Upsampling of Prostate Volumes

The application of magnetic resonance imaging (MRI) in detecting and localizing prostate cancer lends itself naturally to 3D volume rendering, allowing the physician to observe the entire gland and navigate at will. While MR images can be obtained with good intra-slice resolution, inter-slice gaps are significantly larger. Because of this, when visualizing a prostate segmented from MR image slices in 3D, the result is very faceted. In addition to the overall gland, a further item of concern is the separate segmentation of the peripheral zone (PZ) from the central gland (CG). As these two regions present different characteristics in the MR images, it is important to keep them separated in the segmentation, so any upsampling of the gland must also upsample the CG and PZ region segmentations while preserving the entire gland segmentation. A first step is to increase the interslice resolution of the volume by interpolating intermediate slices. This is accomplished by iterative erosion and dilation of regions to ensure that both the overall and region segmentations are maintained. This is performed multiple times, until the interslice spacing is reduced to the level of the intra-slice spacing. Rendering a volume upsampled this way will produce better results, but there will still be a blocky step-like appearance, though now reduced to smaller steps. In prostate imaging, it is common to acquire slices in axial, coronal, and sagittal views. Combining these three views together allows for a superior result which is significantly smoother. Another advantage is that the final shape can be more accurate, as small areas around the boundary that may not be segmented properly due to their appearance in one view can be contributed to the final volume by an alternate view. Keywords–prostate; medical imaging; interpolation; volume rendering; visualization;