关键词: 化学交换饱和转移(CEST), 酰胺质子转移(APT), 磁共振成像(MRI), 酸碱度

Abstract: Acquisition parameters for chemical exchange saturation transfer (CEST) imaging were optimized on a GE Signa HDe 1.5 T magnetic resonance imaging (MRI) scanner with phantoms and clinical cases. The effects of matrix size, number of averages (NEX) and flip angles on the quality of CEST images were assessed. It was shown that the signal-to-noise ratio (SNR) of the CEST images acquired on the 1.5 T scanner was relatively low, and the stability and uniformity of the B₀ field affected the outcome significantly. Reducing matrix size and increasing NEX improved the SNR of the CEST images. Optimal flip angle for magnetization transfer was found to be 105°. With a NEX of 2, usable Z spectra could be obtained. The Z spectra indicated that, with the saturation pulse frequency centered at -294~-194 Hz, signal differences could be observed for 30% Glu, I₃₂₀, H₂O, and Cr. Maximal signal differences were observed when the saturation pulse applied at -244~-214 Hz. Amide proton transfer (APT) imaging on patients showed that 25 cases of brain tumor had high CEST signals, 12 cases of cerebral infarction had low CEST signals. It was therefore possible to differentiate brain tumor from infarction with CEST imaging. There were also 12 cases which failed due to long acquisition time, patient movements, and temperature changes in the scanner room.

Key words: chemical exchange saturation transfer (CEST), amide proton transfer (APT), magnetic resonance imaging (MRI), pH