Basics of MRI BRAIN

Dr.Nermeen Shenouda , Msc Clinical Neurophysiology

Kuwait6 May 2015

• MR utilizes a strong magnetic field combined with radiofrequency pulses to obtain signal from the brain

• ß  Changes in signal are processed by computer to form images

• ß  Does not use radiation

• While pregnancy is not a contraindication owing to a lack of ionizing radiation, minimum use of MRI is still recommended. Gadolinium-based contrast agents are able to cross the placenta and should not be administered, particularly during the first trimester.[5]

T1 Black on T1: Air, Calcifications , Dense bone.Dark on T1: CSF , Edema , Most lesions. Grey on T1: white matter, gray matterBright on T1 :Fat , Blood , Gadolinium.• Useful for: Borders between brain and CSF (e.g., sulci, ventricles, cysts) • Not very sensitive to lesions • Recognition: Pre-contrast image

T2• T1-weighted images with Gd contrast •  Sensitive to presence of vascular or extravascular Gd •  Useful for visualization of: Normal vessels ,Vascular

changes & Disruption of blood-brain barrier

•  Look for: Bright on Gd and NOT bright on non- contrast

•  Recognition • o Displayed after non-enhanced images (usually

performed last) • o Like non-contrast T1 but with bright arteries and veins

• Enhancement

• – Gadolinium is injected intravenously • – Normal brain does not enhance due

to the Blood Brain Barrier • – Presence of enhancement will affect

the differential diagnosis

T2

• Black on T2 (no protons) : Air , Calcium,• Dense bone . • Dark on T2 (long T2) : White matter ,Gray Matter

Bright on T2 (short T2) :CSF, Blood (except deoxyhemoglobin) ,Edema, Most lesions .• Useful for: Brain anatomy ,(show CSF spaces),most

brain lesions , but cannt distinguish lesions from CSF ( intraventricular lesions )

• Recognition • CSF (ventricles, cisterns, sulci): bright • Scalp: bright• Eyes: bright• Vessels: black (flow void)

Flair Fluid Attenuated inversion recovery

• Basically it is T2 without CSF brightness•  Most pathology is BRIGHT  Useful for: Same as T2,Most lesions, Especially good for lesions near ventricles or sulci (MS).

T2 Star or SWI• Form of T2-weighted image which is more

susceptible to iron or calcium •  Blood, bone, calcium appear dark •  Area of blood often appears much larger than

reality • (“blooming”) •  Useful for: • o Identification of early hemorrhage •  Look for: DARK only

Recognition :Like T2 except • o Cranium, scalp are dark or absent

o Dark areas near frontal and temporal bones o Hemorrhage is darker than brain

Diffusion-weighted image (DWI)

• Sensitive to passive diffusion of water • Areas of restricted diffusion are bright• Restricted diffusion occurs in cytotoxic

edema:• Ischemia, seizures , Abscess

• Look for Bright only • Recognition : low resolution image .

Apparent diffusion coefficient ADC map

ADC is mapped out of the DWI  Areas of restricted diffusion are dark  Useful for: Excluding T2-shine through Real restricted diffusion is bright on DWI, dark on ADC

•  Look for: DARK only

•  Recognition Images marked ADC Grainy dark images .

Rule:• High signal DWI + low signal ADC=

True abnormality.• High signal DWI + high signal ADC=

False positive

Ischemic lesion

Heamorhage

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