STATISTICAL DISTRIBUTIONS OF DCT COEFFICIENTS AND THEIR APPLICATION TO AN INTERFRAME COMPRESSION ALGORITHM FOR 3-D MEDICAL IMAGES

We present displacement estimated interframe (DEI) coding, a new codin g scheme for 3-D medical image data sets such as x-ray CT or MR images . To take advantage of the correlation between contiguous slices, a di splacement-compensated difference image based on the previous image is encoded. We have determined the best fitting distribution functions f or the discrete cosine transform (DCT) coefficients obtained from disp lacement compensated difference images, and used the results in alloca ting bits and optimizing quantizers for the coefficients. The DEI sche me is compared with a 2-D block DCT as well as a full-frame DCT using the bit allocation technique by Lo and Huang [1]. For x-ray CT head im ages, our bit allocation and quantizer design using an appropriate dis tribution model resulted in a 13 dB improvement in the SNR compared to the full-frame DCT using the bit allocation technique. For an image s et with 5 mm slice thickness, the DEI method compared to the 2-D block DCT gave about 5 percent improvement in the compression ratio on aver age and less blockiness at the same distortion. The performance gain i ncreases to about 10 percent when the slice thickness decreases to 3 m m.