Study of pH-sensitive magnetization transfer imaging in hyperacute brain infarction using a clinical 1.5 Tesla scanner

When cerebral nervous tissue lacks of blood and oxygen, neurocyte is altered in metabolism, following with intracellular acid-base disturbance. Alteration of intracellular pH value can influence the magnetization transfer ratio (MTR). So pH-sensitive magnetization transfer imaging can reflect the alteration in metabolism. Using this technology to image ischemic brain may make an early detection and prognose ischemic penumbra. In our study, twelve male cats weighing 2.4 to 2.8 kg underwent permanent MCAO, and ischemic evolution was observed at a clinical 1.5-T scanner through clinical T1WI, T2WI, DWI and MT-imaging. MT-imaging readout was as spin-echo imaging with an offset frequency of 3.5 ppm. At last, compare the ability of clinical imaging and MT-imaging to detect cerebral infarct within the hyperacute stage. From the experiment results we could find that in 7 of 12 animals they displayed hypointensity in the occlusion side in the MT-imaging, when there were no any alterations in the clinical imaging yet. In other 5 of 12 animals, we could observe the intensity alterations in DWI and MT-imaging at the same time. In the experiment we found that MT-imaging was sensitive to detect infarct prior to current clinical sequences such as T1WI, T2WI and DWI. Meanwhile, 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 MT-imaging may also approximate to the penumbra. We also come to a conclusion that CEST-imaging may be able to prognose ischemic penumbra.