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

Area of Science:

• Gastroenterology
• Medical Imaging
• Pharmacology

Background:

• Opioids are known to impact gastrointestinal motility.
• However, their precise effects on human colonic fluid absorption and secretion remain unclear.

Purpose of the Study:

• To investigate the impact of prolonged-release oxycodone on colonic fecal volume and stool dryness.
• To utilize a novel magnetic resonance imaging (MRI)-based technique for this assessment.

Main Methods:

• A prospective, randomized, double-blinded, crossover study involving 25 healthy male volunteers.
• Subjects received either prolonged-release oxycodone or a placebo for 5 days, with MRI scans of the abdomen performed.
• Semiautomatic k-means-based segmentation software was used to quantify colonic fecal volumes, and MRI signal intensity served as a proxy for stool dryness.

Main Results:

• Oxycodone treatment significantly increased total colonic fecal volume by 100 mL compared to placebo (P = 0.001).
• The ascending colon/cecum showed the largest increase in fecal volume (24%, P = 0.001).
• MRI signal analysis indicated increased stool dryness after oxycodone treatment, as evidenced by increased Dixon signal and decreased T2-weighted signal (P < 0.001 and P = 0.002, respectively).

Conclusions:

• Five-day treatment with prolonged-release oxycodone increases colonic fecal volume and stool dryness.
• This noninvasive MRI-based method offers potential for characterizing gastrointestinal content and symptoms, including constipation.