Novel MRI tests of orocecal transit time and whole gut transit time: studies in normal subjects

Abstract

Background: Colonic transit tests are used to manage patients with Functional Gastrointestinal Disorders. Some tests used expose patients to ionizing radiation. The aim of this study was to compare novel magnetic resonance imaging (MRI) tests for measuring orocecal transit time (OCTT) and whole gut transit time (WGT), which also provide data on colonic volumes.

Methods: 21 healthy volunteers participated. Study 1: OCTT was determined from the arrival of the head of a meal into the cecum using MRI and the Lactose Ureide breath test (LUBT), performed concurrently. Study 2: WGT was assessed using novel MRI marker capsules and radio-opaque markers (ROMs), taken on the same morning. Studies were repeated 1 week later.

Key results: OCTT measured using MRI and LUBT was 225 min (IQR 180-270) and 225 min (IQR 165-278), respectively, correlation r(s) = 0.28 (ns). WGT measured using MRI marker capsules and ROMs was 28 h (IQR 4-50) and 31 h ± 3 (SEM), respectively, correlation r(s) = 0.85 (p < 0.0001). Repeatability assessed using the intraclass correlation coefficient (ICC) was 0.45 (p = 0.017) and 0.35 (p = 0.058) for MRI and LUBT OCTT tests. Better repeatability was observed for the WGT tests, ICC being 0.61 for the MRI marker capsules (p = 0.001) and 0.69 for the ROM method (p < 0.001) respectively.

Conclusions & inferences: The MRI WGT method is simple, convenient, does not use X-ray and compares well with the widely used ROM method. Both OCTT measurements showed modest reproducibility and the MRI method showed modest inter-observer agreement.

Keywords: MRI; correlation; marker capsule; transit time.

Figure 1

¹³C breath excretion curve. Example ¹³C breath excretion curve from Lactose Ureide Breath Test in one healthy volunteer with indication of the orocecal transit time (OCTT). The OCTT is taken as the time at which there is an increase in breath ¹³C which is 2.5 times the SD of all previous points above the running average of all previous points.

Figure 2

Magnetic resonance imaging (MRI) marker capsule. Example of a capsule which consists of two polyoxymethylene half shells glued together, and hand filled with 0.4 mL 15 μM Gadoteric acid (Gd-DOTA). Leakage tests performed on 20% of each batch using a spectrophotometer. Capsules have the dimensions of 20 × 7 mm.

Figure 3

Maximum intensity projection (MIP) magnetic resonance imaging (MRI) image. Showing five MRI marker capsules in the colon (indicated by close arrows). Images created using water only images acquired using the T1 weighted multi-echo FFE pulse sequence. Such images were used to locate the number and position of capsules remaining at 24 h to calculate a whole gut transit time.

Figure 4

Segmented Colon. Showing the segmented colon used to score the MRI marker capsules at 24 h, where 0 = not found (presumed to be excreted), 1 = sigmoid and rectum, 2 = descending colon, 3 = left transverse colon, 4 = right transverse colon, 5 = upper ascending colon, 6 = lower ascending colon, 7 = small bowel.

Figure 5

(A) Correlation between Lactose Ureide Breath Test (LUBT) and magnetic resonance imaging (MRI). Scatter plot with line of identity, comparing the orocecal transit time (OCTT) measured using the LUBT and MRI. The degree of correlation was assessed using the Spearman's rank correlation coefficient test, and we report a Spearman's r-value of 0.28 (not significant). (B) Agreement between OCTT measurements. Bland-Altman plot showing the average OCTT measured using the LUBT and MRI on the x-axis, and the difference between the OCTT measured using the two methods on the y-axis. This plot shows that there was a mean difference of −7.32 min between the LUBT and MRI (middle dotted line), with the limits of agreement ranging from 183.0 to −197.6 min (upper and lower dotted lines).

Figure 6

(A) Correlation between radio-opaque markers (ROM) and magnetic resonance imaging (MRI) markers. Plot comparing the whole gut transit time (WGT) measured using ROMs and MRI marker capsules showing the line of best fit as y = 0.03x ± 0.12. The degree of correlation was assessed using the Spearman's rank correlation coefficient test, and we report a Spearman's r-value of 0.85 (p < 0.0001). (B) Agreement between WGT measurements. Bland-Altman plot showing the average WGT measured using the ROMS and MRI marker capsules on the x-axis, and the difference between the WGT measured using the two methods on the y-axis. This plot shows that there was a mean difference of −0.005 h between test types (middle dotted line), with limits of agreement ranging from 25.68 to −25.69 h (upper and lower dotted lines).