title: APT-weighted and NOE-weighted image contrasts in glioma with different RF saturation powers based on magnetization transfer ratio asymmetry analyses.
abstract: OBJECTIVE
  To investigate the saturation-power dependence of amide proton transfer (APT)-weighted and nuclear Overhauser enhancement-weighted image contrasts in a rat glioma model at 4.7 T.
  
  
  METHODS
  The 9L tumor-bearing rats (n = 8) and fresh chicken eggs (n = 4) were scanned on a 4.7-T animal magnetic resonance imaging scanner. Z-spectra over an offset range of ±6 ppm were acquired with different saturation powers, followed by the magnetization transfer-ratio asymmetry analyses around the water resonance.
  
  
  RESULTS
  The nuclear Overhauser enhancement signal upfield from the water resonance (-2.5 to -5 ppm) was clearly visible at lower saturation powers (e.g., 0.6 µT) and was larger in the contralateral normal brain tissue than in the tumor. Conversely, the APT effect downfield from the water resonance was maximized at relatively higher saturation powers (e.g., 2.1 µT) and was larger in the tumor than in the contralateral normal brain tissue. The nuclear Overhauser enhancement decreased the APT-weighted image signal, based on the magnetization transfer-ratio asymmetry analysis, but increased the APT-weighted image contrast between the tumor and contralateral normal brain tissue.
  
  
  CONCLUSIONS
  The APT and nuclear Overhauser enhancement image signals in tumor are maximized at different saturation powers. The saturation power of roughly 2 μT is ideal for APT-weighted imaging at clinical B0 field strengths.
authors: Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA. jzhou@mri.jhu.edu
authors: Jinyuan
authors: J
authors: Zhou
authors: Xiaohua
authors: X
authors: Hong
authors: Xuna
authors: X
authors: Zhao
authors: Jia-Hong
authors: JH
authors: Gao
authors: Jing
authors: J
authors: Yuan
mesh_terms: D000465:Algorithms; D000818:Animals; D001932:Brain Neoplasms / Q000473:pathology*; D045744:Cell Line, Tumor; D002642:Chick Embryo; D005910:Glioma / Q000473:pathology*; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051381:Rats; D011916:Rats, Inbred F344; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: APT-weighted imaging; CEST imaging; MT asymmetry; NOE-weighted imaging; brain tumor; magnetization transfer
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