Detection of thrombus size and protein content by ex vivo magnetization transfer and diffusion weighted MRI.
BACKGROUND
To utilize a rabbit model of plaque disruption to assess the accuracy of different magnetic resonance sequences [T1-weighted (T1W), T2-weighted (T2W), magnetization transfer (MT) and diffusion weighting (DW)] at 11.7 T for the ex vivo detection of size and composition of thrombus associated with disrupted plaques.


METHODS
Atherosclerosis was induced in the aorta of male New Zealand White rabbits (n = 17) by endothelial denudation and high-cholesterol diet. Subsequently, plaque disruption was induced by pharmacological triggering. Segments of infra-renal aorta were excised fixed in formalin and examined by ex vivo magnetic resonance imaging (MRI) at 11.7 T and histology.


RESULTS
MRI at 11.7 T showed that: (i) magnetization transfer contrast (MTC) and diffusion weighted images (DWI) detected thrombus with higher sensitivity compared to T1W and T2W images [sensitivity: MTC = 88.2%, DWI = 76.5%, T1W = 66.6% and T2W = 43.7%, P < 0.001]. Similarly, the contrast-to-noise (CNR) between the thrombus and the underlying plaque was superior on the MTC and DWI images [CNR: MTC = 8.5 ± 1.1, DWI = 6.0 ± 0.8, T1W = 1.8 ± 0.5, T2W = 3.0 ± 1.0, P < 0.001]; (ii) MTC and DWI provided a more accurate detection of thrombus area with histology as the gold-standard [underestimation of 6% (MTC) and 17.6% (DWI) compared to an overestimation of thrombus area of 53.7% and 46.4% on T1W and T2W images, respectively]; (iii) the percent magnetization transfer rate (MTR) correlated with the fibrin (r = 0.73, P = 0.003) and collagen (r = 0.9, P = 0.004) content of the thrombus.


CONCLUSIONS
The conspicuity of the thrombus was increased on MTC and DW compared to T1W and T2W images. Changes in the %MTR and apparent diffusion coefficient can be used to identify the organization stage of the thrombus.
Division of Imaging Sciences and Biomedical Engineering, King's College London, London, UK. alkystis.1.phinikaridou@kcl.ac.uk
Alkystis
A
Phinikaridou
Ye
Y
Qiao
Nick
N
Giordano
James A
JA
Hamilton
D000818:Animals; D001013:Aorta, Thoracic / Q000737:chemistry / Q000473:pathology*; D001018:Aortic Diseases / Q000175:diagnosis* / Q000378:metabolism; D003937:Diagnosis, Differential; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D058226:Plaque, Atherosclerotic / Q000737:chemistry* / Q000150:complications / Q000473:pathology; D011506:Proteins / Q000032:analysis*; D011817:Rabbits; D015203:Reproducibility of Results; D013927:Thrombosis / Q000175:diagnosis* / Q000209:etiology / Q000378:metabolism
D011506:Proteins