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VP Watch – September 25, 2002 – Volume 2, Issue 38
Multicontrast MRI for Classification of Human
David Saloner, PhD
VA Medical Center, University of California San Francisco
There has been a steady improvement in
the quality of MR methods for assessing
A number of ex vivo studies have
validated the abilities of MRI using
histology as the gold standard
particularly in studies of carotid disease
where a surgical specimen is available
MR Imaging of Atherosclerosis
A powerful feature of MRI is the ability to
obtain images with different weighting of
the physiological composition of the soft
tissue in the atheroma 4-5
Recent studies have shown that major
components of plaque can be
characterized in vivo and that this
determination is aided by acquiring several
sequences with different contrast
In Vivo MRI of Plaque
MRI is able to assess both the lumenal contours (using
bright blood MRA methods) and the composition of the
atheroma (using black blood spin echo methods)
Fig.1 Contrast-enhanced MR angiogram of carotid bifurcation showing multiple projections
of the 3D data and reformations in the common, most stenotic ICA, and distal ICA.
Most investigators report good success in
imaging atheroma using double inversion
black blood methods which effectively null
all signal from flowing blood 6
High sensitivity coils are important for
obtaining acceptable image quality 7
A classification scale has been developed by
the AHA to categorize atherosclerotic lesions
into different classes of complexity 8
Reported this week in VP Watch: Cai et al
performed a blinded study to determine
whether readers who categorized lesions into
different categories on the basis of multi
contrast in vivo MRI were in agreement with
classification performed on those lesions
following endarterectomy surgery 9
Atherosclerosis Classification Scales
Sixty consecutive patients scheduled for
endarterectomy surgery were recruited to the
Patients were imaged within one week prior to
MR imaging was performed from 2cm proximal
to the flow divider to 2cm distal to the flow
Patients and Imaging
Four image contrasts were obtained: 3D TOF;
T1 -weighted double IR 2D Fast Spin Echo; and
a shared echo PD-weighted and T2-weighted
Fast Spin Echo.
Fat suppression was used.
Typical acquired resolution was 0.5mm x
0.5mm x 2mm.
Endarterectomy specimens were sectioned and
stained with Mallory’s trichrome and H&E.
MR images were reviewed and classified by a
blinded reader as were the histological slices.
Comparisons were made of 4 - 6 levels per
Comparison of in vivo MRI and histology
• MRI correctly classified lesion types in 80.2% of
Lesion type Sensitivity Specificity
Type I-II 67% 100%
Type III 81% 98%
Type IV-V 84% 90%
Type VI 82% 91%
Type VII 80% 94%
Type VIII 56% 100%
High resolution MRI has good abilities in
characterizing intermediate to advanced
This capability is of high importance for the
conduct of longitudinal studies designed to
determine the natural progression of
atherosclerosis or the response of
atherosclerosis to pharmacologic
Multi center studies are needed to
demonstrate the generalizability of these
Better methods are needed to improve spatial
resolution - in particular 3D methods for
providing reduced partial voluming and
multiplanar reformatting abilities.
Blood products have variable signal
appearances and methods for identifiying
these should be pursued.
More time-efficient methods would be helpful.
The application of extravascular and
intravascular contrast agents should provide
additional information on plaque composition.
• Is MRI/A able to assess the lumenal surface,
the plaque composition, or both?
• What is an important advantage of studying
the carotid territory in defining the utility of
• What are typical spatial resolution
capabilities of MRI?
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for identifying lipid-rich necrotic cores and intraplaque hemorrhage in advanced
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resolution imaging of the carotid arteries. J Magn Reson Imaging, 1996. 6(1): p.
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9. Cai, J-M, Hatsukami, T, Ferguson, M et al Classification of Human Carotid
Atherosclerotic Lesions With In-Vivo Multicontrast Magnetic Resonance
imaging. Circulation, 2002. 106: p 1368-73