Objective analysis of ultrasound images by use of a computational observer

Abstract

The design, implementation, and testing of a computational observer method for objective evaluation of ultrasound images are presented. The method uses digitized ultrasound B-scan images of a test phantom (the contrast-detail phantom), and is able to calculate the detectability of a target (signal) from its background (background noise). A quantitative detectability index, based on the measured signal-to-noise ratio of the image data, that is measured for both the human and the computational observer on the same scale is generated. It is shown that the computational observer (CO) method may be a more useful, objective way of evaluating ulrasound images and imaging systems than methods that rely solely on human observers. It may also be applicable to other types (i.e. other than ultrasound) of imaging systems which produce noisy images. The relevance of the CO method when compared to human observer two-alternative-forced-choice (2AFC) readings of the same data by showing a high correlation between the CO detectability results and those of human observers for the same set of images. The method is (1) quantitative, (2) reproducible, (3) absolute, (4) takes into account, and can calculate the value of TPF and FPF for each target, for the given system, and (5) speeds up the evaluation of an image or imaging system (compared to using human observers), given the right conditions and equipment.