Abstract
The purpose of this research is to achieve uniform spatial resolution in CT (computed tomography) images without hardware modification. The main idea of this study is to consider geometry optics model, which can provide the approximate blurring PSF (point spread function) kernel, which varies according to the distance from X-ray tube to each pixel. The FOV (field of view) was divided into several band regions based on the distance from X-ray source, and each region was deconvolved with different deconvolution kernels. Though more precise calculation for the PSF for deconvolution is possible as the number of subbands increases, we set the number of subbands to 11. 11 subband settings seem to be a balancing point to reduce noise boost, while MTF (modulation transfer function) increase still remains. As the results show, subband-wise deconvolution makes image resolution (in terms of MTF) relatively uniform across the FOV. The results show that spatial resolution in CT images can be uniform across the FOV without using additional equipment. The beauty of this method is that it can be applied to any CT system as long as we know the specific system parameters and determine the appropriate PSF for deconvolution maps of the system. The proposed algorithm shows promising result in improving spatial resolution uniformity while avoiding the excessive noise boost.
Highlights
Image quality is of primary concern in diagnostic and screening imaging
The spatial resolution of a CT image is affected by a number of factors including the focal spot size of X-ray tube, detector size, scattering, magnification, the number of projections per rotation, and the reconstruction process [1]
It is known that the resolution in the FOV decreases as the distance from isocenter increases, which results in spatial variation of resolution
Summary
Among many elements that affect the image quality, resolution is one of the most concerned. For the early detection of diseases, high spatial resolution imaging is very important. The spatial resolution of a CT image is affected by a number of factors including the focal spot size of X-ray tube, detector size, scattering, magnification, the number of projections per rotation, and the reconstruction process [1]. The spatial variation of resolution can be considered as spatial variation of PSF This variation affects the image quality, which sometimes can cause mistakes in inspection, such as overlooking a calcification at the periphery region. Because of the spatial variation of resolution, the patient table is steered so that the heart of the imaged patient should be located at the isocenter. If the problem of the spatial variation of resolution is alleviated, it can be beneficial for improving the imaging workflow
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