Framework for Photon Counting Quantitative Material Decomposition

Abstract

In this paper, the accuracy of material decomposition (MD) using an energy discriminating photon counting detector was studied. An MD framework was established and validated using calcium hydroxyapatite (CaHA) inserts of known densities (50 mg/cm 3 , 100 mg/cm 3 , 250 mg/cm 3 , 400 mg/cm 3), and diameters (1.2, 3.0, and 5.0 mm). These inserts were placed in a cardiac rod phantom that mimics a tissue equivalent heart and measured using an experimental photon counting detector cone beam computed tomography (PCD-CBCT) setup. The quantitative coronary calcium scores (density, mass, and volume) obtained from the MD framework were compared with the nominal values. In addition, three different calibration techniques, signal-to-equivalent thickness calibration (STC), polynomial correction (PC), and projected equivalent thickness calibration (PETC) were compared to investigate the effect of the calibration method on the quantitative values. The obtained MD estimates agreed well with the nominal values for density (mass) with mean absolute percent errors (MAPEs) 8 ± 11% (9 ± 15%) and 4 ± 6% (9 ± 14%) for STC and PETC calibration methods, respectively. PC displayed large MAPEs for density (27 ± 9%), and mass (25 ± 12%). Volume estimation resulted in large deviations between true and measured values with notable MAPEs for STC (40 ± 90%), PC (40 ± 80%), and PETC (40 ± 90%). The framework demonstrated the feasibility of quantitative CaHA mass and density scoring using PCD-CBCT.

Photon Counting CT: Clinical Applications and Future Developments

“…In addition, the ability to quantify the mass density of materials such as calcium, at high spatial resolution may improve calcium scoring. For instance, Juntunen et al [63] proposed a material decomposition framework (using regularized nonlinear decomposition in projection space) to obtain quantitative calcium density score using PCD-CT as an alternative to the traditional Agatston scoring system widely employed in clinical coronary calcium scoring. While the study was performed in static phantoms, the results demonstrate that a robust and improved calcium scoring method could be achieved using PCD-CT and material decomposition.…”

Quantitative dual contrast photon-counting computed tomography for assessment of articular cartilage health

“…TE and HE images were acquired during imaging and the low energy (LE) images were calculated offline as LE = TE − HE. The LE and HE bins were chosen based on the K-edges of iodine (33.2 keV) and gadolinium (50.2 keV) and on energy response of the PCD-CT system, which shows high-energy drift for photons over 40 keV 40 . Therefore, the upper threshold was set at 60 keV.…”

“…To minimize the effect of beam hardening, we used STC with aluminum plates. STC provides better image quality with less noise than conventional flat field correction 40,41 . This is due to the increased fraction of photoelectric absorption of aluminum, which makes it relatively more comparable to the attenuation properties of iodine and gadolinium.…”

Optimizing iterative reconstruction for quantification of calcium hydroxyapatite with photon counting flat-detector computed tomography: a cardiac phantom study

“…With this simplified imaging model, we do not consider the motion of the heart, nor the attenuation in the torso, but rather focus on the impact of IR on CaHA quantification. Since we have addressed the utility of spectral PC-FDCT for quantification of CAC as previous research, 37 in this study, we focus on low-dose CAC scoring. In contrast to the existing studies, we also compare the CAC scoring performance of IR at different regularization strengths to FBP using customized IR algorithms as they allow more flexibility in their regularization parameter selection than the proprietary algorithms found on commercial scanners.…”