Method of reading out data in a radiation detector, radiation detector and imaging apparatus
A method of reading out data in a radiation detector having pixels and associated readout circuits, which each have a register. After the pixels detect radiation, data indicative of the radiation is stored in the register(s) of each readout circuit, each time during a plurality of data acquisition periods. Data is read out from the register(s) of each readout circuit, each time during a plurality of readout periods. Each readout period follows a data acquisition period, and each readout period being either a low energy readout period or a high energy readout period. Only data from a single register of each readout circuit indicative of radiation energy above a low energy level is read out during each low energy readout period. Data indicative of radiation energy above a high energy level, higher than the low energy level, is read out during each high energy readout period.
1. A method of reading out data in a radiation detector, wherein the radiation detector comprises a plurality of pixels and a plurality of readout circuits associated with the pixels, and wherein each readout circuit comprises a plurality of registers, the method comprising:
detecting radiation by means of the pixels and storing data indicative of the radiation in one or more of the registers of each readout circuit, each time during a plurality of data acquisition periods; and
reading out data from one or more of the registers of each readout circuit, each time during a plurality of readout periods, each readout period following a data acquisition period, and each readout period being either a low energy readout period or a high energy readout period;
wherein only data from a first register of the registers of each readout circuit indicative of radiation energy above a low energy level is read out during each low energy readout period; and
wherein data from a second register of the registers of each readout circuit indicative of radiation energy above a high energy level, higher than the low energy level, and the data from the first register is read out during each high energy readout period.
2. The method of claim 1 , wherein the low energy level is defined by a first threshold value and the high energy level is defined by a second threshold value, higher than the first threshold value.
3. The method of claim 2 , wherein the second threshold value is variable and set to different values different high energy readout periods.
4. The method of claim 1 , wherein each of the low energy level and the high energy level is defined by a corresponding variable threshold.
5. The method of claim 1 , wherein the readout periods comprise a sequence of a plurality of low energy readout periods between a first high energy readout period and a next high energy readout period following the first high energy readout period.
6. The method of claim 4 , wherein each readout period at least partially overlaps with a next data acquisition period.
7. A radiation detector comprising:
a plurality of pixels configured to detect radiation energy; and
a plurality of readout circuits associated with the pixels, and each readout circuit comprises:
a plurality of comparators, each comparator configured to compare an electrical signal representative of the radiation energy from one of the pixels against a corresponding threshold;
a plurality of registers coupled in series, each register coupled to a corresponding one of the comparators and configured to store data indicative of an electrical signal from the one of the pixels above the corresponding threshold value;
a serial output; and
a switch configured to selectively bypass at least one of the registers such that in a first state, the at least one of the registers is decoupled from the serial output and in a second state, the at least one of the registers is coupled to the serial output.
8. The radiation detector of claim 7 , wherein for each readout circuit:
the comparators comprise:
a first comparator configured to compare the electrical signal from the one of the pixels against a first threshold value representing the radiation energy above a low energy level, and
a second comparator configured to compare the electrical signal from the one of the pixels against a second threshold value representing the radiation energy above a high energy level higher than the low energy level; and
the registers comprise:
a first register configured to store low energy data indicative of the electrical signal from the one of the pixels above the first threshold value, and
a second register configured to store high energy data indicative of the electrical signal from the one of the pixels above the second threshold value.
9. The radiation detector of claim 8 , wherein for each readout circuit:
the comparators comprise:
a third comparator configured to compare the electrical signal from the one of the pixels against a third threshold value representing the radiation energy above a second high energy level; and
the registers comprise:
a third register configured to store high energy data indicative of the electrical signal from the one of the pixels above the third threshold value.
10. The radiation detector of claim 7 , wherein each readout circuit further comprises:
an amplifier configured to receive and amplify the electrical signal from the one of the pixels, and
a pulse shaper configured to shape a waveform of the electrical signal from the one of the pixels, and the pulse shaper is operatively coupled to inputs of the comparators.
11. The radiation detector of claim 7 , further comprising:
a threshold setting device configured to set the threshold values for each readout circuit.
12. The radiation detector of claim 11 , wherein the threshold setting device comprises at least one digital to analog converter (DAC) configured to set at least one of first threshold value and a second threshold value of the threshold values.
13. The radiation detector of claim 11 , wherein for each readout circuit:
the switch is coupled to a serial data input of a first register of the registers and a serial data output of a second register of the registers.
14. The radiation detector of claim 13 , wherein for each readout circuit, the switch is at least a single pole and a double throw (SPDT) switch.
15. The radiation detector of claim 7 , wherein;
the readout circuits comprise a first readout circuit, a last readout circuit, and a plurality of intermediate readout circuits serially coupled between the first readout circuit and the last readout circuit; and
each intermediate readout circuit includes the serial output coupled to a serial input of a next readout circuit.
16. The radiation detector of claim 13 , wherein each of the pixels comprises a conversion element including cadmium telluride (CdTe).
17. An imaging apparatus comprising:
the radiation detector of claim 7 ;
and
a control unit operatively connected to the radiation detector and configured to read radiation data from the radiation detector.
18. The imaging apparatus of claim 17 , wherein:
the control unit is further configured to control the switches of the readout circuits of the radiation detector such that the switch is in the first state for a duration at least 50% longer than a second state.
19. The imaging apparatus of claim 17 , wherein:
the control unit is further configured to variably set the threshold value of a corresponding comparator of each of the readout circuits of the radiation detector to different values in different readout periods.