Abstract
BackgroundTo 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.MethodsAtherosclerosis 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.ResultsMRI 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.ConclusionsThe 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.
Highlights
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
The segments were fixed in 10% formalin overnight and transferred in phosphate-buffer saline (PBS) for ex vivo magnetic resonance imaging (MRI) followed by histology
MRI assignments were corroborated by histopathology (Figure 1E and 1F), Figure 1 Diffusion weighted and magnetization transfer contrast images distinguish the thrombus from the underlying plaque
Summary
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. MRI studies of thrombosis in experimental animals both in vitro [5] and in vivo [6], and histological evaluations of arteries from sudden death victims [7,8], have revealed compositional changes that occurred over variable time periods (days to weeks) during thrombus evolution. MRI has been successfully applied for detection of thrombus in hematoma [12,13], venous thrombosis [14,15], intraplaque hemorrhage [16,17], and arteries [6,18,19] by exploiting the T1-shortening effects of meth-hemoglobin. Meth-hemoglobin is usually formed in the acute stages of thrombosis because of the local hypoxic environment of occlusive thrombus but is not present during the chronic stage. A non-invasive, non-contrast enhanced imaging method to image thrombus characteristics may have significant diagnostic and therapeutic value
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