Gino Banco

Quantitative analysis of peristaltic and segmental motion in vivo in the rat small intestine using dynamic MRI.

Conventional methods of quantifying segmental and peristaltic motion in animal models are highly invasive; involving, for example, the external isolation of segments of the gastrointestinal (GI) tract either from dead or anesthetized animals. The present study was undertaken to determine the utility of MRI to quantitatively analyze these motions in the jejunum region of anesthetized rats (N = 6) noninvasively. Dynamic images of the GI tract after oral gavage with a Gd contrast agent were acquired at a rate of six frames per second, followed by image segmentation based on a combination of three‐dimensional live wire (3D LW) and directional dynamic gradient vector flow snakes (DDGVFS). Quantitative analysis of the variation in diameter at a fixed constricting location showed clear indications of both segmental and peristaltic motions. Quantitative analysis of the frequency response gave results in good agreement with those acquired in previous studies using invasive measurement techniques. Principal component analysis (PCA) of the segmented data using active shape models resulted in three major modes. The individual modes revealed unique spatial patterns for peristaltic and segmental motility. Magn Reson Med, 2009.

A multiscale lattice Boltzmann model of macro- to micro-scale transport, with applications to gut function

Nutrient absorption in the small intestine cannot occur until molecules are presented to the epithelial cells that line intestinal villi, finger-like protrusions under enteric control. Using a two-dimensional multiscale lattice Boltzmann model of a lid-driven cavity flow with ‘villi’ at the lower surface, we analyse the hypothesis that muscle-induced oscillatory motions of the villi generate a controlled ‘micro-mixing layer’ (MML) that couples with the macro-scale flow to enhance absorption. Nutrient molecules are modelled as passive scalar concentrations at high Schmidt number. Molecular concentration supplied at the cavity lid is advected to the lower surface by a lid-driven macro-scale eddy. We find that micro-scale eddying motions enhance the macro-scale advective flux by creating an MML that couples with the macro-scale flow to increase absorption rate. We show that the MML is modulated by its interactions with the outer flow through a diffusion-dominated layer that separates advection-dominated macro-scale and micro-scale mixed layers. The structure and strength of the MML is sensitive to villus length and oscillation frequency. Our model suggests that the classical explanation for the existence of villi—increased absorptive surface area—is probably incorrect. The model provides support for the potential importance of villus motility in the absorptive function of the small intestine.

Quantifying the effects of inactin vs Isoflurane anesthesia on gastrointestinal motility in rats using dynamic magnetic resonance imaging and spatio-temporal maps.

Anesthetics are commonly applied in animal studies of gastrointestinal (GI) function. Different anesthetics alter smooth‐muscle motility in different ways. The aim of this study is to quantify and compare non‐invasively with magnetic resonance imaging (MRI) the motility patterns of the rat gut when anesthetized with inactin vs isoflurane anesthetics in the fed state.

Development of a Lattice-Boltzmann Method for Multiscale Transport and Absorption with Application to Intestinal Function

We describe a lattice-Boltzmann model with a multigrid strategy and moving boundaries to solve coupled multiscale flow problems with scalar transport. Whereas we present the details of a two-dimensional model, the method is directly generalizable to 3-D. We apply the methods to our application of nutrient uptake at the epithelium of the small intestine. In this model, the fine grid is embedded within a coarse grid, with an overlap region between the two grids. The transfer of information between the two grids conserves mass and momentum and enforces continuity of stress. The modified moment propagation method is applied to the scalar, allowing higher Schmidt numbers than competing methods. We treat the moving boundaries with second-order boundary conditions that interpolate to the exact wall position. For scalar and scalar flux boundary condition, we formulate the scalar transport from the boundary to a temporary lattice node, and then transfer it back to the node adjacent to the boundary by extrapolation. We demonstrate the application of the method by simulating a macro-scale cavity flow with micro-scale finger-like protuberances in pendular motion on the lower surface as a model of the macro-micro scale interactions in fluid motions, scalar mixing, and scalar uptake at the surface of the villi that line the epithelium of the human intestines.

Motility and absorption in the small intestines: Integrating MRI with lattice Boltzmann models

Nutrients are absorbed in the small intestines at a mucosal epithelium that covers multitudes of villi, fingerlike protrusions ∽200–400 μm in scale. The villi line the mucosal surface and have been observed to move in response to local stimulation. Luminal contractions (motility) create macro-scale fluid motions that transport nutrient molecules to the epithelium surrounding these moving micro-scale villi. We combine multi-scale modeling with dynamic magnetic resonance imaging (MRI) of the motions of the gut lumen to investigate the hypothesis that gut function requires the coupling of macro-micro scale fluid motions generated by lumen-scale motility with micro-scale motions generated by moving villi. We have developed 2-D models within the lattice-Boltzmann framework with second-order moving boundary conditions for velocity and for passive “nutrient” scalar concentrations. The first model was used to study the relative contributions of macro-scale peristaltic and segmental contractions on transport, mixing and absorption in the intestines. The macro-scale gut motions were quantified from time-resolved MRI of the in vivo rat jejunum using three-dimensional segmentation. The simulations show that segmental and peristaltic motions have disparate roles in fluid motion and nutrient absorption. The gut wall motions were decomposed with principle component analysis and analyzed using topographic space-time representations of deformation. These results suggest that the neurophysiology can produce a wide range of complex contractile patterns by stimulating only a few basic modes with varying phase relationship (MRI) and that absorption is optimized with segmental contraction with peristalsis interfering in absorption (modeling). To analyze the role of the villi in absorption, we designed a second 2-D model that mimics intestinal macro-micro scale flow interactions. Along the lower surface of a lid-driven macro-scale cavity flow we modeled a series of micro-scale “villi” with controlled coordinated motions using a multi-grid lattice-Boltzmann method. We discover the existence of a villi-induced “micro-mixing” layer that couples with the macro-scale motions to enhance absorption and show that a common assumption is incorrect in 2-D. These models have recently been extended to 3-D and will be combined in the future.