The relationship between regional integrated backscatter levels and regional strain

Integrated backscatter (IB) and its cyclic variation (CV) are echographic parameters often used for tissue characterization. To study the origin of CV, we correlated changes in IB with regional strain in healthy volunteers. Both radiofrequency (RF) and color Doppler myocardial imaging (CDMI) data were acquired from 10 volunteers (parasternal long axis view, posterior wall), using a clinical scanner at high frame rate. IB was extracted from the RF data. Regional radial strain was calculated by integrating the strain rate (SR) curve, extracted from the velocity data. For each volunteer, 3 consecutive heart cycles were averaged. The individual phases of the cardiac cycle (ejection, fast filling, diastasis and atrial contraction) of all datasets, were averaged. The negative radial strain (NRS) curve was plotted on top of the IB curve. During all phases of the cardiac cycle, NRS paralleled IB apart from early systole, where IB increased while NRS decreased. These results can be explained by correlating IB to regional three-dimensional strain (rather than just the radial component, e.g. wall thickening). NRS results in an increase in mean scatterer spacing and hence a decrease in IB level. Moreover, it has been shown that longitudinal contraction precedes the radial one. This could explain the increase in IB level during early systole since this early longitudinal strain could initially decrease scatterer spacing. Changes in myocardial reflectivity as measured by regional IB levels seem to be directly related to regional three-dimensional strain.