Elastographic characterization of HIFU-induced lesions in canine livers

The elastographic visualization and evaluation of high-intensity focused ul trasound (HIFU)-induced lesions were investigated, The lesions were induced in vitro in freshly excised canine livers, The use of different treatment intensity levels and exposure times resulted in lesions of different sizes. Each lesion was clearly depicted by the corresponding elastogram as being an area harder than the background. The strain contrast of the lesion/backg round was found to be dependent on the level of energy deposition. A lesion /background strain contrast between -2.5 dB and -3.5 dB was found to comple tely define the entire zone of tissue damage, The area of tissue damage was automatically estimated from the elastograms by evaluating the number of p ixels enclosed inside the isointensity contour lines corresponding to a str ain contrast of -2.5, -3 and -3.5 dB, The area of the lesion was measured f rom a tissue photograph obtained at approximately the same plane where elas tographic data were collected, The estimated lesion areas ranged between ap proximately 10 mm(2) and 110 mm(2), A high correlation between the damaged areas as depicted by the elastograms and the corresponding areas as measure d from the gross pathology photographs was found (r(2) = 0.93, p value < 0. 0004, n = 16), This statistically significant high correlation demonstrates that elastography has the potential to become a reliable and accurate moda lity for HIFU therapy monitoring. (C) 1999 World Federation for Ultrasound in Medicine & Biology.