Use of Ultrasound Imaging in Pelvic Organ Prolapse: an Overview

Pelvic floor imaging with MR defecography: correlation with gynecologic pelvic organ prolapse quantification

PURPOSE

Pelvic organ prolapse (POP) is assessed differently by gynecologists and radiologists. It is clinically staged by physical examination using the POP-Q (Pelvic Organ Prolapse Quantification) system and radiologically staged by modalities such as by Magnetic Resonance Defecography (MRD). The purpose of this study was to correlate the two methods of staging pelvic organ prolapse for each pelvic compartment by comparing correlative anatomic points and differences in technique. This understanding will help synthesize information from two different perspectives and bridge the gap between multiple specialists who participate in the care of patients with complex pelvic floor disorders.

METHODS

A retrospective single institution study comparison of patients who underwent both dynamic magnetic resonance pelvic floor imaging and pelvic organ prolapse quantification (POP-Q) at our medical center was done. Two urogynecologists performed the POP-Q and one fellowship-trained radiologist interpreted the MRD and both staged pelvic organ prolapse independently.

RESULTS

A total of 280 patients underwent magnetic resonance imaging (MRI) of the pelvic floor from 1/2013 to 12/2017, of whom 68 met our inclusion criteria. When compared to POP-Q, MRI has strong, moderate, and weak correlation for quantification of anterior, middle, and posterior compartment prolapse, respectively. POP-Q measurements Aa, Ba, C, and D are analogous to true pelvic anatomical landmarks which are directly and consistently measurable by MRI, hence accounting for the better correlation in anterior and middle compartments when compared to measurements Ap and Bp which do not correlate with true anatomical landmarks, and hence can explain the weak correlation for posterior compartment prolapse.

CONCLUSION

When comparing POP-Q to MRI, anterior and middle compartment prolapse have better correlation than posterior compartment prolapse. Inherent differences that exist in technique and anatomic landmarks used for staging pelvic organ prolapse by clinical exam and imaging criteria account for this. MRD, however, still provides anatomic details on static images, real time simultaneous overview of multi-compartmental prolapse, characterizes contents of cul-de-sac hernias and rectal evacuation on dynamic imaging. Corroborative information derived from both methods of staging organ will result in optimum patient care.

M3VR-A multi-stage, multi-resolution, and multi-volumes-of-interest volume registration method applied to 3D endovaginal ultrasound

Heterogeneity of echo-texture and lack of sharply delineated tissue boundaries in diagnostic ultrasound images make three-dimensional (3D) registration challenging, especially when the volumes to be registered are considerably different due to local changes. We implemented a novel computational method that optimally registers volumetric ultrasound image data containing significant and local anatomical differences. It is A Multi-stage, Multi-resolution, and Multi-volumes-of-interest Volume Registration Method. A single region registration is optimized first for a close initial alignment to avoid convergence to a locally optimal solution. Multiple sub-volumes of interest can then be selected as target alignment regions to achieve confident consistency across the volume. Finally, a multi-resolution rigid registration is performed on these sub-volumes associated with different weights in the cost function. We applied the method on 3D endovaginal ultrasound image data acquired from patients during biopsy procedure of the pelvic floor muscle. Systematic assessment of our proposed method through cross validation demonstrated its accuracy and robustness. The algorithm can also be applied on medical imaging data of other modalities for which the traditional rigid registration methods would fail.