the rate of the dark currents in the plurality of avalanche photodiodes.

10. The radiation detector as set forth in claim 9 , wherein the non-shielded avalanche photodiodes break down in response to light photons and dark currents and wherein the reference avalanche photodiode breaks down in response to a dark current and further including:
a recharge circuit configured to recharge the avalanche photodiodes in response to the breakdown of the reference avalanche photodiode.

11. The radiation detector as set forth in claim 1 , wherein the at least one reference avalanche photodiode has a cathode connected to a bias voltage line and a floating anode, the output pulse being generated at the cathode; and
wherein the control circuit includes:
a first feedback circuit configured to control the bias voltage on the bias voltage line; and,
a second feedback circuit configured to control the cooling element.

12. The radiation detector as set forth in claim 11 , further including:
a recharge circuit configured to connect the anode of the reference avalanche photodiode to ground in response to each reference avalanche photodiode output pulse to bias the shielded reference avalanche photodiode back to the Geiger mode.

13. The radiation detector as set forth in claim 11 , wherein the breakdown of each avalanche photodiode causes an avalanche current flowing from the cathode to the anode to raise a voltage at the anode toward the bias voltage, the avalanche current stopping when the anode voltage is raised substantially to the bias voltage such that the voltage at an output at the anode rises toward the bias voltage during the avalanche current, and further including a recharge circuit which, in response to the output voltage substantially reaching the bias voltage, is configured to connect the anode with a ground line such that the output becomes low;
wherein the control circuit is configured to adjust the bias voltage based on an amplitude of the output voltage such that the amplitude of the output voltage has a preselected amplitude indicative of a logic 1.

14. A radiation detector for use in imaging comprising:
a plurality of avalanche photodiodes, at least one of the avalanche photodiodes being a reference photodiode which is shielded from light;
a biasing circuit configured to bias the avalanche photodiodes to operate in a Geiger mode in which the avalanche photodiodes breakdown in response to receiving radiation generating an output pulse and the biasing circuit being configured to bias each photodiode back to the Geiger mode after each breakdown;
a first cooling element thermally coupled to the photodiodes and configured to remove heat from the photodiodes;
a control circuit configured to:
measure a breakdown voltage across the at least one reference photodiode and adjust the bias voltage of the photodiodes to a predetermined characteristic logic voltage level,
measure the breakdowns of the at least one reference photodiode and
control the first cooling element in accordance with a rate of the output pulses from the at least one shielded avalanche photodiode.

Assignees

• Koninklijke Philips Nv

Inventors

• Frach Thomas

Classifications

• G01T1/20188

  Auxiliary details, e.g. casings or cooling · CPC title

• G01T1/20182

  Modular detectors, e.g. tiled scintillators or tiled photodiodes (stacked detectors G01T1/20181) · CPC title

• G01T7/005 Primary

  calibration techniques (stabilization of spectrometer G01T1/40) · CPC title

• G01T1/244

  Auxiliary details, e.g. casings, cooling, damping or insulation against damage by, e.g. heat, pressure or the like · CPC title

• G01T1/247 Primary

  Detector read-out circuitry (for processing gain or off-set correction H04N) · CPC title