Comparison of the low-contrast detectability of two ultrasound systems using a grayscale phantom.

The purpose of the present study was to use a commercially available grayscale phantom to compare two ultrasound systems regarding their ability to reproduce clinically relevant low-contrast objects at different sizes and depths, taking into account human observer variability and other methodological issues related to observer performance studies. One high-end and one general ultrasound scanner from the same manufacturer using the same probe were included. The study was intended to simulate the clinical situation where small low-contrast objects are embedded in relatively homogeneous organs. Images containing 4 and 6.4 mm objects of four different contrasts were acquired from the grayscale phantom at different depths. Six observers participated in a 4-alternative forced-choice study based on 960 images. Case sample and human observer variabilities were taken into account using bootstrapping. At four of sixteen depth/size/contrast combinations, the visual performance of the high-end scanner was significantly higher. Thus, it was possible to use a grayscale phantom to discriminate between the two evaluated ultrasound systems in terms of their ability to reproduce clinically relevant low-contrast objects. However, the number of images and number of observers were larger than those usually used for constancy control. PACS number(s): 87.57.C-, 87.63.dh.