BACKGROUND: Bladder drainage via catheter is standard during diuretic nuclear renography and magnetic resonance urography (MRU). Bladder fullness can be observed occasionally despite the drainage catheter, raising doubts regarding the functional study’s validity. We aim to determine whether bladder fullness during MRU influences functional parameters.
METHODS: IRB approved retrospective study of 270 MRU’s performed from 11/17/2021 to 10/19/2023 in healthy children <18 years. Of these, 110 were included and the rest excluded due to excessive motion, bilateral hydronephrosis, solitary kidney, horseshoe kidney, other structural renal anomaly, neurogenic bladder, bladder augmentation, posterior urethral valves, or other bladder anomalies.
Bladder volumes (BV) were measured using third-party image post-processing software (SyngoVia). Pre-furosemide BV were measured from T2-weighted axial images obtained at the beginning of the MRU. Post-furosemide BV were measured from post-contrast T1-weighted axial images after the dynamic phase imaging, approximately 27 minutes post-furosemide and 12 minutes post-Gadolinium. Expected bladder capacity was estimated for infants <1 year old (weight(kg)x7), and for children >1 year old ([age(years)+2]x30).
RESULTS: 110 studies met inclusion criteria, 71 males 39 females. Average age was 3.7 years (0.2 - 17.3, SD 4.5 years). 63 studies were performed on a 3T and 47 on 1.5T MRI.
Pre- and post-furosemide BV were 44.96 mL (SD, 63.29) and 53.23 mL (SD, 85.02) respectively (p-value, 0.41), with change in BV 8.27 mL (SD 59.73). Mean pre- and post-furosemide percent bladder capacities achieved were 29.80% (SD, 29.79) and 34.36% (SD, 34.21) respectively (p-value, 0.29). In the pre-furosemide group, 6 of 110 patients had BV >100% capacity, and post-furosemide 7 had BV >100% capacity.
For the entire cohort, overall MRU functional parameters were within normal range. Calyceal transit time (CTT) was 125.55 seconds (SD, 22.41), mean transit time (MTT) was 53.69 seconds (SD, 14.87), renal transit time (RTT) was 151.28 seconds (SD, 38.29), peak time was 167.26 seconds (SD, 36.37), and unit glomerular filtration rate (uGFR) was 0.32 ml/min per mL of tissue (SD, 0.1).
There was no statistically significant correlation between MR functional parameters (CTT, MTT, RTT, Peak time, uGFR) and bladder measurements.
In sub-group analysis, MTT in the upper third pre-furosemide percent bladder capacity group was significantly longer compared to the lower third group in our initial analysis with all data samples (p-value, 0.041). On closer analysis, statistically significant differences in the MTT, CTT, and RTT were only observed when pre-furosemide percent bladder capacity =/>100%, compared to the group with <100% capacity. No statistically significant difference in the functional parameters was observed between the lower and upper third post-furosemide percent bladder capacity measurements. No significant difference was observed in the MR functional parameters between the lower and upper third bladder measurements in the pre-furosemide BV, post-furosemide BV, and change in BV analysis.
CONCLUSIONS: MRU functional parameters are not influenced by bladder volume if the volume remains within weight or age-adjusted capacity. However, MR renal transit times (MTT, CTT, and RTT) are prolonged if the bladder volume exceeds capacity and emphasizes the importance of adequately emptying the bladder at the beginning of the study.
