Chemical Exchange Saturation Transfer Imaging Of Hyperacute Brain Infarction Using A 1.5 Tesla Scanner

ObjectiveCerebral infarction is the blockage of the flow of blood to the cerebrum, causing or resulting in brain tissue death. Early diagnosis and rapid treatment would help to alleviate symptoms, increase survival, and reduce disability. In the hyperacute infarct stage, routine CT and MRI (T1WI, T2WI and FLAIR) usually are negative. PWI and DWI present as a low perfusion area and hyperintensity area in this stage, but they are are not penumbra-specific. Therefore a new technology which can make an early diagnosis and prognose ischemic penumbra is great significant for clinic. CEST imaging is a new technology which is sensitive to pH change. As we know, when cerebral nervous tissue lacks of blood and oxygen, neurocyte is altered in metabolism, following with acid-base disturbance. So pH- sensitive CEST imaging can reflect the alteration in metabolism. Using this technology to image ischemic brain may make an early detection in the hyperacute infarct stage and have a advantage to prognose ischemic penumbra.Materials and MethodsIn our study, twelve male cats weighing 2.4 to 2.8 kg underwent permanent middle cerebral artery occlusion (MCAO), and ischemic evolution was observed at a clinical 1.5-T scanner through clinical T1WI, T2WI, DWI and the CEST-imaging that the imaging sequence designed by our group. CEST-imaging readout was as spin-echo imaging with an offset frequency of 3.5 ppm. At last, compare the ability of T1WI, T2WI, DWI and CEST-imaging to detect cerebral infarct within the hyperacute stage.ResultsIn 7 of 12 animals, when there are not any alterations in the DWI yet, we can find hypointensity regions in the occlusion side in the CEST-imaging. In other 5 of 12 animals, we can observer the intensity alterations in DWI and CEST-imaging at the same time. The signal intensity in the lesion region is lower than that in the healthy nervous tissue in CEST-imaging, and the darkest part in the CEST-imaging corresponds with the lightest part in the DWI. It may mean the tissue of this area suffers the most serious lack of ischemia and anoxia. In addition, we can see the lesion area displayed in the CEST-imaging is larger than that in the DWI. In the hyperacute infarct stage T1WI and T2WI are negetive.ConclusionsIn this study, we could identify cerebral infarct lesions in the hyperacute infarct stage using CEST at a 1.5 T clinical scanner. CEST-imaging is sensitive to detect infarct prior to current clinical sequences such as T1WI, T2WI and DWI. Analysing from cerebral blood flow (CBF), the CBF level for pH change approximates to the threshold of penumbra, so it indicates that boundary of lesion on CEST-imaging may also approximates to the penumbra. At last we come to a conclusion that CEST-imaging not only can diagnose cerebral infarction, but also may be able to prognose ischemic penumbra.