In 1994 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, Norfolk, Virginia, 30 October-5 November 1994.
The resolution of an imaging systems is frequently described by experimental estimates of the modulation transfer function (MTF). While methods for measuring the MTF of 2D images using slit or edge objects are well documented, the 3D MTF has not been previously investigated. A method which generalizes the conventional 2D method is presented. By imaging a smooth surface, response in the direction normal to the surface in the x, y, and z directions is determined. The set of surface boundary voxels is determined by applying a simple threshold. This is followed by a Hough transform to determine the orientation of the surface. The normal distance of every voxel to the fitted surface is computed and an accumulator bin is incremented by the gray level. This results in an aggregate edge response function, which can be differentiated and Fourier transformed to yield the MTF. This method can be further generalized to use nonlinear shapes, such as a sphere, where precise surface normals are known. These simpler objects are useful in simulations for optimizing imaging parameters such as reconstruction algorithm, collimator design, x-ray focal spot size, detector response, and detector/source orbit. Results of applying this method to volumetric x-ray CT data is shown.