MRI for cva

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MRI in CVA (Cerebrovascular Accident / Stroke)

MRI is the preferred modality for diagnosing and characterizing stroke, superior to CT for early ischemic detection and for posterior fossa lesions. A complete stroke MRI protocol uses several sequences, each answering a different clinical question.

Why MRI Over CT?

CT is still the first-line emergency scan (fast, available, identifies hemorrhage). MRI is used when:

CT is non-diagnostic in early/small infarcts
Posterior fossa (brainstem/cerebellum) stroke is suspected - bone artifact on CT obscures these regions
"Wake-up" stroke - onset time unknown, MRI helps estimate age of infarct
Assessing ischemic penumbra for thrombolysis/thrombectomy decisions beyond standard time windows

"MRI is particularly advantageous in demonstrating small ischemic lesions deep in the hemispheres and brainstem." - Adams and Victor's Principles of Neurology, 12th Ed.

Standard Stroke MRI Protocol

1. Diffusion-Weighted Imaging (DWI) + ADC Map

The most important sequence - the workhorse of acute stroke imaging.

Detects restricted diffusion as early as 5 minutes after infarct onset
Ischemic tissue: bright (hyperintense) on DWI, dark (hypointense) on ADC
The ADC map is essential because DWI alone shows "T2 shine-through" - always read them together
ADC hypointensity reaches a nadir at 3-5 days, remains low until day 7, then "pseudonormalizes" back to baseline in 7-10 days (often 1-4 weeks)
DWI images remain hyperintense even as ADC pseudonormalizes, so DWI cannot be used alone to age a lesion reliably

ADC map for lesion dating:

ADC signal	Estimated age
Hypointense	< 7-10 days
Isointense or hyperintense	> 7-10 days

Acute left MCA territory infarct: CT (A), T2 (B), FLAIR (C), DWI (D), ADC map (E)

Acute left MCA infarct at 7 hours: CT shows subtle low attenuation (A); T2/FLAIR shows hyperintensity and gyral swelling (B, C); DWI shows the full extent including basal ganglia (D); ADC map shows corresponding hypointensity (E). - Grainger & Allison's Diagnostic Radiology

Acute MCA stroke: DWI (left) and ADC map (right)

DWI hyperintensity in left MCA territory (A) with corresponding ADC hypointensity (B). - Bradley and Daroff's Neurology in Clinical Practice

2. FLAIR (Fluid-Attenuated Inversion Recovery)

Suppresses CSF, making periventricular/cortical edema and infarcts stand out
Normal in the hyperacute phase (< 3-6 hours) - this is clinically useful
Signal increases markedly over the first 4 days, then stabilizes
DWI-positive / FLAIR-negative = lesion likely < 4.5 hours old (used to guide thrombolysis in wake-up strokes)
DWI-positive / FLAIR-positive = lesion likely > 4.5-6 hours old
Arterial hyperintensity on FLAIR (loss of normal flow void) = a qualitative sign of reduced perfusion in a proximal vessel

3. T2-Weighted Imaging

Shows edema, infarct core, mass effect
Hyperintense from ~6 hours onward; increases over first 4 days
Less sensitive than DWI in hyperacute phase
Good for: infarcts, inflammation, white matter disease

4. T1-Weighted Imaging

Normal in acute phase; subacute infarcts may show T1 shortening (methemoglobin from petechial hemorrhage)
Good for: subacute blood, cortical laminar necrosis (bright gyri at 1-2 weeks), overall brain anatomy

5. Susceptibility-Weighted Imaging (SWI) / T2* GRE

Detects blood products (hemosiderin, deoxyhemoglobin) as signal voids ("blooming artifact")
Essential for identifying hemorrhagic transformation of infarct
Identifies microbleeds - relevant before thrombolysis/anticoagulation
Also shows thrombus in vessels directly

6. MR Angiography (MRA)

Time-of-flight (TOF) MRA - no contrast needed; uses flowing blood as signal; demonstrates large vessel occlusion (MCA, ICA, basilar artery)
Contrast-enhanced MRA - better for extracranial vessels and venous system
Identifies site of occlusion, stenosis, dissection, or aneurysm
MRV (venography) for cerebral venous sinus thrombosis

7. Perfusion-Weighted Imaging (PWI)

Requires IV gadolinium; rapid image acquisition during contrast passage
Measures: CBF (cerebral blood flow), CBV (blood volume), MTT (mean transit time), Tmax
DWI-PWI mismatch = ischemic penumbra (tissue at risk but potentially salvageable)
- Infarcted core: reduced CBV, matches DWI lesion
- Penumbra: increased transit time / reduced flow with relatively maintained CBV

MRI Sequences Summary Table

Sequence	Acute stroke appearance	Best for
DWI	Bright (from 5 min)	Acute ischemia detection
ADC map	Dark (matches DWI)	Confirm true restriction; age lesion
FLAIR	Normal < 3-6 h; bright after	Lesion age estimation; penumbra
T2	Normal initially; bright > 6 h	Edema, infarct extent
T1	Normal acutely; bright subacutely	Subacute blood, cortical necrosis
SWI/GRE	Dark "blooming"	Hemorrhage, microbleeds, thrombus
MRA	Absent/reduced flow	Vessel occlusion, stenosis
PWI	Perfusion maps	Penumbra vs. core mismatch

(Source: Adams and Victor's Principles of Neurology, 12th Ed., Table 33-3)

Temporal Evolution on MRI

Time from onset	DWI	ADC	FLAIR	T2	T1
< 3-6 h (hyperacute)	Bright	Dark	Normal	Normal/subtle	Normal
6 h - 3 days (acute)	Bright	Dark (nadir at 3-5 d)	Bright	Bright	Normal/subtle
3-7 days (subacute early)	Bright	Dark	Bright	Bright	Bright (petechial Hg)
7-10 days	Bright	Pseudonormalizing	Bright	Bright	Variable
> 2 weeks (chronic)	Dark (or normal)	Bright	Bright/cavity	Bright/cavity	Dark/encephalomalacia

(Source: Bradley and Daroff's Neurology in Clinical Practice; Grainger & Allison's Diagnostic Radiology)

Special Scenarios

Wake-Up Stroke

DWI-FLAIR mismatch is used: if DWI is positive but FLAIR is normal/near-normal, the infarct is likely within the 4.5-hour thrombolysis window. If FLAIR is already clearly positive, onset was likely > 4.5-6 hours ago.

Posterior Fossa / Brainstem Stroke

MRI is far superior to CT here - bone artifact from the posterior fossa significantly limits CT sensitivity. DWI on MRI can detect small brainstem lacunar infarcts that CT misses entirely.

Hemorrhagic Stroke

Acute: SWI/GRE shows signal void; T2 shows hypointensity (deoxyhemoglobin)
Subacute: T1 bright (methemoglobin)
Chronic: T2 dark rim (hemosiderin)

Penumbra Assessment

PWI-DWI mismatch guides revascularization decisions, particularly for patients presenting in extended time windows (6-24 hours) for mechanical thrombectomy.

Sources:

Grainger & Allison's Diagnostic Radiology, "Magnetic Resonance Imaging in Acute Stroke" and "Imaging Strategies in Acute Stroke"
Adams and Victor's Principles of Neurology, 12th Ed., "Imaging Techniques in Stroke," Table 33-3
Bradley and Daroff's Neurology in Clinical Practice, "Temporal evolution of ischemic stroke on MRI"

Which mri to do for cva

Based on the detailed answer I just provided, here is a focused, practical summary of which MRI sequences to order for CVA:

MRI Protocol for CVA - What to Order

Minimum / Emergency Protocol (Acute Stroke)

#	Sequence	Why it's ordered
1	DWI (Diffusion-Weighted Imaging)	Detects infarct from as early as 5 minutes; the single most important sequence
2	ADC Map	Always paired with DWI - confirms true restricted diffusion (not T2 shine-through); helps age the lesion
3	FLAIR	Normal in first 3-6 hours; if DWI positive + FLAIR negative = infarct < 4.5 hours (guides thrombolysis)
4	SWI or T2 GRE*	Rules out hemorrhage before giving thrombolytics
5	MRA Brain	Shows vessel occlusion (MCA, ICA, basilar) - decides thrombectomy

This 5-sequence set answers the three urgent questions: Is it ischemic or hemorrhagic? Where is the clot? Is the patient in the thrombolysis window?

Extended Protocol (Add-On When Needed)

Sequence	When to add
T1-weighted	Subacute stroke, suspect hemorrhagic transformation, general anatomy
T2-weighted	Edema extent, white matter disease, old infarcts
MR Perfusion (PWI)	Extended time window (6-24 h) - identify salvageable penumbra for thrombectomy
MRA Neck (CEs or TOF)	Carotid/vertebral artery disease, dissection suspected
MRV	Cerebral venous sinus thrombosis suspected
Gadolinium contrast T1	Subacute phase - BBB disruption, gyriform enhancement confirms cortical infarct

Decision Guide

Acute stroke < 6 hours, thrombolysis candidate?
  → DWI + ADC + FLAIR + SWI + MRA brain

Wake-up stroke / unknown onset?
  → Same + check DWI-FLAIR mismatch (FLAIR negative = likely within window)

Extended window 6-24 h (thrombectomy candidate)?
  → Add MR Perfusion (PWI-DWI mismatch = penumbra)

Posterior fossa / brainstem symptoms?
  → MRI (not CT) is mandatory - DWI will catch small brainstem infarcts CT misses

Hemorrhagic stroke?
  → SWI/GRE is key; follow with T1 to track blood product evolution

Bottom line: For any acute CVA, order DWI + ADC + FLAIR + SWI + MRA brain as the core set. This gives you diagnosis, lesion age, hemorrhage exclusion, and vascular anatomy in one go.

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