LESION DETECTION IN SIMULATED ELASTOGRAPHIC AND ECHOGRAPHIC IMAGES - A PSYCHOPHYSICAL STUDY

The image quality of two ultrasonic imaging techniques was studied: co nventional echography and the recently introduced elastography. The im age quality was assessed by estimating the detectability of disc-shape d lesions of various sizes and contrast levels. The study was designed to verify the hypothesis that elastograms could show lesions at a hig her subjective and objective level of detectability than echograms of the same object contrast. This hypothesis was adopted because homogene ous elastograms can present a higher point signal-to-noise ratio than uniform echograms. Both elastograms and echograms were generated by tw o-dimensional (2D) simulations. The subjective assessment was performe d by psychophysical experiments using the staircase up-down method. Th e threshold contrast of detection for both modalities was determined a t different diameters of the disc-shaped lesion. These values were use d to construct the contrast-detail curves for both techniques. For ide ntical object contrasts, elastography was found to have significantly higher detectability at all lesion diameters considered. The contrast thresholds were also used for an objective evaluation with the lesion signal-to-noise ratio. The objective measure evaluated at the subjecti ve threshold of detection for both modalities was not found to be iden tical, nor constant over the range of lesion diameters as expected.