title: Simulation, phantom validation, and clinical evaluation of fast pH-weighted molecular imaging using amine chemical exchange saturation transfer echo planar imaging (CEST-EPI) in glioma at 3 T.
abstract: Acidity within the extracellular milieu is a hallmark of cancer. There is a current need for fast, high spatial resolution pH imaging techniques for clinical evaluation of cancers, including gliomas. Chemical exchange saturation transfer (CEST) MRI targeting fast-exchanging amine protons can be used to obtain high-resolution pH-weighted images, but conventional CEST acquisition strategies are slow. There is also a need for more accurate MR simulations to better understand the effects of amine CEST pulse sequence parameters on pH-weighted image contrast. In the current study we present a simulation of amine CEST contrast specific for a newly developed CEST echoplanar imaging (EPI) pulse sequence. The accuracy of the simulations was validated by comparing the exchange rates and Z-spectrum under a variety of conditions using physical phantoms of glutamine with different pH values. The effects of saturation pulse shapes, pulse durations, pulse train lengths, repetition times, and relaxation rates of bulk water and exchangeable amine protons on the CEST signal were explored for normal-appearing white matter (NAWM), glioma, and cerebrospinal fluid. Last, 18 patients with WHO II-IV gliomas were evaluated. Results showed that the Z-spectrum was highly dependent on saturation pulse shape, repetition time, saturation amplitude, magnetic field strength, and T2within bulk water; however, the Z-spectrum was only minimally influenced by saturation pulse duration and the specific relaxation rates of amine protons. Results suggest that a Gaussian saturation pulse train consisting of 3 × 100 ms pulses using the minimum allowable repetition time is optimal for achieving over 90% available contrast across all tissues. Results also demonstrate that high saturation pulse amplitude and scanner field strength (>3 T) are necessary for adequate endogenous pH-weighted amine CEST contrast. pH-weighted amine CEST contrast increased with increasing tumor grade, with glioblastoma showing significantly higher contrast compared with WHO II or III gliomas.
authors.affiliation: UCLA Brain Tumor Imaging Laboratory (BTIL), Center for Computer Vision and Imaging Biomarkers, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA.|Department of Radiological Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA.|Department of Physics and Biology in Medicine, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Harris
authors.affiliation: Department of Neurology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA.
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Cloughesy
authors.affiliation: UCLA Brain Research Institute (BRI), David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA.|Department of Neurosurgery, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA.
authors.forename: Linda M
authors.initials: LM
authors.lastname: Liau
authors.affiliation: Department of Neurology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA.
authors.forename: Phioanh L
authors.initials: PL
authors.lastname: Nghiemphu
authors.affiliation: Department of Neurology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA.|UCLA Brain Research Institute (BRI), David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA.
authors.forename: Albert
authors.initials: A
authors.lastname: Lai
authors.affiliation: Department of Radiological Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA.
authors.forename: Whitney B
authors.initials: WB
authors.lastname: Pope
authors.affiliation: UCLA Brain Tumor Imaging Laboratory (BTIL), Center for Computer Vision and Imaging Biomarkers, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA. bellingson@mednet.ucla.edu.|Department of Radiological Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA. bellingson@mednet.ucla.edu.|Department of Physics and Biology in Medicine, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA. bellingson@mednet.ucla.edu.|UCLA Brain Research Institute (BRI), David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA. bellingson@mednet.ucla.edu.|Department of Bioengineering, Henry Samueli School of Engineering and Applied Science, University of California Los Angeles, Los Angeles, California, USA. bellingson@mednet.ucla.edu.|Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA. bellingson@mednet.ucla.edu.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Ellingson
mesh_terms: D000465:Algorithms; D000588:Amines / Q000737:chemistry / Q000378:metabolism; D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000737:chemistry / Q000378:metabolism*; D001932:Brain Neoplasms / Q000737:chemistry / Q000000981:diagnostic imaging / Q000378:metabolism*; D003198:Computer Simulation; D017352:Echo-Planar Imaging / Q000295:instrumentation / Q000379:methods*; D005910:Glioma / Q000737:chemistry / Q000000981:diagnostic imaging / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008954:Models, Biological; D057054:Molecular Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted
chemical_list: D000588:Amines; D000596:Amino Acids; D014408:Biomarkers, Tumor
keywords: Bloch-McConnell; CEST; EPI; amino acid; glioma; pH; pH-weighted MRI; simulation