LOW CONTRAST DETECTABILITY AND CONTRAST/DETAIL ANALYSIS IN MEDICAL ULTRASOUND.
The first- and second-order statistics of envelope detected ultrasound (US) B-mode images for the case of a scattering phantom with many scatterers per resolution cell have been previously derived. These characteristics are integrated over the region of a simulated focal (disk) lesion and the signal-to-noise ratio (SNR) for lesion detectability is obtained. This SNR requires the average number of independent speckle cells over the lesion area. This number is obtained from autocorrelation analysis (second-order statistics). By setting the SNR expression equal to the threshold value SNR//T required to detect a lesion in the presence of speckle noise, the dependence of lesion contrast on lesion diameter at threshold is found, i. e. , the contrast/detail function. This is a simple inverse relation for ideal observers of US B-scans. It is also found that the contrast/detail results for envelope detection in diagnostic ultrasound are almost identical with the results for square law detection (the usual laser case) with the latter serving as an upper limit for performance in lesion detection. Finally, the results of human observer performance using a contrast/detail phantom are compared with the predictions for optimal or ideal performance.
