Comparison of 2D and 3D ultrasound methods to measure serial bladder volumes during filling: Steps toward development of non-invasive ultrasound urodynamics

OBJECTIVES: Non-invasive methods to objectively characterize overactive bladder (OAB) and other forms of voiding dysfunction using real-time ultrasound are currently under development but require accurate and precise serial measurements of bladder volumes during filling. This study’s objective was to determine the most accurate and precise ultrasound-based method of quantifying serial bladder volumes during urodynamics (UD). METHODS: Twelve female participants with OAB completed an extended UD procedure with the addition of serial bladder ultrasound images captured once per minute. Bladder volume was measured using three ultrasound methods: (1) V(spheroid): two-dimensional (2D) method calculated assuming spheroid geometry; (2) V(bih): 2D correction method obtained by multiplying V(spheroid) by a previously derived correction factor of 1.375; and (3) V(3D): three-dimensional (3D) method obtained by manually tracing the bladder outline in six planes automatically reconstructed into a solid rendered volume. These volumes were compared to a control (V(control)) obtained by adding UD infused volume and the volume of estimated urine production. RESULTS: Based on linear regression analysis, both V(bih) and V(3D) were fairly accurate estimators of V(control), but V(3D) was more precise. V(spheroid) significantly underestimated V(control). CONCLUSIONS: Although the V(bih) and V(3D) methods were more accurate than the more-commonly used V(spheroid) method for measuring bladder volumes during UD, the V(3D) method was the most precise and could best account for non-uniform bladder geometries. Therefore, the V(3D) method may represent the best tool required for the continued development of non-invasive methods to diagnose OAB and other forms of voiding dysfunction.