Table.
Brain Imaging Techniques
| Implement | What it measures | Utilities in gastroenterology |
|---|---|---|
| PET | Measures the annihilation photons from positron-electron annihilation. The positron is emitted from the radioactive tracer that is injected intravenously. | |
| [15O]H2O PET | Measures regional cerebral blood flow | Initial studies during gut stimulations. |
| [18F]FDG PET | Measures the regional metabolic rate of glucose | Used mainly for diagnosis and staging of cancers but also for neurological studies |
| Relevant radioligands | Neurotransmitter system (dopamine, serotonin, opioids, cannabinoid etc) | Studies are limited due to the high cost, the limited availability of relevant ligands, and the complexity of the studies. |
| MRI | A non-invasive technique to assess brain function based on endogenous magnetic properties, | |
| fMRI (BOLD signal) | Measures changes in the proportion of oxygenated vs deoxygenated haemoglobin, which is seen in areas of greater neural activity | Most frequently used in particular task based (eg, gut stimulation) studies. More available and better temporal resolution than PET |
| ASL | Measures cerebral blood flow directly, by using arterial blood as an endogenous tracer. | Suitable to measure baseline cerebral blood flow. |
| rsfMRI | Measures spontaneous, low frequency (< 0.1 Hz) fluctuations in the BOLD signal that occur when a subject is not performing an explicit task. rsfMRI investigates synchronous activations between regions that are spatially distinct, occurring in the absence of a task or stimulus, to identify resting state networks. | Several studies used rsfMRI to investigate the resting state networks between healthy controls and patients in a certain disease condition. |
| MR spectroscopy | Quantitative measure of biochemical concentration in the living brain based on the unique MR spectra of different molecules. | Proton MR spectroscopy can reliably detect metabolites such as Glx (Glutamate and Glutamine), γ-aminobutyric acid (GABA), and N-acetylaspartate (NAA). |
| Structural MRI | T1 weighted high-resolution structural MRI used to produce structural imaging. Dynamic alterations in brain structure have been observed even within 5 days. | Assess baseline differences between groups and the central nervous system effects of treatments, aging, and disease. |
| VBM (gray matter) | Whole brain analysis of the density and volume of gray matter in each voxel, which may involve changes in glial number, dendritic spines. | Influence of environmental factors such as early life event on brain structures. |
| Diffusion imaging | Evaluates white matter integrity and anatomy. The tract integrity is expressed commonly as fractional anisotropy and specific fiber tracts between brain regions are identified by tractography. | Diffusion imaging studies in stroke patients are useful as it shows dynamic remodelling of white matter tracts. Longitudinal studies in therapeutic intervention. |
| MEG | Measures the magnetic field generated by the electrical activity of neurons with millisecond temporal resolution. | MEG is used to measure the time courses of brain activity (eg, due to gut stimulation). Not widely available |
| EEG | Measures direct electrical activity of the brain by surface scalp electrodes with millisecond temporal resolution. | EEG is used for evoked potentials to external stimuli in real time or to measure the time courses of brain activity. |
PET, positron emission tomography; fMRI, functional magnetic resonance imaging; BOLD, blood oxygen level-dependent; ASL, arterial spin labelling; rsfMRI, resting-state functional magnetic resonance imaging; MR, magnetic resonance; VBM, voxel-based morphometry; MEG, Magneto-encephalography; EEG, electro-encephalography.