Background - The human heart is composed of a helical network of muscle fibers. These fibers are organized to form sheets that are separated by cleavage surfaces. This complex structure of fibers and sheets is responsible for the orthotropic mechanical properties of cardiac muscle. The understanding of the configuration of the 3D fiber and sheet structure is important for modeling the mechanical and electrical properties of the heart and changes in this configuration may be of significant importance to understand the remodeling after myocardial infarction.Methods - Anisotropic least square filtering followed by fiber and sheet tracking techniques were applied to Diffusion Tensor Magnetic Resonance Imaging (DTMRI) data of the excised human heart. The fiber configuration was visualized by using thin tubes to increase 3-dimensional visual perception of the complex structure. The sheet structures were reconstructed from the DTMRI data, obtaining surfaces that span the wall from the endo- to the epicardium. All visualizations were performed using the high-quality ray-tracing software POV-Ray. Results - The fibers are shown to lie in sheets that have concave or convex transmural structure which correspond to histological studies published in the literature. The fiber angles varied depending on the position between the epi- and endocardium. The sheets had a complex structure that depended on the location within the myocardium. In the apex region the sheets had more curvature. Conclusions - A high-quality visualization algorithm applied to demonstrated high quality DTMRI data is able to elicit the comprehension of the complex 3 dimensional structure of the fibers and sheets in the heart.

The human heart is composed of a helical network of muscle fibers. Anisotropic least squares filtering followed by fiber tracking techniques were applied to Diffusion Tensor Magnetic Resonance Imaging (DTMRI) data of the excised human heart. The fiber configuration was visualized by using thin tubes to increase 3-dimensional visual perception of the complex structure. All visualizations were performed using the high-quality ray-tracing software POV-Ray. The fibers are shown within the left and right ventricles. Both ventricles exhibit similar fiber architecture and some bundles of fibers are shown linking right and left ventricles on the posterior region of the heart.

The motion of the beating heart is complex and creates artifacts in SPECT and x-ray CT images. Phantoms such as the Jaszczak Dynamic Cardiac Phantom are used to simulate cardiac motion for evaluationof acquisition and data processing protocols used for cardiac imaging. Two concentric elastic membranes filled with water are connected to tubing and pump apparatus for creating fluid flow in and out of the inner volume to simulate motion of the heart. In the present report, the movement of two concentric balloons is solved numerically in order to create a computer simulation of the motion of the moving membranes in the Jaszczak Dynamic Cardiac Phantom. A system of differential equations, based on the physical properties, determine the motion. Two methods are tested for solving the system of differential equations. The results of both methods are similar providing a final shape that does not converge to a trivial circular profile. Finally,a tomographic imaging simulation is performed by acquiring static projections of the moving shape and reconstructing the result to observe motion artifacts. Two cases are taken into account: in one case each projection angle is sampled for a short time interval and the other case is sampled for a longer time interval. The longer sampling acquisition shows a clear improvement in decreasing the tomographic streaking artifacts.

Typically 123I-MIBG is used for the study of innervation and function of the sympathetic nervous system in heart failure. The protocol involves two studies: first a planar or SPECT scan is performed to measure initial uptake of the tracer, followed some 3-4 hours later by another study measuring the wash-out of the tracer from the heart. A fast wash-out is indicative of a compromised heart. In this work, a dual head pinhole SPECT system was used for imaging the distribution and kinetics of 123I-MIBG in the myocardium of spontaneous hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. The system geometry was calibrated based on a nonlinear point projection fitting method using a three-point source phantom. The angle variation effect of the parameters was modeled with a sinusoidal function. A dynamic acquisition was performed by injecting 123I-MIBG into rats immediately after starting the data acquisition. The detectors rotated continuously performing a 360o data acquisition every 90 seconds. We applied the factor analysis (FA)method and region of interest (ROI) sampling method to obtain time activity curves (TACs)in the blood pool and myocardium and then applied two-compartment modeling to estimate the kinetic parameters. Since the initial injection bolus is too fast for obtaining a consistent tomographic data set in the first few minutes of the study, we applied the FA method directly to projections during the first rotation. Then the time active curves for blood and myocardial tissue were obtained from ROI sampling. The method was applied to determine if there were differences in the kinetics between SHR and WKY rats and requires less time by replacing the delayed scan at 3-4 hours after injection with a dynamic acquisition over 90 to 120 minutes. The results of a faster washout and a smaller distribution volume of 123IMIBG near the end of life in the SHR model of hypertrophic cardiomyopthy may be indicative of a failing heart in late stages of heart failure.

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