Pulse-inversion US imaging of testicular ischemia: Quantitative and qualitative analyses in a rabbit model

Purpose: To quantitatively and qualitatively assess perfusion with pulse-inversion (PI) ultrasonography (US) in rabbit model of acute testicular ischemia. Materials and Methods: Institutional animal care committee approval was obtained. After 35 rabbits underwent unilateral spermatic cord occlusion, testicular Doppler US and contrast material -enhanced PI imaging were performed. Enhancement data yielded perfusion measurements including mean value during the first 10 seconds, mean value over entire recorded replenishment curve, and curve slope during the first 5 seconds. Calculated perfusion ratios were compared with radiolabeled microsphere-derived perfusion ratios. Two readers assessed testicular perfusion as none, possible, or definite and relative perfusion as greater to the right testis than to the left, greater to the left testis than to the right, or as equal to both testes. With kappa statistics, interobserver agreement for all imaging methods was determined. Association between qualitative perfusion categories and radiolabeled microsphere-based perfusion measurements was assessed. Quantitative and qualitative determinations of relative perfusion were compared with radiolabeled microsphere-based measurements. Results: Correlations between calculated and radiolabeled microsphere -based perfusion ratios were determined (r = 0.49 - 0.64). Interobserver agreement for presence of perfusion was excellent (kappa = 0.76), and that for relative perfusion assessment was good (kappa = 0.55). Neither kappa value varied significantly with imaging method. The percentage of times a testis classified as having definite perfusion had greater perfusion as measured with radiolabeled microspheres than a testis classified as having no perfusion or possible perfusion was higher with PI imaging than with Doppler US (85% - 98% vs 72% - 89%). Identification of the testis with less perfusion was better with quantitative methods than with qualitative assessment of images by the readers (75% - 79% vs 34% - 60%, P < .004). Conclusion: PI imaging, compared with conventional Doppler US methods, provides superior assessment of perfusion in the setting of acute testicular ischemia.