Determination of the presampled MTF in computed tomography

A technique for measuring the presampled MTF in CT scanners is described. T he technique uses a simple phantom consisting of similar to0.050 mm aluminu m foil sandwiched by flat plastic or tissue equivalent slabs. The aluminum foil is slightly angled with respect to the reconstruction matrix, and CT i mages are acquired. The acquired CT image yields an angled slit image that can be used to synthesize the presampled line spread function (LSF). The pr esampled MTF is calculated from the presampled LSF. The technique is a dire ct extension of that proposed by Fujita et al. [IEEE Trans. Med. Imaging 11 , 34-39 (1993)] for MTF calculation on digital radiography images. While th e MTF in clinical CT scanners often reaches negligible amplitude below the Nyquist frequency, the technique is easy to implement, requires inexpensive materials, is robust to aliasing, and is more resilient to noise due to gr eater data averaging than conventional PSF-integration techniques. Use of t he proposed technique is illustrated on a clinical multiple detector array scanner, and MTFs are shown for several common reconstruction kernels. It i s likely that the proposed technique would be useful for all tomographic im aging systems, including single photon emission computed tomography, positr on emission tomography, magnetic resonance imaging and ultrasound scanners. (C) 2001 American Association of Physicists in Medicine. [DOI: 10.1118/1.1 350438].