Magnetic Resonance Imaging On Transient Focal Cerebral Ischemia And Thrombus In Carotid Artery System In Rabbits And Human

PartⅠ: Quality control for improving the successful rate of intraluminal thread approach in making focal cerebral ischemic reperfusion model in rabbits and evaluation of image featuresObjective: To approach establishment of controllable quantified index so as to improve the successful rate of intraluminal thread approach in making focal cerebral ischemic reperfusion model in rabbits.Methods: Forty-five New Zealand white rabbits were randomly divided into three groups :A, B and C. Group A (n=5) was sham-operated. Group B (n=10), CT angiography(CTA)and digital subtraction angiography(DSA)of carotid arteries were firstly performed to observe the gross morphology of carotid arteries, and then anatomical measurement of carotid arteries were performed after the focal cerebral ischemia reperfusion model were made. Group C (n=30) underwent an operation of focal cerebral ischemic reperfusion brain injury, the rabbits were subjected to 7 minutes (n=10), 15 minutes (n=10) and 30 minutes (n=10) of temporary middle cerebral artery occlusion, the diffusion weighted MR imaging (DWI) and perfusion weighted MR imaging (PWI) were performed.Results: DSA and CTA could show the course and branches of carotid arteries clearly. The controllable quantified indexes by anatomical measurement of internal carotid artery were established, the successful rate was 82.5%.Conclusion: Establishing quantified indexes can obviously impprove the successful rate and operation of intraluminal thread approach in making focal cerebral ischemia model in rabbits. PartⅡ: Ischemic lesions on Magnetic Resonance Imaging and histological outcomes after different transient periods of focal ischemia in rabbitsObjective: The purposes of this study were to investigate the time course of ischemic changes on Magnetic Resonance Imaging(including DWI, PWI and T2-WI) after different transient periods of focal brain ischemia in rabbits and to evaluate the histopathological outcomes in the regions of DWI abnormalities. Repeated measurements of DWI after transient periods of focal ischemia could provide useful information for diagnosis and treatment strategies of TIA patients.Methods: Sixty rabbits were subjected to 7 minutes (n=15); 15 minutes (n=15); 30 minutes (n=15) of temporary middle cerebral artery occlusion ; and sham operation (n=15). Magnetic Resonance Imaging (including DWI, PWI and T2-WI) were performed during before occlusion; 5min after occlusion and at 0.5, 2.0, 6.0, 12, 24, 48, and 72 hours after reperfusion. After the last MRI study at 72 hours after reperfusion, the brains were evaluated by histopathology and immunocytochemistry.Results: No MRI or histological abnormalities were observed in the sham-operated rabbits. In the 7-minute, 15-minute and 30-minute groups, the perfusion deficits and DWI hyperintensities that occurred during occlusion disappeared shortly after reperfusion. The DWI, PWI, and T2-WI results remained normal thereafter in the 7-minute group, whereas secondary DWI hyperintensity and T2-WI abnormalities developed at the 6~12 hour observation point in the 15-minute and 30-minute groups. Histological examinations demonstrated neuronal necrosis in three groups, but the number of necrotic neurons was significantly higher in the 15-minute and 30-minute groups than in the 7-minute group (P <0.001).Conclusions: Transient or permanent resolution of initial DWI lesions after reperfusion depends on the duration of ischemia. Transient resolution of DWI lesions is associated with widespread neuronal necrosis; moreover, permanent resolution of DWI lesions does not necessarily indicate complete salvage of brain tissue from ischemic injury. These results may help to explain the neurological deficits in some patients who have normal DWI results after cerebral ischemia and cognitive deficits in some patients who have experienced transient ischemic attacks.PartⅢ: Molecular magnetic resonance imaging of red and white emboli in middle cerebral artery with EP-2104R in rabbitsObjective: Embolic occlusion of the cerebral artery is one of the major causes of ischemic stroke, and the middle cerebral artery (MCA) is the most common culprit artery. Such emboli present in human in forms of either red emboli which is rich in erythrocyte and contains some fibrin, or white emboli which is rich in fibrin. EP-2104R, a fibrin-targeted contrast agent, has been shown to allow selective visualization of thrombi or/and thrombosis in coronary, pulmonary, carotid arteries and left atrial appendage with MR imaging in experimental animal models. In the present study, we attempted to evaluate the application of EP-2104R into molecular magnetic resonance imaging of red and white emboli in the MCA in rabbits.Methods: The red and white emboli were engineered ex vivo from human blood approximately 24 hours previously . Sixteen male New Zealand White rabbits weighing 2.5 to 3.0 kg were randomly divided into 4 groups, EP-2104R groups (red and white emboli; n=5, respectively) and Gd-DTPA control groups(red and white emboli; n=3, respectively). Under angiography, a 3F catheter was advanced into the proximal part of the left internal carotid artery (ICA). Each group was used for occlusion of the middle cerebral artery(MCA) with 2 either red or white emboli. The emboli had a diameter of 1.0 to 1.5 mm. Subsequent molecular MR imaging was performed with T1-FLAIR and T1-weighted double-inversion recovery (DIR) fast spin echo sequences before and after systemic administration of EP-2104R or Gd-DTPA. Animals were humanely killed immediately after MRI (100 mg/kg IV sodium pentobarbital) and followed by autopsy, and the thrombi were examined.Results: Under the microscopic examination, red emboli consisted of closely packed erythrocytes within a sparse fibrin net ; white emboli consisted of a dense mass of fibrin with only few other blood cells. MR images were analyzed by 2 neuroradiologists, and contrast-to-noise ratio(CNR) in the emboli were assessed. Before contrast media application, no thrombi were visible. After contrast EP-2104R administration, all emboli, regardless of red or white types, were selectively visualized as white spots. But, CNR of the red emboli appeared lower than white emboli, this result might be explained by the fact that there are closely packed erythrocytes within a sparse fibrin net in the emboli which decreases the proportion taken up by the contrast. CNR of the white emboli showed higher than that of red emboli, which might be due to the emboli consisted of a dense mass of fibrin and a few blood cells. In comparison, Gd-DTPA did not significantly improve detection of red and white emboli. Respective localization of emboli all matched the findings seen at autopsy. Conclusions: Molecular MR imaging with the fibrin-targeted contrast-agent EP-2104R allows selective visualization of red and white emboli in middle cerebral artery in rabbitsPartⅣ: Molecular magnetic resonance imaging of Acute and Subacute Thrombus in carotid artery with EP-2104R in rabbitsObjective: Carotid arterial thrombosis plays a critical role in acute ischemic stroke. Therefore, the ability to detect thrombus in vivo has a significant clinical implication. We sought to evaluate the use of a fibrin-targeted contrast agent (EP-2104R) for MR thrombus detection and to compare this modality with non–contrast-enhanced(NCE) MRI and with Gd-DTPA injection in acute and subacute period after thrombus generation.Methods: The carotid artery thrombosis was induced by external injury and stasis in 10 rabbits.MR images were analyzed by 2 neuroradiologists, and contrast-to-noise ratio(CNR) in the carotid artery thrombosis were assessed. MRI was performed before and after contrast agent injection at 6 hours group and 6 day group after injury. Correlation with histopathology was performed.Results: The fibrin-targeted contrast agent accurately detected all thrombi. Gd-DTPA injection was not associated with an improvement of thrombus detection. EP-2104R was superior to both NCE and Gd-DTPA injection (P<0.001).Conclusions: In an experimental animal model of carotid thrombosis, we have demonstrated the superiority of a fibrin-targeted MR contrast agent for in vivo detection of acute and subacute thrombus, compared with NCE MRI and Gd-DTPA injection.PartⅤ: The relationship between DWI-detected findings and clinical factors in patients with transient ischemic attackObjective: To evaluate the diagnostic values of diffusion-weighted MRI(DWI),determine frequency of DWI acute ischemic lesions and the correlation with DWI acute ischemic lesions and clinical factors in patients with transient ischemic attack (TIA).Methods: Clinical, conventional MRI, and DWI data were collected on 126 consecutive patients with TIA from March to December 2006 within 7 days of symptom onset. The relationship between DWI-detected findings and clinical presentation was then analyzed.Results: DWI-detected acute ischemic lesions were present in 52 of 126 cases (52/126,41%, positive group). Lesions were small (mean volume: 1.6 cm3), and ADC was moderately decreased (mean ADC ratio: 76%). A multiple logistic regression model demonstrated that TIA duration greater than or equal to 30 min (OR, 6.9; 95% CI, 3.2-23.4), motor deficit (OR, 4.8; 95% CI,1.9-19.2) and aphasia (OR, 7.8; 95% CI, 1.9-27.9) were independent predictors of DWI lesions. In 19 of 52 cases, the identified lesions were not detected by conventional MRI(T2-WI or T2-FLAIR).Conclusions: In TIA patients, nearly half with DWI lesions, prolonged TIA duration (TIA duration≥30 minutes), motor deficits and aphasia were significantly correlated with detecting an abnormality with DWI.