penVT was designed to simulate a prototype tomosynthesis system with a fixed detector and a rotating arm that holds the x-ray source. The object to be studied is then placed on a glass surface above the detector. While the glass surface is not modeled in penVT, the air gap between the glass and the detector is. The "System Geometry" tab allows you to change various parameters of the system, and the schematic below shows how each variable relates to the system.

Distance from source to center of rotation: This is the length of the rotating arm that holds the source. In other words, it is the radius of the arc that the source follows. Note that the source will always point towards the center of rotation.

Distance from the center of rotation to the detector: This is the distance from the fixed detector to the center of rotation. For example, if you want a system where the source rotates around the midpoint of the detector, you would set this value to zero.

Distance from Voxelized Object to Detector: This is the distance from the bottom of the phantom to the detector. In the prototype tomo system, the phantom would rest on a glass surface. This value is the air gap that the glass surface creates. In other words, it is the distance from the glass surface that the phantom rests on to the detector.

Detector Size (X,Y,Z): This is the size of the detector in the simulated system. In our model, X is the direction of rotation, so to make sure the entire image is captured, the X-length of the detector should be around 2 to 4 times the X-length of the phantom. Also, note that Y is the depth direction; i.e. the phantom sits above the detector in the y direction.

Detector Region of Interest Size (X, Z): To reduce the size of the output images, penVT tracks a region of interest on the detector that moves with each projection. The center of this region of interest will be the point at which the center of rotation is projected onto the detector plane. These fields let you choose the size of this region of interest. Again, note that X is the direction of rotation.

Detector Region of Interest Resolution (X, Z): This is the resolution of the detector region of interest, and, therefore, correlates to the resolution of the detector. For example, for a 100micron resolution detector and a 10cm x10cm region of interest, the resolution should be 1,000pixels by 1,000pixels.