Image reconstruction from data over two orthogonal arcs of limited-angular ranges

Purpose Computed tomography (CT) scanning over limited-angular ranges (LARs) is of practical interest in possible reduction of imaging dose and time and in design of nonstandard scans. This work aims to investigate image reconstruction for two nonoverlapping arcs of LARs, and to demonstrate that they may allow more accurate image reconstruction than may a single arc of LAR. Methods We consider a configuration with two nonoverlapping arcs of LARs alpha 1$\alpha _1$ and alpha 2$\alpha _2$, whose centers are separated by 90 circle$90<^>\circ$, and refer to it as a two-orthogonal-arc configuration. Data are generated from a chest phantom with two-orthogonal-arc configurations over total angular coverage alpha tau=alpha 1+alpha 2$\alpha _\tau =\alpha _1+\alpha _2$ ranging from 18 circle$18<^>\circ$ to 180 circle$180<^>\circ$, and images are reconstructed subsequently by use of the directional-total-variation (DTV) algorithm. For comparison, we also consider image reconstruction for a single-arc configuration of angular range alpha tau$\alpha _\tau$. Quantitative metrics such as the normalized root-mean-square-error (nRMSE) are used for evaluation of image reconstruction accuracy. Results Visual inspection and quantitative analysis of images reconstructed reveal that a two-orthogonal-arc configuration generally yields more accurate image reconstruction than does its single-arc counterpart. As total angular range alpha tau$\alpha _\tau$ increases, the DTV algorithm yields image reconstruction with enhanced accuracy, as expected. Also, if alpha tau$\alpha _\tau$ remains constant, the two-orthogonal-arc configuration with alpha 1=alpha 2$\alpha _1 = \alpha _2$ generally leads to image reconstruction more accurate than those of two-orthogonal-arc configurations with alpha 1 not equal alpha 2$\alpha _1 \ne \alpha _2$, as the nRMSE of the former can be lower than that of the latter for up to more than one order of magnitude. Conclusions Appropriately designed two-orthogonal-arc configurations may be exploited for improving image-reconstruction accuracy in CT imaging with reduced angular coverage. This study may yield insights into the design of innovative CT scans for lowering scan time and radiation dose, and/or for avoiding scan collision in, for example, C-arm CT.