(A) Schematic of the human kidney, showing its position and orientation. The ultrasound probe is positioned in the lower subcostal space along the midaxillary line, imaging the mid-sagittal plane of the kidney. (B) Magnified view of the kidneys from panel (A), detailing the major anatomical components. (C) and (D) Representative B-mode (C) and contrast-enhanced mode (D) ultrasound images of a normal kidney obtained in this study.

Example of B-mode and contrast-enhanced ultrasound (CEUS) cine loops of the kidney used for time-intensity curve (TIC) analysis in the evaluation of ureteropelvic junction obstruction (UPJO). Circular regions of interest (ROIs) on the cortex are used for contrast signal extraction, while a polygonal ROI on the renal sinus in B-mode is used to track kidney motion during the imaging sequence.

Representative examples of time-intensity curves of normal (A and C) and affected (B and D) kidneys, before pyeloplasty of the obstructed kidney (A and B) and after pyeloplasty of the obstructed kidney (C and D). FWHM, full-width at half-maximum; MTT, meantransit time; TTP, time to peak.

Dynamic contrast-enhanced ultraound (DCEUS) mean-transit time (MTT) is significantly different between normal and obstructed kidneys before pyeloplasty of the obstructed kidney, and this difference is resolved after successful pyeloplasty. The distribution of MTT values is shown, comparing normal and obstructed kidneys before pyeloplasty of the obstructed kidneys (n = 8) and normal and previously obstructed kidneys after pyeloplasty of the obstructed kidney (n = 6). Results from subjects 1 and 7 are excluded from the post-pyeloplasty group. Subject 1 did not show up for post-surgery screening. Subject 7 NM T1/2 drainage time was greater than 20 minutes, indicating persistent obstruction (see Table 1 for details). Mean values are marked by horizontal lines across violin plots, and statistically significant differences between groups are noted by the P-values displayed above the plots (paired two-tailed t-test). Outliers, calculated as data points outside of 1:5 IQR (interquartile range), are shown as individual points.

Comparison of NM drainage time and DCEUS MTT showing strong correlation between the two metric. A, Violin plot of DCEUS MTT for kidneys categorized into normal and delayed drainage based on NM T1/2 . The mean values are represented by white horizontal lines across the violin plots. A significant difference in MTT is observed between the two groups (P < 0.001, unpaired t-test). A strong point-biserial correlation is found between NM drainage categories and MTT (r_pb = 0.8, P < 0.0001). B, ROC curve showing the diagnostic performance of MTT in distinguishing between normal and delayed drainage, with an optimal threshold of 30 s determined by the closest point to (0, 1). C, Scatter plot comparing DCEUS MTT with NM T1/2 . Data points associated with kidneys with no drainage (T1/2 > 1000 min) are indicated by upward arrows. The plot is divided into four quadrants: top-right (obstruction agreement, shaded yellow) and bottom-left (no obstruction agreement, shaded green) show where NM and DCEUS results align; the top-left and bottom-right quadrants represent false negatives and false positives, respectively.