Abstract
BackgroundThe nonlinear mechanical properties of internal organs and tissues may be measured with unparalleled precision using ultrasound imaging with phase-sensitive speckle tracking. The many potential applications of this important noninvasive diagnostic approach include measurement of arterial stiffness, which is associated with numerous major disease processes. The accuracy of previous ultrasound measurements of arterial stiffness and vascular elasticity has been limited by the relatively low strain of nonlinear structures under normal physiologic pressure and the measurement assumption that the effect of the surrounding tissue modulus might be ignored in both physiologic and pressure equalized conditions.MethodsThis study performed high-resolution ultrasound imaging of the brachial artery in a healthy adult subject under normal physiologic pressure and the use of external pressure (pressure equalization) to increase strain. These ultrasound results were compared to measurements of arterial strain as determined by finite-element analysis models with and without a surrounding tissue, which was represented by homogenous material with fixed elastic modulus.ResultsUse of the pressure equalization technique during imaging resulted in average strain values of 26% and 18% at the top and sides, respectively, compared to 5% and 2%, at the top and sides, respectively, under physiologic pressure. In the artery model that included surrounding tissue, strain was 19% and 16% under pressure equalization versus 9% and 13% at the top and sides, respectively, under physiologic pressure. The model without surrounding tissue had slightly higher levels of strain under physiologic pressure compared to the other model, but the resulting strain values under pressure equalization were > 60% and did not correspond to experimental values.ConclusionsSince pressure equalization may increase the dynamic range of strain imaging, the effect of the surrounding tissue on strain should be incorporated into models of arterial strain, particularly when the pressure equalization technique is used.
Highlights
The nonlinear mechanical properties of internal organs and tissues may be measured with unparalleled precision using ultrasound imaging with phase-sensitive speckle tracking
The present study evaluates the effect of the surrounding tissue modulus and validates the strain results of artery under both normal physiologic pressure and pressure equalization
Elasticity Imaging The accumulated displacement of the arterial wall was calculated with respect to the pixels of the original frame starting at diastole of the cardiac cycle
Summary
The nonlinear mechanical properties of internal organs and tissues may be measured with unparalleled precision using ultrasound imaging with phase-sensitive speckle tracking. Ultrasound estimates of vessel wall motion have included studies to measure femoral artery diameter and pulsatile changes in diameter to evaluate vessel thickness and stiffness in type 2 diabetes mellitus [8], carotid artery diameter and wall motion to determine the relationship of arterial calcification to vessel stiffness in end-stage renal disease [9], and femoral and carotid artery compliance in chronic dialysis patients [10]. To maximize the accuracy of motion estimation, high-resolution ultrasound with speckle tracking algorithms have been employed [14,15] in the renal setting to measure the mechanical properties of arteries and transplant kidneys, demonstrating the potential to distinguish between normal and fibrotic tissue [16]
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