Classification of Computational Anatomic Phantoms by Format and Morphometric Category (3)
| Parameter | Class 1 | Class 2 | Class 3 | Class 4 |
|---|---|---|---|---|
| Format* | Stylized: organs and total body represented by regular 3-dimensional shapes such as spheres and ellipsoids. | Voxel: CT- or MRI-based 3-dimensional digital representation of segmented organ as assemblies of cubic volume elements (or voxels) | NURBS (nonuniform rational B-spline): anatomic volumes defined by NURBS equations characterized by set of control points; shape and volume of NURBS surface vary with coordinates of control points | Polygon mesh-based: Polygonal mesh is composed of set of vertices, edges, and faces that specify shape of polyhedral object in 3 dimensions; surfaces of phantom are defined by large number of polygonal meshes such as tetrahedrons |
| Category† | Reference: average human anatomy corresponding, for example, to men and women at roughly 50th percentile for heights and weights at discrete ages (newborn, 1-y-old, 5-y-old, 10-y-old, 15-y-old, and adult); there is no match to anatomy of any specific patient; S values can be precomputed for all source/target organ combinations in reference phantom series | Patient-dependent: use of computational phantom library covering various combinations of height and weight percentiles in modeled patient population; internal organ anatomy is volumetrically rescaled to outer body size (contour) but is not patient-specific; S values can be precomputed for all source/target organ combinations for each member of patient-dependent phantom library | Patient-sculpted: use of computational methods to change body contour of selected patient-dependent phantom from phantom library; resulting phantom would then appear to have same body size and shape as that of patient, but again, internal organ anatomy is not patient-specific; as patient-sculpted phantom does not exist until it is created (using patient’s CT/MR-based body contour), S values cannot be precomputed but must be generated by Monte Carlo computer simulation once that phantom is available | Patient-specific: matching of phantom internal and external anatomy to CT- or MRI-measured anatomy of specific patient; as with patient-sculpted phantoms, S values cannot be precomputed until patient-specific phantom is developed |