Generalization of quasi-steady-state reconstruction to CEST MRI with two-tiered RF saturation and gradient-echo readout—Synergistic nuclear Overhauser enhancement contribution to brain tumor amide proton transfer–weighted MRI
Corresponding Author
Phillip Zhe Sun
Emory Primate Imaging Center, Emory National Primate Research Center, Emory University, Atlanta, Georgia, USA
Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia, USA
Correspondence
Phillip Zhe Sun, Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, GA 30329, USA.
Email: [email protected]
Search for more papers by this authorCorresponding Author
Phillip Zhe Sun
Emory Primate Imaging Center, Emory National Primate Research Center, Emory University, Atlanta, Georgia, USA
Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia, USA
Correspondence
Phillip Zhe Sun, Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, GA 30329, USA.
Email: [email protected]
Search for more papers by this authorClick here for author-reader discussions
Funding information: National Institute of Neurological Disorders and Stroke, Grant/Award Number: R01NS083654
Abstract
Purpose
While amide proton transfer–weighted (APTw) MRI has been adopted in tumor imaging, there are concurrent APT, magnetization transfer, and nuclear Overhauser enhancement changes. Also, the APTw image is confounded by relaxation changes, particularly when the relaxation delay and saturation time are not sufficiently long. Our study aimed to extend a quasi-steady-state (QUASS) solution to determine the contribution of the multipool CEST signals to the observed tumor APTw contrast.
Methods
Our study derived the QUASS solution for a multislice CEST-MRI sequence with an interleaved RF saturation and gradient-echo readout between signal averaging. Multiparametric MRI scans were obtained in rat brain tumor models, including T1, T2, diffusion, and CEST scans. Finally, we performed spinlock model–based multipool fitting to determine multiple concurrent CEST signal changes in the tumor.
Results
The QUASS APTw MRI showed small but significant differences in normal and tumor tissues and their contrast from the acquired asymmetry calculation. The spinlock model–based fitting showed significant differences in semisolid magnetization transfer, amide, and nuclear Overhauser enhancement effects between the apparent and QUASS CEST MRI. In addition, we determined that the tumor APTw contrast is due to synergistic APT increase (+3.5 ppm) and NOE decrease (−3.5 ppm), with their relative contribution being about one third and two thirds under a moderate B1 of 0.75 μT at 4.7 T.
Conclusion
Our study generalized QUASS analysis to gradient-echo image readout and quantified the underlying tumor CEST signal changes, providing an improved elucidation of the commonly used APTw MRI.
Supporting Information
| Filename | Description |
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| mrm29570-sup-0001-Supinfo.docxWord 2007 document , 281.6 KB |
Figure S1. The fast multislice CEST-MRI sequence. It includes a relaxation delay time (Td), a long primary saturation time (Ts1), followed by short secondary RF saturation times (Ts2) that are repeated between multislice gradient-echo (GRE) EPI readout and signal averaging loop. Abbreviation: FA, flip angle of GRE EPI Figure S2. Comparison of apparent and quasi-steady-state (QUASS) Z-spectra from the normal and tumor tissues. A, The apparent (red) and QUASS (black) Z-spectra from the contralateral normal tissue region of interest (ROI). B, The apparent (blue) and QUASS (black) Z-spectra from the tumor region of interest (ROI) Table S1. The mean and SDs of the chemical shift and FWHM (in ppm) were solved from the spinlock model–based fitting of the apparent and QUASS Z-spectra |
Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
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