Comparison of Pixelated CdZnTe, CdTe and Si Sensors With the Simultaneously Counting and Integrating CIX Chip

Abstract

CIX is a direct converting hybrid pixel detector designed for medical X-ray imaging applications. Its key feature is the simultaneous counting and integrating of absorbed X-ray quanta, which offers, among other benefits, a large dynamic range as well as the opportunity to calculate the average photon energy of the absorbed spectrum. In this work several different Si, CdTe and CdZnTe sensors are characterized and their suitability as sensor materials for a combined counting and integrating system is assessed. The measurements indicate that temporal stability is an issue for the tested CdTe samples, both on short (ms) and long (s) timescales. Furthermore, the homogeneity of the detector response is addressed and interpreted in terms of lateral polarization. The influence of charge sharing and X-ray fluorescence in the sensor materials will be characterized and their impact on the average photon energy reconstruction will be illustrated through simulations and measurements.

Status of Direct Conversion Detectors for Medical Imaging With X-Rays

“…4 also illustrates the maximum achievable count rate of about 3.3 Mcps/pixel, which corresponds to 26.4 . More performance results of CIX0.2 can be found in [54] and [53].…”

“…This indicates that charge missing in one pixel is recorded in a neighbor pixel, both as additional counts and additional pixel current. This may be explained by a "diversion" of charges, which may be caused by localized polarization effects [52], [53]. Fig.…”

State of the Art of CT Detectors and Sources: A Literature Review

“…In photon counting (PhC) detectors X-ray photons are counted individually and their energy is assessed. To achieve counting of individual photons, the scintillator and photodiode are replaced by a direct conversion material (DiCo) [64,65] and the signal integrating ASIC is replaced by a fast counting ASIC, enabling the processing of charge clouds formed by individual X-ray photons [66][67][68][69]. Photon-counting CT is a disruptive technology, considering the features that contribute to its attractiveness.…”

“…Silicon and GaAs have been considered too for this purpose. A typical ASIC for PhC would have a charge sensitive amplifier to amplify the charge cloud signal and a shaper to shape the signal before discriminating it into energy bin counters [66][67][68][69]. Pixel summing and pile-up correction algorithms are employed to correct the distorted measured spectra [68] and signal pile-up [77].…”

“…2 As a result of the high voltage applied, electrons flow toward a pixelated anode and generate a charge pulse which is amplified by a chargesensitive amplifier and 3 shaped to a signal with a voltage magnitude proportional to the original X-ray photon energy. 4 Discriminating thresholds are set to quantize the voltage signal into energy bins, and 5 counters count the number of photons above set threshold and deliver the number of photons detected within a time unit per energy bin [66][67][68][69] Gantry speeds of 220 r.p.m. in a Philips iCT TM system cause centrifugal accelerations of the tube of 32 g. Hydrodynamic anode bearings have proven to be well scalable with increasing loadings.…”