Rapid measurement of brain macromolecular proton fraction with transient saturation transfer MRI

Self Cite

Purpose To inform quantification of MRI magnetization transfer contrast at high field by measuring the spectral characteristics of 1H protons in semi-solids in human brain at 7 T, while avoiding prohibitive RF tissue heating and confounding effects from chemical exchange. Methods Saturation-recovery type experiments were performed using brief, frequency-specific RF pulses that saturate semi-solid proton magnetization. Analysis of the subsequent recovery of water proton magnetization with a two-pool model of exchange allowed studying spectral characteristics of semi-solid protons. Results We show that in white matter, the semi-solid proton spectrum can be approximated with a symmetric, super-Lorentzian line at −2.58±0.05 ppm from the water resonance and an average transverse relaxation time constant (T2) of 9.6±0.6 µs. Conclusion These results are consistent with studies at lower field that have indicated a major contribution from methylene protons to magnetization transfer contrast and will facilitate the design and quantification of magnetization transfer studies at 7 T.

Section: Resultssupporting

confidence: 86%

“… Note: R 1, MP was assumed as 2.0 s −1 uniform across the brain for all subjects, as determined previously by van Gelderen et al . All rates are reported in s −1 .…”

Section: Resultsmentioning

confidence: 99%

F S_{W P} (t) = 1 - \frac{M_{W P} (t)}{M_{W P} (\infty)} = a_{1} e^{- λ_{1} t} + a_{2} e^{- λ_{2} t}

F S_{M P} (t) = 1 - \frac{M_{M P} (t)}{M_{M P} (\infty)} = \frac{a_{1} (- λ_{1} + k_{W M} + R_{1, W P})}{k_{W M}} e^{- λ_{1} t} + \frac{a_{2} (- λ_{2} + k_{W M} + R_{1, W P})}{k_{W M}} e^{- λ_{2} t}

2 λ_{1, 2} = R_{1, W P} + R_{1, M P} + k_{M W} + k_{W M} \pm \sqrt{{(R_{1, M P} - R_{1, W P} + k_{M W} - k_{W M})}^{2} + 4 k_{M W} k_{W M}}

a_{1, 2} = \pm F S_{W P}

…”

Section: Methodsmentioning

confidence: 99%

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Spectral characteristics of semisolid protons in human brain white matter at 7 T

Gelderen

Duyn

2017

Self Cite

“…Recently, a transient MTC technique that resembles the VDMP approach was used to study the MTC parameters in human brain at 7T MRI, which resembles the VDMP approach, and provided information about the transfer rates and the line shape of the macromolecular components. 47,48 The off-resonance VDMP scheme has the additional capability of separating the fast-transferring and slow-transferring components that exist in Z-spectra. In the mouse brain, at the high saturation power applied in the current study, the amide and aliphatic peaks overlap with the broad slow-MTC line shape.…”

Section: Discussionmentioning

confidence: 99%

Separating fast and slow exchange transfer and magnetization transfer using off‐resonance variable‐delay multiple‐pulse (VDMP) MRI

Chen

Zeng

et al. 2018

“…Two types of pulses are used for CEST: saturation based or excitation based, and a train of such pulses is needed to enhance the detection sensitivity . A pulsed CEST experiment can be performed similarly to CW‐CEST, i.e., by measuring the water signal saturation as a function of saturation or excitation frequency, but its information content can be extended by measuring the water signal reduction as a function of inter‐pulse spacing (transfer delay time), i.e., similar to quantitative pulsed MTC experiments …”

Section: Comparison Of Asl Cest and Mtc Pulse Sequencesmentioning

confidence: 99%

CEST, ASL, and magnetization transfer contrast: How similar pulse sequences detect different phenomena

Knutsson

Ahlgren

et al. 2018

Chemical exchange saturation transfer (CEST), arterial spin labeling (ASL), and magnetization transfer contrast (MTC) methods generate different contrasts for MRI. However, they share many similarities in terms of pulse sequences and mechanistic principles. They all use RF pulse preparation schemes to label the longitudinal magnetization of certain proton pools and follow the delivery and transfer of this magnetic label to a water proton pool in a tissue region of interest, where it accumulates and can be detected using any imaging sequence. Due to the versatility of MRI, differences in spectral, spatial or motional selectivity of these schemes can be exploited to achieve pool specificity, such as for arterial water protons in ASL, protons on solute molecules in CEST, and protons on semi-solid cell structures in MTC. Timing of these sequences can be used to optimize for the rate of a particular delivery and/or exchange transfer process, for instance, between different tissue compartments (ASL) or between tissue molecules (CEST/MTC). In this review, magnetic labeling strategies for ASL and the corresponding CEST and MTC pulse sequences are compared, including continuous labeling, single-pulse labeling, and multi-pulse labeling. Insight into the similarities and differences among these techniques is important not only to comprehend the mechanisms and confounds of the contrasts they generate, but also to stimulate the development of new MRI techniques to improve these contrasts or to reduce their interference. This, in turn, should benefit many possible applications in the fields of physiological and molecular imaging and spectroscopy.