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Tissue characterisation of atherosclerotic carotid plaques by MRI
M Görtler1, A Goldmann, W Mohr
1Department of Neurology, University of Ulm, Germany.
Abstract:
Carotid artery plaques with intraplaque haemorrhage or atheromatous debris have been found to be associated with an increased risk of embolic stroke. Other methods have failed to detect plaque morphology, and it is not clear whether MRI allows differentiation between prognostically and therapeutically relevant plaque types. We examined 17 carotid bifurcation plaques which had been removed in toto by MRI. For quantifying MR signal intensities (I) the contrast-to-noise ratio (CNR) was used: (ITissue-IRef)/SDRef, with normal saline (0.9%) as reference (Ref) and the standard deviation (SD) of the noise. Measurements were correlated with the histopathological appearance of "simple plaques", consisting of fibrous intimal thickening, lipid deposits and/or atheromatous tissue with cholesterol crystals, largely calcified plaques, and "complicated plaques", containing recent intramural haemorrhage or friable atheromatous debris. Significantly different mean CNR could be measured in the three plaque types on T1- and T2-weighted sequences (p < 0.00001) and using the FLASH pulse sequence with a flip angle of 15 degrees (p < 0.001). With the T1-weighted sequence simple plaques showed a CNR of 4.4 +/- 2.3, calcified plaques -4.8 +/- 2.6 and complicated plaques 15.1 +/- 4.3. Using this technique, each single plaque could be correctly classified, an unalterable prerequisite for a clinical application. To date, motion artefacts due to patient movement or insufficiently triggerable vessel pulsation in combination with relative long acquisition times (6-7 min) have limited in vivo investigations. If these problems could be overcome, MRI might become a valuable technique for studying carotid plaque morphology.
Insights
Magnetic Resonance Imaging (MRI) can differentiate between carotid artery plaque types. This technique shows promise for identifying high-risk plaques associated with embolic stroke, aiding in better patient management.
Area of Science:
- Medical Imaging
- Neurology
- Cardiovascular Science
Background:
- Carotid artery plaques with intraplaque hemorrhage or atheromatous debris increase embolic stroke risk.
- Current methods struggle to detect plaque morphology, limiting differentiation of prognostically relevant plaque types.
- The utility of MRI in distinguishing between various carotid plaque types remains unclear.
Purpose of the Study:
- To investigate the capability of MRI in differentiating between various carotid bifurcation plaque types.
- To correlate MRI signal intensities with histopathological findings of plaque morphology.
- To assess the potential of MRI for classifying carotid plaques based on their composition.
Main Methods:
- Examination of 17 surgically removed carotid bifurcation plaques using MRI.
- Quantification of MR signal intensities using contrast-to-noise ratio (CNR).
- Correlation of CNR measurements with histopathological analysis of plaque types: simple, calcified, and complicated.
Main Results:
- Significantly different mean CNR values were observed for the three plaque types across T1- and T2-weighted sequences (p < 0.00001) and FLASH sequences (p < 0.001).
- On T1-weighted sequences, CNR values were: simple plaques 4.4 ± 2.3, calcified plaques -4.8 ± 2.6, and complicated plaques 15.1 ± 4.3.
- Each plaque was correctly classified using this MRI technique, demonstrating high accuracy.
Conclusions:
- MRI can effectively differentiate between simple, calcified, and complicated carotid artery plaques.
- The technique shows potential for classifying plaques based on morphology, which is crucial for predicting stroke risk.
- Overcoming challenges like motion artifacts and long acquisition times could establish MRI as a valuable tool for in vivo carotid plaque analysis.