隨著科技的進步與成熟，目前放射治療已廣泛應用於治療原發性和轉移性腦腫瘤，然而治療劑量對正常腦組織造成傷害引發認知功能障礙等副作用卻無法完全避免。磁振造影 (MRI) 對於腦部病變的診斷與追蹤，扮演著舉足輕重的角色，但它在放射治療對正常腦組織造成傷害的評估與應用上，仍然所知有限。
本研究的目的，希望在臨床使用1.5T MRI機器下，利用不同的脈衝序列 (pulse sequence)，包括T2加權影像 (T2WI)、R2 mapping和擴散張量影像指數 (DTI indices) ，評估經次致死劑量 (30 Gy) 放射線照射兔子半腦前後，在影像上不同腦部結構隨時間 (longitudinal) 的變化。
結果顯示，DTI indices比T2WI更能顯示經放射線照射後外囊(external capsule) 神經纖維結構的變化，而T2WI對於偵測海馬迴 (hippocampus) 經放射線照射後血管性水腫變化 (vasogenic edema) 扮演重要的角色。對於大腦皮質 (cerebral cortex) 與丘腦(thalamus) ，不管是在T2WI、R2 mapping或DTI indices，都無法偵測到顯著的變化趨勢。
根據我們的研究結果，在臨床的1.5T MRI機器下，使用不同的MRI 脈衝序列可幫助我們更了解與追蹤經放射線照射後，在影像上不同腦部結構隨時間的變化。
Radiation therapy is widely used for the treatment of both primary and metastatic brain tumors, but cognitive impairment is a major side effect of radiation-induced brain injury. Although magnetic resonance imaging (MRI) has been used as a non-invasive modality for the detection of brain lesions, its characterization of normal brain tissue to therapeutic doses of radiation is still not well understood.
The objective of our study was to longitudinally evaluate the radiation-induced changes of the brain in a rabbit model after a single sub-lethal high dose irradiation (30 Gy) by using T2 weighted imaging (T2WI), R2 mapping, and diffusion tensor imaging (DTI) indices on a 1.5T clinical MR scanner.
The results showed that DTI indices were more sensitive than T2WI in reflecting histopathological changes in the affected external capsule, but T2WI had the advantage of detecting vasogenic edematous changes in the affected hippocampus. Both cerebral cortex and thalamus showed no significant changes or clear trends on T2WI, R2 mapping or DTI indices in the follow-up time points.
According to our results, it is suggested that both DTI indices and T2WI had their own characterization when detecting changes in different brain compartments, and that these multiparametric MRI measurements can be valuable in monitoring the pathophysiological cascades using a 1.5T clinical MRI scanner during the course of radiation-induced brain injury.
