Huiyu Qiao1, Haikun Qi1, Dongye Li1,2, Dongxiang Xu3, Huijun Chen1, Chun Yuan1,3, and Xihai Zhao1
1Center for Biomedical Imaging Research, Department of Biomedical Engineering, Tsinghua University, Beijing, China, 2Center for Brain Disorders Research, Capital Medical University, Beijing, China, 3Department of Radiology, University of Washington, Seattle, WA, United States
Synopsis
This study sought to investigate the
usefulness of in vivo T1 mapping in quantitative classification of compositions
and vulnerability of carotid artery atherosclerotic plaques. We found that it
is feasible to quantify the T1 values of atherosclerotic plaque compositions in
carotid artery with in vivo T1 mapping. Significant differences in T1 values
between fibrous tissue and other plaque compositions indicate that it is
possible to classify plaque compositional features using T1 mapping. In
addition, our findings of IPH and LRNC with significant different T1 values
from other plaque compositions suggest the potential of T1 mapping in
classification of plaque vulnerability.
Introduction
Vulnerability of carotid artery atherosclerotic plaques is associated with
ischemic stroke. Histologically, vulnerable plaques are characterized by
presence of intraplaque hemorrhage (IPH), large lipid-rich necrotic core (LRNC)
or fibrous cap rupture.
1,2 Therefore, it is important to
characterize carotid vulnerable plaques prior to occurrence of cerebrovascular events. Currently, MR
multi-contrast vessel wall imaging has been demonstrated to be an ideal
non-invasive modality to identify plaque compositions.
3 However,
this technique is time consuming and its quantitative analysis is heavily dependent
on reviewer’s experience. Recently, T1 mapping has been utilized in tissue
quantification in ex-vivo intracranial atherosclerotic plaques.
4,5
However, the capability of T1 mapping in classification of carotid plaque
vulnerability is unknown.
This study sought to investigate the usefulness of in
vivo T1 mapping in assessing compositions and vulnerability of carotid artery
atherosclerotic plaques.Methods
Study sample: Forty-five carotid atherosclerotic plaques
from 24 symptomatic subjects (mean age, 65.0 ± 7.8 years; 20 males) were
recruited and underwent MR imaging. The study protocol was approved by institutional review board and the written consent form was obtained from each patient. MR Imaging: All
carotid arteries were imaged on 3.0T MR scanner (Achieva TX, Philips
Healthcare) with a custom-designed 36-channel cerebrovascular coil or an
8-channel carotid coil. Multi-contrast MR vessel wall imaging and GOAL-SNAP6 imaging
were performed with the parameters in Table 1. The GOAL-SNAP image series along
the IR curve were reconstructed using sliding window and KWIC method7,
similar to the previous study.6 Then, T1 map can be
estimated from the IR image series.6 Image Analysis: Reconstructed
GOAL-SNAP images were reformatted to 2mm axial slice with the same geometry to
T1-QIR for analysis. All MR images were reviewed by two radiologists with >5
years’ experience in cardiovascular MR imaging using “CASCADE” (UW, Seattle,
USA). The boundaries of lumen, outer wall and plaque components were outlined
on each slice. All outlined regions of each slice were exported to a mask
in which lumen, fibrous tissue, LRNC, calcification, IPH and loose matrix were labeled
as different values. T1 fitting was performed on the
marked regions and mean T1 values of different regions were calculated for each
slice. Statistical Analysis: The T1 values of all plaque
components were compared using One Way ANOVA test.Results
Of 586 slices with acceptable image quality from 24 subjects, 302
(51.5%) had LRNC, 134 (22.9%) had calcification, 136 (23.2%) had IPH, and 145
(24.7%) had loose matrix. The T1 values for fibrous tissue and all plaque
components are detailed in Figure 1. Among all components, IPH showed the
shortest T1 value (958.5 ± 394.3 ms) and the loose matrix had the longest T1 value
(1508.7 ± 455.1 ms) (all p<0.001). The T1 value of LRNC (p=0.038) and calcification
(p=0.037) was significantly longer than that of fibrous tissue. No significant
difference in T1 value was found between LRNC and calcification (p=0.440).
Typical carotid atherosclerotic plaque images of multi-contrast vessel wall
and T1 mapping are shown in Figure 2 and 3.Discussion and Conclusion
It is feasible to quantify the T1 values of
atherosclerotic plaque compositions in carotid artery in vivo with MR imaging.
The significant differences in T1 values between fibrous tissue and all plaque
compositions indicate that it might be possible to classify plaque
compositional features using T1 mapping. In addition, our findings of IPH and
LRNC with significant different T1 values from other plaque compositions
suggest the potential of T1 mapping in characterizing carotid plaque
vulnerability. In the present study, the overlap of T1 values
between LRNC and calcification might be due to the partial volume effects,
complexity of microstructure of LRNC and calcification, and susceptibility. Histological
validation of capability of T1 mapping in identification of plaque compositions
is warranted in future studies.
Acknowledgements
This study is supported by a grant of National Natural Science Foundation of China (81771825).References
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