Two Dedicated Software, Voxel-based, Anthropomorphic (torso and Head) Phantoms

We have segmented CT torso+head and MRI head slices of two living human males. The manually segmented 129 x-ray CT transverse slices were used to create a computerized 3dimensional volume array modeling all major internal structures of the body. The original xray CT images were reconstructed in a 512x512 matrix with a resolution of 1 millimeter in the x,y plane. The z-axis resolution is 1 centimeter from neck to mid-thigh and 0.5 centimeter from neck to crown of the head. Each voxel of the volume contains an index number designating it as belonging to a given organ or internal structure; 68 such index numbers are assigned. The final torso+head phantom is interpolated to create a 128x128x243 byte volume with isotropic voxel dimensions of 2.5 mms. Secondly, a dedicated head phantom was created by similar processing in which 124 transverse MRI were outlined. The transverse T2 slices, recorded in a 256x256 matrix have isotropic voxel dimensions of 1.5mm. This dedicated head phantom contains 62 index numbers designating neurological and taxonomical structures in the brain, as well as anatomical regions. The final volume is contained within a 256x256x128 byte array. Both of these volume arrays represent high resolution models of the human anatomy and can serve as a voxel-based anthropomorphic phantom suitable for many computer-based modeling and simulation calculations. We have applied them to Monte Carlo simulations from which realistic image projection data has been generated. INTRODUCTION Models of the human anatomy serve an important role in several aspects of diagnostic and therapy related image processing. Computerized anthropomorphic phantoms can either be defined by mathematical (analytical) functions, or digital (voxel-based) volume arrays. One of the earliest computerized anthropomorphic phantoms was developed for estimating doses to various human organs from internal or external sources of radioactivity and served to calculate the S-factors for internal dose calculations in nuclear medicine [1]. This mathematical phantom models internal structures as either ellipsoids, cylinders, or rectangular volumes. For internal dosimetry purposes, such human model approximations serve quite sufficiently and have the advantage of allowing very fast calculation of the intersection of ray lines with the analytical surfaces which delineate the organs. A version of this mathematical phantom has been updated to include female organs [2]. There are