ASC Stroke Imaging & Diagnostics 2 — Questions and Answers
Question 1: On CT perfusion imaging, which map best identifies the ischemic penumbra (tissue at risk but potentially salvageable)?
- Cerebral blood volume (CBV) map
- Mean transit time (MTT) or Tmax map showing perfusion delay (Correct answer)
- Cerebral blood flow (CBF) map showing severely reduced flow
- Delay-insensitive CT angiography source images
Correct answer: Mean transit time (MTT) or Tmax map showing perfusion delay
Tmax or MTT maps highlight areas with prolonged transit time representing the ischemic penumbra, which differs from the core infarct seen on CBF maps.
Question 2: Which MRI sequence is most sensitive for detecting hyperacute subarachnoid hemorrhage within the first few hours?
- T1-weighted imaging
- T2-weighted FLAIR
- Gradient echo (GRE) T2* (Correct answer)
- Diffusion-weighted imaging (DWI)
Correct answer: Gradient echo (GRE) T2*
GRE/T2* sequences are highly sensitive to blood products due to susceptibility effects of deoxyhemoglobin, making them superior to FLAIR in the hyperacute phase.
Question 3: A patient's CTA reveals a hyperdense basilar artery sign. What does this finding indicate?
- Calcified atherosclerotic plaque without acute occlusion
- Acute thrombus within the basilar artery (Correct answer)
- Artifact from beam-hardening near the skull base
- Normal variant of the basilar artery
Correct answer: Acute thrombus within the basilar artery
A hyperdense basilar artery on non-contrast CT indicates acute thrombus and is associated with basilar artery occlusion requiring urgent intervention.
Question 4: In CT perfusion imaging, the ischemic core is best represented by which parameter threshold?
- Tmax > 6 seconds
- CBF < 30% of contralateral normal tissue (Correct answer)
- MTT prolongation > 145% of normal
- CBV > 2.5 mL/100g
Correct answer: CBF < 30% of contralateral normal tissue
A CBF reduction to less than 30% of normal contralateral tissue is the widely accepted threshold for identifying irreversibly infarcted core tissue.
Question 5: Which artifact on diffusion-weighted MRI can mimic acute ischemic stroke and must be recognized?
- Magnetic susceptibility artifact
- T2 shine-through effect (Correct answer)
- Chemical shift artifact
- Gibbs ringing artifact
Correct answer: T2 shine-through effect
T2 shine-through occurs when subacute lesions with long T2 relaxation times appear bright on DWI without true diffusion restriction, mimicking acute infarct.
Question 6: What is the primary advantage of flat-panel detector CT (DynaCT) used in the angiography suite?
- Higher spatial resolution than conventional MRI for parenchymal detail
- Real-time imaging during endovascular procedures to detect hemorrhage (Correct answer)
- Quantitative CBF measurement without contrast
- Superior detection of acute ischemia compared to DWI
Correct answer: Real-time imaging during endovascular procedures to detect hemorrhage
DynaCT in the angiography suite allows rapid detection of intracranial hemorrhage during endovascular stroke treatment without transferring the patient.
Question 7: On non-contrast CT, the 'insular ribbon sign' in acute MCA stroke indicates loss of distinction between which structures?
- Gray matter and white matter in the insular cortex (Correct answer)
- Caudate and lentiform nuclei
- Thalamus and internal capsule
- Frontal and parietal cortical sulci
Correct answer: Gray matter and white matter in the insular cortex
The insular ribbon sign refers to loss of the normal gray-white differentiation in the insular cortex, an early CT sign of MCA territory ischemia.
ASC Stroke Imaging & Diagnostics 2
On CT perfusion imaging, which map best identifies the ischemic penumbra (tissue at risk but potentially salvageable)?