Aggregated postpartum cerebral autoregulatory curves in normotensive individuals, preeclampsia with severe features, and superimposed preeclampsia with severe features.

Objectives Impaired cerebral autoregulation could contribute to postpartum stroke risk in individuals with preeclampsia. We modeled aggregated static autoregulatory curves in the postpartum period in individuals with no hypertension, preeclampsia, and chronic hypertension with superimposed preeclampsia. Approach This is a retrospective analysis of data from a prospective observational study of postpartum participants.

Benchmarking the Impact of Anatomical Segmentation on In Vivo Magnetic Resonance Spectroscopy.

Purpose: Estimation of metabolite concentrations in brain magnetic resonance spectroscopy (MRS) requires correction for differences in tissue water content, relaxation properties, and the proportions of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF). Accurate knowledge of the relative proportions of these tissue classes within the volume of interest is therefore essential for reliable quantification. Commonly used brain segmentation tools differ in their algorithms, priors, and implementation, potentially introducing variability in MRS-derived concentration estimates.

Constrained optimized water suppression for H MR spectroscopy.

Purpose: Water suppression is a necessary component to standard MR spectroscopy experiments due to the approximately 5000-10 000-fold higher water concentration and signal intensity compared with that of the metabolites and macromolecules of interest. Here, a novel algorithm referred to as constrained optimized water suppression (COWS) was developed, which enables generation of effective water suppression modules with an arbitrary number of radiofrequency (RF) pulses, and flexibly accommodates minimum durations between pulses, minimum total module duration, and maximum flip angles.

Methods: We use the COWS algorithm to create a water-suppression module with seven pulses, the same number of RF pulses as typical VAPOR7, at a reduced module duration of 236 ms, referred to as COWS(7;236), as well as one at the typical VAPOR duration but with an increased number of RF pulses, referred to as COWS(12;626).

Spline Baseline Model Flexibility Independently Affects the Accuracy and Precision of In Vivo Proton Magnetic Resonance Spectral Fitting in a Metabolite-Specific Manner Not Visually Predicted by Fit Residuals.

In vivo proton magnetic resonance spectroscopy (H-MRS) data often exhibit baselines or low-amplitude signal variations resulting from residual water, imperfectly suppressed lipids, low-amplitude metabolites not considered for fitting, and other features not represented in a basis set. While multitudinous approaches exist to model these baselines in H-MR spectral analysis, many continue to lack systematic validation against varied and realistic ground-truth standards. Here, we compare the accuracy (error mean) and precision (error standard deviation) of metabolite scaling estimates by linear combination modeling (LCM) spectral fitting accounting for spectral baselines via smoothed cubic splines at 50 different combinations of fixed knot interval and smoothing weight, either with or without additionally simulated Gaussian basis signals to separately model spectral macromolecules.

Proton Magnetic Resonance Spectroscopy in Post-Traumatic Stress Disorder-Updated Systematic Review and Meta-Analysis.

A stressor-related disorder wherein traumatic experience precipitates protracted disruptions to mood and cognition, post-traumatic stress disorder (PTSD) is associated with wide-ranging abnormalities across the body. While various methods have investigated these deviations, only proton magnetic resonance spectroscopy (H MRS) enables noninvasive measurement of small-molecule metabolites in the living human. H MRS has correspondingly been employed to test hypotheses about the composition and function of multiple brain regions putatively involved in PTSD.

Multiple sclerosis diagnosis and phenotype identification by multivariate classification of in vivo frontal cortex metabolite profiles.

Multiple sclerosis (MS) is a heterogeneous autoimmune disease for which diagnosis continues to rely on subjective clinical judgment over a battery of tests. Proton magnetic resonance spectroscopy (H MRS) enables the noninvasive in vivo detection of multiple small-molecule metabolites and is therefore in principle a promising means of gathering information sufficient for multiple sclerosis diagnosis and subtype classification. Here we show that supervised classification using H-MRS-visible normal-appearing frontal cortex small-molecule metabolites alone can indeed differentiate individuals with progressive MS from control (held-out validation sensitivity 79% and specificity 68%), as well as between relapsing and progressive MS phenotypes (held-out validation sensitivity 84% and specificity 74%).

Concentration of Gallbladder Phosphatidylcholine in Cholangiopathies: A Phosphorus-31 Magnetic Resonance Spectroscopy Pilot Study.

Background: Biliary phosphatidylcholine (PtdC) concentration plays a role in the pathogenesis of bile duct diseases. In vivo phosphorus-31 magnetic resonance spectroscopy ( P-MRS) at 7 T offers the possibility to assess this concentration noninvasively with high spectral resolution and signal intensity.

Purpose: Comparison of PtdC levels of cholangiopathic patient groups to a control group using a measured T relaxation time of PtdC in healthy subjects.

Hippocampal single-voxel MR spectroscopy with a long echo time at 3 T using semi-LASER sequence.

The hippocampus is one of the most challenging brain regions for proton MR spectroscopy (MRS) applications. Moreover, quantification of J-coupled species such as myo-inositol (m-Ins) and glutamate + glutamine (Glx) is affected by the presence of macromolecular background. While long echo time (TE) MRS eliminates the macromolecules, it also decreases the m-Ins and Glx signal and, as a result, these metabolites are studied mainly with short TE.

Are Cramér-Rao lower bounds an accurate estimate for standard deviations in in vivo magnetic resonance spectroscopy?

Due to inherent time constraints for in vivo experiments, it is infeasible to repeat multiple MRS scans to estimate standard deviations on the desired measured parameters. As such, the Cramér-Rao lower bounds (CRLBs) have become the routine method to approximate standard deviations for in vivo experiments. Cramér-Rao lower bounds, however, as the name suggests, are theoretically a lower bound on the standard deviation and it is not clear if and under what circumstances this approximation is valid.

INSPECTOR: free software for magnetic resonance spectroscopy data inspection, processing, simulation and analysis.

In vivo magnetic resonance spectroscopy (MRS) is a powerful tool for biomedical research and clinical diagnostics, allowing for non-invasive measurement and analysis of small molecules from living tissues. However, currently available MRS processing and analytical software tools are limited in their potential for in-depth quality management, access to details of the processing stream, and user friendliness. Moreover, available MRS software focuses on selected aspects of MRS such as simulation, signal processing or analysis, necessitating the use of multiple packages and interfacing among them for biomedical applications.

A semi-LASER, single-voxel spectroscopic sequence with a minimal echo time of 20.1 ms in the human brain at 3 T.

An optimized semi-LASER sequence that is capable of acquiring artefact-free data with an echo time (TE) of 20.1 ms on a standard clinical 3 T MR system was developed. Simulations were performed to determine the optimal TEs that minimize the expected Cramér-Rao lower bound (CRLB) as proxy for quantification accuracy of metabolites.

In Vivo H MR Spectroscopy of Biliary Components of Human Gallbladder at 7T.

Background: Previous 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.

Concentration and effective T relaxation times of macromolecules at 3T.

Purpose: We aimed to investigate the concentration and effective T relaxation time of macromolecules assessed with an ultra-short TE sLASER sequence in 2 brain regions, the occipital and frontal cortex, in both genders at 3T.

Methods: An optimized sLASER sequence was used in conjunction with a double-inversion preparation module to null the metabolites. Eight equally spaced TEs were chosen from 20.

Elevated homocarnosine and GABA in subject on isoniazid as assessed through 1H MRS at 7T.

Typical magnetic resonance spectroscopy J-editing methods designed to quantify GABA suffer from contamination of both overlapping macromolecules and homocarnosine signal, introducing potential confounds. The aim of this study was to develop a novel method to assess accurately both the relative concentrations of homocarnosine as well as GABA free from overlapping creatine, homocarnosine and macromolecule signal. A novel method which utilized the combination of echo time STEAM and MEGA-sLASER magnetic resonance spectroscopy experiments at 7T were used to quantify the concentration of GABA and homocarnsoine independently, which are typically quantified in tandem.

Low-level fat fraction quantification at 3 T: comparative study of different tools for water-fat reconstruction and MR spectroscopy.

Objectives: Chemical Shift Encoded Magnetic Resonance Imaging (CSE-MRI)-based quantification of low-level (< 5% of proton density fat fraction-PDFF) fat infiltration requires highly accurate data reconstruction for the assessment of hepatic or pancreatic fat accumulation in diagnostics and biomedical research.

Materials And Methods: We compare three software tools available for water/fat image reconstruction and PDFF quantification with MRS as the reference method. Based on the algorithm exploited in the tested software, the accuracy of fat fraction quantification varies.

UTE-SPECIAL for3D localization at an echo time of 4 ms on a clinical 3 T scanner.

Reducing the echo time of magnetic resonance spectroscopy experiments is appealing because it increases the available signal and reduces J-evolution of coupled metabolites. In this manuscript a novel sequence, referred to as Ultrashort echo TimE, SPin ECho, full Intensity Acquired Localized (UTE-SPECIAL), is described which is able to achieve ultrashort echo times (4 ms) on a standard clinical 3 T MR system while recovering the entirety of the available magnetization. UTE-SPECIAL obtains full 3D spatial localization through a 2D adiabatic inversion pulse which is cycled "on" and "off" every other repetition, in combination with a slice-selective excitation pulse.

Quantifying the Metabolic Signature of Multiple Sclerosis by Proton Magnetic Resonance Spectroscopy: Current Challenges and Future Outlook in the Translation From Proton Signal to Diagnostic Biomarker.

Proton magnetic resonance spectroscopy (H-MRS) offers a growing variety of methods for querying potential diagnostic biomarkers of multiple sclerosis in living central nervous system tissue. For the past three decades, H-MRS has enabled the acquisition of a rich dataset suggestive of numerous metabolic alterations in lesions, normal-appearing white matter, gray matter, and spinal cord of individuals with multiple sclerosis, but this body of information is not free of seeming internal contradiction. The use of H-MRS signals as diagnostic biomarkers depends on reproducible and generalizable sensitivity and specificity to disease state that can be confounded by a multitude of influences, including experiment group classification and demographics; acquisition sequence; spectral quality and quantifiability; the contribution of macromolecules and lipids to the spectroscopic baseline; spectral quantification pipeline; voxel tissue and lesion composition; and relaxation; B field characteristics; and other features of study design, spectral acquisition and processing, and metabolite quantification about which the experimenter may possess imperfect or incomplete information.

Simultaneous optimization of crusher and phase cycling schemes for magnetic resonance spectroscopy: an extension of dephasing optimization through coherence order pathway selection.

Purpose: To extend the dephasing optimization through coherence order pathway selection (DOTCOPS) algorithm, originally designed solely for gradient crusher schemes, to include tailored phase cycling schemes for arbitrary pulse sequences and arbitrary number of coupled spins.

Theory And Methods: The effects all possible nested and cogwheel phase cycling schemes have on the coherence order pathways for an arbitrary experiment are considered. The DOTCOPS algorithm uses a cost function to maximally eliminate unwanted coherence pathways, with schemes preferentially eliminating unwanted coherence pathways that are less affected by the crusher scheme.

Magnetic resonance Spectrum simulator (MARSS), a novel software package for fast and computationally efficient basis set simulation.

The aim of this study was to develop a novel software platform for the simulation of magnetic resonance spin systems, capable of simulating a large number of spatial points (128 ) for large in vivo spin systems (up to seven coupled spins) in a time frame of the order of a few minutes. The quantum mechanical density-matrix formalism is applied, a coherence pathway filter is utilized for handling unwanted coherence pathways, and the 1D projection method, which provides a substantial reduction in computation time for a large number of spatial points, is extended to include sequences of an arbitrary number of RF pulses. The novel software package, written in MATLAB, computes a basis set of 23 different metabolites (including the two anomers of glucose, seven coupled spins) with 128 spatial points in 26 min for a three-pulse experiment on a personal desktop computer.

Theoretical description of modern H in Vivo magnetic resonance spectroscopic pulse sequences.

This article reviews the most commonly used modern sequences designed to confront the two major challenges of in vivo magnetic resonance spectroscopy (MRS): spatial localization and metabolic specificity. The purpose of this review article is to provide a deeper and clearer understanding of the underlying mechanisms by which all modern MRS sequences operate. A descriptive explanation, consistent pulse sequence diagram, and theoretical concepts of the measured signal are given for five spatial localization sequences and three modules designed to increase metabolic specificity.

Dephasing optimization through coherence order pathway selection (DOTCOPS) for improved crusher schemes in MR spectroscopy.

Purpose: To develop an algorithm which can robustly eliminate all unwanted coherence pathways for an arbitrary magnetic resonance spectroscopy experiment through the adjustment of the relative amplitudes of crusher gradients, thereby reducing the effects of spurious echoes and mislocalization.

Theory And Methods: The effect of crushing gradients for all coherence pathways was modeled according to the associated physics, and a cost function was optimized which maximally crushes all unwanted coherence pathways, while unaffecting the desired coherence pathway(s). The efficacy of the method was tested versus literature schemes from 2 separate MR spectroscopy (MRS) sequences: sLASER and MEGA-sLASER with both phantom and in vivo experiments.

Quantification of glutathione transverse relaxation time T using echo time extension with variable refocusing selectivity and symmetry in the human brain at 7 Tesla.

Glutathione (GSH) is an endogenous antioxidant implicated in numerous biological processes, including those associated with multiple sclerosis, aging, and cancer. Spectral editing techniques have greatly facilitated the acquisition of glutathione signal in living humans via proton magnetic resonance spectroscopy, but signal quantification at 7 Tesla is still hampered by uncertainty about the glutathione transverse decay rate T relative to those of commonly employed quantitative references like N-acetyl aspartate (NAA), total creatine, or water. While the T of uncoupled singlets can be derived in a straightforward manner from exponential signal decay as a function of echo time, similar estimation of signal decay in GSH is complicated by a spin system that involves both weak and strong J-couplings as well as resonances that overlap those of several other metabolites and macromolecules.