Exxim Computing Corporation. Dynamic slice calibration


	Post-Feldkamp phase of automatic binding image densities to air/water scale (auto-water). The problem of density non-uniformity In cases of scanning biological objects usually it is very important or even critical to get accurate object density measurements in every point of the reconstructed image. Often density profiles get corrupted and non-uniform (objects with the same density get very different corresponding values in the image). This artifact may be caused by multiple factors including beam-hardening, scattering, object protrusion, etc. Unfortunately some of those factors are more prominent in a cone-beam setup. The same cross-section with dynamic slice calibration applied Density non-uniformity has been reduced down to ~50 HU Feldkamp reconstruction of a special object with a severe non-uniformity in diameter along Z (skull phantom). A saggital cross-section shows a substantial density non-uniformity (~170 HU) in this direction. Cobra implementation of density profiles correction Cobra incorporates an algorithm, implemented as a post-Feldkamp (post-processing) step, which automatically selects “water-like” and “air-like” objects and aligns density profiles to compensate non-uniformity. The algorithm “binds” water-like image values to water a density (0 HU , 1000 mg/cm3).

Describing a reconstruction task

Within the COBRA reconstruction package, all input, output and intermediate data are kept on the hard disk. The user defines and controls the reconstruction task through a parameter file, a text file with extension .xxm. This file contains tags and assigned values, and describes the scanner hardware setup, input and output data characteristics and representation, and the chosen reconstruction method. Some of the reconstruction options are only accessible through SDK API’s. These are related to synchronization and control of in-line reconstruction (recon concurrent with acquisition), and the setup of COBRA’s working folders.

Tags to control dynamic slice calibration

PARTAG_SLICE_AUTOWATER

If set to a value larger than 0 then the dynamic slice scale calibration algorithm is activated. The algorithm allows aligning density profiles automatically. It is based on reconstructed volume his-togram analysis and controlled by this tag. The tag should be set to a value of density between the observed densities of air and water. Please note that the value is supposed to be set in mg/cm³ (HU+1000).
Value type: integer
Default value: 0

Post-Feldkamp phase of automatic binding image densities to air/water scale (auto-water).

The same cross-section with dynamic slice calibration applied Density non-uniformity has been reduced down to ~50 HU

Feldkamp reconstruction of a special object with a severe non-uniformity in diameter along Z (skull phantom). A saggital cross-section shows a substantial density non-uniformity (~170 HU) in this direction.

PARTAG_SLICE_AUTOWATER