Purpose: The present study comparatively evaluates the performance of conventional Doppler ultrasound and superb microvascular imaging (SMI) in delineating the cortical microvessels of the transplanted kidney and compares the chronic allograft damage index (CADI) based on the examination of biopsy specimens with Doppler ultrasound and SMI findings.
Methods: Sixty-eight renal transplant recipients underwent kidney biopsy with the pre-diagnosis of rejection before undergoing renal Doppler ultrasound examination between January 2020 and October 2020. The distance between the kidney capsule and the vascular structure closest to the kidney capsule was measured at the level of the lower pole in the transplanted kidney using color Doppler ultrasound (CDUS), power Doppler ultrasound (PDUS), and the SMI technique. The kidney size, resistive index at the level of the arcuate artery in the lower pole of the kidney, and renal artery flow rates were also measured.
Results: The mean distance between the kidney capsule and the vessel was 2.44 ± 2.0 mm on CDUS, 1.34 ± 1.2 mm on PDUS, 0.99 ± 1.8 mm using the color SMI (cSMI) technique, and 0.86 ± 1.8 mm using the monochrome SMI (mSMI) technique. The study found that the SMI technique was superior to CDUS and PDUS in delineating the cortical microvasculature of the kidney. Both Doppler ultrasound examinations and the SMI technique proved effective in predicting the CADI (P = 0.006 for CDUS, P = 0.002 for PDUS, P = 0.018 for cSMI, and P = 0.027 for mSMI). Among conventional Doppler ultrasound examinations and the SMI technique, PDUS had the highest sensitivity, and cSMI had the highest specificity in differentiating high and low CADI values. Both the cSMI and mSMI techniques had similar sensitivity values, whereas only cSMI exhibited high specificity. CDUS had the lowest specificity value (P = 0.003 for CDUS, P = 0.002 for PDUS, P = 0.005 for cSMI, and P = 0.004 for mSMI).
Conclusion: The present study is the first in the literature to demonstrate the utility of the distance between the kidney capsule and the vessels in predicting the CADI score and to compare the Doppler ultrasound examinations and SMI technique in doing so.
Keywords: Chronic allograft damage index; Doppler ultrasound; kidney; renal transplant; superb microvascular imaging.