Room: AAPM ePoster Library
Purpose: Photon-counting detector (PCD) based computed tomography (CT) is an emerging spectral imaging technology with great potentials in medical applications. The goal of this work is to analyze the spectral inconsistency of the PCD that is a major common limiting factor to the performance of the PCD based spectral CT, by using flat filters, X-ray tube voltages and energy threshold settings.
Methods: A set of flat filters made of aluminum and Polymethyl Methacrylate (PMMA) are sequentially placed in the beam on our tabletop CT system with an XCounter FilteX1 CdTe PCD (pixel size: 0.1 mm x 0.1 mm). Detector signals are collected at X-ray tube voltages ranging from 80 to 140 kV, and under two energy threshold settings at 24 and 46 keV, respectively. The variability of the measured signals across detector pixels reflects spectral inconsistency as a function of effective spectrum and energy threshold setting. Specifically, during the data processing, air scan without any filter in the beam is divided from the flat filter ones and then row-by-row self-normalized transmission ratios are calculated, which reflect spectral inconsistency of the PCD.
Results: From the row-by-row self-normalized transmission ratios, their values at each pixel varies significantly, with a fluctuation of -10% to +5% when the energy threshold setting and the effective system spectrum changes. Since there are 98% similarity in the cases of changing tube voltages, the variations of energy threshold across detector pixels are seen to play a leading role in the spectral inconsistency, with moderate energy response inconsistency when photon flux is away from the pileup effect.
Conclusion: Our analysis indicates that variation of energy threshold setting across detector pixels is a critical factor that can induce significant spectral inconsistency in photon-counting detector. These findings can provide important physics insights to improve image quality in PCD CT.
Funding Support, Disclosures, and Conflict of Interest: This project was supported in part by the New Faculty Startup Funding of Tsinghua University, Beijing, China (53331100120).