KitGuru Complete Guide to PC Workstations – Part 3

Medical viewset (medical-01)

The medical-01 viewset is representative of a typical volume rendering application that renders a 2D projection of a 3D volumetric grid. A typical 3D grid in this viewset is a group of 3D slices acquired by a scanner (such as CT or MRI).

At every frame, depending on the viewer position, a series of coplanar slices aligned with the viewing angle are computed on the CPU and then sent to the graphics hardware for texturing and further calculations, such as transfer function lookup, lighting and clipping to reveal internal structures. Finally, the slices are blended together before the image is displayed.

The voxel in the 3D grid is a single scalar value. A transfer function – simply a 1D lookup table – maps the 3D density value to color and alpha values. For lighting calculations, the gradients are computed on the fly using the central differences at each voxel. These state changes exercise various parts of the graphics subsystem. This viewset makes use of hardware support for 3D textures and therefore trilinear interpolation.

There are two datasets in this viewset:

• A 4D heart dataset comprising multiple 3D volumes iterated over time. These were obtained from a phase-contrast MRI scanner. The 80MB dataset was contributed by the Department of Radiology, Stanford School of Medicine and Lucile Packard Children's Hospital.
• A stag beetle dataset provided by the Technical University of Vienna. The dataset size is 650MB and represents a workload with larger memory requirements.

The medical viewsets show no benefit whatsoever from CPU speed. Real-time visualisation performance with these kinds of applications are entirely a factor of GPU capability. The benefits from each step up in graphics cost are fairly uniform, although the delta between the K620 and K2200 is most pronounced. So the choice of card depends in a somewhat linear fashion on how much performance you need and can afford. If you do need smoother performance, a more expensive card will provide this, and putting your money into this area is the best choice.

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