title: CEST phase mapping using a length and offset varied saturation (LOVARS) scheme.
abstract: Chemical exchange saturation transfer MRI is a promising new technique for cellular and molecular imaging. This contrast allows the detection of tumors and ischemia without the use of gadolinium as well as the design of microenvironment-sensitive probes that can be discriminated based on their exchange contrast properties and saturation frequency. Current acquisition schemes to detect and analyze this contrast suffer from sensitivity to spatial B0 inhomogeneity and low contrast-to-noise-ratio, which is an obstacle to widespread adoption of the technology. A new method to detect chemical exchange saturation transfer contrast is proposed here, termed "length and offset varied saturation" which acquires a set of images with the saturation parameters varied so as to modulate the exchange contrast. Either fast fourier transform or the general linear model can be employed to decompose the modulation patterns into separate sources of water signal loss. After transformation, a length and offset varied saturation phase map is generated, which is insensitive to B0 inhomogeneity. When collected on live mice bearing 9L gliosarcomas, and compared to the conventional asymmetry in the magnetization transfer ratio map using offset increment correction, the results show that length and offset varied saturation phase mapping obtains about three to four times contrast-to-noise-ratio and exhibits less B0 artifacts.
authors.affiliation: Cellular Imaging Section and Vascular Biology Program, Institute for Cell Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Song
authors.forename: Assaf A
authors.initials: AA
authors.lastname: Gilad
authors.forename: Suresh
authors.initials: S
authors.lastname: Joel
authors.forename: Guanshu
authors.initials: G
authors.lastname: Liu
authors.forename: Amnon
authors.initials: A
authors.lastname: Bar-Shir
authors.forename: Yajie
authors.initials: Y
authors.lastname: Liang
authors.forename: Michael
authors.initials: M
authors.lastname: Gorelik
authors.forename: James J
authors.initials: JJ
authors.lastname: Pekar
authors.forename: Peter C M
authors.initials: PC
authors.lastname: van Zijl
authors.forename: Jeff W M
authors.initials: JW
authors.lastname: Bulte
authors.forename: Michael T
authors.initials: MT
authors.lastname: McMahon
mesh_terms: D000465:Algorithms; D000818:Animals; D014408:Biomarkers, Tumor / Q000032:analysis*; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000378:metabolism*; D045744:Cell Line, Tumor; D018316:Gliosarcoma / Q000175:diagnosis* / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D016513:Mice, SCID; D057054:Molecular Imaging / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D014408:Biomarkers, Tumor