Assessing Water Content of the Human Colonic Chyme Using the MRI Parameter T1: A Key Biomarker of Colonic Function.

Background: The human colon receives 2 L of fluid daily. Small changes in the efficacy of absorption can lead to altered stool consistency with diarrhea or constipation. Drugs and formulations can also alter colonic water, which can be assessed using the magnetic resonance imaging (MRI) longitudinal relaxation time constant, T1. We explore the use of regional T1 assessment in evaluating disorders of colonic function.

Methods: Individual participant data analysis of data from 12 studies from a single center of patients with constipation, irritable bowel syndrome with diarrhea (IBS-D), and healthy volunteers (HV). T1 was quantified by measuring the signal from the tissue at different times after a pulse which inverts the magnetization.

Key results: When diarrhea was induced by a macrogol laxative T1 in the ascending colon, T1AC was negatively correlated with stool bacterial content, r² = 0.78, p < 0.001. T1AC was increased by another laxative, rhubarb. Patients with IBS-D had elevated fasting T1AC (0.78 ± 0.28 s, N = 67) compared to HV (0.62 ± 0.21 s, N = 92) while those with constipation lay within the normal range (HV 10-90th centiles 0.33-0.91 s). Fasting T1AC in IBS-D was reduced by mesalazine treatment. T1 in the descending colon was consistently lower than T1AC, with a bigger reduction in patients with constipation than HV. Pre-feeding dietary fiber (bran, nopal, and psyllium) was associated with fasting T1AC at or above the normal 90th centile.

Conclusions and inferences: T1 is an MRI parameter which could be used to monitor effectiveness of novel agents designed to alter colonic water content and stool consistency.