Acute stroke MR protocol

David Goldemund M.D.
Updated on 11/09/2024, published on 10/09/2024

neuroimaging plays a central role in the evaluation of patients with acute ischemic stroke
improved technology provides information beyond the simple presence or absence of intracranial hemorrhage, including tissue viability, site of occlusion, and collateral status
computed tomography (CT) is a fast and widely available imaging modality; acute stroke CT protocol (which includes non-contrast head CT, CT angiography, and CT perfusion) can be acquired and processed within 10 minutes
MRI has been demonstrated to be more sensitive for the detection of acute ischemia and more specific for the delineation of infarction core volume when compared to CT; the whole protocol could traditionally be obtained in ~ 20 minutes
thanks to advances in MR technology, modified stroke protocols can be obtained within 6-7 minutes, rivaling any comprehensive acute stroke CT protocol (Nael, 2013)

new fast imaging techniques have significantly enhanced the performance of MR imaging in terms of acquisition speed

DWI can detect ischemic tissue within minutes of its onset and has proven to be the most sensitive and specific imaging technique for acute ischemia, far beyond noncontrast CT (NCCT) or any other MRI sequences

~ 60 seconds

~ 60 seconds

detects parenchymal hemorrhage with accuracy comparable to CT
both FLAIR and GRE images have been used to detect intraarterial thrombus with variable sensitivity and specificity

~ 56 seconds

imaging of both intracranial and extracranial vessels is required for proper management of acute stroke
traditionally, time of flight MRA (TOF MRA) has been used in routine stroke protocols
- it overestimates stenosis, has increased false positive rates (usually due to slow flow distal to a subocclusive clot), and has a long acquisition time (5-7 minutes)
contrast-enhanced MR angiography (CE MRA)
- more accurate imaging of extracranial vessel morphology and stenosis degree than TOF
- lower spatial resolution, extra contrast dose
- 2-phase contrast injection can be used to perform fast CE MRA + DSC
phase contrast MR angiography (PCA)
- a technique that can be used to visualize moving fluid without using gadolinium-based contrast agents (this is particularly advantageous for pediatric patients)
- novel high-performance MR scanners encompass the entire head and neck, resulting in acquisition times < 1 minute (Oura, 2023)
- less prone to motion artifacts

~ 20 seconds

perfusion imaging helps identify penumbra
dynamic susceptibility contrast (DSC) perfusion
- faster image acquisition combined with a higher signal-to-noise ratio (SNR) due to the use of gadolinium contrast agents has made dynamic susceptibility contrast (DSC) perfusion a more robust and widely accepted technique compared to arterial spin labeling (ASL)
- a modified 2-phase contrast injection scheme can be used to perform both CE MRA and DSC perfusion without the need for additional contrast, with improved acquisition time and diagnostic image quality
Arterial Spin Labeling (ASL) – takes ~ 1 min

~ 90 seconds

a total volume of 20 mL of gadolinium is diluted with normal saline to a total 50 mL volume
a total of 3 mL of solution (1.2 mL of gadolinium) is injected at 1.5 mL/s to determine the transit time from the arm vein to the cervical carotid arteries
a total of 22 mL of contrast (8.8 mL of gadolinium) is then injected at the same flow rate as the timing injection for the CE MRA acquisition
the remaining 25 mL of contrast solution (10 mL of gadolinium) is injected at 5 mL/s for the MR perfusion scan (DSC), which is performed at the end (Nael, 2013)