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Mass production eva reference11/9/2023 ![]() Organs were touching and even overlapping in some cases Segars’ models have a priority scheme to handle this, which is invoked during voxelization. ![]() Hollow organs had both wall and content components target masses from ICRP 89 were applied to both the wall and the content components. When finalized, the modified models were rendered in voxel format with another software tool (using a resolution of 1.5 × 1.5 × 5 mm) and converted from binary to ASCII format. Age-dependent differences (e.g., head size in young children) were incorporated. Mostly, organs were varied in all 3 dimensions equally, and then individual organs could be translated if needed to maintain internal consistency between the models. The ICRP 89–recommended organ mass values for adults and children of various reference ages (male and female newborn, 1-y-old, 5-y-old, 10-y-old, 15-y-old, and adult) were used as target masses for individual organs in each phantom. Overall scaling of the body was done to provide an appropriate body size and shape, and then organs were individually scaled. In general, the whole models were not simply scaled equally in all 3 dimensions for example, the head size is much larger relative to the size of the whole body in young children than in adults. We started with Segars’ 2 adult models, scaled them to the ICRP 89 reference adult organ masses, and then continued to modify them to represent the smaller models by deforming the surfaces and then adjusting the organs to match the ICRP 89 models for each age. Slice-by-slice viewing of results is also afforded by this software tool. ![]() One or more selected organs may be translated or rotated in any direction, scaled linearly in any direction (uniformly in 3 dimensions from the center by a fixed factor), and otherwise modified by the user. Existing software tools developed by Segars allow for the rapid scaling of human NURBS. We developed a series of models representing adults and children of different ages scaled from these original adult models to match the recommended age-dependent organ masses given in ICRP publication 89 ( 16). NURBS models may be easily deformed to represent different sizes and shapes. Figure 2 shows the adult male and female NURBS models originally developed by Segars. In particular, representing the third generation of anatomic model is the work by Segars, now with Duke University, who used the nonuniform rational b-spline (NURBS) modeling technique ( 15) that has allowed not only a more realistic rendering of the human body but also the attractive capability of rapid and easy scaling of organs and the whole body. Many others have developed individual realistic phantoms of adults ( 10, 11), children ( 12), and pregnant women ( 13, 14), using various technologies, as summarized by Xu and Eckerman ( 5). ( 9) reported on hybrid realistic computational phantoms for adults and used them in retrospective dosimetry analyses for contaminated radiation workers. Similar discrepancies between the stylized and voxelized models were reported using the VIP-Man model, which is based on the Visible Human Project cadaver cross-sectional anatomic images ( 7, 8). created tomographic voxelized models from CT images ( 6) and found that the stylized computational models could over- and underestimate organ absorbed fractions by several tens of percentage points when compared against the more realistic, image-based models. The image-based models are now considered to be the second-generation anatomic models that use the so-called voxel geometry. The stylized models that originated at Oak Ridge National Laboratory some 40 y ago have now been replaced with realistic body models based mostly on human image data ( 5). This series of stylized models was implemented in the MIRDOSE ( 3) and OLINDA/EXM 1.0 ( 4) personal computer codes to facilitate calculation of standardized internal dose calculations.Įxterior view of one of the Cristy/Eckerman 1987 phantoms ( 1). The mathematic descriptions of the organs were formulated on the basis of descriptive and schematic materials from general anatomy references. Several organs and tissues were mathematically defined as occupying finite spaces within the body space and comprised 3 types of tissue: soft tissue, bone, and lung. The models’ exteriors were defined in 3 sections: an elliptic cylinder representing the arm, torso, and hips a truncated elliptic cone representing the legs and feet and an elliptic cylinder representing the head and neck. Figure 1 shows an exterior view of one of the Cristy/Eckerman stylized adult and pediatric models. Anthropomorphic models-also called computational phantoms-applied for dose calculations in nuclear medicine for the past 30 y have used the stylized geometric definitions that were developed for reference adults and children ( 1) and pregnant women ( 2).
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