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Echo time [ms]
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In Vivo T2-mapping and Segmentation of Carotid
Artery Plaque Components Using Magnetic
Resonance Imaging at 1.5T
Bartosz Proniewski1,2, Tomasz Miszalski-Jamka1, Przemysław Jaźwiec1
1Department of Clinical Radiology and Imaging Diagnostics, 4th Military Hospital, Wroclaw, Poland
2AGH University of Science and Technology in Krakow, Poland
1 Introduction
2 Materials & Methods
4 Conclusions
Atherosclerosis is regarded as a lifestyle disease, where artery lumen is reduced due to
deposition of calcium and fatty materials such as cholesterol and triglyceride. These
plaques can become unstable and rupture, resulting in life threatening cardiovascular
events. Multicontrast cardiovascular magnetic resonance (CMR) has been used on 1.5T
and 3T scanners to identify carotid plaques and study their morphology in vivo, however it
does not provide quantitative information.
Protocol for all multi-contrast images
acquired started with a 3D TOF sequence.
Based on the thin MIP reconstruction,
bifurcation of the carotid arteries can be
easily localized. In order to help match the
corresponding plaque features, multicontrast
images were co-registered, so that inner and
outer vessel boundaries detected on T1W
images could then be superimposed on PDW
and T2W images.
Multicontrast imaging of the carotid arteires can be extended to support quantitative
measurements by using T2 relaxation time mapping. Applying a technique similar to
Biasiolli et al. [1], it is possible to analyze plaque components in vivo at 1.5 T. Certain
quality constraints need to be taken into account, and due to lower magnetic field
stenght, more averages need to be acquired.
In the near future, the MATLAB algorithms developed for T2 mapping will be adapted
for the use in Osirix.
3 Results
Carotid arteries of a healthy volunteer and patients with indications of atherosclerosis were
imaged on a 1.5 T Siemens Aera scanner (Siemens Healthcare). A standard phased-array
head-neck Siemens RF coil was used for imaging.
To perform T2 mapping images were acquired using a Multiple-Spin-Echo sequence,
resulting in a set of images with different TE times.
References:
[1] Biasiolli L et al. J Cardiovasc Magn Reson 2013;15:69-78.
Relaxation time is an inherent property of the tissue being imaged and can be used to
provide quantitative information regarding the plaque composition.
Plaque component T2w T1w PDw TOF
Hemorrhage +/- ++ +/- ++
Lipid core +/-- -- ++ +/-
Necrosis +++ -- ++ --
Fibrous tissue +/- +/- ++ -
Calcification -- -- -- --
Tissue contrast is relative to muscle; with FAT SAT
Table 1. Plaque components perception on multicontrast images.
MR SEQUENCE T1w T2w PDw 3D TOF
Readout sequence FSE FSE FSE GRE
TR [ms] 1R-R 3R-R 3R-R 23
TE [ms] 11 48 12 4.57
ETL [ms] 11 19 8 n.a.
Flip angle [deg] 180 180 180 20
Averages 1 1 1 1
FOV [cm] 133x80 210x280 210x280 200x151
Matrix 212x128 336x448 336x448 314x640
In plane resolution 0.6x0.6 0.6x0.6 0.6x0.6 0.3x0.3
No slices 12 12 6 156
Slice thickness [mm] 2 2 2 1
Flow suppression DIR, TI=330ms Inflow Inflow Veins
Scan time [min] 4:33 5:32 6:36 6:03
In some cases more averaging/less slices was used.
Table 2. Sequences used for multicontrast imaging of the carotid arteries.
Inner and outer vessel wall have been manually drawn on the Multi-SE series images.
Voxels were manually selected from all the T2 maps to represent a specific tissue using
multicontrast CMR as a guide, i.e. they were chosen inside a plaque component
identified on multicontrast CMR.
SI=β*exp(-TE/T2)
28 ms
42 ms
56 ms
70 ms
84 ms
98 ms
112 ms
Segmentation was carried out using k-means clusters, assuming 3 classes of tissue. Using
this method, mean ± SD of the T2 values of voxels classified as LRNC (black), fibrous tissue
(grey) and recent IPH (white) were calculated to be 24(8), 48(12) and 80(30) ms,
respectively.
3D Time-of-Flight MIP
Multiple-Spin-Echo
TE=14ms
T2 Map generated
within the vessel wall
K-Means segmented
vessel wall