Yoshimitsu Ohgiya1, Nobuyuki Ohike 2, Naomi Yagi 1, Hiroto Sasamori1, Jiro Munechika 1, Masanori Hirose 1, and Takehiko Gokan 1
1Showa University School of Medicine, Tokyo, Japan, 2Department of Pathology, Showa University Fujigaoka Hospital, Yokohama-shi, Japan
Synopsis
The
purpose of this study was to investigate whether 3D turbo spin-echo (TSE) SPACE
sequence can evaluate plaque characteristics of the carotid artery.
Mann-Whitney test was used to examine differences in the contrast ratio (CR)
between soft plaques and fibrous plaques on T1- and T2-weighted images. The
mean CR of the soft plaques (1.54 ± 0.25) was significantly higher than that of
the fibrous plaques (1.17 ± 0.13) (p < 0.001) on T1-weighted images. In
conclusion, T1-weighted TSE SPACE sequence can evaluate main components of
plaques in the carotid artery with high sensitivity and specificity.PURPOSE
To
investigate whether three-dimensional variable-flip-angle turbo spin-echo (SPACE)
sequence can evaluate plaque characteristics of the carotid artery.
METHODS
This
study included 18 consecutive patients (17 men, 1 woman; mean age, 71.1 years)
who underwent T1- and T2-weighted SPACE sequences and carotid endarterectomy
from June 2013 to May 2014. All MRI examinations were performed using a 1.5-T
MR scanner (MAGNETOM Essenza; Siemens Medical Solutions, Erlagen, Germany).
T1-weighted SPACE (repetition time ms/echo time ms/ flip angle/ turbo factor =
784/13/variable/37; voxel size, 1.0 × 1.0 × 1.0 mm3; field of view, 253 mm;
GRAPPA factor, 2; Acquisition time, 3 min 47 sec) and T2-weighted SPACE
(1400/193/variable/95; voxel size, 1.0 × 1.0 × 1.0 mm3; field of view, 253 mm;
GRAPPA factor, 2; Acquisition time, 4 min 47 sec) sequences were performed in
the neck including the bilateral internal carotid arteries. Signal intensities
of the plaque and adjacent muscle were measured on T1- and T2-weighted images.
Contrast ratio (CR) was calculated by dividing the signal intensity of the
plaque by that of the muscle. A pathologist measured areas of lipid/necrotic
core, hemorrhagic components, fibrous tissue, and calcification. The plaques
were classified into two types: soft plaque consisting of lipid core and/or
hemorrhagic components more than 50%; and fibrous plaque consisting of fibrous
tissue and/or calcification more than 50%. Mann-Whitney test was used to
examine differences in the CR between soft plaques and fibrous plaques on T1-
and T2-weighted images.
RESULTS
Microscopic
examination of endarterectomy specimens revealed 13 soft plaques and 5 fibrous
plaques. Table 1 shows the CRs of the carotid plaques to adjacent muscle on
T1-weighted SPACE and T2-weighted SPACE images. The mean CR of the soft plaques
(1.54 ± 0.25) was significantly higher than that of the fibrous plaques (1.17 ±
0.13) (p < 0.001) on T1-weighted images (Fig 1-3). There was no significant
difference in the mean CR between the soft plaques (2.31 ± 1.07) and the
fibrous plaques (2.33 ± 0.98) on T2-weighted images. When the CR cut-off value
was set at 1.28, soft plaques were diagnosed with 92.3% sensitivity, 80.0%
specificity, and 88.8% accuracy (Fig 4).
DISCUSSION
Plaque
MR imaging is typically performed using 2D turbo spin-echo (TSE) sequence,
which offers flexible tissue contrast, less sensitivity to magnetic field
inhomogeneities, and high signal-to-noise ratio (SNR). A common problem in 2D
imaging is the poor spatial resolution in the slice-select direction, making
images more prone to the partial volume effect and obscurity of fine plaque
structures. In contrast, 3D imaging has several advantages. 1) Intrinsically high
SNR that may be traded for high spatial resolution. 2) Improved anatomic
coverage via a longitudinal acquisition. 3) Capability of retrospective
visualization of vessel wall from arbitrary angle using MPR. In our study, the
main components of the carotid plaque were distinguished with high sensitivity
and specificity by using SPACE sequence. This is because the T1-weighted SPACE
sequence has T1 contrast and an inherent black-blood effect due to variable
flip angles. In the discrimination of soft plaques from fibrous plaques, the
sensitivity and specificity of T1-weighted SPACE sequence in our study were
comparable with previous reports (79%-96% and 84%-100%, respectively) 1-6). The
T2-weighted SPACE sequence was not useful to distinguish soft plaques from
fibrous plaques, partly because TR was shorter than usual TR (e.g. 3000 msec).
CONCLUSION
T1-weighted
SPACE sequence can evaluate main components of plaques in the carotid artery
with high sensitivity and specificity.
Acknowledgements
No acknowledgement found.References
1. Yoshida K, Narumi O, Chin M,
et al. Characterization of Carotid Atherosclerosis and Detection of
Soft Plaque with Use of Black-Blood MR Imaging. AJNR Am J Neuroradiol.
2008;29(5):868-874.
2. Watanabe Y, Nagayama M, Suga
T, et al.Characterization
of atherosclerotic plaque of carotid arteries with histopathological
correlation: vascular wall MR imaging vs. color Doppler ultrasonography (US). J
Magn
Reson
Imaging. 2008;28(2):478-485.
3. Cappendijk
VC, Cleutjens
KBJM, Kessels
AGH, et al. Assessment of Human Atherosclerotic Carotid Plaque Components with Multisequence
MR Imaging: Initial Experience. Radiology. 2005;234(2):487-492.
4. Narumi S, Sasaki M, Ohba
H, et al. Prediction of Carotid Plaque Characteristics Using Non-Gated MR
Imaging: Correlation with Endarterectomy Specimens. AJNR Am J Neuroradiol.
2013;34(1):191-197.
5. Chu B, Kampschulte
A, Ferguson MS, et al. Hemorrhage in the Atherosclerotic Carotid Plaque: A
High-Resolution MRI Study. Stroke. 2004;35(5):1079-1084.
6. Yuan C, Mitsumori
LM, Ferguson MS, et al. In Vivo Accuracy of Multispectral Magnetic Resonance Imaging
for Identifying Lipid-Rich Necrotic Cores and Intraplaque
Hemorrhage in Advanced Human Carotid Plaques. Circulation. 2001;104(17):2051-2056.