Measurement of anal sphincter muscles: Endoanal US, endoanal MR imaging, or phased-array MR imaging? A study with healthy volunteers

PURPOSE: To compare endoanal ultrasonography (US), endoanal magnetic resona nce (MR) imaging, and phased-array MR imaging for anal sphincter muscle mea surement. MATERIALS AND METHODS: Sixty healthy volunteers underwent 1.5-T phased-arra y MR, endoanal MR, and endoanal US examinations. Sphincter muscle thickness es were measured. Measurement reliability was analyzed, and correlations am ong the imaging methods were calculated. Multivariate analysis was performe d to assess the influence of age, weight, height, sex, parity, and obstetri c trauma on sphincter dimensions. RESULTS: Both MR methods had good reliability for measurements of all sphin cter components, whereas endoanal US was reliable for internal sphincter me asurement only. There was little correlation between the techniques, except between the two MR techniques, with a strong correlation for total sphinct er and perineal body thickness. The internal sphincter thickened significan tly (P =.002) with age at endoanal US and endoanal MR imaging but not at ph ased-array MR imaging. There were small sex-based differences in sphincter muscle measurements at phased-array MR imaging only. CONCLUSION: Endoanal US enables reliable measurement of only internal sphin cter thickness, whereas both MR imaging methods enable reliable measurement of all sphincter components. Sphincter measurement with phased-array MR im aging is as reliable as that with endoanal MR imaging.