Imaging Research Of Chronic Cerebral Ischemia

Objective:To investigate imaging characteristics of chronic cerebral ischemia, and to evaluate the clinical application value of combining cerebral CT perfusion (CTP), CT angiography (CTA), diffusion weighted imaging(DWI) and'H magnetic resonance spectroscopy (1H-MRS) in patients with chronic cerebral ischemia.Materials and Methods:Conventional cerebral plain CT, CTP and CTA were performed on 55 patients with clinically diagnosed chronic cerebral ischemia. The cerebral perfusion parameters such as cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT) and time to peak (TTP) within interested regions of the brain were measured. CTA was reconstructed to show carotid and intracerebral arteries. Furthermore, the patients with abnormal perfusion were examined by DWI and 1-MRS. Referencing the parameters maps of CTP, apparent diffusion coefficient (ADC) values in hypoperfusion area in these patients and infarct core in 10 hyperacute cerebral infarction patients as well as the counterpart in the contralateral hemisphere were measured and analyzed on ADC maps. Following up, was performed on these patients by using point resolved spectroscopy (PRESS). Cerebral metabolism was studied by assessing ratios of N-acetylaspartate (NAA) to creatine (Cr) and to choline (Cho) as well as Cho to Cr calculated from the peak areas both in ipsilesional and contralesional regions. Lactate (Lac) was also observed.16 of cerebral hypoperfusion patients with unilateral internal carotid artery (ICA) hige-grade stenosis underwent carotid endarterectomy (CEA). Conventional cerebral plain CT, CTP and CTA as well as 1H-MRS were performed on these 16 cases 10 to 14 days after CEA. The results of quantitative cerebral perfusion parameters, ICA diameter and area of cross section, relative contents of cerebral metabolites were compared between pre-and post-CEA.Results:Abnormal perfusion changes were found in 43 of 55 cases with significantly prolonged MTT and TTP (P<0.01), as well as increased CBV comparing with contralateral side (P<0.05). The differences of CBF were not statistically significant between ipsilateral side and contralateral side (P>0.05). Other 12 cases were normal. CTA demonstrated high-grade stenosis or occlusion of unilateral ICA or middle cerebral artery(MCA) in 40 cases,3 patients with low or medium-grade stenosis. The differences of incidence in hypoperfusion between the former and the latter were statistically significant (χ2=29.991, P<0.01).43 patients with hypoperfusion underwent DWI and 1H-MRS. The abnormal signal was not found in 43 cases on DWI and ADC. There was a mild decline and significant decline in the ADC value of hypoperfusion area and center of infarction, respectively, and both of the decline had a difference of significance (P<0.01).'H-MRS showed significantly decreased NAA/Cr and NAA/Cho(P<0.01)as well as increased Cho/Cr (P<0.05) in the hypoperfusion side comparing with the contralateral side. Lac was detected in diseased side of 9 patients. In 16 cases receiving CEA, the values of CBF were increase (P<0.05)and CBV were mild decline (P>0.05), while MTT and TTP were significant decrease in the affected hemisphere comparing with preoperative perfusion parameters (P<0.01). There was statistically significant difference in measuring the affected ICA diameter and area of cross section with CTA before and after CEA (P<0.01).1H-MRS showed significantly increased NAA/Cho (P<0.01) and decreased Cho/Cr (P<0.05) ipsilateral to the operated side after CEA, whereas the NAA/Cr showed statistically insignificant changes (P>0.05).Conclusions:Chronic cerebral ischemia had abnormal cerebral haemodynamics and metabolism, and there was relative long preclinical phase could be intervened. The combination of CTP, CTA, DWI and 1H-MRS can provide valuable diagnostic and therapeutic information for chronic cerebral ischemia in the aspects of cerebral perfusion, vascular structure, diffusion and metabolism, thus play an important role in avoiding or decreasing effectively the attack rate of cerebral infarct and vascular dementia.