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Figure 5c. Drawings illustrate the steps needed to create a VR image. (a) Step 1: Choose a viewing point. Step 2: Create a histogram of the CT data set to determine the total number of voxels and the total range of Hounsfield units. (b) Step 3: From the histogram, determine the range of Hounsfield units for the tissues of interest. (c) Step 4: Assign opacity values to the tissues of interest. Opacity values range from 0% (transparent) to 100% (fully opaque). The tissue of interest in this example is bone. (d) Step 5: Cast rays from the viewing point to each point in the volume. Step 6: Determine the opacity value of all the voxels along the path of each ray. Step 7: Place the sum of all the opacity values for each ray in the final image. Because the opacity values are summed, there is no depth information (unlike with SSD).
