MRI in Acute Ischemic Infarction Diagnosis

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Questions and Answers

When does arterial enhancement typically become evident?

Between 2 and 6 days

Immediately after the stroke

After 10 days

After 3 days (correct)

What is the primary purpose of susceptibility-weighted imaging (SWI)?

To detect cortical enhancement

To measure ADC values

To diagnose thromboembolic stroke

To identify small hemorrhage and calcium (correct)

What is the typical timeframe for ADC pseudonormalization?

After 20 days

Between 5-10 days

Between 2-6 days

Between 10-15 days (correct)

What is the term for the phenomenon where high T2 signal increases the DWI signal?

T2 shine through Signup and view all the answers

What is a potential indication of an underlying lesion if cortical contrast enhancement persists for more than?

12 weeks Signup and view all the answers

What is Transcranial Doppler ultrasound used for in stroke diagnosis?

Diagnosis of ischemic stroke and vessel occlusion Signup and view all the answers

What is a diagnostic criterion for occlusion of an isolated vessel on Transcranial Doppler ultrasound?

Absence of color flow Doppler signals Signup and view all the answers

What is the role of Transcranial Doppler ultrasound in sonographic monitoring of ischemic stroke complications?

Measurement of optic nerve sheath diameter Signup and view all the answers

What is the focus of acute treatment in ischemic stroke?

Prompt application of reperfusion therapies Signup and view all the answers

What is the significance of adequate visualization of surrounding parenchyma and vessels on Transcranial Doppler ultrasound?

It is a diagnostic criterion for vessel occlusion Signup and view all the answers

What is a characteristic of MRI in the diagnosis of acute ischemic infarction in the first few hours after onset?

Significantly higher sensitivity and specificity Signup and view all the answers

What is demonstrated on DWI within minutes of arterial occlusion?

Increased signal and reduced ADC values Signup and view all the answers

At what stage can high T2 signal be detected after acute ischemic infarction?

After 6 hours Signup and view all the answers

What is seen on T1 imaging after 16 hours of acute ischemic infarction?

Hypointense signal Signup and view all the answers

When can cortical contrast enhancement be seen in incomplete infarction?

After 2-4 hours Signup and view all the answers

Study Notes

MRI in Acute Ischemic Infarction

MRI has higher sensitivity and specificity than CT in diagnosing acute ischemic infarction in the first few hours after onset.

Early Hyperacute Stage

Within minutes of arterial occlusion, diffusion-weighted imaging (DWI) demonstrates increased signal and reduced ADC values.
Affected parenchyma appears normal on other sequences, but changes in flow will be detected (occlusion on MRA) and the thromboembolism may be detected.
Cortical contrast enhancement may be seen as early as 2-4 hours if infarction is incomplete.

Late Hyperacute Stage

After 6 hours, high T2 signal will be detected, initially more easily seen on FLAIR.
T1 hypointensity is only seen after 16 hours and persists.

Acute Stage

During the first week, infarcted parenchyma continues to demonstrate high DWI signal and low ADC signal.
Infarct remains hyperintense on T2 and FLAIR, with T2 signal progressively increasing during the first 4 days.
T1 signal remains low, but some cortical intrinsic high T1 signal may be seen as early as 3 days after infarction.
After day 5, the cortex usually demonstrates contrast enhancement.
Less common patterns of enhancement include arterial enhancement and meningeal enhancement.

Hemorrhage

Hemorrhage is most easily seen on susceptibility-weighted imaging (SWI) and is usually seen after 12 hours and within the first few days.

Subacute Stage

ADC demonstrates pseudonormalization typically occurring between 10-15 days.
DWI remains elevated due to persistent high 2/FLAIR signal (T2 shine through) unless hemorrhage or cystic encephalomalacia.
Cortical enhancement is usually present throughout the subacute period.
T1 weighted sequences continue to show hypointensity throughout the area of infarct with cortical intrinsic high T1 signal.

Chronic Stage

T1 signal remains low with intrinsic high T1 in the cortex if cortical necrosis is present.
T2 signal is high.
Cortical contrast enhancement usually persists for 2 to 4 months.
ADC values are high.
DWI signal is variable, but as time goes on, signal progressively decreases.

Transcranial Doppler Ultrasound

Transcranial Doppler ultrasound can be used for the diagnosis of intracranial vessel occlusion and differentiation between ischemic and hemorrhagic stroke.
Diagnostic criteria for occlusion of an isolated vessel include:
- Complete absence of color flow Doppler signals.
- Absence of pulsed-wave Doppler signals.
- Concurrent adequate visualization of surrounding parenchyma and vessels.

Treatment and Prognosis

Acute treatment focuses on prompt application of reperfusion therapies, including intravenous or intra-arterial thrombolysis.

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Description

This quiz assesses your understanding of Magnetic Resonance Imaging (MRI) in diagnosing acute ischemic infarction, including its advantages and applications in the first few hours after onset. Test your knowledge of MRI's role in detecting acute ischemic infarction and its comparison with CT scans.