Physiology of the small bowel: A new approach using MRI and proposal for a new metric of function

Small-bowel dislocation during long-term MRI observation - insights in intestinal physiology

Magnetic resonance imaging (MRI) of the abdomen is a widely established imaging modality in the diagnostic workup of patients suffering from abdominal disorders. Small-bowel motility analyses using MRI have recently been introduced to provide functional information about the intestine not provided by morphological analyses. This is of clinical importance as motility disorders correlate with inflammation. Yet motility analyses mainly rely on a series of acquisitions in coronal orientation. Temporal displacement of small-bowel loops out of the coronal slice could falsify qualitative and quantitative motility analyses. Thus, our study quantified three-dimensional (3D) dislocation of small-bowel loops during abdominal MRI examinations with the patient lying in prone position to investigate its influence on motility analyses. Our study revealed segmental small-bowel displacement during MRI examinations in prone position to predominantly occur in craniocaudal orientation and in a smaller extent in lateral and ventrodorsal orientation. However, the displacement amplitudes are rather small and might not significantly influence small-bowel motility analyses in 2D coronal plane in general.

Developing a new measure of small bowel peristalsis with dynamic MR: a proof of concept study

BACKGROUND

Small bowel peristalsis is a complex of many individual motion elements. Although each element of peristalsis can be measured there is no current global measure of peristalsis.

PURPOSE

To examine the feasibility of automated computerized assessment of global small bowel motility using simple computational methods.

MATERIAL AND METHODS

Coronal dynamic MR images were obtained from five healthy volunteers who had fasted for 9 h and drunk 1.5 L of water. Images were taken using single breath-hold and ECG triggering. Acquisitions were repeated at 10 and 20 min after an intramuscular injection of hyoscine butylbromide. Parametric maps were generated representing the mean change in signal amplitude (MSA) per voxel for each dynamic acquisition. Two observers independently assessed thresholding for optimal segmentation of small bowel from other sources of signal. Total voxel activity (TVA) for each study was calculated as a sum of MSA per slice and whole examination and TVA profiles were generated.

RESULTS

Independent observations suggest that the automated segmentation method described usefully segments small bowel activity from other signal. Small bowel movement represented as TVA varied three-fold in the five volunteers and was inhibited by anti-muscarinic injection.

CONCLUSION

It is possible to develop a new measure, based on automated segmentation of mean signal amplitude changes, of small bowel peristalsis using dynamic MR.

Use of continuously MR tagged imaging for automated motion assessment in the abdomen: a feasibility study

PURPOSE

To investigate the feasibility of measuring motion in the abdomen using a continuously tagged magnetic resonance imaging sequence.

MATERIALS AND METHODS

To assess (nonperiodic) motion in the abdomen, a nontriggered, continuously tagged transient field echo (TFE) sequence was implemented that acquires one complete 3D dataset per prepulse after a fixed delay. In postprocessing, a frequency analysis approach was developed for compact reviewing of the data and noise suppression. For proof of principle, a simulation was made and one free-breathing dynamic in vivo scan was acquired in a healthy volunteer. During the dynamic scan the volunteer received glucagon intravenously.

RESULTS

The simulation showed that this frequency analysis enables the extraction of motion at low signal-to-noise ratio levels. Motion information was successfully gathered from the in vivo scan. The decline in bowel motion caused by the administration of glucagon could be quantitatively measured using the continuously tagged sequence.

CONCLUSION

Continuously tagged imaging in the abdomen for the purpose of automated gathering of motion information is feasible and could aid the study of bowel motion.