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Tomography. 2018 Sep;4(3):123-137. doi: 10.18383/j.tom.2018.00017.

Improving B0 Correction for pH-Weighted Amine Proton Chemical Exchange Saturation Transfer (CEST) Imaging by Use of k-Means Clustering and Lorentzian Estimation.

Author information

1
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, CA.
2
Department of Radiological Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA.
3
Department of Bioengineering, Henry Samueli School of Engineering and Applied Science, University of California Los Angeles, Los Angeles, CA.
4
Departments of Radiation Oncology.
5
Neurosurgery, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA.
6
Neurology, and.

Abstract

Amine chemical exchange saturation transfer (CEST) echoplanar imaging (EPI) provides unique pH and amino acid MRI contrast, enabling sensitive detection of altered microenvironment properties in various diseases. However, CEST contrast is sensitive to static magnetic field (B0) inhomogeneities. Here we propose 2 new B0 correction algorithms for use in correcting pH-weighted amine CEST EPI based on k-means clustering and Lorentzian fitting of CEST data: the iterative downsampling estimation using Lorentzian fitting and the 2-stage Lorentzian estimation with 4D polynomial fitting. Higher quality images of asymmetric magnetization transfer ratio (MTRasym) at 3.0 ppm could be obtained with the proposed algorithms than with the existing B0 correction methods. In particular, the proposed methods are shown to improve the intertissue consistency, interpatient consistency, and tumor region signal-to-noise ratio of MTRasym at 3.0 ppm images, with nonexcessive computation time.

KEYWORDS:

B0 correction; amine CEST EPI; chemical exchange saturation transfer; pH-weighted MRI

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