Previous studies have demonstrated that carotid intraplaque hemorrhage (IPH) is highly associated with neurovascular events1 and type I (fresh) hemorrhage is more prevalent in symptomatic arteries compared to asymptomatic arteries2. The IPH is identified successfully using T1 weighted image3. However the age of IPH is difficult to depict using existing techniques.
This study sought to distinguish type I (fresh) and type II (recent) hemorrhage in ex vivo carotid atherosclerotic plaques using a gradient echo (GRE) based MR sequence.
Five ex vivo carotid endarterectomy (CEA) specimens were imaged on a 3T MR scanner (Philips Achieva) after formalin fixation. Firstly, a GRE sequence was optimized with different echo time (from 4.1ms to 9.1ms) to obtain the greatest contrast between type I and type II hemorrhages which were verified by histology. Secondly, four contrast MR weightings including T1 weighted (T1W), T2 weighted (T2W), Proton density weighted (PDW) and GRE with optimized parameters (Table 1) were acquired. Histology specimens were stained using hematoxylin and eosin (H&E) and Mallory’s trichrome at the location according to MRI slices. The histologist, blinded to the MR images, outlined IPH regions. Morphological features of lumen, vessel wall, and the relative position of external carotid and internal carotid on histology were used for registration. The regions on MR images corresponding to type I and type II hemorrhage on histological slides were mapped by a trained reviewer. The CNR was compared between these regions.
For optimizing the parameters of GRE sequence, we found that regions of type I hemorrhage grew darker as echo time increased (Figure 1). This indicates that type I hemorrhage has a shorter T2* than other tissues in atherosclerotic plaque. Considering the susceptibility effect due to long echo time, an echo time of 9.1ms was used to balance the image contrast and quality. Sample images acquired by T2, PD, T1 and GRE sequences are shown in Figure 2, with corresponding H&E and Mallory stained slices. The images obtained by the GRE sequence show the best correspondence to histology for tissue boundaries and delineation. 37 type I hemorrhage regions and 14 type II hemorrhage regions were identified to calculate the CNR between type I and type II hemorrhage. CNR for different image contrasts is listed in Table 2. The GRE sequence obtained the best CNR for all protocols. This sequence should be verified in vivo in the future.
Open Access This article is published under license to BioMed Central Ltd. This is an Open Access article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Li, R., Zhao, X., Ferguson, M.S. et al. Distinguishing type I and type II hemorrhage by gradient echo based MR sequence in carotid atherosclerotic plaques.
J Cardiovasc Magn Reson12
(Suppl 1), T12 (2010). https://doi.org/10.1186/1532-429X-12-S1-T12