Diffusion-weighted magnetic resonance imaging for the detection of lipid-rich necrotic core in carotid atheroma in vivo.
BACKGROUND
Research has shown that knowing the morphology of carotid atheroma improves current risk stratification for predicting subsequent thrombo-embolic events. Previous magnetic resonance (MR) ex vivo studies have shown that diffusion-weighted imaging (DWI) can detect lipid-rich necrotic core (LR/NC) and fibrous cap. This study aims to establish if this is achievable in vivo.


METHODS
Twenty-six patients (mean age 73 years, range 54-87 years) with moderate to severe carotid stenosis confirmed on ultrasound were imaged. An echo-planar DWI sequence was performed along with standard high-resolution MR imaging. Apparent diffusion coefficient (ADC) maps were evaluated. Two independent readers reported the mean ADC values from regions of interest defining LR/NCs and fibrous caps. For subjects undergoing carotid endarterectomy (n = 19), carotid specimens were obtained and stained using Nile red.


RESULTS
The mean ADC values were 1.0 × 10(-3) mm(2)/s (±SD 0.3 × 10(-3) mm(2)/s) and 0.7 × 10(-3) mm(2)/s (±SD 0.2 × 10(-3) mm(2)/s) for fibrous cap and LR/NC, respectively; the difference was significant (p < 0.0001). The intra-class correlation coefficients summarising the agreement between the two independent readers were 0.84 and 0.60 for fibrous cap and LR/NC, respectively. Comparison of quantitative ADC values and histology (by subjective grading of lipid content) showed a significant correlation: heavier lipid staining matched lower ADC values (r = -0.435, p = 0.005).


CONCLUSIONS
This study indicates that DWI can be used to distinguish LR/NC and the fibrous cap. The study also suggests that the mean ADC value may be linearly related to subjective graded LR/NC content determined by histology.
Young
Victoria Eleanor
VE
University Department of Radiology, Addenbrooke's Hospital, Box 218, Hills Road, Cambridge, CB2 0QQ, UK. vy207@cam.ac.uk
Patterson
Andrew J
AJ
Sadat
Umar
U
Bowden
David J
DJ
Graves
Martin J
MJ
Tang
Tjun Y
TY
Priest
Andrew N
AN
Skepper
Jeremy N
JN
Kirkpatrick
Peter J
PJ
Gillard
Jonathan H
JH
D000368:Aged; D000369:Aged, 80 and over; D002340:Carotid Artery Diseases / Q000378:metabolism* / Q000473:pathology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D050356:Lipid Metabolism; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009336:Necrosis / Q000378:metabolism / Q000473:pathology; D058226:Plaque, Atherosclerotic / Q000378:metabolism* / Q000473:pathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity