1. An E-mode imaging apparatus comprising: (a) a probe containing an ultrasound transducer for (i) transmitting ultrasonic beams toward a material to be image and (ii) receiving ultrasound echo signals produced by the ultrasonic beams to provide electrical echo signals; (b) an interface circuitry programmed to receive and process the electrical echo signals to provide digital values; (c) a processor for receiving the digital values and producing a series of echo images imaged during different stages of deformation of the material to be imaged, each image comprised of multiple image values; (d) a memory for storing the image values of the series of echo images and a stored operating program; and (e) an operator interface communicating with the processor to communicate a quality value of the image values to an operator manipulating the probe; wherein the processor receives the image values of the series of echo images and executes the stored operating program held in a non-transient medium to calculate: (i) E-mode data indicating a stiffness of the material determined from displacement of corresponding elements of the material represented in image values between different images; (ii) a quality value indicating a quality of E-mode data wherein the quality value is a combination of two different evaluations of the image values of two images, a first evaluation indicating a similarity of corresponding image values in the two images providing a higher first evaluation value when the similarity increases and a second evaluation indicating a degree of variation in values of an E-mode image formed of the image values of the two images provides a higher second evaluation value when the degree of variation increases; wherein the quality value increases as the first evaluation value increases and as the second evaluation value increases.