Magnetization transfer contrast–suppressed imaging of amide proton transfer and relayed nuclear overhauser enhancement chemical exchange saturation transfer effects in the human brain at 7T

Xu, Xiang; Yadav, Nirbhay N.; Zeng, Haifeng; Jones, Craig K.; Zhou, Jinyuan; Zijl, Peter van; Xu, Jiadi

doi:10.1002/mrm.25990

Cited by 66 publications

(111 citation statements)

References 42 publications

(49 reference statements)

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“…Since the NOE coupling rate is slow (39), a long irradiation time (usually a few seconds) is required for the spin system to reach steady state. In addition, a moderate irradiation power is required to avoid much direct water saturation effect which becomes significant when the resonance frequency of solute molecules is close to water line.…”

Section: Discussionmentioning

confidence: 99%

A new NOE-mediated MT signal at around −1.6ppm for detecting ischemic stroke in rat brain

Zhang

Wang

Afzal

et al. 2016

Magnetic Resonance Imaging

131

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In the present work, we reported a new nuclear Overhauser enhancement (NOE)-mediated magnetization transfer (MT) signal at around −1.6 ppm (NOE(−1.6)) in rat brain and investigated its application in the detection of acute ischemic stroke in rodent model. Using continuous wave (CW) MT sequence, the NOE(−1.6) is reliably detected in rat brain. The amplitude of this new NOE signal in rat brain was quantified using a 5-pool Lorentzian Z-spectral fitting method. Amplitudes of amide, amine, NOE at −3.5 ppm (NOE(−3.5)), as well as NOE(−1.6) were mapped using this fitting method in rat brain. Several other conventional imaging parameters (R 1 , R 2 , apparent diffusion coefficient (ADC), and semi-solid pool size ratio (PSR)) were also measured. Our results showed that NOE(−1.6), R 1 , R 2 , ADC, and APT signals from stroke lesion have significant changes at 0.5-1 h after stroke. Compared with several other imaging parameters, NOE(−1.6) shows the strongest contrast differences between stroke and contralateral normal tissues and stays consistent over time until 2 h after onset of stroke. Our results demonstrate that this new NOE(−1.6) signal in rat brain is a new potential contrast for assessment of acute stroke in vivo and might provide broad applications in the detection of other abnormal tissues.

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Section: Discussionmentioning

confidence: 99%

A new NOE-mediated MT signal at around −1.6ppm for detecting ischemic stroke in rat brain

Zhang

Wang

Afzal

et al. 2016

Magnetic Resonance Imaging

131

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“…The specificity of this method needs further evaluation through both simulations and phantom studies. Another method applying variable-delay multiple-pulses saturation (VDMP) was also developed to remove confounding factors, which also uses different DC (31,32). However, the underlying mechanism for these two methods are quite different: the VDMP produces the same direct saturation and MT effects through different delay times, while our proposed method produces the same direct saturation and MT effects through using the same average irradiation power.…”

Section: Discussionmentioning

confidence: 99%

Measurement of APT using a combined CERT-AREX approach with varying duty cycles

et al. 2017

Magnetic Resonance Imaging

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The goal is to develop an imaging method where contrast reflects amide-water magnetization exchange, with minimal signal contributions from other sources. Conventional chemical exchange saturation transfer (CEST) imaging of amides (often called amide proton transfer, or APT, and quantified by the metric MTRasym) is confounded by several factors unrelated to amides, such as aliphatic protons, water relaxation, and macromolecular magnetization transfer. In this work, we examined the effects of combining our previous chemical exchange rotation (CERT) approach with the non-linear AREX method while using different duty cycles (DC) for the label and reference scans. The dependencies of this approach, named AREXdouble,vdc, on tissue parameters, including T1, T2, semi-solid component concentration (fm), relayed nuclear Overhauser enhancement (rNOE), and nearby amines, were studied through numerical simulations and control sample experiments at 9.4 T and 1 µT irradiation. Simulations and experiments show that AREXdouble,vdc is sensitive to amide-water exchange effects, but is relatively insensitive to T1, T2, fm, nearby amine, and distant aliphatic protons, while the conventional metric MTRasym, as well as several other APT imaging methods, are significantly affected by at least some of these confounding factors.

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“…By choosing a t delay at which MTC effects are equal, a VDMP difference spectrum can be calculated that removes MTC and DS effects independent of any asymmetry. This is illustrated in Figure 9(b) and (c) for human brain at 7 T, 73 and allows pure APT and NOE effects to be calculated. Note that the rNOE effects are equal for WM and GM, consistent with results for the mobile MM baseline from MRS studies.…”

Section: Saturation-based Editing Sequencesmentioning

confidence: 99%

“…This approach can be employed with a high B 1 and a limited number of pulses (16-64, B 1 = 3.4 μT, t sat = 20 ms) to provide a sufficient CEST effect. 69,73 The RF pulses serve both as a relaxation filter for the interfering saturation contributions as well as an exchange rate filter for the CEST contributions. This enables application to many different types of protons.…”

Section: Exchange Transfer Sequences Employing Excitationmentioning

confidence: 99%

“…It is no doubt clear from the previous sections that there is a lot of ongoing effort by CEST researchers to analyze the different contributions to the Z-spectrum and edit these in or out 73,120,[125][126][127][128][129][130][131] to provide more specific measurements of individual spectral components. The reason of course is to quantify endogenous and contrast-agent contributions as well as other parameters in the CEST equations that can provide information regarding physiological processes in vivo.…”

Section: Quantification Of Cest-related Parametersmentioning

confidence: 99%

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Proton Chemical Exchange Saturation Transfer (CEST) MRS and MRI

Zijl

Sehgal

2016

eMagRes

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Proton magnetic resonance spectroscopy ( 1 H MRS) of biological systems has higher specificity than MRI because resonances of multiple metabolites can be distinguished, reflecting chemistry and physiology in situ. Unfortunately, this approach has very low sensitivity as the metabolites are typically at millimolar concentrations compared to the molar signal strength of water-based MRI. As a consequence, even though 1 H MRS is a powerful and common research tool, its inroad into daily clinical practice has been limited. Until very recently, 1 H MRS applications have focused on the resonances upfield (i.e., at lower frequency) of the water resonance. This article deals with protons that are generally not observed in a typical water-suppressed spectrum, namely, the exchangeable protons found predominantly downfield from water. These can usually be detected by MRS only if the transfer of water proton saturation (established during water suppression) is not a confounding factor, or by using water exchange (WEX) spectroscopy, in which RF labeling of the water protons is transferred to the exchangeable protons and subsequently detected. More importantly, it has recently become clear that the presence of such exchangeable protons on low concentration solute molecules can be detected via the water signal by RF labeling of these protons and subsequent transfer of this label to water protons. This process, leading to saturation of the water signal and enhancement of the effect through repeated exchange, can be used for the imaging of metabolite signals or exchangeable-proton-based contrast agents with enhanced sensitivity. This has given rise to the field of chemical exchange saturation transfer (CEST) MRI, which has greatly increased the potential for translating spectroscopic methods to the clinic. Examples include the measurement of pH, temperature, and enzyme activity as well as detection of cellular metabolites, ions, and proteins and peptides. In addition, bio-organic compounds can now be used for contrast agents, cell and nanoparticle labeling, and reporter genes.

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Magnetization transfer contrast–suppressed imaging of amide proton transfer and relayed nuclear overhauser enhancement chemical exchange saturation transfer effects in the human brain at 7T

Cited by 66 publications

References 42 publications

A new NOE-mediated MT signal at around −1.6ppm for detecting ischemic stroke in rat brain

A new NOE-mediated MT signal at around −1.6ppm for detecting ischemic stroke in rat brain

Measurement of APT using a combined CERT-AREX approach with varying duty cycles

Proton Chemical Exchange Saturation Transfer (CEST) MRS and MRI

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