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) Vspheroid: two-dimensional (2D) method calculated assuming spheroid geometry; (2) Vbih: 2D correction method obtained by multiplying Vspheroid by a previously derived correction factor of 1.375; and (3) V3D: 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 (Vcontrol) obtained by adding UD infused volume and the volume of estimated urine production. RESULTS Based on linear regression analysis, both Vbih and V3D were fairly accurate estimators of Vcontrol, but V3D was more precise. Vspheroid significantly underestimated Vcontrol. CONCLUSIONS Although the Vbih and V3D methods were more accurate than the more-commonly used Vspheroid method for measuring bladder volumes during UD, the V3D method was the most precise and could best account for non-uniform bladder geometries. Therefore, the V3D method may represent the best tool required for the continued development of non-invasive methods to diagnose OAB and other forms of voiding dysfunction.