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Magn Reson Med. 2018 Nov;80(5):1962-1978. doi: 10.1002/mrm.27204. Epub 2018 Apr 6.

Simultaneous pH-sensitive and oxygen-sensitive MRI of human gliomas at 3 T using multi-echo amine proton chemical exchange saturation transfer spin-and-gradient echo echo-planar imaging (CEST-SAGE-EPI).

Author information

1
UCLA Brain Tumor Imaging Laboratory, Center for Computer Vision and Imaging Biomarkers, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California.
2
Department of Radiological Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California.
3
Physics and Biology in Medicine, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California.
4
Department of Bioengineering, Henry Samueli School of Engineering and Applied Science, University of California Los Angeles, Los Angeles, California.
5
UCLA Brain Research Institute, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California.
6
Department of Neurosurgery, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California.
7
Department of Neurology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California.
8
Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California.

Abstract

PURPOSE:

To introduce a new pH-sensitive and oxygen-sensitive MRI technique using amine proton CEST echo spin-and-gradient echo (SAGE) EPI (CEST-SAGE-EPI).

METHODS:

pH-weighting was obtained using CEST estimations of magnetization transfer ratio asymmetry (MTRasym ) at 3 ppm, and oxygen-weighting was obtained using R2' measurements. Glutamine concentration, pH, and relaxation rates were varied in phantoms to validate simulations and estimate relaxation rates. The values of MTRasym and R2' in normal-appearing white matter, T2 hyperintensity, contrast enhancement, and macroscopic necrosis were measured in 47 gliomas.

RESULTS:

Simulation and phantom results confirmed an increase in MTRasym with decreasing pH. The CEST-SAGE-EPI estimates of R2 , R2*, and R2' varied linearly with gadolinium diethylenetriamine penta-acetic acid concentration (R2  = 6.2 mM-1 ·sec-1 and R2* = 6.9 mM-1 ·sec-1 ). The CEST-SAGE-EPI and Carr-Purcell-Meiboom-Gill estimates of R2 (R2  = 0.9943) and multi-echo gradient-echo estimates of R2* (R2  = 0.9727) were highly correlated. T2 lesions had lower R2' and higher MTRasym compared with normal-appearing white matter, suggesting lower hypoxia and high acidity, whereas contrast-enhancement tumor regions had elevated R2' and MTRasym , indicating high hypoxia and acidity.

CONCLUSION:

The CEST-SAGE-EPI technique provides simultaneous pH-sensitive and oxygen-sensitive image contrasts for evaluation of the brain tumor microenvironment. Advantages include fast whole-brain acquisition, in-line B0 correction, and simultaneous estimation of CEST effects, R2 , R2*, and R2' at 3 T.

KEYWORDS:

CEST; SAGE; glioma; hypoxia; pH-weighted MRI

PMID:
29626359
PMCID:
PMC6107417
[Available on 2019-11-01]
DOI:
10.1002/mrm.27204
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