Imaging Acute Stroke

and Cerebral Ischemia

John R. Hesselink, M.D.

Department of Radiology

University of California

San Diego

Causes of Stroke

Arterial stenosis

Thrombosis

Embolism

Dissection

Hypotension

Anoxia / hypoxia

Hypoglycemia

Imaging Acute Stroke

Abnormal vascular density / signal

Vascular enhancement

Loss of gray / white contrast

Cortical swelling

Sulcal effacement

Ventricular compression

MRA \ CTA

Conventional Imaging

History: 85 y/o man with a right hemiparesis

291

Dx: MCA embolus with

cerebral infarction

{Page 2}

History: 62 y.o. male with transient

weakness on the right side

O2027

Dx: Left carotid occlusion

{Page 2}

History: 58 y.o. man

with altered mental status

History: 59 y/o woman with headache

and left-sided weakness

187

Weakness {Page 2}

T1 - FATSAT

1

2

3

T2W

Dx: Right ICA dissection

{Page 3}

History: 37 y/o HIV+ female with acute

right sided weakness

172

Dx: Acute MCA infarct

18 hours later {Page 2}

History: 50 y/o male with acute right hemianopsia

following coronary artery angioplasty & stenting

666

{Page 2}

Treated with intra-arterial TPA

1 day later

{Page 3}

Dx: Hemorrhagic occipital infarct

{Page 4}

History: 77 y/o woman

with right-sided weakness

733

{Page 2}

Dx: Amyloid angiopathy

{Page 3}

Diffusion and

Perfusion Imaging

Cerebral Ischemia / Infarction

Brain requires glucose & oxygen

Normal CBF 50-55 ml/100gm/min

If CBF < 18, electrical activity ceases

If CBF < 10, neuronal metabolism stops

CBF 10-18 called the "ischemic penumbra"

Pathologic effect depends on the degree

& duration of ischemia

Physiology

Diffusion Weighted Imaging

Random molecular movement

or "Brownian motion"

Addition of a pair of strong gradient pulses

1st pulse - dephases the spins

2nd pulse - rephases spins if no net movement

If net movement of spins occurs between gradient

pulses, signal attenuation occurs

Physical Principles

Warach S: Diffusion & Perfusion MRI, in Clinical MRI, Edelman et al, Saunders, Chap. 26, pp 828-850

Acute Cerebral Ischemia

Diffusion-Weighted Imaging

CBF lowered to < 10 ml/100gm/min

Cell membrane Na – K pump fails

Net movement of water from extracellular

to intracellular compartment

Diffusion restricted by cell membranes

ADC & signal intensity on DWI

History: 47 y/o man with von-Hippel-Lindau

disease & new left arm weakness

486

Dx: Infarct & MCA stenosis

{Page 2}

ADC

DWI

History: 80 y/o woman with a fluent aphasia

405

{Page 2}

DWI

Dx: Acute & chronic strokes

{Page 3}

DWI

History: 73 y/o woman with weakness

427

Dx: Acute pontine infarct

{Page 2}

{Video clip}

History: 76 y.o. male with vertebral-basilar TIA's

119

Dx: FLAIR & Diffusion - DWMI

TIA's {Page 2}

History: 64 y/o man with bilateral

leg weakness & ataxia

347

{Page 2}

Dx: Acute infarcts in pons

& left corona radiata

Leg weakness

{Page 3}

DWI

History: 16 y/o male

with new onset of seizures

350

{Page 2}

Diffusion

Dx: Brain abscess -

Streptococcus milleri

{Page 3}

History: 63 y/o man with seizures for 8 years

365

{Page 2}

Dx: Epidermoid

{Page 3}

Diffusion

Other Causes of Positive DWI

Bacterial abscess, Epidermoid tumor

Acute demyelination

Acute encephalitis

Tumors undergoing central necrosis

Tumors with high nuclear:cytoplasmic ratios

Creutzfeldt-Jakob disease

Diffuse axonal injury

T2 shine-through (High ADC)

Perfusion Techniques

Cerebral blood flow PET

Xenon CT

CT and MRI Vascular transit time

Cerebral blood volume

CT Perfusion

80-120 kVp, 180-250 mAs

2 – 8 sections / 5 – 10 mm thick

Acquire 1 image set per second

40 second acquisition

40 ml of contrast (300-370 mg I/ml)

Inject 5-8 ml / sec

Technique

CT Perfusion

Time – Density Curve

5 10 15 20 25 30 35

Injection Time (sec)

rCBF = rCBV / MTT

HU

Baseline

TTP

Normal

Area = rCBV MTT

TTP CVA

History: 38 y/o male with a left hemiparesis

752

DWI

ADC

{Page 2}

Dx: MCA embolus & stroke

{Page 3}

MTT CBV CBF

Tomandl BF, et al: Radiographics 23:565-92, 2003

76 y/o woman developed a complete aphasia

& right hemiplegia 35 minutes earlier

Symptoms resolved completely within 2 hours

24 hours later

History: 18 y/o male with confusion & 7 seizures

633

{Page 2}

Dx: Moya Moya

{Page 3}

MR Perfusion Methods

Intravascular magnetic susceptibility

- Inject bolus of gadolinium

- Obtain time-intensity curve

- Measure area under curve

EPISTAR (QUIPSS)

- Tag in-flowing blood with 180o inversion pulse

- Presaturate slice of interest

- 90o readout pulse to slice

- Repeat sequence without tag

- Subtract 4 from 3

- Signal difference proportional to perfusion

EPI Perfusion Sequence

Gadolinium injection

TR = 1000 msec; 90o flip angle

TE = 60 msec

Fat saturation

Matrix = 128 x 128

Acquisition time = 40 sec

EPI Perfusion

Time – Intensity Curve

5 10 15 20 25 30 35

rCBF = rCBV / MTT

SI

Baseline Normal

Area = rCBV

TTP

MTT

Injection Time (sec)

Baseline

TTP

CVA

History: 38 y/o man with altered mental

status & a right hemiparesis

631

DWI

ADC

Dx: Embolic MCA infarct – right

ventricular cardiac thrombus

{Page 2}

Perfusion TTP rMTT

rCBV CBV/MTT= rCBF

FLAIR DWI b=1000 ADC

History: 59 y.o. woman with an upper GI bleed developed

a left hemiparesis & slurred speech

623

3D-TOF

CE-MRA CTA

{Page 2}

Perfusion TTP rMTT

DWI rCBV CBV/MTT=rCBF

CT perfusion

{Page 4}

rCBV rCBF

rMTT

Dx: DWI/PWI mismatch

{Page 5}

CT perfusion

Interpretation

Right ACA-MCA watershed DWI abnormalities

Perfusion imaging (4-5cc Gd/sec)

TTP

MTT

CBV (auto-regulation compensatory vasodilatation

– reduced functional reserve)

CBF (CBV/MTT)

Large DWI/PWI mismatch (penumbra)

(large volume of tissue at risk = salvageable brain)

N

Ischemic Penumbra

DWI / PWI Mismatch

Diffusion Abnormality

CBF < 10 ml/100g/min

Cytotoxic edema

Irreversible ischemia

Perfusion Abnormality

CBF = 10-18 ml/100g/min

Neuronal paralysis

Reversible ischemia Penumbra

History: 56 y/o woman with hypertension

& hyperlipidemia developed

dysarthria & left facial droop

635

Dx: Acute infarct with matched

DWI and perfusion

{Page 2} MTT

rCBV

rCBF TTP

History: 40 y/o male metamphetamine

abuser developed acute bilateral arm

numbness, leg weakness & dysarthria

627

{Page 2}

R

L

Pons

{Page 3}

Perfusion

Imaging

rCBV rMTT CBV/MTT=rCBF

{Page 4}

Dx: Basilar thrombosis &

posterior fossa ischemia

{Page 5}

Post tPA Day 3

Acute Cerebral Ischemia

CT scan

MRI (T2/FLAIR)

DWI

Perfusion

Imaging Sensitivity

24-36 hours

6-12 hours

< 1.5 hours

Instantly

Acute Cerebral Ischemia

T2 / FLAIR sequences

Diffusion imaging (Diagnostic)

Perfusion imaging (Prognostic)

MR Angiography (Site for therapy)

The Integrated MR Exam

UCSD Neuroradiology Teaching File Website

URL - http://spinwarp.ucsd.edu/NeuroWeb/