Improvement of edge response in multi-detector row CT by high-spatial-frequency sampling of projection data

Abstract

The edge response behavior of multi-detector row computed tomography (MDCT) in high-spatial- frequency sampling may diminish due to fluctuations, so a method for improving the edge response was developed and tested. MDCT enables thin-slice and high-speed scanning compared with conventional single-detector row CT (SDCT). However, MDCT uses increased volume scanning with a simultaneous increase in the radiation dose to patients. Recently, we proposed a fluctuation reduction method using high-spatial-frequency data sampling; however, the edge response in the processed image decreased. In this research, we investigate the edge response behavior in the high-spatial-frequency sampling, and propose a method for improving the edge response. To verify this method, a large water phantom that consists of five resinous rods and a small phantom with a similitude rate of 0.5, which is topologically similar to the former large phantom were scanned, and projection data sampling using high-spatial-frequency was simulated. Thereafter, reconstructed images were obtained by averaging the high-spatial-frequency sampling data, edge gradients of profiles were calculated, and the increased rate of the gradient values were evaluated. This method increased the image noise slightly and provided higher gradient values with the same image matrix size as the conventional scans could be obtained without special image processing. In this phantom study, in order to simulate the high-spatial-frequency sampling, a large phantom was scanned and the fluctuation of transmitted X-rays was increased, thereby increasing the noise. A phantom study of projection data sampling by high-spatial-frequency sampling was simulated in the x- and y-direction by scanning two phantoms, and the improvement in the edge response by this method produced 25–97% improvement using double-spatial-frequency sampling. If low-noise or high-sensitivity detector is developed, this method may be more effective.