Radiology 401

John R. Hesselink, M.D.

MR Imaging MR Imaging of the Brainof the Brain

MR System Components

Computer

Gradient Amplifier

Receiver

Transmitter

Digitizer

RF Coil

Gra

dien

t

RF CoilG

radient

Magnet

MR Imaging

Proton density

T1 relaxation time

T2 relaxation time

Flow effects

Source of Signal and Contrast

Spin-echo Pulse SequenceSingle Echo T1-weighted

RF

Signal

TR

TE

1st

echo2nd

echo

Spin-echo Pulse SequenceDual Echo T2-weighted

1st

echo2nd

echo

RF

Signal

TR

TETE

T2-Weighted Images

Proton Density Weighted Images

Normal FLAIR ImagesTR = 6000 msec, TI = 2000 msec, TE = 102 msec

T1-Weighted Images

MR Signal ofMR Signal ofBrain LesionsBrain Lesions

SolidBrainLesion PDW

T2W T1W

CysticLesion

T2W

T1W

FLAIR

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SubacuteHemorrhage

PDW

T1W

T2W

AcuteHemorrhage

T2W

FLAIR

T1WGRE

History: 9 y/o boy with prior head trauma

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Hemorrhage SequenceGradient-echo

PDW

Fator

Lipoma

T2W

T1W

MR Signal Intensities

T2WI PD/FLAIR T1WI

Solid mass Bright Bright Dark

Cyst Bright Dark Dark

Subacute blood Bright Bright Bright

Acute & chronic blood Dark Dark Gray

Fat Dark Bright Bright

Acute Stroke SequenceDiffusion Weighted Imaging

MR Angiography

Dx: Anaplastic astrocytoma > GBM

MR Spectroscopy

Brain Screening Protocol

Axial T2-weighted images Axial FLAIR images If normal:

Stop If abnormal:

T1-weighted images Gd-DTPA enhancement

History: 46 y.o. manwith headaches & increasing confusion

21

T2W PDW

{Page 2}

5

34

T1W

T1W / Gd

T1W

Dx: Meningioma & right MCA infarct

Increasing confusion {Page 3}

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