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Modeling the performance of a photon counting x-ray detector for CT: Energy response and pulse pileup effects
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10.1118/1.3539602
/content/aapm/journal/medphys/38/2/10.1118/1.3539602
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/2/10.1118/1.3539602

Figures

Image of FIG. 1.
FIG. 1.

(Top) The basic architecture of an individual channel in the ASIC. (Bottom) When the pulse height exceeds a given energy threshold value, a count will be added to an associated counter. Coincident photons will be recorded as one event with a higher energy level than the original energies.

Image of FIG. 2.
FIG. 2.

The paralyzable detection model (middle) and the nonparalyzable detection model (bottom). Quasicoincident events will result in lost counts and a distorted recorded spectrum.

Image of FIG. 3.
FIG. 3.

The DXMCT-1 (left) and the experimental setting (right).

Image of FIG. 4.
FIG. 4.

The energy response curve, i.e., the photon energy-pulse height curve. The circles and the error bars are the means and the standard deviations of measurements obtained over all of the comparators. The curve is plotted by Eq. (1) with the means of the three parameters , , and of all of the comparators.

Image of FIG. 5.
FIG. 5.

(Left) The recorded count rates . The curves were plotted using the models with the mean of the estimated parameters of all the comparators. The circles and error bars show the mean counts and the standard deviation over multiple comparators measured at each of the tube current settings. (Right) Probability of events being counted, , plotted using the means of the parameters and estimated for each of the two detector models.

Image of FIG. 6.
FIG. 6.

Area plots of the probability of pileup order given the events-of-interest being recorded, .

Image of FIG. 7.
FIG. 7.

The following three energy spectra for a tube setting of 80 kVp are shown: the mean energy spectrum measured by all of the comparators of DXMCT-1 (labeled in the figure); the energy spectrum predicted by the model of the spectral distortion caused by pulse pileup effects with the nonparalyzable detection model (labeled ); and the scaled incident spectrum, . The estimated incident count rate and deadtime loss ratio under the four tube current settings were and 31% loss at , and 48% loss at , and 58% loss at , and and 64% loss at .

Image of FIG. 8.
FIG. 8.

The following energy spectra for a tube setting of 80 kVp are shown: the mean energy spectrum measured by all of the comparators of DXMCT-1 (labeled in the figure); the energy spectrum estimated by the model of the distorted, recorded spectrum with the nonparalyzable detection model (labeled in the figure); and those with pulse pileup orders (labeled , 1, 2, and 3, respectively, in the figure). The other conditions are the same as in Fig. 7.

Image of FIG. 9.
FIG. 9.

The following three energy spectra for a tube setting of 80 kVp are shown: the mean energy spectrum measured by all of the comparators of DXMCT-1 (labeled in the figure); the energy spectrum predicted by the model of the spectral distortion caused by pulse pileup effects with the paralyzable detection model (labeled ); and the scaled incident spectrum, . The estimated incident count rate and deadtime loss ratio under the four tube current settings were and 19% loss at , and 34% loss at , and 46% loss at , and and 56% loss at .

Image of FIG. 10.
FIG. 10.

The following energy spectra for a tube setting of 80 kVp are shown: the mean energy spectrum measured by all of the comparators of DXMCT-1 (labeled in the figure); the energy spectrum estimated by the model of the distorted, recorded spectrum with the paralyzable detection model (labeled in the figure); and those with pulse pileup order (labeled , 1, 2, and 3, respectively, in the figure). The other conditions are the same as in Fig. 9.

Image of FIG. 11.
FIG. 11.

The flowchart of the method to incorporate the effect of the shift-variant energy resolution into the estimation of the recorded spectrum with pulse pileup effects .

Image of FIG. 12.
FIG. 12.

The effect of the shift-variant finite energy resolution. (a) The incident spectra of the typical comparator: , measured by DXMCT-1 (dashed curve); , processed by the procedure described in Appendix (solid curve); and , filtered with the shift-variant energy resolution (dotted curve). (b) The recorded spectra of the typical comparator, at with paralyzable detection model, estimated with the shift-variant finite energy resolution, , and without, . A linearly scaled incident spectrum is shown as a reference.

Tables

Generic image for table
TABLE I.

Key symbols, abbreviations, and acronyms used in this paper.

Generic image for table
TABLE II.

The RMSD and the COV calculated against the recorded spectra measured by all of the comparators of the DXMCT-1. The numbers in brackets below the tube current values are the mean counts per keV between 30 and 150 keV.

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/content/aapm/journal/medphys/38/2/10.1118/1.3539602
2011-02-01
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Modeling the performance of a photon counting x-ray detector for CT: Energy response and pulse pileup effects
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/2/10.1118/1.3539602
10.1118/1.3539602
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