ABSTRACT
Objective To compare the hemodynamic characteristics in internal carotid artery models, which were obtained by multi-scale unidirectional and bidirectional coupling models, so as to provide references for selecting models in further studies. Methods Based on the nuclear magnetic resonance image of one patient with mild stenosis of internal carotid artery, the lumped parameter model of the circle of Willis and the three-dimensional model of internal carotid artery were constructed. Those two different multi-scale models were constructed by unidirectional and bidirectional coupling. Results With the increase of stenosis degree, the inlet and outlet blood pressure and the outlet blood flow of internal carotid artery all decreased under two kinds of coupling method. The distribution of low time average wall shear stress (TAWSS) and high oscillatory shear index (OSI) of the internal carotid artery both increased with the increase of stenosis degree under two kinds of coupling method in general. The anterior cerebral artery segment showed lower shear stress and higher OSI with bidirectional coupling in 70% stenosis, and the blood flow direction of posterior communicating artery was changed, which was significantly different from unidirectional coupling results. Conclusions At a low degree of stenosis, the result of those two kinds of coupling method were consistent in general, but there was a significant difference in 70% stenosis, and the result of bidirectional coupling was closer to physiological parameters. The research findings can be better applied to the hemodynamic study of cerebrovascular diseases.
ABSTRACT
Objective To assess whether asymmetric spin echo version of echo planar imaging (ASE EPI) sequence can reflect cerebral oxygen metabolism by means of the changes in oxygen extraction fraction values before and after surgical operations in the canine model of ischimia. Methods A total of 12 healthy crossbreed dogs were enrolled in this study. All canines underwent cerebral MR imaging including coronal T2WI, DWI, MRA, ASE EPI and 3D PCASL. The bilateral carotid arteries (CA) were separated by surgical operations. The bilateral CA were ligated in 6 dogs, and the other 6 dogs had embolization in ligated bilateral CA. The cerebral MR imaging with the above protocol was repeated at 1 hour after surgical operation for each dog. All dogs were executed when they finished the MR examinations. Then the whole brains of the dogs were taken out for cutting coronal sections and 2, 3, 5-triphenyltetrazolium chloride (TTC) staining. The ASE EPI data were processed by the Functool software in the workstation to generate OEF maps. For measuring the OEF values before and 1 hour after surgical operations, one and the same region of interest (ROI) was respectively placed in the left and right hemispheres on the OEF maps for each dog. 3D PCASL data were processed by the Functool software in the workstation to yield CBF maps. The method for measuring the CBF values before and 1 hour after surgical operations on CBF maps was same as that for measuring on OEF maps. The changes of measurements before and after surgical operations were compared between the dogs with ligated bilateral CA and the dogs with embolization in ligated bilateral CA by using an independent samples t test. The measurements before and after surgical operations were respectively compared in the dogs with ligated bilateral CA and the dogs with embolization in ligated bilateral CA by using a paired t-test. The cutting slices with TTC staining were analysed for determining ischimia. Results The CBF values of the dogs with ligated bilateral CA were (59.81±23.59) and (38.56± 12.98) ml/(min · 100 g) before and after surgical operations, respectively. The CBF values of the dogs with embolization in ligated bilateral CA were (58.94±18.35) and (28.01±11.41) ml/(min·100 g) before and after surgical operations, respectively. The CBF values were significantly lower before surgical operations than after surgical operations in the dogs with ligated bilateral CA and the dogs with embolization in ligated bilateral CA, respectively (t=8.92 and 13.42, respectively; P=0.00, respectively). The CBF values were decreased more significantly in the dogs with embolization in ligated bilateral CA than in the dogs with ligated bilateral CA (t=2.92, P=0.00). The OEF values of the dogs with ligated bilateral CA were 0.29±0.02 and 0.32 ± 0.06 before and after surgical operations, respectively. The OEF values of the dogs with embolization in ligated bilateral CA were 0.29 ± 0.02 and 0.35 ± 0.06 before and after surgical operations, respectively. The OEF values were significantly higher before surgical operations than after surgical operations in the dogs with ligated bilateral CA and the dogs with embolization in ligated bilateral CA, respectively (t=-7.21 and-4.43, respectively;P=0.00, respectively). The OEF values were increased more significantly in the dogs with embolization in ligated bilateral CA than in the dogs with ligated bilateral CA (t=2.18, P=0.03). The pathological results showed that the dogs with embolization in ligated bilateral CA had swollen cortex with focal infarction which was matched with the hyperintensity areas on the OEF and DWI images. However, the dogs with ligated bilateral CA only had swollen cortex whereas didn't have focal infarction. Conclusions ASE EPI sequence can reliably reflect cerebral oxygen metabolism in ischemia. This sequence has an important role for assessing hemodynamic state in patients with cerebral vascular diseases.