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/cm3, 100 mg/cm3, 250 mg/cm3, 400 mg/cm3), 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.
Highlights
S PECTRAL computed tomography (CT) enables discrimination of different materials and improved tissue contrast by utilizing polychromatic X-ray attenuation information [1]–[3]
This study aims to establish a framework for material decomposition (MD) using dual-energy photon counting detectors (PCDs) measurements and apply it for quantifying coronary artery calcium (CaHA) in an experimental setting
3) Projected Equivalent Thickness Calibration (PETC): In this study, we suggest a modification of the signal-to-equivalent thickness calibration (STC) method, by accounting for two calibration materials (PMMA and Al) in an attempt to incorporate the differences in beam-hardening and scattering properties of calcifications and soft tissues more accurately
Summary
S PECTRAL computed tomography (CT) enables discrimination of different materials and improved tissue contrast by utilizing polychromatic X-ray attenuation information [1]–[3]. It has been applied for several diagnostic tasks such as bone and calcium removal from CT angiography [2], characterization of gout [4], and assessment of myocardial blood flow [5], [6]. As photon counting detectors (PCDs) can discriminate photons of different energies through pulse-height analysis, they enable multi-energy spectral CT [8], quantitative MD [9], and K-edge imaging [10], [11]. PCDs with more than three bin counters allow decomposition of more than three materials [12]
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