Development and application of the new dynamic NURBS-based cardiac-torso (NCAT) phantom


W. Paul Segars, B.M.W. Tsui, D.S. Lalush, E.C. Frey, D. Manocha, and M.A. King


Simulation is a powerful tool for characterizing, evaluating, and optimizing medical imaging systems. An important aspect of simulation is to have a realistic phantom or model of the human anatomy. We develop a realistic and flexible computerized dynamic torso phantom and investigate its usefulness in medical imaging research.  


The organ shapes are modeled with non-uniform rational b-splines or NURBS surfaces using a unique, detailed human image dataset as the basis for the formation of the surfaces. With its basis upon human data and the inherent flexibility of the NURBS primitives, the phantom can model organ shape more realistically than phantoms based on simple geometric primitives while maintaining the flexibility to model anatomical variations and patient motion. An important innovation of the research is the extension of NURBS to four (4D) dimensions to model the cardiac and respiratory motions. The NURBS cardiac model was developed based upon a tagged magnetic resonance imaging (MRI) dataset of a normal patient and three-dimensional (3D) angiogram data. NURBS models for the remaining torso organs were developed based on the Visible Human Project CT data set from the National Library of Medicine. Affine transformations were applied to the control points defining the respiratory structures to simulate respiration. The transformations were based on known respiratory mechanics and high-resolution respiratory-gated CT data of a normal patient. The cardiac and respiratory motions were defined by a set of time curves to create time continuous 4D NURBS surface models. The cardiac motion was additionally extended to create a 4D NURBS solid model for the left ventricle (LV) capable of defining the motion of any point within the LV wall. The final goal of the research was to demonstrate the usefulness of the NURBS phantom in simulation studies for different medical imaging techniques including single photon emission computed tomography (SPECT) and x-ray computed tomography (CT).

Fig. 1.  (Left) Anterior view of the 4D NCAT phantom. (Middle) Cardiac and respiratory motion models of the NCAT phantom. (Right) Emission and transmission simulations performed using the phantom.


The 4D NCAT phantom was found to provide a realistic and flexible model of the human anatomy and cardiac and respiratory motions, Fig. 1.  Combined with accurate models of the imaging process, it can be used to produce simulated imaging data that closely mimics that of actual patients. The simulation results of the pilot simulation studies using the NCAT phantom were found to be consistent with that found in patient studies.


With its realistic model of the human anatomy and physiology, the 4D NCAT phantom provides a unique and useful tool in medical imaging research especially when the effects of cardiac and respiratory motions are important.


NIH research grant R01EB000168