How to Perform and Interpret Functional Magnetic Resonance Imaging Studies in Functional Gastrointestinal Disorders

Abstract

Functional neuroimaging studies have revealed the importance of the role of cognitive and psychological factors and the dysregulation of the brain-gut axis in functional gastrointestinal disorder patients. Although only a small number of neuroimaging studies have been conducted in functional gastrointestinal disorder patients, and despite the fact that the neuroimaging technique requires a high level of knowledge, the technique still has a great deal of potential. The application of functional magnetic resonance imaging (fMRI) technique in functional gastrointestinal disorders should provide novel methods of diagnosing and treating patients. In this review, basic knowledge and technical/practical issues of fMRI will be introduced to clinicians.

Keywords: Brain; Functional magnetic resonance imaging; Functional neuroimaging; Gastrointestinal diseases.

Figure 1

Example of hemodynamic response (A) and time series blood oxygen level dependent (BOLD) signal from a voxel (B). (A) Neurons respond rapidly to internal or external changes and allow the alterations of blood flow and oxygenation in the close area (hemodynamic response) that drives the peak of BOLD signal few seconds after the onset of internal or external changes. BOLD signal slowly returns to baseline level following an undershoot. (B) Within the field of view, each slice consists of a certain number of voxels determined by the size of the measurement matrix. The BOLD signal of each voxel is recorded at consecutive time points and this time trace is further analysed to interfere with functional brain activation.

Figure 2

Examples of block design (A) and event-related design (B). (A) Example 1 shows the block design with a single task (Task A) and Example 2 with multiple tasks (Task A, B). (B) Event-related design with a single task (Example 1, Task A) and multiple tasks (Example 2, Task A, B). In both designs, the number of tasks and time durations are laid down in accordance with the type of task, hypothesis, and planned analysis scheme.

Figure 3

Illustration of expected and measured blood oxygen level dependent (BOLD) signal from single voxel in task functional magnetic resonance imaging. (A) Example of expected BOLD signal using hemodynamic response function (red). (B) Illustration of measured BOLD signal in task-specific activated voxel (blue) and simulated BOLD signal (red) from (A). In the general linear model, the linear relationship between observed (blue) and expected BOLD signal (red) is estimated.