Quantitative characterization of nuclear overhauser enhancement and amide proton transfer effects in the human brain at 7 tesla

Liu, Dapeng; Zhou, Jinyuan; Xue, Rong; Zuo, Zhentao; An, Jing; Wang, Danny J.J.

doi:10.1002/mrm.24560

Cited by 92 publications

(157 citation statements)

References 44 publications

(53 reference statements)

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“…The exact field strength allowed is a complicated question, as SAR will also be affected by the choice of transmit coil and use of smaller transmit coils (108) or parallel transmit coils (109) can reduce the deposition of heat. However, in the case that the hardware doesn't allow sufficiently strong cw pulses for saturation, an alternative is to use a train of shaped pulses instead (110), often called pulsed-CEST MRI.…”

Section: Introductionmentioning

confidence: 99%

“…There are several imaging process methods that have been reported to address this problem. For instance, we have been using a priori determined SNR maps to calculate CNR maps and filter out pixels with low CNR (3,91,108), based on the assumption that low CNR is due to either low SNR or low contrast. The advantage of using a CNR filter is that not only noisy pixels are filtered out but also those containing a low ‘background’ CEST contrast, allowing the filtered maps to highlight pixels possessing more reliable CEST contrast.…”

Section: Introductionmentioning

confidence: 99%

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Nuts and bolts of chemical exchange saturation transfer MRI

et al. 2013

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Chemical Exchange Saturation Transfer (CEST) has emerged as a novel MRI contrast mechanism that is well suited for molecular imaging studies. This new mechanism can be used to detect small amounts of contrast agent through saturation of rapidly exchanging protons on these agents, allowing a wide range of applications. CEST technology has a number of indispensable features, such as the possibility of simultaneous detection of multiple “colors” of agents and detecting changes in their environment (e.g. pH, metabolites, etc) through MR contrast. Currently a large number of new imaging schemes and techniques have been developed to improve the temporal resolution and specificity and to correct the influence of B0 and B1 inhomogeneities. In this review, the techniques developed over the last decade have been summarized with the different imaging strategies and post-processing methods discussed from a practical point of view including describing their relative merits for detecting CEST agents. The goal of the present work is to provide the reader with a fundamental understanding of the techniques developed, and to provide guidance to help refine future applications of this technology. This review is organized into three main sections: Basics of CEST Contrast, Implementation, Post-Processing, and also includes a brief Introduction section and Summary. The Basics of CEST Contrast section contains a description of the relevant background theory for saturation transfer and frequency labeled transfer, and a brief discussion of methods to determine exchange rates. The Implementation section contains a description of the practical considerations in conducting CEST MRI studies, including choice of magnetic field, pulse sequence, saturation pulse, imaging scheme, and strategies to separate MT and CEST. The Post-Processing section contains a description of the typical image processing employed for B0/B1 correction, Z-spectral interpolation, frequency selective detection, and improving CEST contrast maps.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Nuts and bolts of chemical exchange saturation transfer MRI

et al. 2013

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“…For example, issues that limit APT/MT in its current state include eliminating direct water saturation effect, increasing the SNR, and improving image contrast [44, 45]. Safety concerns also warrant consideration, in regard to the specific absorption rate (SAR) of radiofrequency energy and the trade-off with acceptable scan time, saturation power, and flip angle.…”

Section: Discussionmentioning

confidence: 99%

Magnetization Transfer and Amide Proton Transfer MRI of Neonatal Brain Development

Yang

Wang

Zhao

2016

BioMed Research International

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Purpose. This study aims to evaluate the process of brain development in neonates using combined amide proton transfer (APT) imaging and conventional magnetization transfer (MT) imaging. Materials and Methods. Case data were reviewed for all patients hospitalized in our institution's neonatal ward. Patients underwent APT and MT imaging (a single protocol) immediately following the routine MR examination. Single-slice APT/MT axial imaging was performed at the level of the basal ganglia. APT and MT ratio (MTR) measurements were performed in multiple brain regions of interest (ROIs). Data was statistically analyzed in order to assess for significant differences between the different regions of the brain or correlation with patient gestational age. Results. A total of 38 neonates were included in the study, with ages ranging from 27 to 41 weeks' corrected gestational age. There were statistically significant differences in both APT and MTR measurements between the frontal lobes, basal ganglia, and occipital lobes (APT: frontal lobe versus occipital lobe P = 0.031 and other groups P = 0.00; MTR: frontal lobe versus occipital lobe P = 0.034 and other groups P = 0.00). Furthermore, APT and MTR in above brain regions exhibited positive linear correlations with patient gestational age. Conclusions. APT/MT imaging can provide valuable information about the process of the neonatal brain development at the molecular level.

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“…The six pool protons are defined in the initial offset frequency values as water at 0 ppm, amide at 3.5 ppm, amine at 3.0 ppm, hydroxyl at 0.9 ppm, the nuclear overhauser effect (NOE) at -3.5 ppm, and the magnetization transfer (MT) at -1.5 ppm. 8,[30][31][32] The problems with this Lorentizian fitting are that the fitted results are strongly depended on the initial values and the calculation takes relatively long time compared to that to obtain the asymmetry value.…”

Section: )mentioning

confidence: 99%

Physical Modeling of Chemical Exchange Saturation Transfer Imaging

Jahng

2017

Prog Med Phys

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Chemical Exchange Saturation Transfer (CEST) imaging is a method to detect solutes based on the chemical exchange of mobile protons with water. The solute protons exchange with three different patterns, which are fast, slow, and intermediate rates. The CEST contrast can be obtained from the exchangeable protons, which are hydroxyl protons, amine protons, and amide protons. The CEST MR imaging is useful to evaluate tumors, strokes, and other diseases. The purpose of this study is to review the mathematical model for CEST imaging and for measurement of the chemical exchange rate, and to measure the chemical exchange rate using a 3T MRI system on several amino acids. We reviewed the mathematical models for the proton exchange. Several physical models are proposed to demonstrate a two-pool, three-pool, and four-pool models. The CEST signals are also evaluated by taking account of the exchange rate, pH and the saturation efficiency. Although researchers have used most commonly in the calculation of CEST asymmetry, a quantitative analysis is also developed by using Lorentzian fitting. The chemical exchange rate was measured in the phantoms made of asparagine (Asn), glutamate (Glu), γ-aminobutyric acid (GABA), glycine (Gly), and myoinositol (MI). The experiment was performed at a 3T human MRI system with three different acidity conditions (pH 5.6, 6.2, and 7.4) at a concentration of 50 mM. To identify the chemical exchange rate, the "lsqcurvefit" built-in function in MATLAB was used to fit the pseudofirst exchange rate model. The pseudo-first exchange rate of Asn and Gly was increased with decreasing acidity. In the case of GABA, the largest result was observed at pH 6.2. For Glu, the results at pH 5.6 and 6.2 did not show a significant difference, and the results at pH 7.4 were almost zero. For MI, there was no significant difference at pH 5.6 or 7.4, however, the results at pH 6.2 were smaller than at the other pH values. For the experiment at 3T, we were only able to apply 1 s as the maximum saturation duration due to the limitations of the MRI system. The measurement of the chemical exchange rate was limited in a clinical 3T MRI system because of a hardware limitation.

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Quantitative characterization of nuclear overhauser enhancement and amide proton transfer effects in the human brain at 7 tesla

Cited by 92 publications

References 44 publications

Nuts and bolts of chemical exchange saturation transfer MRI

Nuts and bolts of chemical exchange saturation transfer MRI

Magnetization Transfer and Amide Proton Transfer MRI of Neonatal Brain Development

Physical Modeling of Chemical Exchange Saturation Transfer Imaging

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