Pelvic floor function in nulliparous women using three-dimensional ultrasound and magnetic resonance imaging

OBJECTIVE: To compare biometric measures of pelvic floor function obtained using three-dimensional (3D) ultrasound and magnetic resonance imaging (MRI) in a group of nulliparous asymptomatic young women. METHODS: Twenty-seven asymptomatic nulliparous volunteers were assessed prospectively, using translabial 3D ultrasound and multiplanar 3D MRI. Levator hiatal dimensions were measured in the axial plane in both modalities. All participants were imaged supine, after voiding with data acquired at rest, on maximum Valsalva and maximum pelvic floor contraction. Interobserver variability was determined for both methods. Normally distributed continuous ultrasound data were compared with equivalent MRI parameters, and intraclass correlation coefficients were used to estimate correlation between the two methods. Bland-Altman analysis was also used to estimate agreement between methods. RESULTS: Interobserver repeatability was fair to excellent for all parameters measured with both methods. Moderate-to-substantial agreement between methods was shown for all tested parameters (intraclass correlation coefficients 0.587-0.783). There was a systematic but nonsignificant difference between methods, in that measurements on Valsalva tended to be larger for MRI, and the poorest agreement (intraclass correlation coefficient 0.587) was found for hiatal area on Valsalva. CONCLUSION: Agreement between the two methods was moderate to substantial for all parameters except for hiatal area on Valsalva. Magnetic resonance imaging yielded higher area measurements on Valsalva, which may indicate difficulties in identifying the plane of minimal dimensions due to poorer temporal resolution compared with ultrasound imaging.