Preliminary Study of Image Reconstruction for Breast DECT with Limited-Angular-Range Data

Dual-energy computed tomography (DECT) is a useful technique in clinical applications, including breast examinations for breast cancer staging and differentiation between benign and malignant tumors. DECT can lead to accurate estimation of physical quantities, such as iodine contrast concentration, which is highly desired for the quantitative analysis and capturing of the contrast-update kinetics used in these clinical applications. Meanwhile, low- and high-kVp data in DECT are usually collected with two full-angular ranges (FARs) of 360°, or at least with short-scan ranges. DECT with limited-angular-range (LAR) data may then allow potential reduction of radiation dose, scan time, and motion effect, and avoidance of possible collision between the moving gantry of the scanner and the imaged object. In this work, we investigate accurate image reconstruction for DECT with LAR data by correcting for both the beam-hardening (BH) and LAR effects with a two-step method. Noiseless and noisy data are generated from a digital breast phantom, using a nonlinear data model with low- and high-kVp spectra. A single-arc (SA) or two-orthogonal-arc (TOA) scan was employed with completely overlapping rays of low and high kVp, where the LAR spans from 60° to 120°. The generated low- and high-kVp data of LAR are first decomposed into basis data of LAR using a standard data-domain decomposition algorithm. Basis images are then reconstructed directly from the basis data by use of the directional-total-variation (DTV) algorithm previously developed. From basis images obtained, monochromatic images can be combined for visual inspection and iodine contrast concentrations can be estimated for quantitative assessment. Results suggest that the two-step method can, for the LARs and noise levels investigated in this work, yield monochromatic images with reduced BH and LAR artifacts and accurate estimation of iodine contrast concentration as compared to the reference values from the full-angular-range data. Additionally, TOA scans seem to be more effective in artifact reduction and quantitative estimation than SA scans of the same total LAR. The observations and results in the work may engender insights into the design of DECT with LAR scanning configurations of practical application significance.