Exxim Computing Corporation. Noise reduction


	Post-Feldkamp phase of reducing noise. The problem of noise In many cases reconstructed images come out noisy. This problem is typically caused by one (or combination) of the following factors. A human patient safety requires reducing X-Ray dose, which may cause a photon starvation. A detector may have insufficient dynamic range so the dose cannot be set up high enough to avoid a photon starvation in highly attenuating regions. X-Ray source may have insufficient power. A scanned object material may define a necessity to apply high kVs. Same slice with post-Feldkamp noise reduction applied. Noise standard deviation is 30 Feldkamp reconstruction of a dental scan. Noise standard deviation is 100 Cobra implementation of noise reduction COBRA provides 3-dimensional smoothing as a post-processing feature, controlled by a set of parameters. This is a boundary-preserving de-noising procedure.

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 defining noise reduction

PARTAG_POSTPROFACTOR

COBRA provides 3-dimensional smoothing as a post-processing feature, controlled by a set of parameters. This is a boundary-preserving de-noising procedure. It is assumed that reconstruction is being performed into a bigger slice size cube. Using of an increased cube typically is beneficial for the further steps. (The final cube size is defined by PARTAG_CUBESIZEX, PAR-TAG_CUBESIZEY). The alignment of a cube size (down-sampling from an intermediate size to a final one) is the internal step of the algorithm.
PARTAG_POSTPROFACTOR is to set a smoothing sigma factor, a good estimate for this parameter is the standard deviation of noise in the image.
Value type: integer
Default value: 0

PARTAG_POSTPROAPRTHRZ

PARTAG_POSTPROAPRTHRZ is to set a horizontal aperture of a smoothing 3D filter.
Value type: integer
Default value: 3

PARTAG_POSTPROAPRTVRT

PARTAG_POSTPROAPRTVRT is to set a vertical aperture of a smoothing 3D filter.
Value type: integer
Default value: 3

PARTAG_POSTPROMEDIANAPRT

PARTAG_POSTPROMEDIANAPRT is to set the aperture of 2D median filter.
Value type: integer
Default value: 3

PARTAG_POSTPROFILTERMODE

Currently this parameter is for internal Cobra use. Must be kept 0
Value type: integer
Default value: 0

PARTAG_INTERCUBESIZE

Value type: integer
Default value: equal to PARTAG_CUBESIZEX setting

Post-Feldkamp phase of reducing noise.