Quantitative Dynamic Contrast-Enhanced Ultrasound Confirms Renal Obstruction: A Feasibility Study

To evaluate dynamic contrast-enhanced ultrasound (DCEUS) potential for diagnosing ureteropelvic junction obstruction (UPJO). We hypothesize that DCEUS can identify differences in renal parenchymal microcirculation between normal and obstructed kidneys.

This prospective study included 8 subjects (16 kidneys) with unilateral renal obstruction clinically determined to need surgery and confirmed by nuclear medicine (NM) diuretic half-time ( $t_{1/2}\ge 20\min$ ). Subjects underwent pre- and post-surgery DCEUS and NM imaging at a tertiary care institution (Dec 2021 to Oct 2024). DCEUS-derived time-intensity curves were analyzed to calculate mean-transit time (MTT), time-to-peak (TTP), and full-width at half-maximum (FWHM). DCEUS MTT was compared between normal and affected kidneys and to NM $t_{1/2}$ . Statistical significance was determined using two-sided paired and unpaired Student t-tests.

MTT was significantly longer in obstructed kidneys compared to normal kidneys before surgery ( $52\pm 7s$ vs. $18\pm 3s;P=.002$ ) and normalized after pyeloplasty ( $13\pm 3s$ vs. $14\pm 2s;P=.8$ ). A point-biserial correlation between DCEUS MTT and NM drainage time categories was found to be $r_{\mathrm{pb}}=0.8$ ( $P<.0001$ ). Similar patterns were observed for TTP and FWHM, however, they were not statistically significant. The results showed potential of DCEUS MTT in categorizing kidneys into delayed and normal, according to their NM drainage time (ROC AUC = 0.97, 95% CI = [0.9, 1.0]).

DCEUS MTT shows promise as a diagnostic tool for assessing UPJO, potentially serving as a stand-alone or complementary modality to NM without additional ionizing radiation. Further trials with larger cohorts and those with non-obstructing hydronephrosis are required to confirm its clinical utility.