Affiliation:
1. Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, London SM2 5NG, UK
Abstract
X-ray photon counting spectral imaging (x-CSI) determines a detected photon’s energy by comparing the charge it induces with several thresholds, counting how many times each is crossed (the standard method, STD). This paper is the first to demonstrate that this approach can unexpectedly delete counts from the recorded energy spectrum under some clinically relevant conditions: a process we call negative counting. Four alternative counting schemes are proposed and simulated for a wide range of sensor geometries (pixel pitch 100–600 µm, sensor thickness 1–3 mm), number of thresholds (3, 5, 8, 24 and 130) and medically relevant X-ray fluxes (106–109 photons mm−2 s−1). Spectral efficiency and counting efficiency are calculated for each simulation. Performance gains are explained mechanistically and correlated well with the improved suppression of “negative counting”. The best performing scheme (Shift Register, SR) entirely eliminates negative counting, remaining close to an ideal scheme at fluxes of up to 108 photons mm−2 s−1. At the highest fluxes considered, the deviation from ideal behaviour is reduced by 2/3 in SR compared with STD. The results have significant implications both for generally improving spectral fidelity and as a possible path toward the 109 photons mm−2 s−1 goal in photon-counting CT.
Funder
STFC Cancer Diagnosis Network+
NHS
Subject
Electrical and Electronic Engineering,Biochemistry,Instrumentation,Atomic and Molecular Physics, and Optics,Analytical Chemistry
Reference22 articles.
1. Siemens (2021, November 28). NAEOTOM Alpha® with Quantum Technology. Available online: https://www.siemens-healthineers.com/computed-tomography/photon-counting-ct-scanner/naeotom-alpha.
2. Photon-counting CT for simultaneous imaging of multiple contrast agents in the abdomen: An in vivo study;Symons;Med. Phys.,2017
3. MARS for Clinicians (2021, February 24). MARS Bioimaging Limited. Available online: https://www.marsbioimaging.com/clinicians/.
4. Evaluation of spectral photon counting computed tomography K-edge imaging for determination of gold nanoparticle biodistribution: In vivo;Cormode;Nanoscale,2017
5. GE Healthcare (2021, November 30). Karolinska Institutet & MedTechLabs Kickoff The World’s First Clinical Evaluation of GE Healthcare’s Photon Counting CT Technology with Deep Silicon Detectors. Available online: https://www.ge.com/news/press-releases/karolinska-institutet-medtechlabs-kickoff-the-worlds-first-clinical-evaluation-of-ge#_edn1.