Performance characterization of a prototype dual‐layer cone‐beam computed tomography system

Abstract

Conventional cone-beam computed tomography CT (CBCT) provides limited discrimination between low-contrast tissues. Furthermore, it is limited to full-spectrum energy integration. A dual-energy CBCT system could be used to separate photon energy spectra with the potential to increase the visibility of clinically relevant features and acquire additional information relevant in a multitude of clinical imaging applications. In this work, the performance of a novel dual-layer dual-energy CBCT (DL-DE-CBCT) C-arm system is characterized for the first time. Methods: A prototype dual-layer detector was fitted into a commercial interventional C-arm CBCT system to enable DL-DE-CBCT acquisitions. DL-DE reconstructions were derived from material-decomposed Compton scatter and photoelectric base functions. The modulation transfer function (MTF) of the prototype DL-DE-CBCT was compared to that of a commercial CBCT. Noise and uniformity characteristics were evaluated using a cylindrical water phantom. Effective atomic numbers and electron densities were estimated in clinically relevant tissue substitutes. Iodine quantification was performed (for 0.5-15 mg/ml concentrations) and virtual noncontrast (VNC) images were evaluated. Finally, contrast-to-noise ratios (CNR) and CT number accuracies were estimated. Results: The prototype and commercial CBCT showed similar spatial resolution, with a mean 10% MTF of 5.98 cycles/cm and 6.28 cycles/cm, respectively, using a commercial standard reconstruction. The lowest noise was seen in the 80 keV virtual monoenergetic images (VMI) (7.40 HU) and the most uniform images were seen at VMI 60 keV (4.74 HU) or VMI 80 keV (1.98 HU), depending on the uniformity measure used. For all the tissue substitutes measured, the mean accuracy in effective atomic number was 98.2% (SD 1.2%) and the mean accuracy in electron density was 100.3% (SD 0.9%). Iodine quantification images showed a mean difference of −0.1 (SD 0.5) mg/ml compared to the true iodine concentration for all blood and iodine-containing objects. For VNC images, all blood substitutes containing iodine averaged a CT number of 43.2 HU, whereas a blood-only substitute measured 44.8 HU. All water-containing iodine substitutes measured a mean CT number of 2.6 in the VNC images. A noise-suppressed dataset showed a CNR peak at VMI 40 keV and low at VMI 120 keV. In the same dataset without noise suppression applied, a peak in This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

One-step inversion algorithms for spectral CT, with application to dynamic Cone Beam CT

“…Using a dual energy CBCT simulation obtained from brain phantoms, we compare the proposed one-step methods with methods which were previously published. Simulation data used parameters of a C-arm DECT system close to the prototype described in [41]. Therefore these promising results could probably be validated on clinical data obtained with this prototype.…”

Computed Tomography

“…128 In addition to such specialized source-side designs, it is likely that multilayer FPDs 129 will be implemented in musculoskeletal CBCT in the near future, similar to the layered detector systems for conventional DECT. Initial imaging physics performance evaluation studies of multilayer FPDs in DE-CBCT confirmed near-perfect accuracy in measurements of atomic number and electron density 130 and few errors in calcium and iodine concentration measurements. 129 The formation of material concentration images in DE-CBCT has been reported using all major categories of computational approaches known from DECT: pre-reconstruction projection-domain decomposition, 126 postreconstruction image-domain decomposition, 131 and direct iterative 1-step model-based material decomposition (MBMD).…”

“…In addition to such specialized source-side designs, it is likely that multilayer FPDs 129 will be implemented in musculoskeletal CBCT in the near future, similar to the layered detector systems for conventional DECT. Initial imaging physics performance evaluation studies of multilayer FPDs in DE-CBCT confirmed near-perfect accuracy in measurements of atomic number and electron density 130 and few errors in calcium and iodine concentration measurements 129 …”

Feasibility of dual‐energy CBCT material decomposition in the human torso with 2D anti‐scatter grids and grid‐based scatter sampling

“…14 Dual or multilayer flat panel detectors were also proposed recently, where a constant kV is used during a CBCT scan, and low-high energy X-rays are detected by different layers of the detector. [15][16][17] Finally, photon counting detectors are promising in their potential to differentiate the energy of individual photons using one detector in a constant kV scan. [18][19][20] The second major challenge in DE CBCT involves addressing the poor accuracy of X-ray transmission measurements, which can degrade the fidelity of the DE processing.…”