Evaluation of a new technique for the measurement of the two dimensional MTF of digital radiographic systems

David A. Reimann, Ehsan Samei, and Holly A. Jacobs

American Association of Physicists in Medicine, 43rd Annual Meeting, Salt Lake City, Utah, 22-26 July. Medical Physics, 28(6):1187, June 2001. Poster SU-EE-EXH C-02. Link to AAPM site

In this work we evaluate a new method for determining the two-dimensional modulation transfer function (MTF) of digital radiography systems using an attenuating disk. Traditional methods such as the edge and slit methods only measure the MTF in one direction. With these methods, the edge or slit must be re-oriented and other images acquired to measure the MTF at more than one direction. In the disk method, the MTF can be obtained at any direction using a single acquisition. The method relies on the image data from a precise disk test object. The ideal Fourier transform of the disk object is deconvolved with the acquired image resulting in the MTF. The application of this method was tested on a digital radiography system (GE XQ/i) using a standard beam quality and the results were compared with those obtained using an established edge method. The disk test object was constructed from a 1.2 cm diameter, 0.25 mm thick circular lead foil laminated between two 1 mm slabs of acrylic. The results show excellent agreement between the edge and disk methods in low and mid frequency ranges, but at high frequencies the disk results were slightly elevated due possibly to aliasing. The results indicate that the disk method can be employed to easily measure the two-dimensional MTF of digital radiography imaging systems for both quality assurance and comparative analysis among systems, especially those with an asymmetric point spread function.

David Reimann (Left) and Ehsan Samei (Right) with poster at the meeting. Holly Jacobs was unable to attend.

Copyright © 2001, David A. Reimann. All rights reserved.