Dynamic evaluation of female pelvic floor muscle function using 2D ultrasound and image processing methods

Abstract

The aim of this study was to define new quantitative parameters of dynamic Pelvic Floor Muscle (PFM) function using 2D transperineal (TP) ultrasound imaging combined with image processing methods (IPM).

Ultrasound and digital vaginal data were obtained from a volunteer convenience sample of 23 continent and 9 Stress Urinary Incontinent (SUI) women recruited from the San Francisco Bay Area community, California, U.S.A.

Two methods of IPM were used; speckle tracking for measuring displacement of the ano-rectal angle (ARA) and symphysis pubis (SP); and segmentation IPM for measuring displacement of the urethra. Good to excellent inter and intra observer reliability was established for processing the ultrasound images on stored audio-visual imaging files (AVI). Intraclass correlation coefficient (ICC) values: 0.61 to 0.99; 95% confidence intervals (CI) 0.08?0.84 to 0.97?0.99; standard error of measurement (SEM) 0.01to 0.25 cm. There was good agreement between measures on Bland and Altman analysis: mean difference 0.06 to -0.21 cm; 95% CI 0.02?0.45cm to -0.01?0.20cm. Validity of the IPM was confirmed with digital palpation, and furthermore indicated good sensitivity and specificity. Technical and methodological limitations of the IPM, and suggestions for future studies were discussed.

Several research questions were addressed using TP ultrasound combined with IPM that enabled the dynamic evaluation of pelvic floor (PF) displacement throughout an entire manoeuvre, rather than limiting the quantification from static images at rest to the end of the manoeuvre. In this way, IPM determined unique quantitative data regarding the automatic displacement, velocity and acceleration of the ARA and urethra during a cough, Valsalva, voluntary PFM contraction, The Knack and a Transversus Abdominis contraction. During automatic events that raised intra-abdominal pressure (IAP), normal PFM function produced timely compression of the PF and additional external support to the urethra, reducing the displacement, velocity, and acceleration. In women with SUI, who have weaker urethral attachments, this shortening contraction did not occur; consequently, the urethra of women with SUI moved further and faster for a longer duration.

Caution regarding the generalisability of this study is warranted due to the small number of women in the SUI group and the significant difference in parity between groups. However this non-invasive physiological measurement tool demonstrated a new way of assessing the PFM. It is envisaged that this study will provide the foundation for future studies with larger parity matched populations and eventually improve the rehabilitation of women with SUI and other PF disorders.

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Identifiers

ORCID for Maria Stokes: orcid.org/0000-0002-4204-0890

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