Measuring Ischemic Stroke Volume on CT or MRI

Introduction to Ischemic Stroke Measurement

The American Heart Association recommends using specialized software that performs region-of-interest analysis on contiguous brain slices to measure ischemic stroke volume, with the measurement technique varying by imaging modality 1, 2, 3

The American College of Radiology recommends obtaining contiguous, discrete (non-helical) 5mm slice thickness images to enable accurate volumetric quantification of early infarct 1
Manual planimetric measurement involves outlining the hypodense ischemic region on each slice and multiplying by slice thickness, though this has limited sensitivity in the hyperacute phase (detecting only 61-65% of strokes within 6 hours) 2
The accuracy for detecting ischemic areas involving more than one-third of the middle cerebral artery territory is approximately 70-80% 4
CT Perfusion (CTP) provides quantitative maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) that can be analyzed with region-of-interest measurements 5, 6
The ischemic core is defined by regions with >75% reduction in CBF or CBV <2 mL/100g, which has >95% positive predictive value for infarction despite recanalization 6
Normalized (relative) CBF is the most robust parameter: >66% reduction in CBF indicates nonviable penumbra (95% specificity for infarction), while <50% reduction indicates benign oligemia (95% sensitivity for tissue survival) 6
CTA Source Images (CTA-SI) provides qualitative cerebral blood volume maps that detect the infarct core and can be used for whole-brain assessment 6, 7
A CTA-SI lesion volume <100 mL predicts good/fair outcome, while >100 mL predicts poor outcome despite complete recanalization 6

The American Stroke Association recommends using Diffusion-Weighted Imaging (DWI) as the most sensitive and specific technique for measuring acute infarct volume, with 88-100% sensitivity and 95-100% specificity 4, 2, 3
Hyperintense regions on DWI represent cytotoxic edema in the ischemic core and can be measured using manual or semi-automated segmentation across all slices 5, 2
Apparent Diffusion Coefficient (ADC) maps must be used alongside DWI to eliminate T2 "shine-through" effect and increase specificity 3
Perfusion-Weighted Imaging (PWI) demonstrates the total area of acute ischemia using dynamic susceptibility contrast-enhanced T2/T2*-weighted imaging 5, 2

For acute stroke (<6 hours), the American College of Emergency Physicians recommends measuring early ischemic changes on 5mm NECT slices, obtaining CTP to quantify core and penumbra, and using CTA-SI for whole-brain assessment if using CT 6, 1
For acute stroke (<6 hours), the American Academy of Neurology recommends measuring hyperintense lesion on DWI with ADC confirmation, obtaining PWI to identify mismatch, and calculating volumes using planimetric methods if using MRI 2, 3
For extended window (6-24 hours), multimodal imaging with perfusion assessment is essential, and measuring both core and total hypoperfusion to calculate salvageable tissue volume is recommended 8, 7

The American College of Radiology recommends never relying on visual estimation alone—use quantitative software for volumetric analysis, as visual assessment has only 70-80% accuracy 4
Account for gray-white matter differences when using perfusion thresholds, as baseline CBF values differ significantly between tissue types 6
Exclude large vascular structures from perfusion calculations, as vascular pixels contaminate mean CBF values 6
Do not use standard T2-weighted or FLAIR sequences for acute volume measurement—they detect <50% of acute strokes and are relatively insensitive compared to DWI 4, 3