Full-frame compression of tomographic images using the discrete Fourier transform

Abstract

The unacceptability of block artifacts in medical image data compression has led to systems employing full-frame discrete cosine transform (DCT) compression. Although the DCT is the optimum fast transform when block coding is used, it is outperformed by the discrete Fourier transform (DFT) and discrete Hartley transform for images obtained using positron emission tomography and magnetic resonance imaging. Such images are characterized by a roughly circular region of non-zero intensity bounded by a region R in which the image intensity is essentially zero. Clipping R to its minimum extent can reduce the number of low-intensity pixels, but the practical requirement that images be stored on a rectangular grid means that a significant region of zero intensity must remain an integral part of the image to be compressed. The DCT therefore loses its advantage over the DFT because neither transform introduced significant artificial discontinuities.<>