[Evaluation of the accuracy of line spread function (LSF) and point spread function (PSF) measured in the computed tomography.].

We propose a method to estimate the accuracy of the line spread function (LSF) in computed tomography (CT). When we assume an object for scanning has a shape and CT-value in the x-y scan-plane that are constant in the z-direction perpendicular to the scan-plane, blurring in the image of the object is predicted with calculation by the LSF measured in the scanner. When using the precise LSF, the calculated image must agree well with the scanned image of the phantom corresponding to the object. Then, verification of LSF is performed by comparing the calculated image with the scanned image. We measured the LSF in our scanner, and scanned a cylindrical phantom with constant diameter and CT-value in which the direction of cylinder was parallel to the z-direction, as mentioned above. Images calculated by using the LSF corresponded well to scanned images, indicating the validity of the LSF. We obtained another LSF by an inappropriate manner, and calculated images using it. Those images showed an apparent difference with scanned images, indicating the inaccuracy of the LSF. Our technique is effective to evaluate the accuracy of LSF, PSF, and also modulation transfer function (MTF) derived from the LSF or PSF.