Imaging Acute Stroke and Cerebral Ischemia

Department of Radiology University of California San Diego Imaging Acute Stroke and Cerebral Ischemia John R. Hesselink, M.D.

Causes of Stroke Arterial stenosis Thrombosis Embolism Dissection Hypotension Anoxia / hypoxia Hypoglycemia

Imaging Acute Stroke Conventional Imaging Abnormal vascular density / signal Vascular enhancement Loss of gray / white contrast Cortical swelling Sulcal effacement Ventricular compression MRA \ CTA

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

1 Weakness {Page 2} 2 T1 - FATSAT T2W 3

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}

{Page 4} Dx: Hemorrhagic occipital infarct

History: 77 y/o woman with right-sided weakness 733

{Page 2}

{Page 3} Dx: Amyloid angiopathy

Diffusion and Perfusion Imaging

Cerebral Ischemia / Infarction Physiology 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

Diffusion Weighted Imaging Physical Principles 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 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

{Page 2} DWI ADC Dx: Infarct & MCA stenosis

History: 80 y/o woman with a fluent aphasia 405

{Page 2} DWI

{Page 3} DWI Dx: Acute & chronic strokes

History: 73 y/o woman with weakness 427

{Page 2} {Video clip} Dx: Acute pontine infarct

History: 76 y.o. male with vertebral-basilar TIA's 119

TIA's {Page 2} Dx: FLAIR & Diffusion - DWMI

History: 64 y/o man with bilateral leg weakness & ataxia 347

{Page 2}

Leg weakness {Page 3} Dx: Acute infarcts in pons & left corona radiata 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}

{Page 3} Diffusion Dx: Epidermoid

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 Technique 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

CT Perfusion Time Density Curve TTP CVA TTP rcbf = rcbv / MTT MTT Area = rcbv HU Baseline Injection 5 10 15 20 25 30 35 Time (sec) Normal

History: 38 y/o male with a left hemiparesis DWI ADC 752

{Page 2}

MTT CBV CBF {Page 3} Dx: MCA embolus & stroke

76 y/o woman developed a complete aphasia & right hemiplegia 35 minutes earlier Tomandl BF, et al: Radiographics 23:565-92, 2003

Symptoms resolved completely within 2 hours 24 hours later

History: 18 y/o male with confusion & 7 seizures 633

{Page 2}

{Page 3} Dx: Moya Moya

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 180 o inversion pulse - Presaturate slice of interest - 90 o 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; 90 o flip angle TE = 60 msec Fat saturation Matrix = 128 x 128 Acquisition time = 40 sec

EPI Perfusion Time Intensity Curve Baseline TTP CVA rcbf = rcbv / MTT Baseline Normal MTT Area = rcbv SI Injection TTP 5 10 15 20 25 30 35 Time (sec)

History: 38 y/o man with altered mental status & a right hemiparesis ADC DWI 631

{Page 2} Dx: Embolic MCA infarct right ventricular cardiac thrombus rcbv CBV/MTT= rcbf Perfusion TTP rmtt

History: 59 y.o. woman with an upper GI bleed developed a left hemiparesis & slurred speech FLAIR DWI b=1000 ADC 623

{Page 2} 3D-TOF CE-MRA CTA

Perfusion TTP rmtt DWI rcbv CBV/MTT=rCBF

{Page 4} rmtt CT perfusion rcbv rcbf

{Page 5} CT perfusion Dx: DWI/PWI mismatch

Interpretation Right ACA-MCA watershed DWI abnormalities Perfusion imaging (4-5cc Gd/sec) N 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)

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 Penumbra Reversible ischemia

635 History: 56 y/o woman with hypertension & hyperlipidemia developed dysarthria & left facial droop

{Page 2} MTT rcbv TTP rcbf Dx: Acute infarct with matched DWI and perfusion

History: 40 y/o male metamphetamine abuser developed acute bilateral arm numbness, leg weakness & dysarthria 627

{Page 2}

{Page 3} L R Perfusion Imaging Pons

{Page 4} rcbv rmtt CBV/MTT=rCBF

{Page 5} Post tpa Day 3 Dx: Basilar thrombosis & posterior fossa ischemia

Acute Cerebral Ischemia Imaging Sensitivity CT scan MRI (T2/FLAIR) DWI Perfusion 24-36 hours 6-12 hours < 1.5 hours Instantly

Acute Cerebral Ischemia The Integrated MR Exam T2 / FLAIR sequences Diffusion imaging (Diagnostic) Perfusion imaging (Prognostic) MR Angiography (Site for therapy)

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