title: CEST signal at 2ppm (CEST@2ppm) from Z-spectral fitting correlates with creatine distribution in brain tumor.
abstract: In general, multiple components such as water direct saturation, magnetization transfer (MT), chemical exchange saturation transfer (CEST) and aliphatic nuclear Overhauser effect (NOE) contribute to the Z-spectrum. The conventional CEST quantification method based on asymmetrical analysis may lead to quantification errors due to the semi-solid MT asymmetry and the aliphatic NOE located on a single side of the Z-spectrum. Fitting individual contributors to the Z-spectrum may improve the quantification of each component. In this study, we aim to characterize the multiple exchangeable components from an intracranial tumor model using a simplified Z-spectral fitting method. In this method, the Z-spectrum acquired at low saturation RF amplitude (50 Hz) was modeled as the summation of five Lorentzian functions that correspond to NOE, MT effect, bulk water, amide proton transfer (APT) effect and a CEST peak located at +2 ppm, called CEST@2ppm. With the pixel-wise fitting, the regional variations of these five components in the brain tumor and the normal brain tissue were quantified and summarized. Increased APT effect, decreased NOE and reduced CEST@2ppm were observed in the brain tumor compared with the normal brain tissue. Additionally, CEST@2ppm decreased with tumor progression. CEST@2ppm was found to correlate with the creatine concentration quantified with proton MRS. Based on the correlation curve, the creatine contribution to CEST@2ppm was quantified. The CEST@2ppm signal could be a novel imaging surrogate for in vivo creatine, the important bioenergetics marker. Given its noninvasive nature, this CEST MRI method may have broad applications in cancer bioenergetics.
authors.affiliation: Department of Radiology, University of Illinois College of Medicine, Chicago, IL, USA.
authors.forename: Kejia
authors.initials: K
authors.lastname: Cai
authors.forename: Anup
authors.initials: A
authors.lastname: Singh
authors.forename: Harish
authors.initials: H
authors.lastname: Poptani
authors.forename: Weiguo
authors.initials: W
authors.lastname: Li
authors.forename: Shaolin
authors.initials: S
authors.lastname: Yang
authors.forename: Yang
authors.initials: Y
authors.lastname: Lu
authors.forename: Hari
authors.initials: H
authors.lastname: Hariharan
authors.forename: Xiaohong J
authors.initials: XJ
authors.lastname: Zhou
authors.forename: Ravinder
authors.initials: R
authors.lastname: Reddy
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism / Q000473:pathology; D001932:Brain Neoplasms / Q000378:metabolism*; D003401:Creatine / Q000378:metabolism*; D006801:Humans; D008279:Magnetic Resonance Imaging; D011916:Rats, Inbred F344; D012815:Signal Processing, Computer-Assisted
chemical_list: D003401:Creatine
keywords: amide proton transfer (APT); brain tumor; chemical exchange saturation transfer (CEST); creatine; magnetic resonance spectroscopy (MRS); nuclear Overhauser effect (NOE)