Julius Juhyun Chung1,2, Tao Jin3, Jung Hee Lee1,2,4,5, Seong-Gi Kim1,2,4. 1. Center for Neuroscience Imaging Research, Institute for Basic Science, Suwon, Korea. 2. Samsung Advanced Institute for Health Sciences and Technology, Sungkyunkwan University, Seoul, Korea. 3. Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania. 4. Department of Biomedical Engineering, Sungkyunkwan University, Seoul, Korea. 5. Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Abstract
PURPOSE: To determine the exchange parameters for the CEST of phosphocreatine (PCrCEST) in phantoms and to characterize PCrCEST in vivo in the muscle at different saturation powers and magnetic fields. METHODS: Exchange parameters were measured in PCr solutions using varying saturation power at 15.2 T. Z-spectra were analyzed using multipool Lorentzian fitting in the hindlimb using various powers at 2 different fields: 9.4 T and 15.2 T. Modulation of PCr signal in PCrCEST and phosphorus MRS was observed in the mouse hindlimb before and after euthanasia. RESULTS: The exchange rate of PCr at physiological pH in phantoms was confirmed to be in a much slower exchange regime compared with Cr: kex at pH 7.3 and below was less than 400 s-1 . There was insufficient signal for detection of PCrCEST in the brain, but PCrCEST in the hindlimb was measured to be 2.98% ± 0.43 at a B1 of 0.47 μT at 15.2 T, which is 29% higher than 9.4T values. The value of PCrCEST at a B1 of 0.71 μT was not significantly different than that measured at a B1 of 0.47 μT. After euthanasia, PCrCEST signal dropped by 82.3% compared with an 85% decrease in PCr in phosphorus MRS, whereas CrCEST signal increased by 90.6%. CONCLUSION: The PCrCEST technique has viable sensitivity in the muscle at high fields and shows promise for the study of metabolic dysfunction and cardiac systems.
PURPOSE: To determine the exchange parameters for the CEST of phosphocreatine (PCrCEST) in phantoms and to characterize PCrCEST in vivo in the muscle at different saturation powers and magnetic fields. METHODS: Exchange parameters were measured in PCr solutions using varying saturation power at 15.2 T. Z-spectra were analyzed using multipool Lorentzian fitting in the hindlimb using various powers at 2 different fields: 9.4 T and 15.2 T. Modulation of PCr signal in PCrCEST and phosphorus MRS was observed in the mouse hindlimb before and after euthanasia. RESULTS: The exchange rate of PCr at physiological pH in phantoms was confirmed to be in a much slower exchange regime compared with Cr: kex at pH 7.3 and below was less than 400 s-1 . There was insufficient signal for detection of PCrCEST in the brain, but PCrCEST in the hindlimb was measured to be 2.98% ± 0.43 at a B1 of 0.47 μT at 15.2 T, which is 29% higher than 9.4T values. The value of PCrCEST at a B1 of 0.71 μT was not significantly different than that measured at a B1 of 0.47 μT. After euthanasia, PCrCEST signal dropped by 82.3% compared with an 85% decrease in PCr in phosphorus MRS, whereas CrCEST signal increased by 90.6%. CONCLUSION: The PCrCEST technique has viable sensitivity in the muscle at high fields and shows promise for the study of metabolic dysfunction and cardiac systems.
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