Incorporation of the Living Heart Model into the 4D XCAT Phantom for Cardiac Imaging Research

Abstract

The 4D extended cardiac-torso (XCAT) phantom has provided a valuable tool to study the effects of anatomy and motion on medical images, especially cardiac motion. One limitation of the XCAT was that it did not have a physiological basis which to realistically simulate variations in cardiac function. In this work, we incorporate into the XCAT anatomy the four-chamber FE Living Heart Model (LHM) developed by the Living Heart Project (LHP). The LHM represents the state of the art in cardiac FE simulation because of its ability to accurately replicate the biomechanical motion of the entire heart and its variations. We create a new series of 4D phantoms capable of simulating patients with varying body sizes and shapes; cardiac positions, orientations, and dynamics. While extendable to other imaging modalities and technologies, our goal is to use the FE-enhanced XCAT models to investigate the optimal use of computed tomography (CT) for the evaluation of coronary artery disease (CAD). With the ability to simulate realistic, predictive, patient quality 4D imaging data, the enhanced XCAT models will enable optimization studies to identify the most promising systems or system parameters for further clinical validation.

Keywords: Biomedical imaging phantoms; cardiac motion compensation; computed tomography; finite element analysis; image analysis; medical diagnostic imaging; medical simulation.

Fig. 1.

(Top) XCAT series of computational phantoms. (Bottom) Cardiac model of the XCAT phantom. Motion was based upon the analysis of tagged MRI data. Cardiac CT data was used to add details such as the coronary vessels. The right atria (RA), left atria (LA), right ventricle (RV) and left ventricle (LV) are labeled in the figure.

Fig. 2.

Components of the Living Heart Model including (A) the finite element mesh, (B) the fiber architecture of the muscle tissue for mechanical contraction, (C) the Purkinje network for electrical stimulation, and (D) the lumped parameter model for blood flow based on Pilla et al [14].

Fig. 3.

Living heart model and example XCAT anatomy as imported into the Rhinoceros modeling software. Layers are automatically created to sort the structures. Only the lungs, liver, stomach, spleen, heart, and pancreas are shown for the XCAT; the remaining structures are hidden.

Fig. 4.

(A) The LHM is manually positioned and oriented into the XCAT using the original XCAT heart surfaces and vessels (shown in wireframe) as a guide. (B) XCAT lungs are deformed to encase the new heart and the vessel surfaces are joined with those of the LHM, plugging the heart into the background anatomy.

Fig. 5.

LHM combined with a male XCAT phantom.

Fig. 6.

Modeling of a coronary plaque using Rhinoceros. Contours were taken through a vessel (left), halved to represent a 50% blockage (middle), then lofted into a NURBS surface (right).

Fig. 7.

Renderings of the XCAT adult male phantom with the LHM defined at end-diastole and end-systole

Fig. 8.

Volumes of the left and right atria and ventricles over the cardiac cycle (one beat over a period of one second) for the example LHM heart within the XCAT adult male.

Fig. 9.

Anatomically variable LHM-XCAT phantoms. Four males (top) and four females (bottom) are shown with their weight and height percentiles indicated for each.

Fig. 10.

Simulated CT data of an XCAT-LHM phantom defined at end-diastole and end-systole. Transaxial (top) and coronal (bottom) slices are shown.

Fig. 11.

Location of the three plaques simulated in the study. Plaques shown at end-diastole (left) and end-systole (right). White dots indicate the diastolic position to show the motion of each plaque.

Fig. 12.

(Left) Simulated CT data of the male LHM-XCAT phantom with and without cardiac motion during the quiescent phase of the heart. Zoomed in views of the coronary segments containing the plaques are shown. (Right) Profile plots through the plaques taken along the directions indicated by the arrows in the CT data.