Biomedical Engineering Reference
In-Depth Information
Fig. 2.5.
Cardiac cycle-dependent variation in ultrasonic integrated backscatter
from the myocardium of the left ventricular posterior wall in a human subject
magnitude of both ultrasonic attenuation and backscatter in excised heart
tissue depends critically on the angle of insonification [5]. Tissue water con-
tent and hematocrit both influence myocardial scattering and attenuation;
however, nutritive blood flow per se may not be necessary for the produc-
tion of cardiac cycle-dependent variation of myocardial backscatter [6]. The
dynamic aspect of ultrasonic scattering was first described by Madaras and
associates [7]. They observed that backscatter intensity varies throughout the
cardiac cycle, with maximal levels at end-diastole and minimal levels at end-
systole (Fig. 2.5). This variation is observed in both experimental animals
and human subjects. The magnitude of cyclic variation of backscatter is re-
lated to intrinsic myocardial contractile performance, but is independent of
perfusion with blood [8,9]. Several hypotheses have been advanced to explain
the cyclic alteration of myocardial acoustic properties: these include cyclic
alterations of myocardial elastic characteristics and alteration of myocardial
scatterer geometry. However, no simple explanation yet appears sucient
to account for the entire range of evidence from experimental animals and
human subjects.
