TITLE:

Development of a 4D Digital Mouse Phantom for Molecular Imaging Research

AUTHORS:

W. Paul Segars1, B.M.W. Tsui1, E.C. Frey1, G.A. Johnson2, and S.S. Berr3

1Johns Hopkins University, 2Duke University, 3University of Virginia

PURPOSE:

We develop a realistic and flexible 4D digital mouse phantom and investigate its usefulness in molecular imaging research.  

METHODS AND MATERIALS:

The organ shapes are modeled with non-uniform rational b-spline (NURBS) surfaces, which are widely used in 3D computer graphics. High-resolution 3D magnetic resonance microscopy (MRM) data obtained from the Duke Center for In Vivo Microscopy was used as the basis for the formation of the surfaces. With its basis upon actual imaging data and the inherent flexibility of the NURBS primitives, the phantom models organ shapes realistically while maintaining the flexibility to model anatomical variations and involuntary motions such as the cardiac and respiratory motions. These motions were modeled using a gated black-blood magnetic resonance imaging (bb-MRI) dataset of a normal mouse as the basis for the cardiac model and respiratory-gated MRI and known respiratory mechanics as the basis for the respiratory model, using images obtained from the University of Virginia. In each case, the time-changing 3D surfaces are defined by a set of time curves to create time continuous dynamic or 4D NURBS surface models. We demonstrate the usefulness of the mouse phantom in initial simulation studies in single photon emission computed tomography (SPECT) and x-ray computed tomography (CT).

Fig. 1.  (Left) Anterior view of the 4D MOBY phantom. (Middle) Cardiac and respiratory motions of the MOBY phantom. (Right) MicroCT and MicroSPECT images simulated using the phantom.

RESULTS:

The NURBS primitives accurately model the complex organ shapes, providing the basis for a realistic model of the 3D mouse anatomy. In addition, the flexibility of the NURBS allows for realistic 4D modeling of the cardiac and respiratory motions, Fig. 1. For both pilot simulation studies (SPECT and CT), the simulated images were found to be comparable to those obtained experimentally. This demonstrates the great potential the new 4D mouse phantom has in molecular imaging research. Combined with accurate models of the imaging process, the phantom can be used to produce realistic molecular imaging data from which imaging devices and techniques can be evaluated.  

CONCLUSIONS:

We conclude that NURBS are an efficient and flexible way to accurately describe the anatomy and cardiac and respiratory motions for a realistic 4D digital mouse phantom. The phantom provides a unique and useful tool in molecular imaging research, especially in the development of new imaging instrumentation, image acquisition strategies, and image processing and reconstruction methods.

FUNDING SOURCES:

NIH Research Grant R01EB00168