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.