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XCAT, MOBY and ROBY Phantom Series


Figure 1. XCAT series of human phantoms. Adult male (top), adult female (middle), and 16 month old boy (bottom) are shown as example. Different levels of detail are displayed building up to the whole model for each, shown with transparency.

Figure 2. MOBY (top) and ROBY (bottom) phantoms modeling the mouse and rat anatomies.
Figure 3. Imaging simulations performed using the XCAT adult male as compared to actual patient data. Examples are shown for different regions of the body using 11C-raclopride PET, CT, and In-111 ProstaScint® SPECT.
  Figure 4. Imaging simulations performed using the MOBY phantom as compared to actual small animal imaging data. Transaxial CT and coronal Tc-99m Medronate Disodium Phosphate SPECT (bonescan) images are shown as examples.  
As new imaging techniques and diagnostic methods emerge in response to disease, a major challenge is how to evaluate which technique is best in terms of patient diagnosis and treatment. It is essential for the advancement of emerging imaging systems to have a tool that can be used for technique testing, evaluation, and comparison. It would not be feasible to test every combination of scanning parameters and every clinical task on patients under clinical conditions, especially for x-ray systems given the relatively high radiation dose. The use of physical phantoms is also limited in that it would be prohibitively expensive to fabricate physical phantoms to simulate a realistic range of patient sizes especially when physiologic motion needs to be considered. The only practical approach to optimization and evaluation is through realistic computer simulation.


Computer simulation involves computational phantoms and models of the imaging process. Computer phantoms define the subject's anatomy and physiology. Given a model of the physics of the imaging process, acquired data of a computer phantom can be generated as if it were an actual live subject. The major advantage to using computer-generated phantoms in simulation studies is that the exact anatomy and physiological functions are known, thus providing a gold standard from which to quantitatively evaluate, improve, and compare medical imaging devices and techniques.

Highly realistic phantoms are required in order for simulation results to have merit. Without this, the results of the simulation may not be indicative of what would occur in actual patients or animal subjects. Dr. Paul Segars has been leading the development of realistic computational phantoms for use in medical imaging research. Foremost among these are the 4D extended Cardiac-Torso (XCAT), the Mouse Whole-Body (MOBY), and Rat Whole-Body (ROBY) phantoms.

The XCAT series of phantoms was developed to model anatomical variations of the human body (male and female) at different ages from newborn to adult to serve as virtual subjects for imaging studies, Fig. 1. The MOBY and ROBY phantoms were developed to model the laboratory mouse and rat respectively for small animal imaging studies, Fig. 2. Based on state-of-the-art computer graphics techniques and high-resolution imaging data, the phantoms can accurately model the complex anatomy of different subjects. In addition, the phantoms are also very flexible and can be easily manipulated through user-defined parameters to model anatomical variations and patient motions such as the cardiac and respiratory motions.

When combined with accurate models for the imaging process, the phantoms are capable of providing a wealth of realistic multi-modality imaging data from subjects of various anatomies and motions, Figs. 3 and 4. With this ability, the phantoms have enormous potential to study the effects of anatomical, physiological, physical, and instrumentational factors on medical and small animal imaging and to research new instrumentation, image acquisition strategies, image processing and reconstruction methods and image visualization and interpretation techniques.

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