Quantitative analysis of in vivo peristaltic and segmental motion 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 magnetic resonance imaging (MRI) to quantitatively analyze these motions in the jejunum region of anesthetized rats (N=6) non-invasively. Dynamic images of the GI tract after oral gavage with a gadolinium (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. The results of integrated and Fourier analysis of peristaltic and segmental motility suggest that the neurophysiology underlying the control of motility can be considered much simpler. For example the results of integrated analysis suggest segmental vs. peristaltic wave patterns must be represented primarily by the phase relationships among the principal components. Alternatively the results of Fourier analysis suggest peristalsis is represented by a single wave propagating in the aboral direction and a simple segmental pattern is a resultant of two waves propagating in opposite directions. A complex segmental motility requires a third high frequency segmental mode to complete the complex patterning. MRI results also show that inactin anesthesia does not have the same inhibitory effects on the gut motility as isoflurane, confirming indirect data in the literature acquired using invasive techniques, but also adding detailed knowledge of the changes in gastrointestinal motions produced by these anesthetics.