Brain MRI: A Systematic Reading

MRI Diffusion Left MCA stroke

Brain MRI: A Systematic Reading

Weights and Planes

MRI images are commonly viewed in three planes: axial, coronal, and sagittal.

MRI planesShades of Gray Matter

The routine MRI is presented as black and white images, not color. The various shades of gray are described in terms of their “signal intensity.” “Low signal intensity” means “dark,” and “high signal intensity” means “bright.”

Remember that this is different from CT, where lesions are described in terms of “density.” A dark lesion on CT is called “hypodense,” and a bright lesion is “hyperdense.” How can you remember this? The word “den – SITY” rhymes with “C – T.”

MRI Weighting: T1, T2, others

The most commonly used techniques for MRI imaging are T1-weighted, T2-weighted, Flair and Diffusion-weighted.

T1 weighted images are useful for brain parenchyma. Brain appears medium gray and CSF is dark gray, and air is nearly black. Most tumors appear dark, with low signal intensity. Fat has high signal intensity on T1 but “drops out” on T2 weighted images where it becomes dark. Gadolinium contrast added to the T1 may “light up” a tumor or abscess. If a lesion has dark signal on T1, and bright signal with gadolinium, it is a “contrast enhancing” lesion. The enhancement may be the same throughout the lesion, making it “homogeneously enhancing.”MRI T1 with gadolinium: Left occipital meningioma

Or it may enhance only around the edges, making it “ring enhancing” as in a brain abscess, or in this lung met.MRI T1 with contrast: Ring enhancing lesion

T2 weighted images are great to evaluate CSF spaces, which appear bright white. Brain appears light gray. Use the T2 sequence to check the size and symmetry of the ventricles, and look for bright signal of edema surrounding an aggressive tumor or a subacute stroke or hemorrhage. Also check the T2 images for Multiple Sclerosis, with its characteristic periventricular white matter changes–bright splotches around the lateral ventricles. The bright signal is the scarring of the myelin sheath in the white matter–the “sclerosis” shows up on T2 images. MRI T2 axial: Multiple sclerosis

The flair sequence is “a T2 with dark CSF,” very sensitive to edema and to parenchymal abnormalities like a low grade glioma. In fact a grade 1 astrocytoma will be virtually invisible on T1, but will be unmistakable on Flair. The flair sequence is useful for surveillance of a low grade glioma, as you watch for signs of enlargement like fattening of the gyri.MRI Flair: right cerebellar tumor with edema

Diffusion weighted images have one purpose: to visualize an area of acute ischemia. Say a person has new onset of stroke symptoms. A CT shows no blood, proving that the stroke is not hemorrhagic.  An MRI will show the stroke as bright signal on the Diffusion-weighted images, and dark on the diffusion ADC sequence.MRI Diffusion: Left MCA stroke

MRI Diffusion ADC Left MCA stroke

An MRI is the study of choice for tumor, multiple sclerosis, and ischemic stroke. Add gadolinium contrast to evaluate tumor and abscess. For brain hemorrhage, however, CT is the go-to study.

23 thoughts on “Brain MRI: A Systematic Reading

  1. nice and simple presentation for radiologists who don’t have the opportunity of reporting MRI. thanks for your simple approach.


  3. Dr Rupali
    Its a good and simple explanation for beginner but if diagram are pointed with arrow it still becomes more easy

  4. I really enjoyed the presentation and the simple approach it took on towards the subject. Thank you so much for your time and effort.

  5. Pingback: Gradient Echo Weighted Images | Fairy of Disenchantment

    • My MRI findings: Cerebral Hemispheres/Basal Ganglia: Subcentimeter serpiginous focus in the lateral left frontal lobe (series 401 and 501, images #23) is either a developmental venous anomaly or prominent perivascular space. No acute infarct. No mass effect. No hemosiderin. Brainstem/Cerebellum: Unremarkable. Ventricles/Sulci: Within normal limits for age. No abnormal extra-axial fluid collection. Basilar Cisterns: Clear. Vasculature: Normal flow voids. Ectatic left vertebral-basilar arteries. Paranasal Sinuses: Clear. Bones/Soft Tissues/Orbits: Unremarkable. IMPRESSION: No acute intracranial process What does this mean?

  6. Simple and systematic brain mri reading approach. Expecting such more presentatins dealing chest, abdomen and spine in near future . Many thanks.

  7. Hello,
    I am 30 yr old female that had had a history of hormonal imbalances including hypothyroid to hyperthyroidism, pituitary adenoma, PCOS, and some lipid panel numbers out of range. I had a MRI done to see if I still had the pituitary adenoma and according to the report it was no linger there after. Few years of treatment. However, and incidental finding stated the following. [Incidental note is made of a left anterior frontal poetical modal focus of enhancement in yr brain parenchyma. Common new compared to prior exam dated 2 years back. Advise correlation with dedicated MRI of the brain with and without gadolinium. A demyelinating focus must be considered.] So this MRI was done with and without contrast when they found this marking. Went to a Neurologist and he advised it could simply just be a light/glare on the machine while taking images. My endocrinologist didn’t see a need to repeat a MRI since I had met with the Neurologist. I’ve been having some tingling and prickling over both feet, and body now when going outside in heat or taking hot baths. I am afraid that this could be MS fr reading about symptoms. I don’t know if the tingling that has been in my feet off and on for almost 2 years is hormone related/stress/anxiety, or what. Please help! Vision, balance, muscles, are all fine. It’s just the tingling.

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