Ultrasonic axial strain measurement for lateral tissue deformation.

An axial strain measurement technique and a one-dimensional (1D) shear modulus reconstruction technique were developed previously by using the multidimensional radio-frequency (RF) echo phase matching method and an axial strain ratio, respectively. In this study, these techniques have been applied using a conventional ultrasound (US) imaging system with the constraint that the tissue deforms predominantly in the lateral direction, orthogonal to the ultrasound beam axis. Conventionally, axial strain measurement and axial strain ratio are used when the tissue deforms predominantly in the axial direction by extracorporeally applied pressure or vibration. In any case, an axial strain can be accurately measured using the multidimensional RF-echo phase matching method; such a measurement will be useful and will enable a simple reconstruction in a lateral deformation case. The usefulness of these techniques is demonstrated by agar phantom experiments; several problems related to their use in cases such as accuracy, bias error and detectability of inhomogeneity (contrast-to-noise ratio) are addressed. These techniques will be effective for deep regions-of-interest (ROIs) such as liver tissues, which are inaccessible from the body surface and normally deformed by heart motion or pulsation. Moreover, such techniques will enable the evaluation of the elasticity of various tissues under normal motion such as the arm and leg muscles during exercise.