Importance

Image quality is strongly dependent on correct description of the scan geometry. Static deviations from idealized parameters (misalignment), can be handled through PARTAGS in xxm description file, or through precise scanner alignment, if possible. Dynamic geometry parameters, which change from projection to projection due to gravity, centrifugal force or lack of balancing, can also be handled by COBRA. The geometrical calibration is provided at two levels, for static and dynamic parameters, respectively.

Calibration Phantom

The calibration process is based on scanning a specially designed sample containing easy-to-recognize high-density markers. Exxim provides an optional calibration phantom which is suitable for scanners with a FOV of about 5~20 cm in diameter, to be used with the COBRA calibration tool. The phantom is an acrylic cylinder with four sets of metal beads, with diameter at 32, 70, or 100 mm. Each set of beads lies in a plane perpendicular to the cylinder’s axis and contains 2 to 8 beads (d = 1.6 mm or 1.0 mm) at 45 degree angles.
The user can consider scanning his/her own phantom, in which case Exxim should be contacted regarding additional details.

Interface

The calibration functionality is available both through Cobra graphical user interface and as a part of SDK.  In the case of SDK a user program communicates with calibration utility through in-process COM interface.