Photon counting detector with comparator and switchover rate analyzer
The invention relates to detectors for radiological imaging, and more particularly the X-ray matrix detectors, produced in the form of a CMOS technology pixel matrix, associated with a structure for converting X-rays into electrons. Each pixel comprises a reading circuit comprising on the one hand a comparator (COMP 1 ) switching over each time a charge increment arrives resulting from the integration of a charge current generated by the lighting and on the other hand a counting circuit (CPT 1 , CPT 2 ) for counting the number of switchovers of the comparator. The circuit for reading each pixel comprises a circuit (CMC) for analyzing the rate of the switchovers of the comparator, this analysis circuit acting on the counting circuit to modify its operation according to the result of the rate analysis. For example, the analysis circuit switches the counting pulses to one counter (CPT 1 ) or another counter (CPT 2 ) depending on the result of the analysis. Applicable in particular to bi-energy radiology and X-photon impact spectrometry analysis.
1. A radiation detector comprising:
one or more detection pixels, in which each pixel comprises a detecting element adapted to generate a current in response to impinging radiation, said pixel comprising:
a reading circuit comprising a capacitor for integrating said current, a comparator switching over each time a predetermined charge increment has been received in the capacitor, means for re-injecting into the capacitor, after said switchover, a compensating charge corresponding to said predetermined charge increment, and a counting circuit for counting a number of switchovers of the comparator, said number representing an energy of radiation received by the detection pixels,
wherein the circuit for reading each pixel comprises a circuit for analyzing a rate of the switchovers of the comparator, this analysis circuit acting on the counting circuit to modify its operation according to the result of the rate analysis.
2. The radiation detector as claimed in claim 1 , wherein the rate analysis circuit is arranged to determine the time interval (T n −T n−1 ) existing between successive switchovers and comparing it to a threshold (V th2 ).
3. The radiation detector as claimed in claim 2 , wherein the reading circuit comprises means for preventing the counting circuit from being incremented if the rate is below a bottom lower threshold value.
4. The radiation detector as claimed in claim 2 , wherein the reading circuit comprises two counters which are used alternately depending on whether the measured rate is above or below a threshold.
5. The radiation detector as claimed in claim 1 , wherein the reading circuit comprises means for interrupting the counting if the switchover rate rises abruptly.
6. The radiation detector as claimed in claim 5 , comprising means for restoring the counting when the switchover rate falls.
7. The radiation detector as claimed in claim 1 , wherein the counting switchover rate analysis circuit comprises means for detecting an abrupt rise or fall in the rate and means for controlling the incrementing of a first counter or of a second counter according to this detection.
8. The radiation detector as claimed in claim 1 , wherein the rate analysis circuit comprises a means of detecting a rapid burst of switchovers, a means for counting the number of switchovers in the burst, and a means for incrementing a first or a second counter depending on whether the number of switchovers in the burst is greater than or less than a threshold.
9. The radiation detector as claimed in claim 1 , wherein the rate analysis circuit comprises a means of detecting a rapid burst of switchovers, a means for counting the number of switchovers in the burst, and a means for switching a counting pulse at the end of the burst to one of several counters according to the number of switchovers in the burst.
10. The radiation detector as claimed in claim 1 , wherein the rate analysis circuit comprises a circuit for integrating a fixed current (I O ) in a capacitor (C O ) for a time interval between two successive switchovers of the comparator.
11. The radiation detector as claimed in claim 1 , which comprises a means for determining a variation, during a series of switchovers, in the time interval between a current switchover and a preceding switchover.
12. The radiation detector as claimed in claim 2 , wherein the reading circuit comprises means for interrupting the counting if the switchover rate rises abruptly.
13. The radiation detector as claimed in claim 3 , wherein the reading circuit comprises means for interrupting the counting if the switchover rate rises abruptly.
14. The radiation detector as claimed in claim 2 , wherein the counting switchover rate analysis circuit comprises means for detecting an abrupt rise or fall in the rate and means for controlling the incrementing of a first counter or of a second counter according to this detection.
15. The radiation detector as claimed in claim 3 , wherein the counting switchover rate analysis circuit comprises means for detecting an abrupt rise or fall in the rate and means for controlling the incrementing of a first counter or of a second counter according to this detection.
16. The radiation detector as claimed in claim 2 , wherein the rate analysis circuit comprises a means of detecting a rapid burst of switchovers, a means for counting the number of switchovers in the burst, and a means for incrementing a first or a second counter depending on whether the number of switchovers in the burst is greater than or less than a threshold.
17. The radiation detector as claimed in claim 3 , wherein the rate analysis circuit comprises a means of detecting a rapid burst of switchovers, a means for counting the number of switchovers in the burst, and a means for incrementing a first or a second counter depending on whether the number of switchovers in the burst is greater than or less than a threshold.
18. The radiation detector as claimed in claim 2 , wherein the rate analysis circuit comprises a means of detecting a rapid burst of switchovers, a means for counting the number of switchovers in the burst, and a means for switching a counting pulse at the end of the burst to one of several counters according to the number of switchovers in the burst.
19. The radiation detector as claimed in claim 3 , wherein the rate analysis circuit comprises a means of detecting a rapid burst of switchovers, a means for counting the number of switchovers in the burst, and a means for switching a counting pulse at the end of the burst to one of several counters according to the number of switchovers in the burst.
20. The radiation detector as claimed in claim 2 , wherein the rate analysis circuit comprises a circuit for integrating a fixed current (I O ) in a capacitor (C O ) for a time interval between two successive switchovers of the comparator.