T2 Decay Research Articles

Characterisation of oil sludges from different sources before treatment: High-field nuclear magnetic resonance (NMR) in the determination of oil and water content

Oil sludges are wastes from the oil industry containing complex mixtures of oil hydrocarbons, water, sediments, and heavy metals. These wastes are of main importance for the petroleum industry since it is estimated that more than a billion tons have been stored worldwide. There are several types of oil sludges, but the oil tank bottom sludges are the most studied. Therefore, it is necessary to analyse a variety of oil sludges to establish a detail characterisation, with fast and reliable methods before selecting a suitable treatment. Five sludges were analysed in this study: an oil drilling, oil refinery, oil-water separator, and two waste engine oil sludges. This is a rare report detailing the use of high-field (500 MHz) nuclear magnetic resonance (NMR) to determine oil and water contents in oil sludges, which are more commonly analysed by low-field NMR (below 100 MHz). The proposed NMR procedure was validated by the analysis of oil-water calibration standards (experimental errors < 15%). There was a good agreement among the data obtained from the 1D proton spectra and the Carr-Purcell-Meiboom-Gill (CPMG) T2 decays (percentage differences < 5%). The T2 decays data showed that all sludges had only two components attributed to oil and water, and their relative ratios were determined. The sediment content was determined by the oven-drying method, and the oil hydrocarbon fractions and trace elements were assessed. The oil sludges presented different ranges in the oil, water, sediment and heavy metals contents. The higher presence of C10-C18 aliphatic fractions in the oil from the sludges was an indicator of the potential to be reused as diesel fuel. The sludges had potentially toxic elements (PTEs) values under the limit of the landfilling standards established by the European Union, except for the WSS sludge. Ca and Fe had the highest concentrations in all sludges, which are characteristic of these wastes. The techniques used in this study can be an alternative for a rapid characterisation of the oil sludges, so their most appropriate treatment can be established.

Synthesis and evaluation of 13C-labeled 5-5-dimethyl-1-pyrroline-N-oxide aimed at in vivo detection of reactive oxygen species using hyperpolarized 13C-MRI

Effective means to identify the role of reactive oxygen species (ROS) mediating several diseases including cancer, ischemic heart disease, stroke, Alzheimer's and other inflammatory conditions in in vivo models would be useful. The cyclic nitrone 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) is a spin trap frequently used to detect free radicals in vitro using Electron Paramagnetic Resonance (EPR) spectroscopy. In this study, we synthesized 13C-labeled DMPO for hyperpolarization by dynamic nuclear polarization, in which 13C NMR signal increases more than 10,000-fold. This allows in vivo 13C MRI to investigate the feasibility of in vivo ROS detection by the 13C-MRI. DMPO was 13C-labeled at C5 position, and deuterated to prolong the T1 relaxation time. The overall yield achieved for 5–13C-DMPO-d9 was 15%. Hyperpolarized 5–13C-DMPO-d9 provided a single peak at 76 ppm in the 13C-spectrum, and the T1 was 60 s in phosphate buffer making it optimal for in vivo 13C MRI. The buffered solution of hyperpolarized 5–13C-DMPO-d9 was injected into a mouse placed in a 3 T scanner, and 13C-spectra were acquired every 1 s. In vivo studies showed the signal of 5–13C-DMPO-d9 was detected in the mouse, and the T1 decay of 13C signal of hyperpolarized 5–13C-DMPO-d9 was 29 s. 13C-chemical shift imaging revealed that 5–13C-DMPO-d9 was distributed throughout the body in a minute after the intravenous injection. A strong signal of 5–13C-DMPO-d9 was detected in heart/lung and kidney, whereas the signal in liver was small compared to other organs. The results indicate hyperpolarized 5–13C-DMPO-d9 provided sufficient 13C signal to be detected in the mouse in several organs, and can be used to detect ROS in vivo.

Considerations for the acquisition and inversion of NMR T2 data in shales

Low-field Nuclear Magnetic Resonance (NMR) is a non-invasive method widely used in the petroleum industry for the evaluation of reservoirs. Pore structure and fluid properties can be evaluated from transverse relaxation (T2) distributions, obtained by inverting the raw NMR signal measured at subsurface conditions or in the laboratory. This paper aims to cast some light into the best practices for the T2 data acquisition and inversion in shales, with a focus on the suitability of different inversion methods. For this purpose, the sensitivity to various signal acquisition parameters was evaluated from T2 experiments using a real shale core plug. Then, four of the most common inversion methods were tested on synthetic T2 decays, simulating components often associated with shales, and their performance was evaluated. These inversion algorithms were finally applied to real T2 data from laboratory NMR measurements in brine-saturated shale samples. Methods using a unique regularization parameter were found to produce solutions with a good balance between the level of misfit and bias, but could not resolve adjacent fast T2 components. In contrast, methods applying variable regularization – based on the noise level of the data – returned T2 distributions with better accuracy at short times, in exchange of larger bias in the overall solution. When it comes to reproducing individual T2 components characteristic of shales, the Butler-Reeds-Dawson (BRD) algorithm was found to have the best performance. In addition, our findings suggest that threshold T2 cut-offs may be derived analytically, upon visual inspection of the T2 distributions obtained by two different NMR inversion methods.

Constant gradient elastography with optimal control RF pulses

This article presents a new motion encoding strategy to perform magnetic resonance elastography (MRE). Instead of using standard motion encoding gradients, a tailored RF pulse is designed to simultaneously perform selective excitation and motion encoding in presence of a constant gradient. The RF pulse is designed with a numerical optimal control algorithm, in order to obtain a magnetization phase distribution that depends on the displacement characteristics inside each voxel. As a consequence, no post-excitation encoding gradients are required. This offers numerous advantages, such as reducing eddy current artifacts, and relaxing the constraint on the gradients maximum switch rate. It also allows to perform MRE with ultra-short TE acquisition schemes, which limits T2 decay and optimizes signal-to-noise ratio. The pulse design strategy is developed and analytically analyzed to clarify the encoding mechanism. Finally, simulations, phantom and ex vivo experiments show that phase-to-noise ratios are improved when compared to standard MRE encoding strategies.

Water retention value predicts biomass recalcitrance for pretreated lignocellulosic materials across feedstocks and pretreatment methods

Understanding the causes of lignocellulosic biomass recalcitrance is necessary for developing robust biomass conversion processes for fuels and chemicals. A key factor in biomass recalcitrance is the physical and chemical relationship between biomass and water. Water is known to be important for enzymatic hydrolysis both because it is a co-substrate for cellulose hydrolysis, but also because it acts as a swelling agent that allows enzymes access to the substrate. It has been shown that the water retention value, and water constraint as measured by spin–spin low field NMR (T2 LFNMR) techniques, correlated to biomass recalcitrance for similar lignocellulosic materials pretreated at different severities. In this work, water retention and water constraint was measured across species and pretreatment methods and compared to the enzymatic digestibility of the cellulose fraction. There is an overall positive correlation between the water retention value and glucose hydrolysis yields. Average water constraint in the samples (as represented by monocomponent T2 decay times) could not be correlated to biomass recalcitrance; however a relationship was found between the relative amount of more highly constrained water measured and hydrolysis performance. Feedstock heterogeneity and differences in sample morphology may account for the variation in the sample set. Further research is needed to develop these predictive methods, but can be applied with good accuracy on specific feedstock types or for specific pretreatment methods.

Multiband multi-echo simultaneous ASL/BOLD for task-induced functional MRI.

Typical simultaneous blood oxygenation-level dependent (BOLD) and arterial spin labeling (ASL) sequences acquire two echoes, one perfusion-sensitive and one BOLD-sensitive. However, for ASL, spatial resolution and brain coverage are limited due to the T1 decay of the labeled blood. This study applies a sequence combining a multiband acquisition with four echoes for simultaneous BOLD and pseudo-continuous ASL (pCASL) echo planar imaging (MBME ASL/BOLD) for block-design task-fMRI. A multiband acceleration of four was employed to increase brain coverage and reduce slice-timing effects on the ASL signal. Multi-echo independent component analysis (MEICA) was implemented to automatically denoise the BOLD signal by regressing non-BOLD components. This technique led to increased temporal signal-to-noise ratio (tSNR) and BOLD sensitivity. The MEICA technique was also modified to denoise the ASL signal by regressing artifact and BOLD signals from the first echo time-series. The MBME ASL/BOLD sequence was applied to a finger-tapping task functional MRI (fMRI) experiment. Signal characteristics and activation were evaluated using single echo BOLD, combined ME BOLD, combined ME BOLD after MEICA denoising, perfusion-weighted (PW), and perfusion-weighted after MEICA denoising time-series. The PW data was extracted using both surround subtraction and high-pass filtering followed by demodulation. In addition, the CBF/BOLD response ratio and CBF/BOLD coupling were analyzed. Results showed that the MEICA denoising procedure significantly improved the BOLD signal, leading to increased BOLD sensitivity, tSNR, and activation statistics compared to conventional single echo BOLD data. At the same time, the denoised PW data showed increased tSNR and activation statistics compared to the non-denoised PW data. CBF/BOLD coupling was also increased using the denoised ASL and BOLD data. Our preliminary data suggest that the MBME ASL/BOLD sequence can be employed to collect whole-brain task-fMRI with improved data quality for both BOLD and PW time series, thus improving the results of block-design task fMRI.

Towards quantification of myelin by solid-state MRI of the lipid matrix protons

PurposeDirect assessment of myelin has the potential to reveal central nervous system abnormalities and serve as a means to follow patients with demyelinating disorders during treatment. Here, we investigated the feasibility of direct imaging and quantification of the myelin proton pool, without the many possible confounds inherent to indirect methods, via long-T2 suppressed 3D ultra-short echo-time (UTE) and zero echo-time (ZTE) MRI in ovine spinal cord. MethodsZTE and UTE experiments, with and without inversion-recovery (IR) preparation, were conducted in ovine spinal cords before and after D2O exchange of tissue water, on a 9.4T vertical-bore micro-imaging system, along with some feasibility experiments on a 3T whole-body scanner. Myelin density was quantified relative to reference samples containing various mass fractions of purified myelin lipid, extracted via the sucrose gradient extraction technique, and reconstituted by suspension in water, where they spontaneously self-assemble into an ensemble of multi-lamellar liposomes, analogous to native myelin. ResultsMR signal amplitudes from reference samples at 9.4T were linearly correlated with myelin concentration (R2 = 0.98–0.99), enabling their use in quantification of myelin fraction in neural tissues. An adiabatic inversion-recovery preparation was found to effectively suppress long-T2 water signal in white matter, leaving short-T2 myelin protons to be imaged. Estimated myelin lipid fractions in white matter were 19.9%–22.5% in the D2O-exchanged spinal cord, and 18.1%–23.5% in the non-exchanged spinal cord. Numerical simulations based on the myelin spectrum suggest that approximately 4.59% of the total myelin proton magnetization is observable by IR-ZTE at 3T due to T2 decay and the inability to excite the shortest T2* components. Approximately 380 μm of point-spread function blurring is predicted, and ZTE images of the spinal cord acquired at 3T were consistent with this estimate. ConclusionIn the present implementation, IR-UTE at 9.4T produced similar estimates of myelin concentration in D2O-exchanged and non-exchanged spinal cord white matter. 3T data suggest that direct myelin imaging is feasible, but remaining challenging on clinical MR systems.

A minimum-phase Shinnar-Le Roux spectral-spatial excitation RF pulse for simultaneous water and lipid suppression in 1H-MRSI of body extremities

PurposeTo develop a spectral-spatial (SPSP) excitation RF pulse for simultaneous water and lipid suppression in proton (1H) magnetic resonance spectroscopic imaging (MRSI) of body extremities. MethodsAn SPSP excitation pulse is designed to excite Creatine (Cr) and Choline (Cho) metabolite signals while suppressing the overwhelming water and lipid signals. The SPSP pulse is designed using a recently proposed multidimensional Shinnar-Le Roux (SLR) RF pulse design method. A minimum-phase spectral selectivity profile is used to minimize signal loss from T2⁎ decay. ResultsThe performance of the SPSP pulse is evaluated via Bloch equation simulations and phantom experiments. The feasibility of the proposed method is demonstrated using three-dimensional, short repetition-time, free induction decay-based 1H-MRSI in the thigh muscle at 3T. ConclusionThe proposed SPSP excitation pulse is useful for simultaneous water and lipid suppression. The proposed method enables new applications of high-resolution 1H-MRSI in body extremities.

Self-Calibrating Wave-Encoded Variable-Density Single-Shot Fast Spin Echo Imaging.

It is highly desirable in clinical abdominal MR scans to accelerate single-shot fast spin echo (SSFSE) imaging and reduce blurring due to T2 decay and partial-Fourier acquisition. To develop and investigate the clinical feasibility of wave-encoded variable-density SSFSE imaging for improved image quality and scan time reduction. Prospective controlled clinical trial. With Institutional Review Board approval and informed consent, the proposed method was assessed on 20 consecutive adult patients (10 male, 10 female, range, 24-84 years). A wave-encoded variable-density SSFSE sequence was developed for clinical 3.0T abdominal scans to enable high acceleration (3.5×) with full-Fourier acquisitions by: 1) introducing wave encoding with self-refocusing gradient waveforms to improve acquisition efficiency; 2) developing self-calibrated estimation of wave-encoding point-spread function and coil sensitivity to improve motion robustness; and 3) incorporating a parallel imaging and compressed sensing reconstruction to reconstruct highly accelerated datasets. Image quality was compared pairwise with standard Cartesian acquisition independently and blindly by two radiologists on a scale from -2 to 2 for noise, contrast, confidence, sharpness, and artifacts. The average ratio of scan time between these two approaches was also compared. A Wilcoxon signed-rank tests with a P value under 0.05 considered statistically significant. Wave-encoded variable-density SSFSE significantly reduced the perceived noise level and improved the sharpness of the abdominal wall and the kidneys compared with standard acquisition (mean scores 0.8, 1.2, and 0.8, respectively, P < 0.003). No significant difference was observed in relation to other features (P = 0.11). An average of 21% decrease in scan time was achieved using the proposed method. Wave-encoded variable-density sampling SSFSE achieves improved image quality with clinically relevant echo time and reduced scan time, thus providing a fast and robust approach for clinical SSFSE imaging. 1 Technical Efficacy: Stage 6 J. Magn. Reson. Imaging 2018;47:954-966.

A novel method for T2 quantification in presence of B1 inhomogeneities

IntroductionT2 relaxometry as a quantitative MRI technique offers a more precise characterization of tissue, compared with qualitative T2 weighted imaging. The issue, however, is that in typically used T2 relaxometry sequences such as a multi-spin echo sequences, incorrect refocussing flip angles and B1 inhomogeneities cause inaccuracies in T2 determination. The work presented here within presents a new technique for modelling T2 decay curves and thereby correcting T2 times altered by inhomogeneities. Materials and methodsThe proposed technique models the signal decay acquired by multi-spin echo sequences based on extended phase graph theory. We have then put this new correction technique to test under both noise free and noise affected simulated signal and compared it to other previously introduced correction methods. To compare the efficacy of the T2 correction techniques, it was applied to MRI data acquired at 9.4Tesla. Results and conclusionThe results show that the proposed technique is able to minimize the systematic error in T2 relaxometry for a wide range of T2 times. Beyond that, the technique reveals the actual refocussing pulse angle in the respective voxel and reduces the error in So, which is mandatory if one aims for quantification of proton density.

T2 mapping with magnetization-prepared 3D TSE based on a modified BIR-4T2 preparation.

The purpose of this work was to investigate the performance of the modified BIR-4 T2 preparation for T2 mapping and propose a method to remove T2 quantification errors in the presence of large B1 and B0 offsets. The theoretical investigation of the magnetization evolution during the T2 preparation in the presence of B1 and B0 offsets showed deviations from a mono-exponential T2 decay (two parameter fit). A three parameter fit was used to improve T2 accuracy. Furthermore, a two parameter fit with an additional saturation preparation scan was proposed to improve T2 accuracy and precision. These three fitting methods were compared based on simulations, phantom measurements and an in vivo healthy volunteer study of the neck musculature using a 3D TSE readout. The results based upon the pure two parameter fit overestimated T2 in regions with high B0 offsets (up to 40% in phantoms). The three parameter fit T2 values were robust to B0 offsets but with higher standard deviation (up to 40% in simulations). The two parameter fit with the saturation preparation yielded high robustness towards B0 offsets with a noise performance comparable to that of the two parameter fit. In the volunteer study the T2 values obtained by the pure two parameter fit showed a dependence on the field inhomogeneities, whereas the T2 values from the proposed fitting approach were shown to be insensitive to B0 offsets. The proposed method enabled accurate and precise T2 mapping in the presence of large B1 and B0 offsets.

Determination of Biodiesel Content in Diesel Fuel by Time-Domain Nuclear Magnetic Resonance (TD-NMR) Spectroscopy

Considering the need for knowing the amount of biodiesel in fuels, in order to attend several legislations around the world, this work aimed to develop a new, rapid, and nondestructive time-domain nuclear magnetic resonance (TD-NMR)-based method for the biodiesel content determination in diesel–biodiesel blends. Main findings have revealed that both the transverse relaxation time (T2) and signal areas from relaxation spectra are highly correlated to biodiesel content in the fuel samples. The highest correlation was reached by applying PLS multivariate regression over T2 decay curve profiles. Therefore, both univariate and multivariate approaches were able to determine biodiesel content in diesel–biodiesel blends with high accuracy directly from fuel samples in a simple, fast, and inexpensive way.

Carbonation front in cement paste detected by T2 NMR measurements using a low field unilateral magnet

Unilateral magnetic resonance was used to obtain the CPMG T2 decay at different positions along 6 cm long cement paste samples. The aim was to detect the carbonation front based on changes in the pore structure caused by accelerated carbonation and to compare the results with the phenolphthalein test. Cement pastes at water-to-cement ratios of 0.60, 0.50, and 0.40 were prepared using ordinary Portland cement. After moist curing and conditioning at 65% RH and 35 °C, the pastes were subjected to accelerated carbonation with 4% by volume CO2 at 65% RH and 35 °C. Carbonation increases the magnetic resonance T2 lifetime compared with the control and compared with the noncarbonated region of the samples. A reduction in porosity and changes in the pore size distribution are caused by carbonation. The position with the highest rate of T2 change was consistent with the fully carbonated front determined by the phenolphthalein test.

Time-Domain Nuclear Magnetic Resonance (TD-NMR) and Chemometrics for Determination of Fat Content in Commercial Products of Milk Powder.

This study shows the use of time-domain (TD)-NMR transverse relaxation (T2) data and chemometrics in the nondestructive determination of fat content for powdered food samples such as commercial dried milk products. Most proposed NMR spectroscopy methods for measuring fat content correlate free induction decay or echo intensities with the sample's mass. The need for the sample's mass limits the analytical frequency of NMR determination, because weighing the samples is an additional step in this procedure. Therefore, the method proposed here is based on a multivariate model of T2 decay, measured with Carr-Purcell-Meiboom-Gill pulse sequence and reference values of fat content. The TD-NMR spectroscopy method shows high correlation (r = 0.95) with the lipid content, determined by the standard extraction method of Bligh and Dyer. For comparison, fat content determination was also performed using a multivariate model with near-IR (NIR) spectroscopy, which is also a nondestructive method. The advantages of the proposed TD-NMR method are that it (1) minimizes toxic residue generation, (2) performs measurements with high analytical frequency (a few seconds per analysis), and (3) does not require sample preparation (such as pelleting, needed for NIR spectroscopy analyses) or weighing the samples.

T2 selective π Echo-Planar Imaging for porous media MRI

The π Echo Planar Imaging (PEPI) method has recently been modified to permit proton density imaging of fluids in porous media with moderate T2 and short T2∗ signal components. In many applications, it is desirable to discriminate multiple T2 components within each image voxel. T2 selective imaging is explored in this paper through adiabatic inversion as a magnetization preparation with PEPI readout. When prior information of the sample relaxation times is known, responses of different species to broadband adiabatic inversion pulses can be predicted by Bloch equation simulation. Different relaxation components can be acquired by combining the images with and without inversion preparation pulses.T2 weighting can be easily introduced in the PEPI sequence by shifting the spatial encoding gradients based on its spin echo nature. T2 decay curves can be extracted for each image voxel from a series of T2 weighted images and spatially resolved T2 distributions can be generated. This method is reliable but slow. The two methods were implemented to image porous media samples with PEPI the common basis of spatial resolution. The results of both methods agree remarkably well.

MR measurement of luminal water in prostate gland: Quantitative correlation between MRI and histology.

To determine the relationship between parameters measured from luminal water imaging (LWI), a new magnetic resonance imaging (MRI) T2 mapping technique, and the corresponding tissue composition in prostate. In all, 17 patients with prostate cancer were examined with a 3D multiecho spin echo sequence at 3T prior to undergoing radical prostatectomy. Maps of seven MR parameters, called N, T2-short , T2-long , Ashort , Along , geometric mean T2 time (gmT2 ), and luminal water fraction (LWF), were generated using nonnegative least squares (NNLS) analysis of the T2 decay curves. MR parametric maps were correlated to digitized whole-mount histology sections. Percentage area of tissue components, including luminal space, nuclei, and cytoplasm plus stroma, was measured on the histology sections by using color-based image segmentation. Spearman's rank correlation test was used to evaluate the correlation between MR parameters and the corresponding tissue components, with particular attention paid to the correlation between LWF and percentage area of luminal space. N, T2-short , Along , gmT2 , and LWF showed significant correlation (P < 0.05) with percentage area of luminal space and stroma plus cytoplasm. T2-short and gmT2 also showed significant correlation (P < 0.05) with percentage area of nuclei. Overall, the strongest correlation was observed between LWF and luminal space (Spearman's coefficient of rank correlation = 0.75, P < 0.001). Results of this study show that LWF measured with MRI is strongly correlated with the fractional amount of luminal space in prostatic tissue. This result suggests that LWI can potentially be applied for evaluation of prostatic diseases in which the extent of luminal space differs between normal and abnormal tissues. 1 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:861-869.

High-resolution distortion-free diffusion imaging using hybrid spin-warp and echo-planar PSF-encoding approach

High-resolution diffusion-weighted imaging (DWI) has great potential to provide unique information about tissue microstructure in-vivo. Although single-shot echo-planar imaging (EPI) is a most popular tool for DWI, its application for high-resolution DWI is limited due to T2* blurring and susceptibility- and eddy-current-induced geometric distortions, especially at ultra-high field (UHF) such as 7T. In this study, we adapt a hybrid spin-warp and echo-planar encoding strategy inspired by point spread function (PSF) mapping and optimize it for high-resolution and distortion-free diffusion imaging applications. More specifically, a 2D navigator echo is added into the original sequence for shot-to-shot motion-induced phase error estimation and correction. The spatial encoding is shared between the PSF and the EPI phase encoding dimension allowing short echo trains to preserve the diffusion and navigator signals efficiently at UHF, where T2 decay is relatively fast. In addition, variable k-space spacing was applied in the PSF dimension and combined with parallel imaging in the EPI-PE dimension to further accelerate the PSF acquisition. The results demonstrate that this method can yield isotropic submillimeter resolution without T2* blurring and geometric distortions at 7T and enables a clear and detailed delineation of human brain structures in-vivo with the diffusion contrasts. In addition, results of the proposed approach for high-resolution diffusion imaging at 3T are presented.

New rapid, accurate T2 quantification detects pathology in normal-appearing brain regions of relapsing-remitting MS patients.

IntroductionQuantitative T2 mapping may provide an objective biomarker for occult nervous tissue pathology in relapsing-remitting multiple sclerosis (RRMS). We applied a novel echo modulation curve (EMC) algorithm to identify T2 changes in normal-appearing brain regions of subjects with RRMS (N = 27) compared to age-matched controls (N = 38).MethodsThe EMC algorithm uses Bloch simulations to model T2 decay curves in multi-spin-echo MRI sequences, independent of scanner, and scan-settings. T2 values were extracted from normal-appearing white and gray matter brain regions using both expert manual regions-of-interest and user-independent FreeSurfer segmentation.ResultsCompared to conventional exponential T2 modeling, EMC fitting provided more accurate estimations of T2 with less variance across scans, MRI systems, and healthy individuals. Thalamic T2 was increased 8.5% in RRMS subjects (p < 0.001) and could be used to discriminate RRMS from healthy controls well (AUC = 0.913). Manual segmentation detected both statistically significant increases (corpus callosum & temporal stem) and decreases (posterior limb internal capsule) in T2 associated with RRMS diagnosis (all p < 0.05). In healthy controls, we also observed statistically significant T2 differences for different white and gray matter structures.ConclusionsThe EMC algorithm precisely characterizes T2 values, and is able to detect subtle T2 changes in normal-appearing brain regions of RRMS patients. These presumably capture both axon and myelin changes from inflammation and neurodegeneration. Further, T2 variations between different brain regions of healthy controls may correlate with distinct nervous tissue environments that differ from one another at a mesoscopic length-scale.

T2 relaxation mapping MRI of healthy and inflamed gingival tissue.

To investigate the use and reproducibility of MRI transverse relaxation time (T2) mapping in healthy and inflamed gingivae. 21 subjects were recruited into 2 groups: those without evidence of gingivitis ("healthy"; n = 11, age 24.0 ± 3.66 years) by visual assessment and those with moderate to severe gingivitis ("gingivitis"; n = 10, age 28.9 ± 6.03 years) exhibited across the second mandibular premolar and first mandibular molar buccal gingivae. Subjects were imaged by MRI twice in a single day. Three T2 weighted turbo spin-echo volumes with 0.25 × 0.25 × 0.8-mm3 resolution were acquired at echo times of 16, 32 and 48 ms for T2 decay fitting. Image analysis was fully blinded; the two imaging sessions were not identifiable as coming from the same subject. Each imaging session had independent regions of interest drawn on the first echo image and applied to the calculated T2 decay maps. The coefficient of variation was low and similar in healthy and gingivitis populations: 6.10 and 5.25% populations, respectively, with 5.65% populations across both groups. Bland-Altman analysis revealed no bias (mean -2.93%; 95% confidence intervals -22.20 to 16.34%) between sessions. The intersession agreement was good (r = 0.744, ρ = 0.568, intraclass correlation coefficient = 0.68). T2 mapping did not differentiate healthy from gingivitis groups. The mean T2 value in the healthy group (63.7 ms) was similar to that of the gingivitis group (65.23 ms) (p = 0.30). Mapping of the T2 decay in the gingivae was a repeatable process; however, T2 value alone did not differentiate those with clinical examination-determined gingivitis from those without signs of gingivitis.

Myelin Water Fraction Is Transiently Reduced after a Single Mild Traumatic Brain Injury--A Prospective Cohort Study in Collegiate Hockey Players.

Impact-related mild traumatic brain injuries (mTBI) are a major public health concern, and remain as one of the most poorly understood injuries in the field of neuroscience. Currently, the diagnosis and management of such injuries are based largely on patient-reported symptoms. An improved understanding of the underlying pathophysiology of mTBI is urgently needed in order to develop better diagnostic and management protocols. Specifically, dynamic post-injury changes to the myelin sheath in the human brain have not been examined, despite ‘compromised white matter integrity’ often being described as a consequence of mTBI. In this preliminary cohort study, myelin water imaging was used to prospectively evaluate changes in myelin water fraction, derived from the T2 decay signal, in two varsity hockey teams (45 players) over one season of athletic competition. 11 players sustained a concussion during competition, and were scanned at 72 hours, 2 weeks, and 2 months post-injury. Results demonstrated a reduction in myelin water fraction at 2 weeks post-injury in several brain areas relative to preseason scans, including the splenium of the corpus callosum, right posterior thalamic radiation, left superior corona radiata, left superior longitudinal fasciculus, and left posterior limb of the internal capsule. Myelin water fraction recovered to pre-season values by 2 months post-injury. These results may indicate transient myelin disruption following a single mTBI, with subsequent remyelination of affected neurons. Myelin disruption was not apparent in the athletes who did not experience a concussion, despite exposure to repetitive subconcussive trauma over a season of collegiate hockey. These findings may help to explain many of the metabolic and neurological deficits observed clinically following mTBI.