Comparative analysis of three different modalities for characterization of the seismocardiogram

Abstract

We introduce and compare three different modalities to study seismocardiogram (SCG) and its correlation with cardiac events. We used an accelerometer attached to the subject sternum to get a reference measure. Cardiac events were then approximately identified using echocardiography. As an alternative approximation, we used consecutive Cine-MRI images of the heart to capture cardiac movements and compared them with the experimental SCG. We also employed an anatomically accurate, finite element base electromechanical model with geometry built completely from DT-MRI to simulate a portion of the cardiac cycle as observed in the SCG signal. The preliminary results demonstrate the usability of these newly proposed methods to investigate the mechanism of SCG waves and also demonstrate the usability of echocardiograph in interpretation of these results in terms of correlating them to underlying cardiac cycle events.

Figure 1

A cycle of ECG (top) and SCG (bottom) signals and the sequence of cardiac events.

Figure 2

the simultaneous continuous Doppler, SCG (blue) and ECG (green) signals of a healthy heart.

Figure 3

Cine-MRI based 3D model: a) Different views of Snakes based segmentation; b) Rough Estimation of left/right ventricle volumes in end-diastole; c) End-diastolic and end-systolic states of the ventricles obtained from cine MRI. Line labeled with D shows how we could use these deformable meshes to capture acceleration of cardiac vibrations by computing second derivative of D’s displacement changes over mesh deforms.

Figure 4

Cardiac mechanics model: a) generated finite element mesh (anterior view). Arrow shows axis in which projection of acceleration for the center of mass was calculated; b) Cross-sectional snapshots during contraction with fiber strain (FS). Red shows stretching, while blue shows contraction. c) The anterior wall of the ventricles at end-diastole (ED) and end-systole (ES). Thick, black lines were included to make the twisting effect more obvious.

Figure 5

Cine-MRI results: Rough Estimation of left/right ventricular volumes and driven SCG in an observation point shown in Figure 3c.

Figure 6

Cardiac mechanics model results: a) applied left and right ventricular volumes; b) Center of mass acceleration in the direction shown in Figure 4a.