MRI analysis of fecal volume and dryness: Validation study using an experimental oxycodone‐induced constipation model

Abstract

Background Opioids are known to affect gastrointestinal motility, but their effect on fluid absorption and secretion is poorly understood in humans. Purpose To investigate the effect of oxycodone on colonic fecal volume and stool dryness by using a novel MRI‐based technique. Study Type Prospective, randomized, double‐blinded, crossover study. Subjects Twenty‐five healthy male volunteers (median age: 24 years [range: 21–56]; mean body mass index [BMI]: 23.9 kg/m2 [range: 22.9–25.0]) without known gastrointestinal disease. Field Strength/Sequence T2‐weighted and two‐point Dixon MRI scans of the abdomen at 1.5 T. Assessment Subjects were treated for 5 days with prolonged‐release oxycodone or a placebo. Imaging was performed on the first and last study day in each period. Images of the colon were analyzed with semiautomatic k‐means‐based segmentation software. Regional colonic fecal volumes were quantified excluding gas volume and colon wall. Two‐point Dixon and T2‐weighted MRI signal intensity were assessed as a proxy of colonic stool dryness. Data were obtained in a previously reported study. Statistical Tests Intraclass correlation coefficients were used to test the reliability of measurements between days, while repeated measures mixed models were applied to test treatment effects. Results After oxycodone treatment, total colonic fecal volume was significantly increased compared with placebo (mean change 100 mL vs. –13 mL; P = 0.001), with the largest increase (24%) observed in the ascending colon/cecum (P = 0.001). Dixon signal increased (less water in colon content) after oxycodone treatment compared with placebo (mean 0.09 vs. –0.02; P < 0.001). T2‐weighted signal decreased (less water in colon content) after oxycodone treatment compared with placebo (mean –0.03 vs. 0.03; P = 0.002). Data Conclusion The 5‐day oxycodone treatment increased colonic fecal volume and increased stool dryness compared with placebo. This imaging‐based method for noninvasive analysis of colon content has the potential to characterize gastrointestinal symptoms in general, such as in constipation. Level of Evidence: 2 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019;50:733–745.

Although tapentadol and oxycodone both increase colonic volume, tapentadol treatment resulted in softer stools and less constipation: a mechanistic study in healthy volunteers

“…The fact, that this was not observed in the other treatment arms, suggests that tapentadol may increase the water content compared to oxycodone. The water in colonic luminal content can be assessed using detailed analysis of MR images, which we previously have shown using both T2-weighted and DIXON-type water images [8]. However, our current data were sub-optimal for this analysis and image acquisition should be optimized in future studies so that information on the water in the colonic content can be further investigated.…”

“…The analgesic effect of tapentadol has been investigated in previous studies [5,6], however, its mechanic effect on colon function and how this interacts with gastrointestinal (GI) symptoms lacks evidence. It has previously been shown that magnetic resonance imaging (MRI) of segmental colorectal volumes provides an advantageous insight into colonic function, and how it can be affected due to diets or opioid treatment in healthy subjects [7,8]. The method has been found to have low inter-reader and day-to-day variability, high spatial resolution, and includes no contrast-enhancing agents or irradiation [9].…”

Novel Bionics Assessment of Anorectal Mechanosensory Physiology

“…Colon anatomy is well suited for 3D modeling of transit. A recent analysis has been utilized for classification of different motility patterns based on the velocity and length of magnetic capsule movements [2][3][4]. Insight into colonic motility offers many possibilities for classification of dysmotility symptoms or interventional testing of pharmacological treatments.…”

Colonic volume in patients with functional constipation or irritable bowel syndrome determined by magnetic resonance imaging

“…If so, assessment of colonic volumes may allow clinicians to stratify patients and thereby guide treatment. In addition, future developments with postprocessing of MRI data will allow separation of colonic content into solid, fluid, and gas 32 . Such information may be important for evaluating individual patients and the effects of treatment or diet.…”