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Insight into the quantitative metrics of chemical exchange saturation transfer (CEST) imaging.

ABSTRACT: To evaluate the reliability of four CEST imaging metrics for brain tumors, at varied saturation power levels and magnetic field strengths (3-9.4 Tesla (T)).A five-pool proton exchange model (free water, semisolid, amide, amine, and NOE-related protons) was used for the simulations. For the in vivo study, eight glioma-bearing rats were scanned at 4.7?T. The CEST ratio (CESTR), CESTR normalized with the reference value (CESTRnr ), inverse Z-spectrum-based (MTRRex ), and apparent exchange-related relaxation (AREX) were compared.The simulated CEST signal intensities using MTRRex and AREX were substantially increased at relatively high radiofrequency (RF) saturation powers at 3?T and 4.7?T, whereas CESTR and CESTRnr metrics remained relatively stable. There were tremendously high MTRRex and AREX signals around the water frequency at all field strengths because of the small denominators. In the rat tumor study at 4.7?T, both CESTR and CESTRnr showed clear contrasts in the tumor with respect to the normal tissue across all saturation power levels (0.5-3??T), whereas the AREX showed negligible to negative insignificant contrasts.CEST metrics must be carefully selected based on the different experimental settings. CESTR and CESTRnr are more reliable at 3?T (a clinical field strength) and 4.7?T. Magn Reson Med 77:1853-1865, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

SUBMITTER: Heo HY

PROVIDER: S-EPMC5107181 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

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Insight into the quantitative metrics of chemical exchange saturation transfer (CEST) imaging.

Heo Hye-Young HY Lee Dong-Hoon DH Zhang Yi Y Zhao Xuna X Jiang Shanshan S Chen Min M Zhou Jinyuan J

Magnetic resonance in medicine 20160512 5

<h4>Purpose</h4>To evaluate the reliability of four CEST imaging metrics for brain tumors, at varied saturation power levels and magnetic field strengths (3-9.4 Tesla (T)).<h4>Methods</h4>A five-pool proton exchange model (free water, semisolid, amide, amine, and NOE-related protons) was used for the simulations. For the in vivo study, eight glioma-bearing rats were scanned at 4.7 T. The CEST ratio (CESTR), CESTR normalized with the reference value (CESTR<sup>nr</sup> ), inverse Z-spectrum-based ...[more]

PMID: 27170222

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Project description:Accurate quantification of chemical exchange saturation transfer (CEST) effects, including dipole-dipole mediated relayed nuclear Overhauser enhancement (rNOE) saturation transfer, is important for applications and studies of molecular concentration and transfer rate (and thereby pH or temperature). Although several quantification methods, such as Lorentzian difference (LD) analysis, multiple-pool Lorentzian fits, and the three-point method, have been extensively used in several preclinical and clinical applications, the accuracy of these methods has not been evaluated. Here we simulated multiple-pool Z spectra containing the pools that contribute to the main CEST and rNOE saturation transfer signals in the brain, numerically fit them using the different methods, and then compared their derived CEST metrics with the known solute concentrations and exchange rates. Our results show that the LD analysis overestimates contributions from amide proton transfer (APT) and intermediate exchanging amine protons; the three-point method significantly underestimates both APT and rNOE saturation transfer at -3.5 ppm (NOE(-3.5)). The multiple-pool Lorentzian fit is more accurate than the other two methods, but only at lower irradiation powers (?1 ?T at 9.4 T) within the range of our simulations. At higher irradiation powers, this method is also inaccurate because of the presence of a fast exchanging CEST signal that has a non-Lorentzian lineshape. Quantitative parameters derived from in vivo images of rodent brain tumor obtained using an irradiation power of 1 ?T were also compared. Our results demonstrate that all three quantification methods show similar contrasts between tumor and contralateral normal tissue for both APT and the NOE(-3.5). However, the quantified values of the three methods are significantly different. Our work provides insight into the fitting accuracy obtainable in a complex tissue model and provides guidelines for evaluating other newly developed quantification methods.

Dataset Information

Insight into the quantitative metrics of chemical exchange saturation transfer (CEST) imaging.

Publications

Insight into the quantitative metrics of chemical exchange saturation transfer (CEST) imaging.

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