Left - Ventricular Mechanical Parameters based on Echocardiography and SPECT

Gil Zwirn1, Solange Akselrod2
In collaboration with Micha Feinberg2, Aaron Miller1 and Pierre Chouraqui 2,3

1 The Abramson Center of Medical Physics, Tel Aviv University, Tel Aviv, Israel
2 Heart Institute, Sheba Medical Center, Ramat Gan, Israel
3 Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel


OBJECTIVES
The aim of this study was to investigate Left - Ventricular Mechanical Parameters and in particular the correlation between the local myocardial contractility, as measured by GE Healthcare's 2D Strain software package, and the local perfusion, measured by 201Tl SPECT (Single Photon Emission Computerized Tomography) imaging. The 2D Strain algorithm provides quantitative measurements of the local strain within the cardiac muscle, based on Echocardiographic imaging.

BACKGROUND
Various pathologies, such as Hibernating Tissue and Stunned Myocardium, may cause inconsistencies between the local contractility and the local perfusion of the cardiac muscle. Values reported in literature for the correlation coefficient between the local contractility, visually estimated by Echocardiography, and the local perfusion, as measured by SPECT imaging, are 0.67* and 0.71**.

METHODS
Nineteen ICCU (Intensive Care Cardiac Unit) patients have undergone both Echocardiography (Vivid 7, GE) and SPECT imaging (Varicam rotating scintillation camera, GE) on the same day.

The Echocardiographic data was obtained in three different views: Apical 4-Chamber, Apical 2-Chamber, and Apical Long-Axis. The data for each view has been processed by the 2D Strain algorithm, to produce six peak-longitudinal-strain measurements, one per segment. The resulting measurements were compared to the corresponding regions within the SPECT's bull's-eye map (at rest). In order to handle inaccuracies in the positioning of the Echo transducer, the two datasets had first to undergo registration. Both translation (of up to 0.3 segments) and rotation (up to 300) of each Echo view have been allowed, with respect to the theoretical geometric configuration. The linear correlation coefficient at the optimal configuration has been computed for each view of each patient.

RESULTS
The mean correlation coefficients between Echo and SPECT for the Apical 4-Chamber, Apical 2-Chamber, and Apical Long-Axis views are 0.75, 0.68, and 0.62 respectively. The overall mean correlation coefficient is 0.68. As expected, the correlation coefficients are in many cases 0.9 or above, but there are also a few cases with a correlation coefficients of 0.1 or below. The standard deviation of the correlation for each view separately, and for the entire dataset, is thus 0.3.

CONCLUSIONS
The correlation coefficient between 2D Strain and SPECT imaging, 0.68, is comparable to the values reported in literature for the correlation between the clinical diagnosis of local contractility, based on Echo, and the local perfusion, based on SPECT. These results validate the ability of the 2D Strain software to automatically determinates mechanical LV features.

* Rechavia E et al.. Eur Heart J 1995; 16:18451850.
**Oh JK et al. Am Heart J 1996; 131:3237.