Spatiotemporal Visualization of the Regional Myocardial Tissue
Authors: Sheharyar Ali , Linsen Lars , Bouhali Othmane , Chitiboi Teodora 
Published: July 2019

According to the World Health Organization (WHO), cardiovascular disease is the leading cause of deaths worldwide. The left ventricle (LV), one of the four chambers of the human heart, plays a crucial role in the performance of the entire heart. The abnormal motion of its wall muscle (myocardium) is an important indicator for multiple cardiac pathologies. Nearly, half of all heart failure cases occur due to the decline in its performance. Therefore, early detection, monitoring and accurate diagnosis of left ventricle pathologies is of critical importance. Usually, the global cardiac function parameters such as ejection fraction, and ventricular volume, etc., are used to assess the cardiac structure and functions. However, the regional abnormalities are often overlooked. The regional alterations in the heart motion are important biomarkers of several cardiac pathologies such as coronary artery disease, cardiomyopathy or hypertrophic heart disease.

The myocardium moves in a complex pattern in all three directions (radial, longitudinal, and circumferential) over the cardiac cycle. It contracts/expands (narrows/widens) and twists/untwists (clockwise/counterclockwise rotation) in short axis orientation and shortens/lengthens along the long axis direction. This complex 3D motion can be captured in a non-invasive manner using the velocity-encoded MR imaging method known as Tissue Phase Mapping (TPM). TPM offers high spatial (1–3 mm) and temporal resolution (13.8 msec) in comparison with other acquisition techniques such as tagging, tissue Doppler imaging, etc., and has proven to be a robust tool for the assessment of regional and global myocardial motion.

TPM produces spatiotemporal data that are usually visualized as a series of many static images (one for each time step). Traditionally, these static images are produced using the American Heart Association (AHA) based 17-segment model that divides the LV into 17 segments and projects them on a 2D plane perpendicular to the long axis of the heart. Also, there has been some work on the visualization of the temporal relationships but they neglect the structural or spatial information. To our knowledge, there has been no work that combines both the spatial and temporal relationships in a single representation that offers a dynamic visualization of the LV over the cardiac cycle.

In this work, we propose a novel method for the dynamic visualization of the myocardium motion over the entire heart cycle. We display both spatial and temporal relationships simultaneously for improved analysis. We propose using multiple coordinated views to show all three components (radial, longitudinal, and circumferential) of the velocity vectors in separate views (one view per component). Each component is displayed as a bulls-eye or polar plot that is color-coded with respect to its corresponding component value. The layout of the plot is such that the angular axis represents the segments of the myocardium wall, and the radial axis follows along the time dimension. The coordinated views leverage human perceptual capabilities and help in bringing out the correlations and/or disparities in the myocardial motion data. The primary objective of our work is to enhance the visual analysis to improve the understanding of the physiology and pathophysiology of the heart.