Abstract: A computer program for manipulating diagnostic images obtained with computed tomography or magnetic resonance systems stores acquired voxel data in addresses in an electronic memory related to the spatial location of the voxels. Sample lines are identified in the space of the voxels and interpolated values are determined for points along these sample lines by accessing the volume data in the electronic memory as a "tube" which includes voxel data having spatial coordinates which vary only in the dimension of the sample line. The tube of data may be more easily accessed from the electronic memory than would a series of random accesses and also allows the sharing of interpolation calculations for the interpolated points along the sample lines.