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

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.

Anatomy and mechanical properties of the anal sphincter muscles in healthy senior volunteers

“…Two methodological developments distinguish this study from previous works in the field. First, by employing an MR‐based FLIP‐like measurement technique (MR‐FLIP) an anatomical reference system was created that allowed spatial registration of conventional FLIP measurements to the underlying anatomy of the sphincter organ. Such identification of anatomical markers is a prerequisite for the superposition and scaling of AC measurements and thus for the statistical analysis of these properties across a cohort.…”

“…Compliance and squeeze properties of the AC tissue were assessed in all volunteers using FLIP and a FLIP‐like technique (MR‐FLIP) that has been described previously . In both cases, a fluid filled balloon was gently inserted into the AC and progressively inflated up to a volume of 50 mL following a step‐distension protocol.…”

“…MR‐FLIP measurements relied on a custom‐made MR‐compatible version of the EndoFLIP ® catheter EF‐325N (Crospon Ltd, Galway, UK) without any integrated sensors for balloon diameter or pressure measurement. Instead, AC cross‐sectional information was derived from T2‐weighted MR images (3 Tesla, Skyra system Siemens, Erlangen, Germany), and pressure was recorded by an external pressure gauge (Fluke 700GA4, Fluke, Everett, USA) at the beginning and end of each MR‐sequence …”

“…For MR‐FLIP, the balloon diameter was obtained from the MR imaging data (Figure ). For each patient, both measurement modalities, EndoFLIP and MR‐FLIP, were registered to establish spatial correspondence between the data acquired using the EndoFLIP system and the patient's anatomy obtained from MRI …”

“…Compliance and squeeze properties of the AC tissue were assessed in all volunteers using FLIP and a FLIP-like technique (MR-FLIP) that has been described previously. 9 In both cases, a fluid filled balloon was gently inserted into the AC and progressively inflated up to a volume of 50 mL following a step-distension protocol. Muscle anatomy and the anatomical markers were acquired with MR-FLIP measurements, whereas passive compliance and active squeeze properties were assessed using a conventional FLIP device ( Figure 2…”