| Inversion recovery | Susceptibility-weighted | SWI | Spoiled gradient recalled echo (GRE), fully flow compensated, long echo time, combines phase image with magnitude image[12] | Detecting small amounts of hemorrhage (diffuse axonal injury pictured) or calcium.[12] |
| Short tau inversion recovery | STIR | Fat suppression by setting an inversion time where the signal of fat is zero.[13] | High signal in edema, such as in more severe stress fracture.[14] Shin splints pictured: | |
| Fluid-attenuated inversion recovery | FLAIR | Fluid suppression by setting an inversion time that nulls fluids | High signal in lacunar infarction, multiple sclerosis (MS) plaques, subarachnoid haemorrhage and meningitis (pictured).[15] | |
| Double inversion recovery | DIR | Simultaneous suppression of cerebrospinal fluid and white matter by two inversion times.[16] | High signal of multiple sclerosis plaques (pictured).[16] | |
| Diffusion weighted (DWI) | Conventional | DWI | Measure of Brownian motion of water molecules.[17] | High signal within minutes of cerebral infarction (pictured).[18] |
| Apparent diffusion coefficient | ADC | Reduced T2 weighting by taking multiple conventional DWI images with different DWI weighting, and the change corresponds to diffusion.[19] | Low signal minutes after cerebral infarction (pictured).[20] | |
| Diffusion tensor | DTI | Mainly tractography (pictured) by an overall greater Brownian motion of water molecules in the directions of nerve fibers.[21] |
| |
| Perfusion weighted (PWI) | Dynamic susceptibility contrast | DSC | Measures changes over time in susceptibility-induced signal loss due to gadolinium contrast injection.[23] |
|
| Arterial spin labelling | ASL | Magnetic labeling of arterial blood below the imaging slab, which subsequently enters the region of interest.[25] It does not need gadolinium contrast.[26] | ||
| Functional MRI (fMRI) | Dynamic contrast enhanced | DCE | Measures changes over time in the shortening of the spin–lattice relaxation (T1) induced by a gadolinium contrast bolus.[27] | Faster Gd contrast uptake along with other features is suggestive of malignancy (pictured).[28] |
| Blood-oxygen-level dependent imaging | BOLD | Changes in oxygen saturation-dependent magnetism of hemoglobin reflects tissue activity.[29] | Localizing brain activity from performing an assigned task (e.g. talking, moving fingers) before surgery, also used in research of cognition.[30] | |
| Magnetic resonance angiography (MRA) and venography | Time-of-flight | TOF | Blood entering the imaged area is not yet magnetically saturated, giving it a much higher signal when using short echo time and flow compensation. | Detection of aneurysm, stenosis, or dissection[31] |
| Phase-contrast magnetic resonance imaging | PC-MRA | Two gradients with equal magnitude, but opposite direction, are used to encode a phase shift, which is proportional to the velocity of spins.[32] | Detection of aneurysm, stenosis, or dissection (pictured).[31] (VIP) |
Hyperintensity (=T2 hyperintensity)
- Definition
- A hyperintensity is an area that appears lighter in color than the surrounding tissues;
- Cf) a hypointensity would be darker in color
- Synonyms
- =T2 hyperintensity, = bright signal
- REGION
- Most commonly WM
- Example
- Cause
- any tissue with a high water or protein content will tend to appear very bright on the T2 sequence.
- dilated perivascular spaces, or demyelination caused by reduced local blood flow.[7]
- ischemia, micro-hemorrhages, gliosis, damage to small blood vessel walls, breaches of the barrier between the cerebrospinal fluid and the brain, or loss and deformation of the myelin sheath.[8]
- interpretation
- Hyperintensity on a T2 sequence MRI basically means that the brain tissue in that particular spot differs from the rest of the brain. A bright spot, or hyperintensity, on T2 scan is nonspecific by itself and must be interpreted within clinical context
- Disease
- Normal aging
- MS, vasculitis (inflammation)
DBM (Deformation-Based Morphometry,)
a method for identifying macroscopic anatomical differences among the brains of different populations of subjects. The method involves spatially normalizing the structural MR images. Characterization using DBM can be global, pertaining to the entire field as a single observation, or can proceed on a voxel by voxel basis to make inferences about regionally specific positional differences.
7T MRI
| 1.5T | 3T | 7T | |
|---|---|---|---|
| • |
higher signal-to-noise-ratio, spatial resolution, and contrast than 1.5T and 3T MR, (signal to noise ratio is more than doubled), higher signal-to-noise (SNR) and contrast-to-noise ratio (CNR) enhanced detail in cortical imaging, reducing blurring between gray and white matter.
| ||
| CONS |
| ||
| In PD |
[van der Kolka 2013] Cho et al. [45] showed that 7 T MRI was superior in delineating these areas compared to 1.5 T and 3.0 T. Bajaj et al. [46] showed that 7 T MRI could distinguish subregions of the substantia nigra, and found an increased iron content in a part of this basal ganglion in PD patients compared to healthy volunteers. Recently, Oh et al. [47] visualized differences in anatomical patterns of the substantia nigra between healthy controls and PD patients with 7 T MRI, possibly enabling earlier diagnosis of PD | ||
| How common? | The number of magnetic resonance imaging (MRI) scanners operating at 7 T world-wide now exceeds 70 (Huber, 2018). | ||
Repetition Time (TR) is the amount of time between successive pulse sequences applied to the same slice. Time to Echo (TE) is the time between the delivery of the RF pulse and the receipt of the echo signal.
sequence
- Definition
- a number of radiofrequency pulses and gradients that result in a set of images with a particular appearance.
- Types of sequence
| T1-weighted | T2-weighted | Fluid Attenuated Inversion Recovery (Flair) | |
|---|---|---|---|
| short TE and TR times. | longer TE and TR times. | similar to a T2-weighted image except that the TE and TR times are very long | |
| CSF | Dark | bright | dark. |
| WM | light | Dark gray | Dark gray |
| cortex | gray | Light gray | Light gray |
| Fat (within bone marrow) | bright | light | Light |
Uncertain Spans
| location | transcription | uncertainty |
|---|---|---|
| MRI sequences table top edge | (table header row) | The header row of the MRI sequences table (Group / Full name / Abbreviation / Physics / Main clinical use / Example) is cropped above this capture; only body rows from “Susceptibility-weighted SWI” downward are visible. |
| Hyperintensity Cause bullet | dilated perivascular spaces, or demyelination caused by reduced local blood flow.[7] | Numbered citation [7] follows the sentence; preserved as printed. |
| 7T MRI 1.5T column | (mostly empty) | The 1.5T column for the body rows visible on this capture is empty in the source; preserved as empty cells. |