Radiology 401 MR Imaging of the Brain John R. Hesselink, M.D.

MR System Components Computer Magnet RF Coil Gradient Gradient RF Coil Transmitter Gradient Amplifier RF Coil Gradient Computer Gradient RF Coil Magnet Receiver Digitizer

Source of Signal and Contrast MR Imaging Source of Signal and Contrast Proton density T1 relaxation time T2 relaxation time Flow effects

Spin-echo Pulse Sequence Single Echo T1-weighted RF Signal TR TE 1st echo 2nd echo

Spin-echo Pulse Sequence Dual Echo T2-weighted RF Signal TR TE 1st echo 2nd echo

T2-Weighted Images

Proton Density Weighted Images

Normal FLAIR Images TR = 6000 msec, TI = 2000 msec, TE = 102 msec

T1-Weighted Images

MR Signal of Brain Lesions

T1W T2W Solid Brain Lesion PDW

T1W Cystic Lesion FLAIR T2W 236

Subacute Hemorrhage PDW T1W T2W

Acute Hemorrhage T2W FLAIR T1W GRE

History: 9 y/o boy with prior head trauma 466

Hemorrhage Sequence Gradient-echo

Fat or Lipoma T2W PDW 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

Diffusion Weighted Imaging Acute Stroke Sequence Diffusion Weighted Imaging

MR Angiography

MR Spectroscopy Dx: Anaplastic astrocytoma > GBM

Brain Screening Protocol Axial T2-weighted images Axial FLAIR images If normal: Stop If abnormal: T1-weighted images Gd-DTPA enhancement

with headaches & increasing confusion History: 46 y.o. man with headaches & increasing confusion 1 2 T2W PDW

4 3 T1W T1W 5 {Page 2} T1W / Gd

Increasing confusion {Page 3} 6 7 Dx: Meningioma & right MCA infarct