Introduction MRI plays a significant role in the post embolization follow-up of patients who have undergone coil embolization of cerebral aneurysms. We have utilized a rat aneurysm model to study the aneurysm healing process. Based on the extrapolation of signal characteristics of endovascular thrombus in humans, we have determined that gradient echo sequences (T2* weighted images) would be the optimal method to quantify amount of endoluminal thrombus. We aim to correlate the MRI findings with histopathological findings in this experimental rat aneurysm model.

Methods This experimental aneurysm study in a rat model was approved by the University Committee on Use and Care of Animals. Male Sprague Dawley rats were anesthetized with transperitoneal injection of 50–60 mg/kg pentobarbital. In each animal an artificial aneurysm was created by permanent ligation of the rat external carotid artery (ECA) 5 mm from the carotid bifurcation (ECA blind pouch aneurysm). Subsequently a 5 mm coil segment was inserted into this aneurysm by an arteriotomy and then a ligature was placed proximal to the arteriotomy. Five rat aneurysms were treated with platinum coils and five others were treated with hydrocoils. 14 days post-treatment, animals underwent MRI analysis of the treated aneurysms as well as being sacrificed for histopathological analysis. The volume of the thrombus formation was calculated by measuring the maximal area (ROI) of blooming artifact × slice thickness (mm)/matrix (256) using NIH Image J software version 1.43U. The histological specimens were studied under high-field microscope and thrombus formation was demarcated following staining. Measurements were performed on the MR images and histological specimens independently in a blinded fashion. The measured values on MRI and histological sections were then analyzed using the Pearson correlation coefficient (PCC) by SPSS V.15.0.

Results Our results demonstrate a significant correlation between the extent of luminal thrombus formation on histology and signal characteristics on T2* GRE MRI sequences when the rats were treated with bare platinum coils PCC=0.987 (p=0.002). The hydrogel coated coils did not show MR correlation with area of thrombus formation PCC=0.344 (p=0.571).

Conclusion We report the first correlation extent of luminal thrombus formation on histology with signal characteristics on T2* GRE MRI sequences in a rat aneurysm model. Our hypothesis of direct correlation between the above mentioned variables holds true in the bare platinum coil group and not in the hydrocoil group. Such positive correlation could allow for non-invasive evaluation of treated experimental aneurysm models.

Competing interests None.