Water-suppressed Sequence Research Articles

A Portable Chip-Based NMR Relaxometry System With Arbitrary Phase Control for Point-of-Care Blood Analysis.

In this article, we present a portable NMR relaxometry system optimized for the point-of-care analysis of body liquids such as blood. The presented system is centered on an NMR-on-a-chip transceiver ASIC, a reference frequency generator with arbitrary phase control, and a custom-designed miniaturized NMR magnet with a field strength of 0.29 T and a total weight of 330 g. The NMR-ASIC co-integrates a low-IF receiver, a power amplifier, and a PLL-based frequency synthesizer on a total chip area of 1100 × 900 μm 2. The arbitrary reference frequency generator enables the use of conventional CPMG and inversion sequences, as well as modified water-suppression sequences. Moreover, it is used to implement an automatic frequency lock to correct temperature-induced magnetic field drifts. Proof-of-concept measurements on NMR phantoms and human blood samples show an excellent concentration sensitivity of v[Formula: see text] = 2.2 mM/[Formula: see text]. This very good performance renders the presented system an ideal candidate for the future NMR-based point-of-care detection of biomarkers such as the blood glucose concentration.

Breast Magnetic Resonance Spectroscopy at 3 T in Biopsy-Proven Breast Cancers

The role of functional techniques, such as magnetic resonance spectroscopy (H-MRS), as noninvasive tools to increase breast MR imaging reliability has been widely investigated during the last 2 decades. Considering the growing interest in tumor biology and its influence on functional parameters, the aim of this study was to investigate the relationship between H-MRS parameters and breast cancer biomarkers and to evaluate whether the results of H-MRS at 3 T can correlate with established breast cancer prognostic factors in our clinical experience. One hundred two patients with biopsy-proven breast cancer underwent 3 T breast MR imaging. Single-voxel H-MRS was performed after the T1-weighted sequence, using a PRESS water-suppressed sequence (BREASE). Data were collected from a single rectangular volume of interest that encompassed the lesion. Magnetic resonance images and spectra of 102 Breast Imaging Reporting and Data System 6 lesions were prospectively evaluated by 2 radiologists in consensus. H-MRS results were considered positive if the choline peak signal-to-noise ratio was 2 or higher. H-MRS findings were then compared with morphological features and to histological findings, such as lesion size, nuclear grade, Ki-67, hormone receptor status, and Her2 expression. Elevated levels of total choline were detectable in 68/102 cases (66.67%) and undetectable in 34/102 (33.33%). A statistically significant association between the presence of choline peak and higher tumor grading (P < 0.0001), greater Ki-67 value (P < 0.0001), and larger lesion size (P < 0.0001) was found. No statistically significant associations were observed between choline peak and the luminal subgroups, even if higher levels of choline were more frequent in nonluminal A lesions. Our study confirms that 3 T breast H-MRS can be a valid additional tool to obtain further information about breast cancer biology and to predict tumor aggressiveness, because the detection of elevated levels of total choline in the spectrum is associated with a biologically aggressive breast cancer phenotype (large dimensions, grade 3, high values of Ki-67). Our results need to be validated in standardized larger-scale studies.

Water suppression in the human brain with hypergeometric RF pulses for single-voxel and multi-voxel MR spectroscopy.

To develop and investigate a novel water suppression sequence with hypergeometric pulses at 3 T. Simulations were used to optimize the delays and amplitudes of 5 hypergeometric prepulses, to minimize the residual water over a range of T1 and B1 values. Single-voxel data with hypergeometric water suppression (HGWS) prepulses were acquired in the centrum semiovale, 2 parietal regions, and insula of 7 subjects, and compared with VAPOR water suppression. Magnetic resonance spectroscopic imaging (MRSI) data using both VAPOR and HGWS prepulses were also collected and compared. Water suppression performance was calculated as the residual water peak height relative to the unsuppressed water peak. MRSI voxel-by-voxel comparison was performed by calculating the ratio between HGWS and VAPOR residual water peaks. In simulations, HGWS and VAPOR are insensitive to B1 and water T1 variations, but with no B1 variation, HGWS has a lower average residual water fraction (0.0033) than that of VAPOR (0.0091). In single-voxel acquisitions, HGWS performs better than VAPOR in all regions with a 2.3-fold to 5.7-fold lower residual water. In MRSI acquisitions, HGWS performs on average 2.3-fold better than VAPOR in 98.9% of the voxels. HGWS provides better water suppression than VAPOR in both single-voxel and multivoxel acquisitions with a shorter sequence duration.

Visualisation of cakes differing in oil content with magnetic resonance imaging

ABSTRACTMagnetic resonance imaging (MRI) is a non-invasive imaging technique that can visualise samples’ interior by using the signal coming from mobile protons. The aim of this study was to examine the effects of oil content and peanut/raisin addition on cake quality and to illustrate the power of MRI in analysis of moisture and oil distribution. For this purpose, MR images were acquired with a spin echo sequence and relaxation times T1 and T2, and moisture content and firmness of cakes were measured. High oil cakes (HOC) had higher moisture content and lower firmness than low oil cakes (LOC). However, addition of raisin/peanut did not affect the firmness of cakes significantly. In MR images, HOC cake crumb, owing to its higher oil content, displayed larger signal intensities. Signal acquired from different slices demonstrated an increase in moisture content from crust to centre of the cakes. Peanut and raisin signals were suppressed in fat and water suppression sequences, respectively. Significant correlation between transverse relaxation time (T2a) and oil content (R2 = 0.99) was found. Moreover, longitudinal relaxation time (T1) was found to be strongly correlated with moisture content (R2 = 0.99). The results demonstrated MRI’s power as an accurate and non-invasive analysis method in baking.

Tailored spiral in-out spectral-spatial water suppression pulses for magnetic resonance spectroscopic imaging.

To develop short water suppression sequences for 7 T magnetic resonance spectroscopic imaging, with mitigation of subject-specific transmit RF field ( B1+) inhomogeneity. Patient-tailored spiral in-out spectral-spatial saturation pulses were designed for a three-pulse WET water suppression sequence. The pulses' identical spatial subpulses were designed using patient-specific B1+ maps and a spiral in-out excitation k-space trajectory. The subpulse train was weighted by a spectral envelope that was root-flipped to minimize peak RF demand. The pulses were validated in in vivo experiments that acquired high resolution magnetic resonance spectroscopic imaging data, using a crusher coil for fast lipid suppression. Residual water signals and MR spectra were compared between the proposed tailored sequence and a conventional WET sequence. Replacing conventional spectrally-selective pulses with tailored spiral in-out spectral-spatial pulses reduced mean water residual from 5.88 to 2.52% (57% improvement). Pulse design time was less then 0.4 s. The pulses' specific absorption rate were compatible with magnetic resonance spectroscopic imaging TRs under 300 ms, which enabled spectra of fine in plane spatial resolution (5 mm) with good quality to be measured in 7.5 min. Tailored spiral in-out spectral-spatial water suppression enables efficient high resolution magnetic resonance spectroscopic imaging in the brain. Magn Reson Med 79:31-40, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Does superficial fat affect metabolite concentrations determined by MR spectroscopy with water referencing?

It has recently been reported in this journal that local fat depots produce a sizable frequency-dependent signal attenuation in magnetic resonance spectroscopy (MRS) of the brain. If of a general nature, this effect would question the use of internal reference signals for quantification of MRS and the quantitative use of MRS as a whole. Here, it was attempted to verify this effect and pinpoint the potential causes by acquiring data with various acquisition settings, including two field strengths, two MR scanners from different vendors, different water suppression sequences, RF coils, localization sequences, echo times, and lipid/metabolite phantoms. With all settings tested, the reported effect could not be reproduced, and it is concluded that water referencing and quantitative MRS per se remain valid tools under common acquisition conditions.

Large variations in acidity of terminal amide bonds in histamine-containing peptides as measured by proton DNMR

The main objective of these studies is to quantitatively estimate pK variations of individual amide bonds as a function of the ionization state of end groups in peptides, determined on measuring macro- and micro- (if any) ionization constants. 1H NMR spectra of aqueous solutions of eight model substrates were consequently recorded using a water suppression sequence, within large pH ranges. A set of programs was devised to treat NMR data over the entirety of pH-dependent NMR patterns, in order to smooth out errors arising in handling individual spectra. Rates of amide proton abstraction by hydroxide ions were obtained from the coalescence of methylene coupled protons and the decrease of NH bond signal intensities, allowing us to estimate and discuss peptide pKs on assuming back reprotonation at a diffusion-limited rate. Cis–trans isomerization rates in two substrates bearing a tert-Butyloxycarbonyl terminal group were put in parallel with the acidity of carbamic protons.

Evaluation of metabolomic changes as a biomarker of chondrogenic differentiation in 3D-cultured human mesenchymal stem cells using proton (1H) nuclear magnetic resonance spectroscopy.

PurposeThe purpose of this study was to evaluate the metabolomic changes in 3D-cultured human mesenchymal stem cells (hMSCs) in alginate beads, so as to identify biomarkers during chondrogenesis using 1H nuclear magnetic resonance (NMR) spectroscopy.Materials and MethodshMSCs (2×106 cells/mL) were seeded into alginate beads, and chondrogenesis was allowed to progress for 15 days. NMR spectra of the chondrogenic hMSCs were obtained at 4, 7, 11, and 15 days using a 14.1-T (600-MHz) NMR with the water suppression sequence, zgpr. Real-Time polymerase chain reaction (PCR) was performed to confirm that that the hMSCs differentiated into chondrocytes and to analyze the metabolomic changes indicated by the NMR spectra.ResultsDuring chondrogenesis, changes were detected in several metabolomes as hMSC chondrogenesis biomarkers, e.g., fatty acids, alanine, glutamate, and phosphocholine. The metabolomic changes were compared with the Real-Time PCR results, and significant differences were determined using statistical analysis. We found that changes in metabolomes were closely related to biological reactions that occurred during the chondrogenesis of hMSCs.ConclusionsIn this study, we confirm that metabolomic changes detected by 1H-NMR spectroscopy during chondrogenic differentiation of 3D-cultured hMSCs in alginate beads can be considered as biomarkers of stem cell differentiation.

Low-power water suppression by hyperbolic secant pulses with controlled offsets and delays (WASHCODE).

A class of chemical-shift-selective (CHESS) water suppression (WS) schemes is presented in which the characteristic frequency-domain excitation profiles of "adiabatic" full-passage (AFP) RF pulses are utilized for frequency-selective excitation of the water resonance. In the proposed WS schemes, dubbed WASHCODE, hyperbolic secant (HS) pulses were used as the AFP pulses. Besides the high immunity of WS efficiency toward B(1) inhomogeneity, these sequences also exhibit extraordinary insensitivity to the dispersion of the water T(1) relaxation times. The actual performance of the proposed WS schemes was achieved in particular by optimizing the frequency offsets of WS HS pulses and the time intervals between them. To reduce the RF power requirements of these WS sequences for in vivo applications, HS pulses with the minimum possible frequency bandwidths were employed, which also substantially reduced the adverse effects on the observed proton MR spectra. The proposed WS schemes were evaluated by simulations based on the Bloch equations. Several WS sequences which looked particularly promising were verified experimentally on the human brain on a 3 T MR scanner using very short echo-time STEAM for volume selection and a standard single-loop surface coil for both signal transmission and reception. Routinely, water-suppression factors ranging from 2000 to 4000 were achieved in vivo without additional adjustment of parameters for individual subjects and without violating legal safety limits.

Comparison of single‐shot localization methods (steam and press) for In vivo proton NMR spectroscopy

Two single-shot localization techniques, STEAM and PRESS, are analyzed with regard to specifications for in vivo localized proton NMR. In particular, attention is paid to optimum signal intensity per unit volume, sensitivity to motion and diffusion, shortest attainable echo time, water suppression and editing possibilities. Experimental results are shown for cat brain at 4.7 T and human brain at 1.5 T. Both STEAM and PRESS are highly effective localization methods. For long echo times, PRESS is the method of choice, because it offers a factor of two gain in signal intensity. In addition, the method is less sensitive to motion and diffusion, and not susceptible to multiple-quantum effects. STEAM offers advantages for observation of (coupled) metabolites with short T2, because (a) shorter TEs can be attained and (b) effective water suppression sequences can be implemented without penalty in echo time. Differences relating to editing possibilities and B1 dependence, possibly important in choosing a method, are discussed.

In vivo localized proton spectroscopic studies of human gastrocnemius muscle.

In vivo proton magnetic resonance spectroscopy studies of gastrocnemius muscle were performed in six normal volunteers. Both spatially resolved spectroscopy (SPARS) and stimulated echo acquisition mode (STEAM) sequences were used for volume localization. A number of water suppression sequences have been combined with these localization schemes. Among the various techniques investigated in these studies, STEAM with an inversion pulse (T1-discriminated spectrum) seems to have the best potential for in vivo localized high-resolution proton spectroscopy studies of human muscle.

1H in Vivo NMR spectroscopy with surface coils. Hard-pulse water suppression sequences and spatial localization

The use of binomial pulse sequences to achieve water suppression in the inhomogeneous B 1 field of surface coils is analyzed. It is shown that the frequency response to the binomial excitation sequences is dependent on the spatial coordinates. Therefore the shape and the location of the sensitive volume can be strongly dependent on the chemical shift, and the frequency response cannot be accurately known. The drawbacks of the binomial excitation sequences can be overcome by using a pulse angle small enough so that the spin system behaves as a linear system. However, this is at the cost of a reduction in the signal-to-noise ratio, and of the loss of the ability of surface coils to obtain spectra from tissues located at some depth beneath the surface of the sample. The use of phase-cycled binomial refocusing pulses is then analyzed. It is shown that they never introduce an additional phase shift. Moreover, the particularly simple response obtained with the 2 2 and 2 42 refocusing pulses when used with the Exorcycle phase-cycling scheme is emphasized. It is shown that the use of spin-echo sequences greatly improves the spatial localization properties of binomial excitation sequences. Finally, spin-echo sequences which allow water suppression without any phase correction and which give a frequency response independent of the shape of the sample are proposed.