(A, B) Simulated time course of a bladder, filled at 20 μl/min, that fully voids at time point 300 s (black trace; no averaging). Panel B zooms in on the 4 s surrounding the void, showing individual time points in a 30 Hz recording, similar to the fluoroscopy imaging used in this study. Also shown in are the time courses of bladder volume that would be calculated when using a rolling average with the indicated number of frames (N). These time courses were determined based on the assumption that, when averaging N images, the derived length of the long and short radii of the detected bladder circumference of the averaged image are equal to the mean value of the long and short radii of the N images. (C) Simulated time courses of the urethral flow rate (UFR) during a void, determined as minus the time derivative of the volume traces in (A, B). A rolling average of 15 frames, as used in this work, leads to a small (<5%) decrease in maximal UFR, with little effect on the time course of the void. As expected, further increasing the number of images for averaging (30 or 60 frames) leads to a gradual broadening of the void, associated with a shift and decrease of the voiding peak. Note that this simulation was done for a void with a short duration (t20–80 = 1.2 s), comparable to the results obtained in catheterized mice. The effect a 15-image rolling average will be even smaller for the fluoroscopic volumetry experiments in noncatheterized animals, where void durations were significantly longer (t20–80 = 2–5 s).