A Novel Neutron Computed Tomography Partial Volume Voxel Water Quantification Technique

Open Access
Author:
Heller, Arthur Kevin
Graduate Program:
Nuclear Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 12, 2010
Committee Members:
  • Jack Brenizer Jr., Dissertation Advisor
  • Jack Brenizer Jr., Committee Chair
  • Kenan Unlu, Committee Member
  • Matthew M Mench, Committee Member
  • Richard Laurence Tutwiler, Committee Member
Keywords:
  • Neutron Imaging
  • Neutron Computed Tomography
  • Neutron Radiography
  • Water Quantification
  • Partial Volumes
  • Partial Volume Voxels
  • un-sharpness correction
  • deconvolution
  • NCT
Abstract:
A method was developed for the precise quantification of water mass in neutron computed tomography (NCT) reconstructions. An NCT reconstruction is comprised of individual volume elements, or voxels. The gray level value of a voxel represents the total macroscopic cross section, , of the material present at the voxel’s spatial location. For voxels along interfaces, the gray level represents a combination of s for the various materials present. The fractional amount of water, known as a partial volume, represented by such a voxel must be quantified for an accurate result. This calculation requires removing the influence of other materials on the voxel’s gray level. This is accomplished by background normalizing the raw projection data. The resulting reconstruction contains voxels that represent only water. Normalizing to the gray level value of a voxel of known water mass produces a voxel matrix with gray levels representing fractional water amounts. These fractional amounts are tallied and multiplied by the known water mass of the normalizing voxel to determine the total. The NCT water quantification technique was tested using MCNP simulations of samples containing liquid phase water and ice phase water. Quantification of the MCNP simulations yielded results within 0.2% of the theoretical. For liquid phase and ice phase water samples at ~30mm from the detector, results were within 2% of the theoretical. The ability to quantify an ice water mixture to within 2% of the theoretical was also demonstrated. For liquid phase water samples at 140mm from the detector, significant error in the quantified water mass, as large as 47%, was observed and determined to be the result of geometric un-sharpness effects and cupping artifacts. Deconvolution of the imaging system’s blurring function was performed to correct for geometric un-sharpness. Results showed a reduction in geometric un-sharpness by ~14.4% yielding a 6.7% average increase in quantified water mass. The effects of magnification and cupping artifacts on the final quantification results were also investigated. Magnification was determined to have no effect while cupping artifacts accounted for 1.4% of the error. Geometric un-sharpness accounted for 45% of the error, making it the dominant error source.