Region of Interest Image Coding for Digital Mammography

In this paper, we investigate region-based wavelet compression methods and describe a region-based coder based on the Set Partitioning in Hierarchical Trees (SPIHT) algorithm, called unbalanced spatial orientation trees (UBT), applied to digital mammograms. We compare this method against the region-based extension of SPIHT (ROI-SPIHT), and the ROI coding unit of JPEG2000 (JP2K) algorithm on five digital mammograms compressed at rates ranging from 0.1 to 1.0 bits per pixel (bpp). We show that UBT is competitive in PSNR with the other two region-based coding methods, also providing a more general multiregion multiquality coding framework rather than ROI/non-ROI coding. Unlike ROI-SPIHT, UBT allows encoding of diagnostically significant regions with best possible fidelity while allocating less number of bits to remaining regions.