A contrast‐detail analysis of diagnostic ultrasound imaging

Abstract

For diagnostic ultrasound imaging, as in computed tomography, a feature of prime importance is the detection of focal lesions of varying size and contrast (echo amplitude) from surrounding tissue. This study describes a new tissue-simulating phantom which has been used to measure the threshold detection of varying contrast, simulated lesions. The phantom consists of a block of tissue-mimicking gelatin which contains a row of conical targets at a depth of 7 cm. Each cone contains a different tissue-mimicking material so that the echo amplitude of the cones relative to the background material covers a dynamic range of 20 dB. Cross-sectional B-scans, perpendicular to the lengths of the cones, result in images of disks of constant diameter but varying contrast. Parallel cross-sectional scans yield lesions varying in diameter from 20-1 mm. Relative contrast of the cones vs. background tissue is obtained by varying scattering particle sizes from 90-300 .mu.m. Ultrasound B-scans of the phantom were examined by medical physicist observers to determine threshold detection of lesions as a function of size and contrast. Apparently, detection of high contrast targets is limited by the imaging system''s spatial resolution. Detection of low contrast targets is limited by the image speckle, i.e., coherent noise.