Calibration methods for improving uniformity in X-ray photon counting detectors
Various aspects include methods for use in X-ray detectors for adjusting count measurements from pixel detectors within a pixelated detector module to correct for the effects of pileup events that occur when more than one photon is absorbed in a pixel detector during a deadtime of the detector system. In various embodiments, count measurements may be obtained at two different X-ray tube currents, from which the detector system deadtime may be calculated based on the two count measurements and a ratio of the two X-ray tube currents. Using the calculated deadtime, a pileup correction factor may be determined appropriate for the behavior of the detector system in response to pileup events. The pileup correction factor may be applied to pixel detector count values after the counts have been corrected for pixel-to-pixel differences using a flat field correction.
1. A method of correcting the output from pixel detectors within a pixelated detector of an imaging X-ray system, comprising:
determining a pileup correction factor based on count measurements obtained at two different X-ray tube current levels; and
applying the pileup correction factor to pixel detector count measurements obtained while imaging an object to obtain pixel detector counts corrected for pileup effects;
wherein the determining the pileup correction factor based on count measurements obtained at two different X-ray tube current levels comprises:
obtaining first count measurements in the pixel detectors while operating the imaging X-ray system at a first X-ray tube current level;
obtaining second count measurements in the pixel detectors while operating the imaging X-ray system at a second X-ray tube current level, wherein the second X-ray tube current level is different from the first X-ray tube current level;
using the first and second count measurements and a ratio of the first X-ray tube current level to the second X-ray tube current level to determine a deadtime of the pixelated detector; and
determining the pileup correction factor based upon the determine deadtime of the pixelated detector and a pileup model appropriate to a response of the pixelated detector to pileup events.
2. The method of claim 1 , wherein the pileup correction factor is equal to (1−M×τ), in which M is the measured counts to be corrected and τ is the determined deadtime of the pixelated detector.
3. The method of claim 1 , wherein applying the pileup correction factor to pixel detector count measurements obtained while imaging an object to obtain pixel detector counts corrected for pileup effects comprises:
applying a flat field correction to the pixel detector count measurements obtained while imaging the object to obtain pixel detector counts corrected for pixel-to-pixel variability; and
applying the pileup correction factor to the pixel detector counts corrected for pixel-to-pixel variability to obtain pixel detector counts corrected for pileup effects.
4. The method of claim 3 , further comprising determining the flat field correction by:
obtaining dark-field noise measurements of the pixel detectors with the X-ray tube off; and
determining the flat field correction based on the dark-field noise measurements and the first count measurements.
5. An imaging X-ray detector comprising a plurality of pixel detectors and means for performing functions of the method of claim 1 .
6. Circuitry for use with an X-ray detector comprising a plurality of pixel detectors and means for performing functions of the method of claim 1 .
7. An imaging X-ray detector, comprising:
a pixelated X-ray detector comprising a plurality of pixel detectors; and
a processor configured with processor-executable instructions to perform operations of the method of claim 1 .