1. A method of determining change in volume of a target sample, the method comprising: receiving, at an imaging processing machine, ultrasound images of a two-dimensional area corresponding to the target sample, where a first ultrasound image is taken at a first time period and a second ultrasound image is taken at a second time period after the first time period; determining, at the imaging processing machine, a change in strain value of the target sample over the two-dimensional area, wherein the strain value is determined from comparing the first ultrasound image to the second ultrasound image, wherein the first ultrasound image and the second ultrasound image are speckle-containing images; determining, at the imaging processing machine, and from the change in strain value, an xy-plane change in area of the target sample between the first time period and the second time period; determining, at the imaging processing machine, an approximate physical z-axis displacement over the two-dimensional area by approximating a change in local curvature of the two-dimensional area between the first time period and the second time period; and determining, at the imaging processing machine, a volume displacement of the target sample from the approximate physical z-axis displacement and change in strain value.