Dataset Information

Localized, gradient-reversed ultrafast z-spectroscopy in vivo at 7T.

ABSTRACT: To collect ultrafast z-spectra in vivo in situations where voxel homogeneity cannot be assured.Saturating in the presence of a gradient encodes the frequency offset spatially across a voxel. This encoding can be resolved by applying a similar gradient during readout. Acquiring additional scans with the gradient polarity reversed effectively mirrors the spatial locations of the frequency offsets so that the same physical location of a positive offset in the original scan will contribute a negative offset in the gradient-reversed scan.Gradient-reversed ultrafast z-spectroscopy (GRUFZS) was implemented and tested in a modified, localized PRESS sequence at 7T. Lysine phantoms were scanned at various concentrations and compared with coventionally-acquired z-spectra. Scans were acquired in vivo in human brain from homogeneous and inhomogeneous voxels with the ultrafast direction cycled between read, phase, and slice. Results were compared to those from a similar conventional z-spectroscopy PRESS-based sequence.Asymmetry spectra from GRUFZS are more consistent and reliable than those without gradient reversal and are comparable to those from conventional z-spectroscopy. GRUFZS offers significant acceleration in data acquisition compared to traditional chemical exchange saturation transfer methods with high spectral resolution and showed higher relative SNR effficiency.GRUFZS offers a method of collecting ultrafast z-spectra in voxels with the inhomogeneity often found in vivo. Magn Reson Med 76:1039-1046, 2016. © 2016 Wiley Periodicals, Inc.

SUBMITTER: Wilson NE

PROVIDER: S-EPMC5023501 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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Localized, gradient-reversed ultrafast z-spectroscopy in vivo at 7T.

Wilson Neil E NE D'Aquilla Kevin K Debrosse Catherine C Hariharan Hari H Reddy Ravinder R

Magnetic resonance in medicine 20160701 4

<h4>Purpose</h4>To collect ultrafast z-spectra in vivo in situations where voxel homogeneity cannot be assured.<h4>Theory</h4>Saturating in the presence of a gradient encodes the frequency offset spatially across a voxel. This encoding can be resolved by applying a similar gradient during readout. Acquiring additional scans with the gradient polarity reversed effectively mirrors the spatial locations of the frequency offsets so that the same physical location of a positive offset in the original ...[more]

PMID: 27367138

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Project description:BackgroundPrevious in vivo proton MR spectroscopy (MRS) studies have demonstrated the possibility of quantifying amide groups of conjugated bile acids (NHCBA), olefinic lipids and cholesterol (OLC), choline-containing phospholipids (CCPLs), taurine and glycine conjugated bile acids (TCBA, GCBA), methylene group of lipids (ML), and methyl groups of bile acids, lipids, and cholesterol (BALC1.0, BALC0.9, and TBAC) in the gallbladder, which may be useful for the study of cholestatic diseases and cholangiopathies. However, these studies were performed at 1.5T and 3T, and higher magnetic fields may offer improved spectral resolution and signal intensity.PurposeTo develop a method for gallbladder MRS at 7T.Study typeRetrospective, technical development.PopulationTen healthy subjects (five males and five females), two patients with primary biliary cholangitis (PBC) (one male and one female), and one patient with primary sclerosing cholangitis (PSC) (female).Field strength/sequenceFree-breathing single-voxel MRS with a modified stimulated echo acquisition mode (STEAM) sequence at 7T.AssessmentPostprocessing was based on the T2 relaxation of water in the gallbladder and in the liver. Concentrations of biliary components were calculated using water signal. All data were corrected for T2 relaxation times measured in healthy subjects.Statistical testsThe range of T2 relaxation time and concentration per bile component, and the resulting mean and standard deviation, were calculated.ResultsThe concentrations of gallbladder components in healthy subjects were: NHCBA: 93 ± 66 mM, OLC: 154 ± 124 mM, CCPL: 42 ± 17 mM, TCBA: 48 ± 35 mM, GCBA: 67 ± 32 mM, ML: 740 ± 391 mM, BALC1.0: 175 ± 92 mM, BALC0.9: 260 ± 138 mM, and TBAC: 153 ± 90 mM. Mean concentrations of all bile components were found to be lower in patients.Data conclusionThis work provides a protocol for designing future MRS investigations of the bile system in vivo.Evidence level2 TECHNICAL EFFICACY STAGE: 1.

Project description:Current advanced laser, optics and electronics technology allows sensitive recording of molecular dynamics, from single resonance to multi-colour and multi-pulse experiments. Extracting the occurring (bio-) physical relevant pathways via global analysis of experimental data requires a systematic investigation of connectivity schemes. Here we present a Matlab-based toolbox for this purpose. The toolbox has a graphical user interface which facilitates the application of different reaction models to the data to generate the coupled differential equations. Any time-dependent dataset can be analysed to extract time-independent correlations of the observables by using gradient or direct search methods. Specific capabilities (i.e. chirp and instrument response function) for the analysis of ultrafast pump-probe spectroscopic data are included. The inclusion of an extra pulse that interacts with a transient phase can help to disentangle complex interdependent pathways. The modelling of pathways is therefore extended by new theory (which is included in the toolbox) that describes the finite bleach (orientation) effect of single and multiple intense polarised femtosecond pulses on an ensemble of randomly oriented particles in the presence of population decay. For instance, the generally assumed flat-top multimode beam profile is adapted to a more realistic Gaussian shape, exposing the need for several corrections for accurate anisotropy measurements. In addition, the (selective) excitation (photoselection) and anisotropy of populations that interact with single or multiple intense polarised laser pulses is demonstrated as function of power density and beam profile. Using example values of real world experiments it is calculated to what extent this effectively orients the ensemble of particles. Finally, the implementation includes the interaction with multiple pulses in addition to depth averaging in optically dense samples. In summary, we show that mathematical modelling is essential to model and resolve the details of physical behaviour of populations in ultrafast spectroscopy such as pump-probe, pump-dump-probe and pump-repump-probe experiments.

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Localized, gradient-reversed ultrafast z-spectroscopy in vivo at 7T.

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Localized, gradient-reversed ultrafast z-spectroscopy in vivo at 7T.

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