Photon Counting Detectors for X-Ray Imaging With Emphasis on CT

Abstract

X-ray imaging is a widely used imaging modality in the medical diagnostic field due to its availability, low cost, high spatial resolution, and fast image acquisition. X-ray photons in standard X-ray sources are polychromatic. Detectors that allow to extract the "color" information of the individual X-rays can lead to contrast enhancement, improved material identification or reduction of beam hardening artifacts at the system level, if we compare them with the widely spread energy integrating detectors. Today, in the field of computed tomography (CT), prototypes of clinical grade systems based on spectral photon counting detectors are currently available for clinical research from different companies. One of the key system components in that development is the X-ray photon detector. This article reviews the photon detection hardware, from the conversion of X-rays into electrical signals to the pulse processing electronics. A review of available photon counting application specific integrated circuits (ASICs) for spectroscopic X-ray imaging is presented with emphasis on the CT medical imaging application.

Assessment of multi‐energy inter‐pixel coincidence counters for photon‐counting detectors at the presence of charge sharing and pulse pileup: A simulation study

“…We believe that parameters for these temporal elements were reasonable choices based on our experiences as explained in the following. The peaking time (which is about a half of the pulse duration) of various PCDs currently known are in the range of 8–1000 ns 32 ; thus, the pulse duration of 20 ns is at a lower end of the available PCDs. The pixel boundary delay of PCDs may depend on various factors such as the uniformity of the electric field strengths and the variation of travel lengths, which can be summarized as the small pixel effect 33 …”

Energy Recovery of Multiple Charge Sharing Events in Room Temperature Semiconductor Pixel Detectors

“…At energies greater than the K-shell absorption energy of the CZT material (26.7, 9.7, and 31.8 keV for Cd, Zn, and Te, respectively), the broadening of the charge cloud size can be also increased by the presence of fluorescent X rays, whose emission probability is very high in CZT materials (≈85% of all photoelectric absorptions) [ 25 , 28 ]. The emission of fluorescent X rays of 23.2 keV (Cd-K α1 ) and 27.5 keV (Te-K α1 ) is more probable, with attenuation lengths of 116 and 69 μm, respectively.…”

CdTe Based Energy Resolving, X-ray Photon Counting Detector Performance Assessment: The Effects of Charge Sharing Correction Algorithm Choice

“…The physical geometry modelled here involved a single crystal of CdTe with a cross-section of 21 mm × 21 mm and a variable thickness, T. T was systematically increased from 1 mm to 3 mm in 0.5 mm steps across the various simulations. This range was chosen as it encompasses the range of CdTe thicknesses currently under consideration in the wider community looking at photon counting CT with CdTe [28]. The X-ray source was defined as a 24 mm × 24 mm square, parallel to the sensor material and with their centres in alignment.…”

“…The exact details of this system are covered by a non-disclosure agreement so will not be discussed further here. Pixel pitches of 100 µm-600 µm were modelled, in 50 µm steps, again consistent with the majority of the systems currently used in the field [28]. The pad spacing was held constant across the various geometries, however the anode size and bias voltage were varied to keep the shaping time constant.…”