Study Of Diffusion Tensor Imaging(DTI) And Enhanced T2*Weighted Angiography (ESWAN) In Cerebral Edema After Radiotherapy

Objective:To make a follow-up measurement and a longitudinal comparison of changes in peritumoral brain tissue at different stages before and after gamma knife radiosurgery for intracranial tumors by Enhanced T2star weighted angiography (ESWAN) and magnetic resonance diffusion tensor imaging (MR-DTI); to preliminarily investigate the application value and clinical significance of ESWAN and MR-DTI in diagnosis of early delayed encephalopathy.Methods:Thirty-two patients with intracranial mass lesions were followed and observed using a Signa HDx3.0T MRI scanner (General Electronics, U.S.). Routine MRI scan, DTI and ESWAN with fMRI were conducted at one day before radiotherapy and1,2,3,4weeks and2,3,4,5and6months after radiotherapy, respectively. Patients were divided into the brain edema group (n=15) and the non-brain edema group (n=17) based on the incidence of brain edema during the observation period. Peritumoral microvessel density (PMVD) changes in different stages, and dynamic changes in apparent diffusion coefficients (ADC) and FA values in peritumoral brain tissue were measured in patients in the brain edema group before and after radiotherapy. Difference in intratumoral microvessel density was compared between pre-and postradiotherapy early delayed encephalopathies, and a correlation analysis was conducted between postradiotherapy severity of brain edema and PMVD. Difference in preradiotherapy number of peritumoral microvessels was assessed by comparison between both groups.Results:PMVD in early delayed encephalopathy increased after gamma knife radiosurgery for intracranial mass lesions, and the result was statistically different. The severity of edema in early delayed encephalopathy was not correlated with PMVD. There was a statistical difference in the number of peritumoral microvessels between brain edema group and the non-brain edema group before radiotherapy. The number of peritumoral microvessels was greater in brain edema group than in non-brain edema group before and after radiotherapy.After radiotherapy, FA values of brain tissue decreased and ADC values increased, which changed markedly in the first month after radiotherapy and level off subsequently. When the postradiotherapy brain edema occurred, FA values of brain tissue decreased further and ADC values increased further.Conclusion:(1) Increased PMVD in early delayed encephalopathy after radiotherapy may contribute to partial vascular stenosis and even occlusion leading to increased compensation of peripheral vessels pathologically, but the severity of postradiotherapy brain edema is not correlated with PMVD. The number of peritumoral microvessels may be one of the influencing factors for the incidence of postradiotherapy brain edema.(2) DTI can be used for observation of peritumoral brain tissue. No abnormality is observed in postradiotherapy brain tissue in acute and subacute stages of brain radiation injury on routine MRI, but there are still changes in microstructures. The advantage of DTI evaluating the brain radiation injury at the molecular level is more apparent in early delayed brain injury, providing objective foundations for prophylaxis of irreversible brain injury.