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Updated: Jun 10, 2026
Integrated Photoacoustic, Ultrasound, and Angiographic Tomography (PAUSAT) for NonInvasive Whole-Brain Imaging of Ischemic Stroke
Published on: June 2, 2023
A simple positron emission tomography-based calibration for perfusion-weighted magnetic resonance maps to optimize
Olivier Zaro-Weber1, Walter Moeller-Hartmann, Wolf-Dieter Heiss
1Max Planck Institute for Neurological Research, Gleueler Str 50, 50931 Cologne, Germany. zaroweber@nf.mpg.de
Background And Purpose:
Perfusion-weighted (PW) MRI is increasingly used to identify the tissue at risk. The adequate PW-MRI map and threshold remain controversial due to a considerable individual variation of values. By comparative positron emission tomography, we evaluated a simple MR-based and positron emission tomography-validated calibration of PW maps.
Methods:
PW-MRI and quantitative positron emission tomography (15O-water) of patients with acute stroke were used to calculate averaged as well as individual thresholds of penumbral flow (positron emission tomography cerebral blood flow (<20 mL/100 g/min) for maps of time to peak, mean transit time, cerebral blood flow, and cerebral blood volume. A linear regression analysis studied the variability of the individual thresholds using 3 different PW reference regions (hemispheric, white matter, gray matter). The best model was used for volumetric analysis to compare averaged and scaled individual thresholds and to calculate look-up tables for PW maps.
Results:
In 26 patients, the averaged thresholds were (median/interquartile range): cerebral blood flow 21.7 mL/100 g/min (19.9 to 32); cerebral blood volume 1.5 mL/100 g (0.9 to 1.8); mean transit time seconds 5.2 (3.9 to 6.9); and relative time to peak 4.2 seconds (2.8 to 5.8). The large individual variability was best explained by the mean value of the hemispheric reference derived from a region of interest on a level with the basal ganglia of the unaffected hemisphere (R(2): cerebral blood flow 0.76, cerebral blood volume 0.55, mean transit time 0.83, time to peak 0.95). Hemispheric reference-corrected thresholds clearly improved the detection of penumbral flow. Look-up tables were calculated to identify the individual thresholds according to the hemispheric reference value.
Conclusions:
The individual variation of PW values, even if calculated by deconvolution, remains a major obstacle in quantitative PW imaging and can be significantly improved by a simple MR-based calibration. Easily applicable look-up tables identify the individual best threshold for each PW map to optimize mismatch detection.
Insights
Individual variations in perfusion-weighted MRI (PW-MRI) values hinder accurate stroke assessment. A simple MR-based calibration using hemispheric reference values significantly improves the detection of tissue at risk by optimizing thresholds.
Area of Science:
- Neuroimaging
- Radiology
- Stroke Imaging
Background:
- Perfusion-weighted (PW) MRI is crucial for identifying tissue at risk in acute stroke.
- Significant individual variability in PW-MRI values complicates accurate interpretation and threshold setting.
Purpose of the Study:
- To evaluate a simple MR-based calibration method for PW maps, validated by positron emission tomography (PET).
- To improve the accuracy of identifying the ischemic penumbra in acute stroke patients.
Main Methods:
- Quantitative PET (15O-water) and PW-MRI were performed in acute stroke patients.
- Individual thresholds for penumbral flow were calculated and analyzed for variability using different PW reference regions.
- Linear regression identified the best model for calibration, leading to volumetric analysis and look-up table generation.
Main Results:
- Averaged thresholds for cerebral blood flow, cerebral blood volume, mean transit time, and time to peak were established.
- Individual variability in PW values was significantly explained by the hemispheric reference region (R² values up to 0.95).
- Hemispheric reference-corrected thresholds improved penumbral flow detection, with generated look-up tables for individual threshold identification.
Conclusions:
- Individual variability in PW-MRI values is a significant challenge in quantitative imaging.
- A simple MR-based calibration using hemispheric reference values effectively improves accuracy.
- Easily applicable look-up tables enable optimized mismatch detection by identifying individual thresholds for PW maps.
