title: MR-FLIP: a new method that combines a functional lumen imaging probe with anatomical information for spatial compliance assessment of the anal sphincter muscles.
abstract: OBJECTIVE
  Continence results from a complex interplay between anal canal (AC) muscles and sensorimotor feedback mechanisms. The passive ability of the AC to withstand opening pressure - its compliance - has recently been shown to correlate with continence. A functional lumen imaging probe (FLIP) is used to assess AC compliance, although it provides no anatomical information. Therefore, assessment of the compliance specific anatomical structures has not been possible, and the anatomical position of critical functional zones remains unknown. In addition, the FLIP technique assumes a circular orifice cross-section, which has not been shown for the AC. To address these shortcomings, a technique combining FLIP with a medical imaging modality is needed.
  
  
  METHODS
  We implemented a new research method (MR-FLIP) that combines FLIP with MR imaging. Twenty healthy volunteers underwent MR-FLIP and conventional FLIP assessment. MR-FLIP was validated by comparison with FLIP results. Anatomical markers were identified, and the cross-sectional shape of the orifice was investigated.
  
  
  RESULTS
  MR-FLIP provides compliance measurements identical to those obtained by conventional FLIP. Anatomical analysis revealed that the least compliant AC zone was located at the proximal end of the external anal sphincter (EAS). The cross-sectional shape of the AC was found to deviate only slightly from circularity in healthy volunteers.
  
  
  CONCLUSIONS
  The proposed method is equivalent to classical FLIP. It establishes for the first time direct mapping between local tissue compliance and anatomical structure, which is key to gaining novel insights into (in)continence. In addition, MR-FLIP provides a tool for better understanding conventional FLIP measurements in the AC by quantifying its limitations and assumptions.
authors.affiliation: Institute for Surgical Technology and Biomechanics (ISTB), University of Bern, Bern, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Brusa
authors.affiliation: Institute for Surgical Technology and Biomechanics (ISTB), University of Bern, Bern, Switzerland.
authors.forename: D
authors.initials: D
authors.lastname: Abler
authors.affiliation: Department of Visceral Surgery and Medicine, Bern University Hospital, University of Bern, Bern, Switzerland.
authors.forename: R
authors.initials: R
authors.lastname: Tutuian
authors.affiliation: Department of Visceral Surgery and Medicine, Bern University Hospital, University of Bern, Bern, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Studer
authors.affiliation: Biomaterials Science Center, University of Basel, Basel, Switzerland.
authors.forename: E
authors.initials: E
authors.lastname: Fattorini
authors.affiliation: Clinic for Visceral- and Thoracic Surgery, Cantonal Hospital Winterthur, Winterthur, Switzerland.|Faculty of Health, Department of Human Medicine, Universität Witten/Herdecke, Witten, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Gingert
authors.affiliation: University Institute of Diagnostic, Interventional and Pediatric Radiology, Bern University Hospital, University of Bern, Bern, Switzerland.
authors.forename: J T
authors.initials: JT
authors.lastname: Heverhagen
authors.affiliation: Department of Visceral Surgery and Medicine, Bern University Hospital, University of Bern, Bern, Switzerland.
authors.forename: L E
authors.initials: LE
authors.lastname: Brügger
authors.affiliation: Institute for Surgical Technology and Biomechanics (ISTB), University of Bern, Bern, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Büchler
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001003:Anal Canal / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000502:physiology; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D005242:Fecal Incontinence / Q000000981:diagnostic imaging / Q000503:physiopathology; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008365:Manometry / Q000379:methods*; D008875:Middle Aged; D009130:Muscle, Smooth / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000502:physiology; D011312:Pressure; D011446:Prospective Studies
keywords: Anal (in)continence; FLIP; MR imaging; compliance; mechanical properties; sphincter muscles