The potential value of non-invasive ultrasound (US) imaging for the analysis of overactive bladder (OAB) has been highlighted in recent studies that have quantified bladder shape and its association with OAB [1, 2]. In these studies, bladder shape parameters have been determined by manual tracing of bladder perimeters in US images. Gray et al., developed a method to estimate bladder sphericity using 2D US images during filling and found that deviations from sphericity correlated with non-voiding bladder contractions [2]. Glass Clark et al., found that bladder height-to-width ratios in 5/11 women with OAB were outside 95% confidence intervals derived from a group of age and body mass index-matched women without OAB [1].  For bladder shape diagnostics for OAB to be clinically relevant, the measures must be sufficiently repeatable. Therefore, the objective of the present study was to assess the repeatability of bladder shape parameters from ultrasound images obtained from multiple fills and during multiple clinic visits.

Healthy participants were recruited to complete an accelerated oral hydration study. Only participants that answered “never” to the question “How often do you rush to the toilet?” on the validated ICIq-OAB questionnaire were enrolled. Each participant completed two consecutive bladder fill-empty cycles during each of two visits approximately one week apart, for a total of four fills per participant. During each fill, abdominal 3D ultrasound images were recorded every 5 min and analyzed using GE 4DView software (Fig1). Bladder perimeters were manually traced in six cross-sectional planes, each 30° apart, and the transverse, sagittal and coronal perimeters were recorded. These measurements were interpolated to standard bladder volumes of 200, 300, and 400ml. To quantify repeatability, the intraclass correlation coefficient (ICC) and the normalized mean absolute difference were calculated for each perimeter at each volume, based on established methods [3].

Data from 16 healthy participants (9 females and 7 males) were analyzed.  The ICCs at 200, 300, and 400ml (n=11, 12 and 10, respectively) for the transverse, sagittal and coronal perimeters are listed in Table 1 (top). In addition, the normalized mean absolute difference (MAD) values for each perimeter are listed in Table 1 (bottom). Five of nine ICCs showed moderate or good repeatability (ICC ≥ 0.5). Furthermore, the mean absolute difference/mean ratio was ≤4% for all three perimeter measurements at all three volumes.

Moderate repeatability was defined as ICC ≥ 0.5 and good repeatability defined as ICC ≥ 0.75. Five of nine ICCs showed moderate or good repeatability. Moreover, the normalized MAD values of less than 4% for all three perimeter measurements across all volumes indicated that perimeter repeatability was consistent through multiple fills and visits.

This study provides initial evidence that bladder shape diagnostics may be repeatable for multiple fills and visits, and therefore, might be feasible as a non-invasive means to improve OAB phenotyping.

Glass Clark S, Nagle A, Bernardo R, Vinod N, Carucci L, Carroll A, Speich J, Klausner A. Use of Ultrasound Urodynamics to Identify Differences in Bladder Shape Between Individuals With and Without Overactive Bladder. Female Pelvic Med. & Reconstr Surg. 2018, DOI:10.1097/spv.0000000000000638.
Gray T, Phillips L, Li W, Buchanan C, Campbell P, Farkas A, Abdi S, Radley S. Evaluation of bladder shape using transabdominal ultrasound: Feasibility of a novel approach for the detection of involuntary detrusor contractions. Ultrasound. 2019;27(3):167-175.
Tan L, Shek K, Atan I, Rojas R, Dietz H. The repeatability of sonographic measures of functional pelvic floor anatomy. Int Urogynecol J. 2015;26(11):1667-1672.