Summary Statistics for Fun Dough Data Acquired at LLNL

Abstract

Executive SummaryLLNL prepared about 50mL of the Fun Dough™ in a polypropylene vial and firmly compressed it immediately prior to the x-ray measurements. Still, layers can plainly be seen in the reconstructed images, indicating that the bulk density of the material in the container is affected by voids and bubbles. We used the computer program IMGREC to reconstruct the CT images. The values of the key parameters used in the data capture and image reconstruction are given in this report. Additional details may be found in the experimental SOP [1] and a separate document.[2] To characterize the statistical distribution of LAC values in each CT image, we first isolated an 80% central-core segment of volume elements ("voxels") lying completely within the specimen, away from the walls of the polypropylene vial. All of the voxels within this central core, including those comprised of voids and inclusions, are included in the statistics. We then calculated the mean value, standard deviation and entropy for (a) the four image segments and for (b) their digital gradient images. (A digital gradient image of a given image was obtained by taking the absolute value of the difference between the initial image and that same image offset by one voxel horizontally, parallel to the rows of the x-ray detector array.) The statistics of the initial image of LAC values are called "first order statistics;" those of the gradient image, "second order statistics." 1 LMHU D : "LLNL modified Hounsfield units with respect to Delrin." To obtain the LAC in LMHU D for some material at a specific energy, one divides the LAC of that material (in units of reciprocal mm) for that energy by the LAC of Delrin for 160kVp (also in reciprocal mm) and multiplies the result by 1400. The result is a dimensionless value. The LAC of Delrin used to normalize all LAC values in this report is the value measured with an x-ray energy of 160kVp with combined aluminum and copper filters.