Hyperecho as the indicator of tissue necrosis during microbubble-assisted high intensity focused ultrasound: Sensitivity, specificity and predictive value

The purpose of this study was to determine the sensitivity, specificity and predictive values of hyperecho in grayscale ultrasonic images as the indicator of tissue necrosis in microbubble-assisted high-intensity focused ultrasound (HIFU) exposure in vivo. Livers and kidneys of the rabbit were exposed to HIFU (control group) or microbubble-assisted HIFU (experimental group); a continuous line of ablation, viz. linear scan, was performed to destruct tissues. Tissue responses were evaluated macroscopically and microscopically 24 h after HIFU. The cases of positive (hyperecho occurred and tissue necrotized), false positive (tissue was unaffected although hyperecho appeared), negative (echo was not changed and tissue was intact) and false negative (tissue was destructed despite the lack of hyperecho) were counted, and then the sensitivity, specificity and positive and negative predictive values of hyperecho were calculated. The sensitivity, specificity, positive predictive value and negative predictive value were 49.25% vs. 79.63% (p < 0.001), 45.45% vs. 30.00%,84.62% vs. 86.00% and 12.82% vs. 21.43% for liver and 76.06% vs. 81.25%, 26.53% vs. 41.67%, 60.00% vs. 82.28% (p = 0.002) and 43.33% vs. 40.00% for kidney, in control and experimental groups, respectively. Rates varied between tissue types in control group. These findings indicated that the use of microbubble during HIFU improved the sensitivity in liver and the positive predictive value in kidney. The specificity and negative predictive value were poor. Hyperecho could only be used as the indicator of tissue necrosis in some tissue types.