title: Insight into the quantitative metrics of chemical exchange saturation transfer (CEST) imaging.
abstract: To evaluate the reliability of four CEST imaging metrics for brain tumors, at varied saturation power levels and magnetic field strengths (3-9.4 Tesla (T)).
  
  
  
  A five-pool proton exchange model (free water, semisolid, amide, amine, and NOE-related protons) was used for the simulations. For the in vivo study, eight glioma-bearing rats were scanned at 4.7 T. The CEST ratio (CESTR), CESTR normalized with the reference value (CESTRnr), inverse Z-spectrum-based (MTRRex), and apparent exchange-related relaxation (AREX) were compared.
  
  
  
  The simulated CEST signal intensities using MTRRexand AREX were substantially increased at relatively high radiofrequency (RF) saturation powers at 3 T and 4.7 T, whereas CESTR and CESTRnrmetrics remained relatively stable. There were tremendously high MTRRexand AREX signals around the water frequency at all field strengths because of the small denominators. In the rat tumor study at 4.7 T, both CESTR and CESTRnrshowed clear contrasts in the tumor with respect to the normal tissue across all saturation power levels (0.5-3 μT), whereas the AREX showed negligible to negative insignificant contrasts.
  
  
  
  CEST metrics must be carefully selected based on the different experimental settings. CESTR and CESTRnrare more reliable at 3 T (a clinical field strength) and 4.7 T. Magn Reson Med 77:1853-1865, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Divison of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.|F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.
authors.forename: Hye-Young
authors.initials: HY
authors.lastname: Heo
authors.affiliation: Divison of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.
authors.forename: Dong-Hoon
authors.initials: DH
authors.lastname: Lee
authors.affiliation: Divison of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Divison of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.
authors.forename: Xuna
authors.initials: X
authors.lastname: Zhao
authors.affiliation: Divison of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.
authors.forename: Shanshan
authors.initials: S
authors.lastname: Jiang
authors.affiliation: Department of Radiology, Beijing Hospital, Beijing, China.
authors.forename: Min
authors.initials: M
authors.lastname: Chen
authors.affiliation: Divison of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.|F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.
authors.forename: Jinyuan
authors.initials: J
authors.lastname: Zhou
mesh_terms: D000465:Algorithms; D000818:Animals; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology; D003198:Computer Simulation; D005910:Glioma / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D009368:Neoplasm Transplantation; D051381:Rats; D011923:Rats, Nude; D015203:Reproducibility of Results
keywords: APT; CEST; MTR; NOE; brain tumor