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Magnetic resonance imaging of the brain
Magnetic Resonance Imaging (MRI) of the brain is a powerful, non-invasive imaging technique that creates detailed pictures of the brain and surrounding structures using magnetic fields and radio waves.
MRI uses a strong magnetic field and radio waves to align hydrogen atoms in the body’s water molecules.
When the radio waves are turned off, these atoms release energy that’s detected by the scanner and converted into detailed images.
Unlike CT scans, MRI doesn’t use radiation.
White matter hyperintensities are common in MRIs of asymptomatic individuals, and their prevalence increases with age from approximately 10%-20% in those approximately 60 years old to close to 100% in those older than 90 years.
More sensitive than CT in the detection of posterior fossa and cervicomedullary lesions, ischemia, white matter abnormalities, cerebral venous thrombosis, subdural and epidural hematomas, neoplasms, meningeal disease, cerebritis and brain abscess than CT scan of the brain.
Brain MRI can visualize:
Gray and white matter structures Blood vessels Cerebrospinal fluid Tumors, cysts, or masses Areas of inflammation or infection Bleeding or stroke damage Structural abnormalities
Common uses to investigate:
– Headaches (especially new, severe, or changing patterns) – Seizures – Dizziness or vertigo – Memory problems or cognitive changes – Stroke symptoms – Multiple sclerosis or other neurological conditions – Brain tumors or infections – Head injuries – Developmental disorders in children
Generally held that MRI better than computed tomography for the diagnosis of acute stroke.
Pituitary pathology, carcinomatosis, diffuse meningeal enhancement in low cerebrospinal fluid pressure syndrome more likely to be detected than by CT scan of the brain.
About 2% are unable to tolerate the study.
White matter hyperintensities are more common in patients with a history of cognitive impairments, dementia, or cerebral vascular disease.
Aging and hypertension are the main predictors of white matter hyperintensities.
Other risk factors associated with white matter hyperintensities include diabetes, hyper cholesterolemia, smoking, carotid artery disease, atrial fibrillation , and heart failure.
Twin studies suggest that white matter hyperintensities have a heritability factor of 55-80%.
White matter hyperintensities are a predictor of future risk of stroke, declining global cognitive performance, executive function, and processing speed, dementia-Alzheimer types, vascular and mixed , and death particularly due to cardiovascular causes.
The presence of white matter hyperintensities on MRI are associated with functional decline, gait disturbance, and depression because they disrupt neural networks.
Magnetic resonance imaging (MRI) of the nervous system uses magnetic fields and radio waves to produce high quality two- or three-dimensional images of nervous system structures.
It does not use of ionizing radiation or radioactive tracers.
Advantages of MRI of the brain over computed tomography of the head is better tissue contrast, fewer artifacts than CT when viewing the brainstem, superiority for pituitary imaging.
MRI of the brain may be less effective at identifying early cerebritis than CT.
In the case of a concussion, an MRI should be avoided unless there are progressive neurological symptoms, focal neurological findings or concern of skull fracture on exam.
In analysis of the fetal brain, MRI provides more information about gyration than ultrasound.
Types of Brain MRI
Standard MRI-Basic structural imaging without contrast
MRI with contrast-Uses gadolinium injection to highlight blood vessels and certain abnormalities more clearly
Functional MRI (fMRI)-Measures brain activity by detecting blood flow changes?
MR angiography (MRA)-Focuses on blood vessels in the brain
MR spectroscopy-Analyzes chemical composition of brain tissues
The scan typically takes 30-60 minutes while lying on a table that slides into a tube-shaped machine.
The machine is noisy.
The process is painless, though some people feel claustrophobic.
MRI is very safe, but one cannot have the scan if you have certain metal implants like pacemakers, some aneurysm clips, or metallic foreign bodies in the eyes.
T1-weighted (T1W) images: Cerebrospinal fluid is dark.
T1-weighted images are useful for visualizing normal anatomy.
T2-weighted (T2W) images: CSF is light, but fat and is white matter that is darker than with T1.
T2-weighted images are useful for visualizing pathology.
Diffusion-weighted images (DWI): DWI uses the diffusion of water molecules to generate contrast in MR images.
Proton density (PD) images: CSF has a relatively high level of protons, making CSF appear bright.
Gray matter is brighter than white matter with proton density (PD) images
Fluid attenuation inversion recovery (FLAIR): useful for evaluation of white matter plaques near the ventricles.
Fluid attenuation is useful in identifying demyelination.