Imaging Acute Stroke and Cerebral Ischemiaspinwarp.ucsd.edu/NeuroWeb/PPT/stroke-acute-45.pdf · Imaging Acute Stroke and Cerebral Ischemia John R. Hesselink, M.D. Department of Radiology

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/