Carr-Purcell-Meiboom-Gill Sequence Research Articles

T1rho and T2rho based myocardial tissue characterisation in small animals at high-field MRI

Abstract Introduction Cardiac tissue characterisation using T2-based MRI promises non-invasive diagnosis or monitoring of inflammatory heart disease, toxic heart damage after chemotherapy and myocardial infarction or post-infarction patients. T2 relaxation is also an indicator for the detection of myocardial oedema or intramyocardial haemorrhage [1]. However, accurate T2 quantification is challenging due to motion, blood flow and field inhomogeneities, especially in high-field MRI [2]. In this work, we present an alternative to T2 imaging that uses spin-locking (SL) to provide a robust measurement of T2ρ relaxation. It is known from relaxation theory that T2ρ has a sensitivity almost identical to T2 [3]. In the small animal study presented here, cardiac T2ρ quantification is tested for the first time using a newly developed pulse sequence and compared with established methods. Methods All measurements were performed on a preclinical 7T MRI. T2 contrast was prepared using a CPMG (Carr-Purcell-Meiboom-Gill) sequence. T2ρ contrast was conventionally generated by a balanced-SL (BSL) preparation [4]. Furthermore, a new approach for T2ρ was developed based on a MLEV sequence (Malcolm-Levitt, [2]). In contrast to [2], all pulse delays were minimised here, producing pure T2ρ contrast (Fig. 1). The new method was first validated in phantom experiments and then tested in three mice with radial image acquisition accelerated for cardio-MRI. Results The results of the phantom study are shown in figure 2. No significant differences were found between BSL and MLEV for T2ρ quantification (mean deviation 0.74%). In vivo, significant artefacts were observed for T2 (Fig. 3), while both T2ρ methods showed improved image quality. For the evaluation of relaxation times in the left ventricle, the mean across all animals was: T2=22.9±2.6ms (R2=0.979), BSL-T2ρ=51.4±5.4ms (R2=0.983) and MLEV-T2ρ=60.0±3.4ms (R2>0.99). Thus, the MLEV-T2ρ method achieves the most robust quantification with a mean R2>0.99 and provides relaxation time maps with diagnostic image quality. Discussion: In the present study, myocardial T2ρ mapping was tested at 7T. While no significant differences between BSL and MLEV appeared in phantom experiments, significant difference was found in vivo. Here, only the MLEV technique could achieve robust quantification. One reason for the improved performance is the continuous refocusing and minimisation of free dephasing of the transverse magnetisation. The results also show that MLEV-T2ρ has improved image quality and more robust quantification compared to CPMG-T2. Conclusion Cardiac T2ρ quantification is a robust alternative to established T2 imaging and can be applied under high-field conditions. A combined measurement of T1ρ and T2ρ relaxation time could be used for native detection of myocardial fibrosis and oedema.Figure 1)Comparison of image qualityFigure 2)Results in a knockout model

Measuring the environment of a Cs qubit with dynamical decoupling sequences

We report the experimental implementation of dynamical decoupling on a small, non-interacting ensemble of up to 25 optically trapped, neutral Cs atoms. The qubit consists of the two magnetic-insensitive Cs clock states and , which are coupled by microwave radiation. We observe a significant enhancement of the coherence time when employing Carr-Purcell-Meiboom-Gill (CPMG) dynamical decoupling. A CPMG sequence with ten refocusing pulses increases the coherence time of 16.2(9) ms by more than one order of magnitude to 178(2) ms. In addition, we make use of the filter function formalism and utilise the CPMG sequence to measure the background noise floor affecting the qubit coherence, finding a power-law noise spectrum with . This finding is in very good agreement with an independent measurement of the noise in the intensity of the trapping laser. Moreover, the measured coherence evolutions also exhibit signatures of low-frequency noise originating at distinct frequencies. Our findings point toward noise spectroscopy of engineered atomic baths through single-atom dynamical decoupling in a system of individual Cs impurities immersed in an ultracold 87Rb bath.

CPMG pulse sequence for relaxation dispersion that cancels artifacts independently of spin states

The relaxation dispersion (rd) of nuclear magnetic resonance provides thermodynamic and kinetic information regarding molecules for which the conformations are exchanging in equilibrium. Experiments have often been implemented with Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences for heteronuclear S-spin in SI and SI3 spin systems. One of the most common CPMG sequences contains a sequence called a P-element in the middle to average the different relaxation rates of anti-phase and in-phase coherences; however, its drawback is that the artifacts that can be compensated for are only those in one of the two S-spin doublet magnetization components, for example, SIα or SIβ in an SI spin system. Thus, when the CPMG sequence is followed by a normal heteronuclear single-quantum correlation (HSQC) sequence, the detected signal will also include the other component with accumulated artifacts. To overcome this issue, we developed a new pulse sequence (AFTAC) that can suppress artifacts in both the magnetization components. Its effectiveness was demonstrated by simulations and actual measurements targeting the methyl groups of dimethylsulfoxide and N, N-dimethyltrichloroacetamide. The results demonstrated that the AFTAC sequence sufficiently suppressed the artifacts, despite being followed by an HSQC sequence that detects both components. AFTAC is particularly suitable for the rd measurements of small molecules, which are usually not deuterated and are not subject to transverse relaxation optimized spectroscopy (TROSY) sequences. AFTAC does not require 1H continuous wave irradiation for I-spin decoupling, which is necessary for certain CPMG methods that maintain S-spin in-phase coherence during the CPMG period (Tcpmg). Therefore, AFTAC places less burden on the probe, even with a long Tcpmg. Furthermore, the AFTAC method achieves a similar artifact suppression quality not only in SI but also in SI2 and SI3 spin systems.

Approximate analytical expressions for the Carr–Purcell–Meiboom–Gill sequences: Decay rates and modulation zeros of the echo train and the relation between the [formula omitted] and [formula omitted] relaxation times

Methods of multi-pulse sequences are widely used in magnetic resonance to study the local properties of magnetic particles and to increase the lifetime of spin coherence. Imperfect refocusing pulses lead to non-exponential signal decay due to the contribution of the coherence pathways in which T1 and T2 relaxation segments are mixed. Here, we present analytical approximations for echoes generated in the Carr-Purcell-Meiboom-Gill (CPMG) sequence. They provide simple expressions for the leading terms of the echo train decay and allow the relaxation times to be estimated for sequences with a relatively small number of pulses. For a given refocusing angle α, the decay times for the fixed phase and alternating phase CPMG sequences can be approximated as (T2-1+T1-1)/2 and T2O, respectively. The ability to estimate relaxation times from short pulse sequences can reduce the acquisition time, which is essential for the methods used in magnetic resonance imaging. In the case of a CPMG sequence with the fixed phase, the relaxation times can also be obtained from the points in the sequence at which the echo changes sign. Numerical comparison of the exact and approximate expressions shows the practical limits of the analytical formulas obtained. It is also shown that a double echo sequence in which the interval between the first two pulses is not equal to half the interval of the subsequent refocusing pulses provides the same information as two separate CPMG (or CP) sequences with fixed and alternating phases of the refocusing pulses. In addition, the two double-echo sequences differ in the parity of the number of intervals with longitudinal magnetization evolution (relaxation), i.e. the echo in one sequence is formed only from those coherence pathways that have an even number of intervals with longitudinal magnetization evolution, while the other sequence has an odd number of such intervals.

Temperature sensing with RF-dressed states of nitrogen-vacancy centers in diamond

Using the electronic spin of nitrogen-vacancy (NV) centers in diamond is a promising approach to realizing high-precision temperature sensors; furthermore, pulsed optically detected magnetic resonance (pulsed-ODMR) is one way to measure the temperature using these NV centers. However, pulsed-ODMR techniques such as D-Ramsey, thermal echo, or thermal Carr–Purcell–Meiboom–Gill sequences require careful calibration and strict time synchronization to control the microwave (MW) pulses, which complicates their applicability. Continuous-wave ODMR (CW-ODMR) is a more advantageous way to measure temperature with NV centers because it can be implemented simply by continuous application of a green laser and MW radiation. However, CW-ODMR has lower sensitivity than pulsed-ODMR. Therefore, it is important to improve the temperature sensitivity of CW-ODMR techniques. Herein, we thus propose and demonstrate a method for measuring temperature using CW-ODMR with a quantum spin state dressed by a radio-frequency (RF) field under a transverse magnetic field. The use of an RF field is expected to suppress the inhomogeneous broadening resulting from strain and/or electric-field variations. The experimental results confirm that the linewidth is decreased in the proposed scheme when compared to the conventional scheme. In addition, we measured the temperature sensitivity to be about 50.4±3.5mK/Hz, and this is approximately eight times better than that of the conventional scheme.

Reducing the effects of weak homonuclear dipolar coupling with CPMG pulse sequences for static and spinning solids

The Carr-Purcell/Meiboom-Gill (CPMG) pulse sequence, initially introduced for measuring transverse relaxation time constants (T2), can provide significant signal enhancements for solid-state NMR (SSNMR) spectra. The proper implementation of CPMG for acquiring spectra influenced by chemical shift anisotropies (CSAs), first and/or second order quadrupolar interactions, or paramagnetic broadening has been well documented to date, as have the effects of heteronuclear dipolar coupling on CPMG echo trains and T2 lifetimes. Homonuclear dipolar coupling can also impact T2 lifetimes and CPMG echo trains; these effects have been thoroughly investigated for spectra of homonuclear dipolar coupled spin-1/2 nuclei typically acquired under static conditions that are predominantly influenced by dipolar broadening (e.g., 1H, 19F, etc.). In particular, it has been shown that short refocusing pulses with small flip angles can extend the effective T2 (T2eff, the observed T2 constant as impacted by experimental conditions) measured by CPMG sequences for strong homonuclear dipolar coupled spin-1/2 pairs under static conditions. To date, these effects have not been explored for (i) spin-1/2 nuclei that have significant CSAs and simultaneously feature weak homonuclear dipolar couplings, (ii) for quadrupolar nuclei that are also weakly homonuclear dipolar coupled, and (iii) for either of these cases under magic-angle spinning (MAS) conditions. Herein, we demonstrate that short refocusing pulses that cause small flip angles can reduce the attenuation of signal in CPMG echo trains resulting from dipolar dephasing caused by the weak homonuclear dipolar couplings. For both spin-1/2 and quadrupolar nuclei, this can lead to significant extensions in T2eff and signal enhancements of up to three times compared to conventional CPMG in favourable cases. These phenomena can occur under both static and magic-angle spinning (MAS) conditions, in the latter of which homonuclear couplings are reintroduced by rotational resonance (R2) recoupling. Experimental examples of 13C (I = 1/2), 2H (I = 1), 87Rb (I = 3/2), 23Na (I = 3/2), and 35Cl (I = 3/2) NMR under static and MAS conditions, as well as simulations of these phenomena, are shown and discussed.

Detection of single 13C spins coupled to NV center via dynamical decoupling design

The adjusted Carr–Purcell–Meiboom–Gill (CPMG) sequence is mathematically simulated to obtain the 13C nuclear spin signals coupled to a negatively-charged nitrogen-vacancy (NV−) center in diamond. The pulse interval ratio and scanning frequency of the sequence were precisely adjusted to achieve the high-resolution 13C nuclear spin detection. The frequency resolution of the sequence was 5.8 times improved than that of the original CPMG sequence, and the full width at half maximum of the coherence dips were less than 1.7 kHz. The adjusted method can be extended to other dynamical decoupling sequence, and offers a promising approach to improve identification of the nuclear spins in coupled electron-nuclear spin systems.

Proton nuclear magnetic resonance J-spectroscopy of phantoms containing brain metabolites on a portable 0.05 T MRI scanner

We examined approaches for obtaining 1H NMR spectra of brain metabolites on a low-field (B0 = 0.05 T) portable MRI scanner, which was developed in our laboratory with the aim of bringing cost-effective radiological services to populations in underserved, remote regions. The low static magnetic field B0 dictates low signal to noise ratio for metabolites in the mM concentration range, and results in an overall spectral region for the 1H resonances of these metabolites narrower than the linewidth obtainable in our scanner. The narrow spectral range also precludes the possibility of suppressing the large contribution of the water resonance at the acquisition stage.We used a spectroscopic Carr-Purcell-Meiboom-Gill (CPMG) sequence to acquire multiecho data from solutions of J-coupled brain metabolites, focusing on lactic acid, a metabolite whose concentration is negligible in the healthy brain and increases significantly in several disease conditions. The J spectra we obtained for lactate from the Fourier transformation of the multiecho data are spectrally well-resolved for a range of echo spacing values. We show that the J spectra at different echo spacings fit well with simulations of the evolution of echo train signal of the lactate under the same conditions. Applying a J-refocused variant of the CPMG sequence, the J modulation of the echo decay is removed, providing a way for subtracting the large contribution of the non-modulated component in the J spectrum in conditions where notching it using post-processing methods is impossible. We also demonstrate by means of experimental data and simulations that in our experimental conditions, J-spectra of other prominent brain metabolites, such as the neurotransmitter glutamate, do not yield discernible peaks and only contribute to a broad peak at zero frequency.

Adiabatic and nonadiabatic behavior of the Carr-Purcell-Meiboom-Gill sequence in time-dependent magnetic fields

We investigate experimentally the effect of time dependent magnetic fields on the spin dynamics of the Carr - Purcell - Meiboom - Gill (CPMG) sequence. Over a wide range of offset fields and ramp rates, the measured response is fully consistent with adiabatic behavior. The echo amplitudes exhibit characteristic modulations that are in excellent agreement with theoretical predictions. Non-adiabatic events are observed at distinct offsets. Abruptly after passing through these offsets, the experimental results deviate from the theoretical adiabatic expressions. These non-adiabatic events occur precisely at the field offsets predicted by theory. It is demonstrated that in the adiabatic regime the effects of field fluctuations are fully reversible, while the occurrence of non-adiabatic events leads to hysteresis. The adiabatic range of field offsets can be increased by modifying the refocusing pulses within the CPMG sequence.

Precise high-fidelity electron–nuclear spin entangling gates in NV centers via hybrid dynamical decoupling sequences

Color centers in solids, such as the nitrogen-vacancy center in diamond, offer well-protected and well-controlled localized electron spins that can be employed in various quantum technologies. Moreover, the long coherence time of the surrounding spinful nuclei can enable a robust quantum register controlled through the color center. We design pulse sequence protocols that drive the electron spin to generate robust entangling gates with these nuclear memory qubits. We find that compared to using Carr-Purcell-Meiboom-Gill (CPMG) alone, Uhrig decoupling sequence and hybrid protocols composed of CPMG and Uhrig sequences improve these entangling gates in terms of fidelity, spin control range, and spin selectivity. We provide analytical expressions for the sequence protocols and also show numerically the efficacy of our method on nitrogen-vacancy centers in diamond. Our results are broadly applicable to color centers weakly coupled to a small number of nuclear spin qubits.

Abstract 3721: Improved fitting of HRMAS NMR spectra for ex vivo metabolomic analysis of glioma tissue

Abstract Gliomas are aggressive brain tumors with high rates of treatment resistance and low survival rates. High-resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR) spectroscopy can quantify metabolite concentrations in glioma tissue, but most analysis techniques require manual peak selection and integration that prevents accurate and reliable quantitation of overlapping peaks and large macromolecule baselines. Our goal was to compare the effectiveness of operator-independent LCModel analysis of glioma spectra acquired from free induction decay (FID) and Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences. HRMAS NMR spectra were acquired using FID and CPMG sequences from 14 histologically-confirmed glioma tissue samples (WHO grade II (n=5), III (n=5), and IV (n=4)) collected during surgical resection from human brain tumor patients. Metabolite concentration ratios and Cramer-Rao lower bounds (CRLBs) were estimated using LCModel. Metabolite CRLBs were compared using a paired two sample t-test. Differences in concentrations as a function of WHO grade were determined with ANOVA and Tukey-Kramer post-hoc tests. Significance was determined by p<.05. Metabolite CRLBs for lactate and myo-inositol were significantly lower for CPMG compared to FID spectra (p<.05). Most metabolites could be quantified with LCModel from spectra acquired with CPMG where many metabolites acquired with the FID sequence were not detected. For example, lactate was quantifiable from 3 of the spectra acquired with FID compared to 12 spectra with CPMG. The use of the CPMG sequence reduces quantification errors by eliminating confounding baseline signals. LCModel facilitates improved separation of overlapping resonances compared to manual peak integration, supporting the use of operator-independent methods for metabolic spectral analysis. Comparison of metabolite concentrations as a function of WHO grade revealed significant differences in lactate and glutamine plus glutamate normalized to creatine (p<.05). 2-hydroxyglutarate (2-HG) was also detected in 9 out of 13 isocitrate dehydrogenase (IDH)-mutated samples using both sequences. IDH-mutated tissue should produce 2-HG; however, these results are promising as 2-HG can be difficult to quantify in 1D NMR due to spectral overlap. In conclusion, LCModel can reliably quantify HRMAS spectra acquired with the CPMG sequence but is less reliable with the FID sequence. Increases in lactate and glutamine plus glutamate concentrations as a function of tumor grade were consistent with previous results using HRMAS for glioma metabolic analysis, and 2-HG was detected in 1D HRMAS spectra acquired with both sequences. We expect that improved spectral fitting will contribute to future NMR-based metabolomics studies in glioma. Note: This abstract was not presented at the meeting. Citation Format: Selin Ekici, Ren Geryak, Stewart G. Neill, Hui-Kuo Shu, Candace C. Fleischer. Improved fitting of HRMAS NMR spectra for ex vivo metabolomic analysis of glioma tissue [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3721.

Measuring Flow Using a Permanent Magnet with a Large Constant Gradient

Nuclear magnetic resonance (NMR) has long been used for measuring flows, as it has the unique advantage of being a truly non-invasive method by which to do so. In this paper, we describe our use of a magnet with a large constant gradient to measure two decades of average velocities (0.002–0.7 m/s), principally using a measurement method developed by Osan et al. that uses the initial decay of a Carr–Purcell–Meiboom–Gill sequence to determine the mean flow velocity. Thanks to the repeatability afforded by the stable gradient, we reliably pinpoint the transition to turbulence for pipe flow through the magnet.

Portable Unilateral NMR Measuring System for Assessing the Aging Status of Silicon Rubber Insulators

Silicon rubber insulators (SRIs) are widely used in power transmission lines as line support and as insulation between the line and the tower. Given that the aging of SRIs threatens the safety and stability of power grids, the accurate assessment of the aging status of SRIs is crucial. In this study, a portable unilateral magnetic resonance (UMR) measuring system for the nondestructive testing of the aging status of SRIs was proposed. The proposed NMR measurement system includes a mini UMR sensor and a measurement circuit. Details of the mini UMR sensor structure and low-cost circuit design were discussed. The Carr–Purcell–Meiboom–Gill sequence was used to record the 1H transverse relaxation curves of SRI sheds. Inverse Laplace transformation was employed to obtain the T2 distribution, and two peaks in the T2 distribution curve were observed. The long T2 component was selected to quantify the aging degree because of its stability compared with the short T2 component. To eliminate the inaccuracy of measurement introduced by the different chemical structures of SRIs produced by different companies, the aging status of the SRIs was represented by the changes in T2 between the surface and internal materials of the SRI.

P077] T1, T2 Relaxation times measurements methods: A comparison between standard sequences performed by an NMR spectrometer and MRI devices from different vendors at 1.5T

Purpose The aim of this study is to evaluate the accuracy and the standardization of measurements of relaxation times values obtained from post-processing phantom images acquired with different vendors MRI scanners used in clinical and an NMR spectrometer, giving the basis for the evaluation of accuracy of T 1 , T 2 mapping for cardiac applications. Methods Six vials filled with agarose doped with gadolinium of an Eurospin phantom (Diagnostic Sonar, Livingston, UK) were scanned with an NMR spectrometer at Pavia University’s laboratory in order to restate the golden standard T 1 , T 2 relaxation times values at 1.5 T. SR (Saturation Recovery), IR (Inversion Recovery), SE (Spin Echo) and CPMG (Carr-Purcell-Meiboom-Gill) sequences were used. The vials were also scanned with a Magnetom Aera (Siemens, 1.5 T) and a Signa (General Electric, 1.5 T) MRI devices using clinical SE and IR sequences. Images were then processed with vendor independent software: cvi42 (Circle Cardiovascular Imaging Inc.), and an open source software developed with Matlab, Segment (http://www.medviso.com). Results Experimental values obtained by MRI devices with IR and SE sequences are in good agreement (10% for both relaxation times) with those measured by SR, IR and CPMG sequences with the NMR spectrometer even though they were measured at different room-temperature (20 °C for Siemens Aera, 21 °C for GE Signa and 23 °C for the NMR spectrometer): a linear dependence from temperature is observed, the same prospected by the Eurospin’s manual. SE sequences performed with the NMR spectrometer give much lower values of T 2 (70%) compared to the other measured ones due to diffusion: this suggests that those sequences named SE in MRI devices are CPMG sequences. Conclusions This is a preliminary study showing a good standardization level of different MRI and NMR devices for relaxation times estimation: next studies may investigate the agreement of values obtained with cardiac mapping sequences (MOLLI, Sh-MOLLI, T 2 -prep TrueFISP) with the standard sequences used in this study.

Separation of 2H NMR spectra assisted by molecular dynamics in diamagnetic and paramagnetic solids

The relaxation-assisted separation method was applied to overlapping 2H nuclear magnetic resonance (NMR) spectra of diamagnetic and paramagnetic solids to separate them based on the different relaxation behaviors caused by molecular motion. Carr–Purcell–Meiboom–Gill sequences for 2H NMR were adopted to build two-dimensional data sets from one-dimensional NMR experiments. For diamagnetic α-glycine, the 2H NMR spectrum collected at 198 K was separated into two components from static –CD2– and dynamic –ND3. In addition, for the paramagnetic Sm(NO3)3·6D2O, the asymmetric 2H NMR spectra obtained at 213 K due to the hyperfine coupling was also separated into two components, which corresponded to coordinated and crystal water molecules undergoing a 180° flip motion with different correlation times.

Three-dimensional ultrashort echo time cones (3D UTE-Cones) magnetic resonance imaging of entheses and tendons

We present three-dimensional ultrashort echo time Cones (3D-UTE-Cones) imaging as well as quantification of T2* and magnetization transfer ratio (MTR) of Achilles tendon and its enthesis of healthy volunteers and patients with psoriatic arthritis (PsA) using a 3T scanner. Quantitative T2*, T2 and magnetization transfer ratio (MTR) measurements of Achilles tendon and its enthesis were performed on healthy volunteers (n=7) and PsA patients (n=9) with 3D-UTE-Cones and clinical sequences at 3T. T2* was measured via single-component fitting of UTE images from two interleaved dual echo 3D-UTE-Cones acquisitions. MTR was measured with a dual echo 3D-UTE-Cones-MT sequence. Clinical morphological imaging and quantification of T2 with a Carr-Purcell-Meiboom-Gill (CPMG) sequence and MTR with a gradient recalled echo (GRE) sequence were also performed on each subject. T2* and MTR were analyzed for the two groups and the significance was evaluated. The 3D-UTE-Cones sequence provided high resolution imaging of entheses and tendons. Cones-T2* and Cones-MTR values were significantly higher for the PsA patients. GRE-MTR values showed no significant differences between the groups. No reliable T2 measurement could be achieved with the CPMG sequence due to insufficient signal from entheses and tendons. The 3D-UTE-Cones sequences can be used for morphological and quantitative evaluation of entheses and tendons in PsA patients.

Simultaneous determination of fast and slow dynamics in molecules using extreme CPMG relaxation dispersion experiments.

Molecular dynamics play a significant rolein how molecules perform their function. A critical method that provides information on dynamics, at the atomic level, is NMR-based relaxation dispersion (RD) experiments. RD experiments have been utilized for understanding multiple biological processes occurring at micro-to-millisecond time, such as enzyme catalysis, molecular recognition, ligand binding and protein folding. Here, we applied the recently developed high-power RD concept to the Carr-Purcell-Meiboom-Gill sequence (extreme CPMG; E-CPMG) for the simultaneous detection of fast and slow dynamics. Using a fast folding protein, gpW, we have shown that previously inaccessible kinetics can be accessed with the improved precision and efficiency of the measurementby using this experiment.

Illustration of inversion‐recovery and Carr‐Purcell‐Meiboom‐Gill sequences by the determination of ethanol content in alcoholic beverages

AbstractIn Nuclear Magnetic Resonance (NMR) education, the introduction of the relaxation phenomenon and the relaxation times (T1 and T2) is an important and compulsory step, as is the description of the Carr‐Purcell‐Meiboom‐Gill (CPMG) and inversion‐recovery (IR) measurement sequences. Indeed those sequences are still used nowadays for, respectively, the measurement of T2 and T1 but also in Magnetic Resonance Imaging (MRI) and NMR spectroscopy. Practical works with the students, performed for example with water, allow to illustrate this part of the teaching. In this work we propose an alternative and funny way to introduce these important topics. With a few microliters of a concentrated Gd3+ solution, a few milliliters of an alcoholic beverage and a low resolution and low field NMR device, it is possible, thanks to the relaxation phenomenon and using CPMG and IR sequences, to measure the alcohol content of the beverage provided that the alcohol proton exchange with water protons is taken into account. First the method is validated with synthetic water‐ethanol mixtures, then it is used to study nine different alcoholic beverages. The correlation of the ethanol volume fractions determined by NMR with the actual ethanol content of the beverages is rather good, especially for the method based on T2 relaxation, with a correlation coefficient r2 = 0.994. However, it seems that the method developed in this work always underestimates the ethanol volume fraction at high ethanol content for a reason which remains to be found.

A simple and accurate protocol for absolute polar metabolite quantification in cell cultures using quantitative nuclear magnetic resonance

Absolute analyte quantification by nuclear magnetic resonance (NMR) spectroscopy is rarely pursued in metabolomics, even though this would allow researchers to compare results obtained using different techniques. Here we report on a new protocol that permits, after pH-controlled serum protein removal, the sensitive quantification (limit of detection [LOD] = 5−25 μM) of hydrophilic nutrients and metabolites in the extracellular medium of cells in cultures. The method does not require the use of databases and uses PULCON (pulse length-based concentration determination) quantitative NMR to obtain results that are significantly more accurate and reproducible than those obtained by CPMG (Carr–Purcell–Meiboom–Gill) sequence or post-processing filtering approaches. Three practical applications of the method highlight its flexibility under different cell culture conditions. We identified and quantified (i) metabolic differences between genetically engineered human cell lines, (ii) alterations in cellular metabolism induced by differentiation of mouse myoblasts into myotubes, and (iii) metabolic changes caused by activation of neurotransmitter receptors in mouse myoblasts. Thus, the new protocol offers an easily implementable, efficient, and versatile tool for the investigation of cellular metabolism and signal transduction.

Rapid T2 mapping of mouse heart using the carr-purcell-meiboom-gill sequence and compressed sensing reconstruction.

To develop and prove preliminary validation of a fast in vivo T2 mapping technique for mouse heart. Magnetic resonance imaging (MRI) experiments were performed on a 7T animal scanner. The standard Carr-Purcell-Meiboom-Gill (CPMG) sequence was modified to minimize the effect of stimulated echoes for accurate T2 quantification. The acquisition was further accelerated with the compressed sensing approach. The accuracy of the proposed method was first validated with both phantom experiments and numerical simulations. In vivo T2 measurement was performed on seven mice in a manganese-enhanced MRI study. In phantom studies, T2 values obtained with the modified CPMG sequence are in good agreement with the standard spin-echo method (P > 0.05). Numerical simulations further demonstrated that with the application of the compressed sensing approach, fast T2 quantification with a spatial resolution of 2.3 mm can be achieved at a high temporal resolution of 1 minute per slice. With the proposed technique, an average T2 value of 25 msec was observed for mouse heart at 7T and this number decreased significantly after manganese infusion (P < 0.001). A rapid T2 mapping technique was developed and assessed, which allows accurate T2 quantification of mouse heart at a temporal resolution of 1 minute per slice. J. Magn. Reson. Imaging 2016;44:375-382.