Saturation Recovery Pulse Sequence Research Articles

Relaxometry and brain myelin quantification with synthetic MRI in MS subtypes and their associations with spinal cord atrophy

Immune-mediated demyelination and neurodegeneration are pathophysiological hallmarks of Multiple Sclerosis (MS) and main drivers of disease related disability. The principal method for evaluating qualitatively demyelinating events in the clinical context is contrast-weighted magnetic resonance imaging (MRI). Moreover, advanced MRI sequences provide reliable quantification of brain myelin offering new opportunities to study tissue pathology in vivo. Towards neurodegenerative aspects of the disease, spinal cord atrophy – besides brain atrophy – is a powerful and validated predictor of disease progression. The etiology of spinal cord volume loss is still a matter of research, as it remains unclear whether the impact of local lesion pathology or the interaction with supra- and infratentorial axonal degeneration and demyelination of the long descending and ascending fiber tracts are the determining factors.Quantitative synthetic MR using a multiecho acquisition of saturation recovery pulse sequence provides fast automatic brain tissue and myelin volumetry based on R1 and R2 relaxation rates and proton density quantification, making it a promising modality for application in the clinical routine. In this cross sectional study a total of 91 MS patients and 31 control subjects were included to investigate group differences of global and regional measures of brain myelin and relaxation rates, in different MS subtypes, using QRAPMASTER sequence and SyMRI postprocessing software. Furthermore, we examined associations between these quantitative brain parameters and spinal cord atrophy to draw conclusions about possible pathophysiological relationships.Intracranial myelin volume fraction of the global brain exhibited statistically significant differences between control subjects (10.4%) and MS patients (RRMS 9.4%, PMS 8.1%). In a LASSO regression analysis with total brain lesion load, intracranial myelin volume fraction and brain parenchymal fraction, the intracranial myelin volume fraction was the variable with the highest impact on spinal cord atrophy (standardized coefficient 4.52). Regional supratentorial MRI metrics showed altered average myelin volume fraction, R1, R2 and proton density in MS patients compared to controls most pronounced in PMS. Interestingly, quantitative MRI parameters in supratentorial regions showed strong associations with upper cord atrophy, suggesting an important role of brain diffuse demyelination on spinal cord pathology possibly in the context of global disease activity. R1, R2 or proton density of the thalamus, cerebellum and brainstem correlated with upper cervical cord atrophy, probably reflecting the direct functional connection between these brain structures and the spinal cord as well as the effects of retrograde and anterograde axonal degeneration.By using Synthetic MR-derived myelin volume fraction, we were able to effectively detect significant differences of myelination in relapsing and progressive MS subtypes. Total intracranial brain myelin volume fraction seemed to predict spinal cord volume loss better than brain atrophy or total lesion load. Furthermore, demyelination in highly myelinated supratentorial regions, as an indicator of diffuse disease activity, as well as alterations of relaxation parameters in adjacent infratentorial and midbrain areas were strongly associated with upper cervical cord atrophy.

Fast field-cycling magnetic resonance detection of intracellular ultra-small iron oxide particles in vitro: Proof-of-concept

PurposeInflammation is central in disease pathophysiology and accurate methods for its detection and quantification are increasingly required to guide diagnosis and therapy. Here we explored the ability of Fast Field-Cycling Magnetic Resonance (FFC-MR) in quantifying the signal of ultra-small superparamagnetic iron oxide particles (USPIO) phagocytosed by J774 macrophage-like cells as a proof-of-principle. MethodsRelaxation rates were measured in suspensions of J774 macrophage-like cells loaded with USPIO (0–200 μg/ml Fe as ferumoxytol), using a 0.25 T FFC benchtop relaxometer and a human whole-body, in-house built 0.2 T FFC-MR prototype system with a custom test tube coil. Identical non-imaging, saturation recovery pulse sequence with 90° flip angle and 20 different evolution fields selected logarithmically between 80 μT and 0.2 T (3.4 kHz and 8.51 MHz proton Larmor frequency [PLF] respectively). Results were compared with imaging flow cytometry quantification of side scatter intensity and USPIO-occupied cell area. A reference colorimetric iron assay was used. ResultsThe T1 dispersion curves derived from FFC-MR were excellent in detecting USPIO at all concentrations examined (0–200 μg/ml Fe as ferumoxytol) vs. control cells, p ≤ 0.001. FFC-NMR was capable of reliably detecting cellular iron content as low as 1.12 ng/µg cell protein, validated using a colorimetric assay. FFC-MR was comparable to imaging flow cytometry quantification of side scatter intensity but superior to USPIO-occupied cell area, the latter being only sensitive at exposures ≥ 10 µg/ml USPIO. ConclusionsWe demonstrated for the first time that FFC-MR is capable of quantitative assessment of intra-cellular iron which will have important implications for the use of USPIO in a variety of biological applications, including the study of inflammation.

Left ventricular extracellular volume expansion does not predict recurrence of atrial fibrillation following catheter ablation.

A recent study reported that diffuse left ventricular (LV) fibrosis is a predictor of atrial fibrillation (AF) recurrence following catheter ablation, by measuring postcontrast cardiac T1 (an error prone metric as per the 2017 Society for Cardiovascular Magnetic Resonance consensus statement) using an inversion-recovery pulse sequence (an error prone method in arrhythmia) in AF ablation candidates. The purpose of this study was to verify the prior study, by measuring extracellular volume (ECV) fraction (an accurate metric) using a saturation-recovery pulse sequence (accurate method in arrhythmia). This study examined 100 AF patients (mean age=62±11 years, 69 males and 31 females, 67 paroxysmal [pAF] and 33 persistent [peAF]) who underwent a preablation cardiovascular magnetic resonance (CMR) exam. LV ECV and left atrial (LA) and LV functional parameters were quantified using standard analysis methods. During an average follow-up period of 457±261 days with 4±3 rhythm checks per patient, 72 patients maintained sinus rhythm. Between those who maintained sinus rhythm (n=72) and those who reverted to AF (n=28), the only clinical characteristic that was significantly different was age (60 ± 12 years vs 66 ± 9years); for CMR metrics, neither mean LV ECV (25.1 ± 3.3%vs 24.7±3.7%), native LV T1 (1093.8 ± 73.5ms vs 1070.2 ± 115.9ms), left ventricular ejection fraction (54.1 ± 11.2%vs 55.7±7.1%), nor LA end diastolic volume/body surface area (42.4 ± 14.8mL/m2 vs 43.4±19.6mL/m2 ) were significantly different (P ≥ .23). According to Cox regression tests, none of the clinical and imaging variables predict AF recurrence. Neither LV ECV nor other CMR metrics predict recurrence of AF following catheter ablation.

Quantitative evaluation of radiation-induced lung injury with hyperpolarized xenon magnetic resonance.

To demonstrate the feasibility of quantitative and comprehensive global evaluation of pulmonary function and microstructural changes in rats with radiation-induced lung injury (RILI) using hyperpolarized xenon MR. Dissolved xenon spectra were dynamically acquired using a modified chemical shift saturation recovery pulse sequence in five rats with RILI (bilaterally exposed by 6-MV x-ray with a dose of 14 Gy 3 mo. prior to MR experiments) and five healthy rats. The dissolved xenon signals were quantitatively analyzed, and the pulmonary physiological parameters were extracted with the model of xenon exchange. The obtained pulmonary physiological parameters and the ratio of (129) Xe signal in red blood cells (RBCs) versus barrier showed a significant difference between the groups. In RILI rats versus controls, the exchange time increased from 44.5 to 112 ms, the pulmonary capillary transit time increased from 0.51 to 1.48 s, and the ratio of (129) Xe spectroscopic signal in RBCs versus barrier increased from 0.294 to 0.484. Hyperpolarized xenon MR is effective for quantitative and comprehensive global evaluation of pulmonary function and structural changes without the use of radiation. This may open the door for its use in the diagnosis of lung diseases that are related to gas exchange. Magn Reson Med 76:408-416, 2016. © 2015 Wiley Periodicals, Inc.

Contrast magnetic resonance imaging for measurement of cartilage glycosaminoglycan content in dogs: A pilot study

To assess the ability of a contrast-enhanced magnetic resonance imaging (MRI) technique to quantitatively determine glycosaminoglycan content in canine articular cartilage. Fifty-four full-thickness cartilage discs were collected from the femorotibial and scapulohumeral joints of three adult dogs immediately following euthanasia. One set of discs from each dog was analysed for glycosaminoglycan content using a colourimetric laboratory assay. The remaining position-matched set of discs from contralateral limbs underwent pre- and post-contrast gadolinium-enhanced MRI, using repeated saturation recovery pulse sequences which were used to generate calculated T1 maps of the cartilage discs. Linear regression analysis was then performed relating delayed gadolinium-enhanced MRI T1 calculated signal intensity to the cartilage glycosaminoglycan content normalized to DNA content. Repeatability of triplicate measurements was estimated by calculating the coefficient of variation. Mean coefficient of variation estimates for the gadolinium-enhanced MRI T1 signal intensity values for nine sampling sites from three dogs ranged from 5.9% to 7.5%. Gadolinium-enhanced MRI T1 signal intensity was significantly correlated (p <0.05) with normalized glycosaminoglycan content in two dogs (r = 0.79, p = 0.011; r = 0.78, p = 0.048), but not in the third dog (r = 0.53, p = 0.071). Gadolinium-enhanced MRI assessment of cartilage may be predictive of glycosaminoglycan content and therefore offer an in vivo assessment of changes in cartilage characteristics over time. Additional studies appear indicated to determine the reliability and clinical applicability of gadolinium-enhanced MRI in detecting changes in cartilage over time.

Investigation of Trans Content in Amorphous Phase of stretched Polyethylene Terephthalate by Solid-state High resolution 13C NMR Spectroscopy

Crystalline, constrained noncrystalline, and amorphous phase structures for polyethylene terephthalate (PET) stretched at 75, 80, and 90°C were investigated by solid-state high resolution 13 C NMR. Saturation recovery pulse sequence is a very powerful tool for investigating not only the molecular structure but also the molecular mobility. Spin-lattice relaxation behavior of trans methylene carbon was decomposed by three components, which are assignable to crystalline, constrained noncrystalline, and amorphous phases. The weight content of each component can be estimated by the relaxation behavior. The stretching process induced the transformation from gauche to trans conformation. The trans content with the longest T 1c corresponds to the crystallinity, which was in good agreement with DSC measurement. The trans content in the amorphous phase was also estimated by the ratio between the gauche content assignable to the amorphous phase and the amorphous component of the trans conformer decomposed by relaxation measurement. The trans content of unstretched PET was as low as 21%, whereas that for five-times stretched PET was about 60%.

A Simple Method for Quantitative Measurement and Analysis of Hyperpolarized 129Xe Uptake Dynamics in Mouse Brain under Controlled Flow

We established a simple method for measuring and quantifying uptake dynamics of hyperpolarized (HP) (129)Xe in mouse brain, which includes application of a saturation recovery pulse sequence under controlled flow of HP (129)Xe. The technique allows pursuit of the time-dependent change in (129)Xe nuclear magnetic resonance signal in the uptake process without effect from radiofrequency destruction of the polarization and the dynamics in mouse lung. The uptake behavior is well described by a simple model that depends only on a decay rate constant comprising cerebral blood flow and the longitudinal relaxation rate of HP (129)Xe in the brain tissue. The improved analysis enabled precise determination of the decay rate constant as 0.107+/-0.013 s(-1) (+/-standard deviation, n=5), leading to estimation of longitudinal relaxation time, T(1i), as 15.3+/-3.5 s.

29 Si MAS NMR relaxation study of shocked Coconino Sandstone from Meteor Crater, Arizona

29Si nuclear magnetic resonance (NMR) spectroscopy was used to characterize the silica phases in a moderately-shocked Coconino sandstone from Meteor Crater, Arizona. The spectra were recorded using direct polarization, magic-angle spinning, and variable delay times in a saturation recovery pulse sequence. Resonances observed at -97.3, -107.1, -113.9 and -191.2 ppm were assigned to a densified hydrous form of amorphous silica (D phase), quartz, coesite and stishovite phases, respectively. The relative percentages were estimated as 1.7, 80.6, 16.4 and 1.3% for the D, quartz, coesite, and stishovite phases. The power-law recoveries of the magnetization for the quartz and coesite phases can be interpreted in terms of their phase geometries.

High temperature 1H spin–spin relaxation in Zr–Ni–Cu–H amorphous alloys

1H spin–spin relaxation time ( T 2) and complementary hydrogen content, PMR spectrum width and spin–lattice relaxation time ( T 1) have been measured in Zr y (Ni 1− x Cu x ) 1− y –H ternary amorphous alloys of different hydrogen content at 0≤ x≤33 at.% Cu and y=33, 50 and 67 at.% Zr concentrations using Carr–Purcell–Meiboom–Gill (CPMG), solid-echo and saturation recovery pulse sequences, respectively. At high hydrogen contents the T 2 measured by the slope of the CPMG echo train depends on both the Zr and Cu content, but is independent of the hydrogen content. The differences in the spin–spin relaxation behaviours can be attributed to the substantial change of correlation time and not to the change of activation energy or local fields. The measurements were made in the “motional narrowing” state, consequently our E a and τ ∞ quantities are averaged to the diffusion motion of protons taking part in this process. At small hydrogen contents T 2 depends on hydrogen content and the T 2 vs. 1/ T curves cannot be fitted by single Arrhenius plots. The hydrogen content measured by echo train has turned out to be systematically smaller than that measured by weight increase, demonstrating that not all the hydrogen takes part in the diffusion process.

PMR measurements on (Ni1 −xCux)0.5Zr0.5-Hy amorphous alloys

Spin-spin relaxation time (T2) and complementary hydrogen content (H/M), PMR spectrum width (FWHM) and spin lattice relaxation time (T1) have been measured in (Ni1 − xCux)0.5Zr0.5-Hy ternary amorphous alloys at 0 ⩽ x ⩽ 29 at.% concentrations using Carr-Purcell-Meiboom-Gill (CPMG), solid-echo and saturation recovery pulse sequences respectively.The T2 relaxation time measured by the slope of the CPMG echo train depends on both the hydrogen and Cu content. The dependence can be attributed to the change of correlation time and not to the change of activation energy or local field. The measurements were made in the ‘motional narrowing’ state; consequently our Eaand τ∞ quantities are averaged to the diffusional motion of protons taking part in this process.The extrapolated amplitude of the echo train measured on the alloy-hydrogen system and normalized to the same quantity in water, gives the value of proton magnetization in thermal equilibrium, that is the hydrogen content free from any perturbing effects. The hydrogen content measured by CPMG echo train has turned out to be systematically smaller than that measured by weight increase.

Bi-exponential nuclear spin-lattice relaxation in solid hexafluoroacetylacetone

The reorientation of CF 3 rotors in solid hexafluoroacetylacetone has been studied using pulsed NMR techniques. The temperature dependence of both fluorine ( 19F) and hydrogen ( 1H) nuclear spin-lattice relaxation has been measured using saturation-recovery pulse sequences. Following saturation of one of the spin reservoirs, the evolution with time of the longitudinal magnetisations associated with both nuclei are observed to be strongly bi-exponential. A theory is presented for the spin-lattice relaxation which is mediated by the heteronuclear dipole-dipole interaction between 19F and 1H nuclei. The experimental results are in good quantitative agreement with this relaxation theory. The spectral density functions have been evaluated using the known molecular structure and they are consistent with the experimental data. From this analysis we conclude that the relaxation is dominated by an intramolecular 19F&.z.sbnd; 1H dipolar interaction. The spectral density function J (0)( ω H- ω F) makes an important contribution to the relaxation theory with the result that the motional spectrum is conveniently sampled at the difference frequency between 1H and 19F Larmor precessions. Two physically distinguishable CF 3 rotors have been identified in this investigation, their dynamics are characterised by activation energies of 7.5 ± 0.4 and 13.3 ± 0.8 kJ mol −1, respectively.

Myocardial creatine kinase exchange rates and 31P NMR relaxation rates in intact pigs.

In this study, we used 31P NMR to investigate the relationship between cardiac workload and creatine kinase flux in intact pigs. NMR measurements were performed on anesthetized miniature swine in which a surface coil was surgically implanted on the surface of the left ventricle. Cardiac workload was varied by infusion of norepinephrine. Phosphate exchange between creatine phosphate and ATP was measured by a combined saturation transfer, saturation recovery pulse sequence. Exchange measurements showed that creatine kinase flux and concentrations of PCr and ATP were independent of workload for a 2.5-fold range of cardiac rate-pressure products. It appears that, if creatine kinase flux is coupled to work load, the pig heart operates in a regime where small changes in metabolite concentrations or creatine kinase flux are sufficient to maintain elevated workloads. Exchange and relaxation measurements, at 2.0 and 4.7 T, yielded T1 relaxation times for creatine phosphate and ATP which are longer than most reported values. Analysis of the T1 data indicates that chemical-shift anisotropy is a plausible mechanism for a portion of the spin-lattice relaxation rate at high field strengths.

The metabolic state of the rat liver in vivo measured by 31P-NMR spectroscopy

Previous 31P nuclear magnetic resonance (NMR) studies have measured the concentrations of phosphates, free Mg 2+, pH and flux through enzyme-catalyzed reactions in a variety of tissues. A surgically-implanted coil has been developed to measure these parameters in the rat liver in vivo, and to assess the effect of external perturbations on the concentrations and physiological environment of phosphorus metabolites in the liver. The sensitive volume and optimal pulse were determined for the coil, which was insulated to exclude signal from surrounding tissues. The metabolic stability of the liver during acquisition of spectra was demonstrated by normal values for [P i], [ATP], [lactate], and [pyruvate] in livers which were freeze-clamped immediately after completion of the NMR experiment. The stability was also confirmed by constant values for intracellular pH (7.2), free [Mg 2+] (0.7 mM), and NMR detectable [ P i ] [ ATP] . The sensitivity of the 31P-NMR spectrum of the liver in vivo to the physiological state of the animals was illustrated by comparing spectra from fed and 48 h fasted rats. The major qualitative differences were an increase in the pyridine nucleotide/adenine nucleotide ratio, and a small, but consistent shift in the frequency of the composite phosphomonoester peak. The spin-lattice relaxation time of each major phosphate resonance was measured in vivo using a modified homospoil saturation recovery pulse sequence; the T 1 of ATP γ-phosphate was 0.17 s. Selective saturation experiments did not detect magnetization transfer between the ATP γ-phosphate and inorganic phosphate.

Signal, noise, and contrast in nuclear magnetic resonance (NMR) imaging

Abstract Calculations of the sensitivity of the saturation recovery and inversion recovery pulse sequences used in nuclear magnetic resonance imaging show the former to be superior in discriminating between tissues with the same proton density but different T1‘s. Two other pulse sequences, which are combinations of the above, have also been analyzed. These have lower T1 discrimination sensitivity, but other considerations, such as self-normalization, may still make them attractive. The calculations are only valid for selective excitation pulse sequences in which the selected slice profiles are approximately rectangular, and thus a sin(bt)/t radio frequency excitation is desirable. In order to ensure that the saturation recovery sequence gives valid results for pulse repetition times comparable to or shorter than T2 it is necessary to destroy the coherence between pulse applications. For this purpose we use a series of “spoiler” gradient pulses between pulse trains. The saturation recovery pulse sequence also has the advantage that, by the correct choice of interpulse spacing, sensitivity close to the optimum T1 discrimination can be achieved over a wide range of T1 values. This has the potential advantage to the clinician of simplifying his choice of parameters for imaging.

Signal, noise, and contrast in nuclear magnetic resonance (NMR) imaging.

Calculations of the sensitivity of the saturation recovery and inversion recovery pulse sequences used in nuclear magnetic resonance imaging show the former to be superior in discriminating between tissues with the same proton density but different T1's. Two other pulse sequences, which are combinations of the above, have also been analyzed. These have lower T1 discrimination sensitivity, but other considerations, such as self-normalization, may still make them attractive. The calculations are only valid for selective excitation pulse sequences in which the selected slice profiles are approximately rectangular, and thus a sin(bt)/t radiofrequency excitation is desirable. In order to ensure that the saturation recovery sequence gives valid results for pulse repetition times comparable to or shorter than T2, it is necessary to destroy the coherence between pulse applications. For this purpose we use a series of "spoiler" gradient pulses between pulse trains. The saturation recovery pulse sequence also has the advantage that, by the correct choice of interpulse spacing, sensitivity close to the optimum T1 discrimination can be achieved over a wide range of T1 values. This has the potential advantage to the clinician of simplifying his choice of parameters for imaging.

Phase-shifted pulse sequence for measurement of spin-lattice relaxation in complex systems

A density matrix analysis of the effects of phase modification in the “nonideal” inversion-recovery pulse sequence upon the apparent magnetization recovery is presented. The apparent magnetization recovery is, in general, nonexponential, depending on the ratio T 1 T 2 ∗ , the relative pulse phases in the inversion-recovery sequence, the off-resonance frequency, the observation direction, the radiofrequency field inhomogeneity, phase-glitch effect, and/or inaccurate settings of the pulse lengths. The interference effects produced by transverse magnetization in the case of T 1 measurements by the inversion-recovery pulse sequence or saturation recovery pulse sequence in the high-resolution NMR spectra can be eliminated successively using the coincident phase and antiphase pulse sequences. This technique has the advantage of simplicity and allows the maximum resolution in the partly relaxed spectrum.