T2 Decay Curves Research Articles

New Insights into the Spread of MRS-Based Water T2 Values Observed in Highly Fatty Replaced Muscles.

The reference standard for assessing water T2 (T2,H2O ) at high fat fraction (FF) is 1 H MRS. T2,H2O (T2,H2O,MRS ) dependence on FF (FFMRS ) has recently been demonstrated in muscle at high FF (i.e. ≥60%). To investigate the relationship between T2,H2O,MRS and FFMRS in the thigh/leg muscles of patients with neuromuscular diseases and to compare with quantitative MRI. Retrospective case-control study. A total of 151 patients with neuromuscular disorders (mean age ± standard deviation = 52.5 ± 22.6 years, 54% male), 44 healthy volunteers (26.5 ± 13.0 years, 57% male). A 3-T; single-voxel stimulated echo acquisition mode (STEAM) MRS, multispin echo (MSE) imaging (for T2 mapping, T2,H2O,MRI ), three-point Dixon imaging (for FFMRI and mapping). Mono-exponential and bi-exponential models were fitted to water T2 decay curves to extract T2,H2O,MRS and FFMRS . Water resonance full-width-at-half-maximum (FWHM) and B0 spread (∆B0 ) values were calculated. T2,H2O,MRI (mean), FFMRI (mean, kurtosis, and skewness), and (mean) values were estimated in the MRS voxel. Mann-Whitney U tests, Kruskal-Wallis tests. A P-value <0.05 was considered statistically significant. Normal T2,H2O,MRS threshold was defined as the 90th percentile in healthy controls: 30.3 msec. T2,H2O,MRS was significantly higher in all patients with FFMRS < 60% compared to healthy controls. We discovered two subgroups in patients with FFMRS ≥ 60%: one with T2,H2O,MRS ≥ 30.3 msec and one with T2,H2O,MRS < 30.3 msec including abnormally low T2,H2O,MRS . The latter subgroup had significantly higher water resonance FWHM, ∆B0 , FFMRI kurtosis, and skewness values but nonsignificantly different (P = 1.00) and long T2,H2O,MRS component and its fraction (P > 0.11) based on the bi-exponential analysis. The findings suggest that the cause for (abnormally) T2,H2O,MRS at high FFMRS is biophysical, due to differences in susceptibility between muscle and fat (increased FWHM and ∆B0 ), rather than pathophysiological such as compartmentation changes, which would be reflected by the bi-exponential analysis. 3 TECHNICAL EFFICACY: Stage 3.

Nanodiamond (ND)-based polyamide (PA) 66 nanocomposite studied with infrared (IR) microscopy and time-domain nuclear magnetic resonance (TD-NMR) combined with two-trace two-dimensional (2T2D) correlation analysis

Nanodiamond/polyamide (ND/PA) nanocomposite was examined with infrared (IR) microscopy and time-domain nuclear magnetic resonance (TD-NMR) to elucidate in detail the interphase between amino functionalized ND (ND-NH2) and PA 66. An IR image of the ND/PA nanocomposite suggested the uniform nanoscale distribution of the ND-NH2 particles thanks to the spherical shape and accessible external surface of ND terminated with reactive amino groups. On the other hand, a substantial level of change was observed in T2 decay curves when the ND-NH2 particles were incorporated in the PA 66. The fine features of the thermally induced changes in the decay curves were readily analyzed with the two-trace two-dimensional (2T2D) correlation method. The variation in the asynchronous correlation intensity indicated that the changes observed in the mechanical properties of the ND/NH2 may be attributed to the development of crosslinking between tie chains in the amorphous region via the interaction between the ND-NH2 and PA 66. Accordingly, such firm links have a substantial effect in preventing the displacement of the amorphous domain, which eventually increases the Young’s modulus but reduces the ductility of the PA.

Abstract EP06: Serum Water T 2 And Its Association With Cardiometabolic Health: The Premier Study

Introduction: Plasma and serum water T 2 are global markers of metabolic syndrome and cardiometabolic health. Serum, in contrast with plasma, lacks fibrinogen, one of the key drivers of the association of plasma water T 2 with metabolic syndrome. Yet, serum water T 2 was able to detect metabolic syndrome with high sensitivity and specificity through its association with other underlying components. Here we examined bio-banked serum samples from a large, diverse study population to investigate the use of serum water T 2 as a marker of cardiometabolic health. Hypothesis: Among PREMIER participants at baseline, serum water T 2 is associated with multiple measures of cardiometabolic health. Materials and Methods: This is an auxiliary study of the PREMIER trial and has an observational, cross-sectional design. A total of 810 mildly hypertensive participants without diabetes or CVD (63% females, 35% black, and 65% non-black) were enrolled in the parent study. Here, a subset of those participants (n=455) were analyzed based on the availability of serum samples that had undergone a single freeze-thaw cycle. Using a Bruker mq20 benchtop nuclear magnetic resonance relaxometer, T 2 decay curves were recorded at 37°C for unmodified human serum. Water T 2 was distinguished from non-water components using a discrete inverse Laplace transform algorithm. The association of serum water T 2 , the outcome variable, with other potential predictors was examined in four stages: (1) screening of predictors using a bootstrap forest machine learning algorithm, (2) clustering of predictors using principal component analysis, (3) associations with serum water T 2 using multiple linear regression, and (4) validation of regression models using a bootstrap forest algorithm. Results: The final model for serum water T 2 included albumin, globulins, non-HDL-cholesterol, household income, urine phosphate, TG/HDL ratio, family history of CVD and the interaction between BMI and race. The adjusted R 2 for this model was 0.55. Thus, serum water T 2 values were independently associated with markers of dyslipidemia, inflammation, insulin resistance, kidney function, family history of CVD, household income, and the categorical interaction between BMI and race. Compared with obese/Black individuals (reference group), non-obese/non-Black individuals showed higher T 2 values (p&lt;0.0001) reflecting improved cardiometabolic health. By contrast, serum water T 2 values for the non-obese/Black (p=0.7417) and obese/non-Black (p=0.7262) participants were not statistically different from the reference group. Conclusion: Analysis of bio-banked samples from PREMIER validates serum water T 2 as a biomarker of cardiometabolic health in mildly hypertensive individuals without diabetes or CVD. Serum water T 2 , while similar to plasma water T 2 , revealed some distinct associations with measures of cardiometabolic health.

Dual nuclear magnetic resonance for probing intrinsic bone structure and a potential gut-bone axis in ovariectomized rats.

Currently, the existence of a gut-bone axis receives massive attention, and while sound premises and indirect proofs exist for the gut-bone axis concept, few studies have provided actual data linking the gut and bone physically. This study aimed to exploit the versatile nature of nuclear magnetic resonance (NMR) to link NMR relaxometry data on bone mineralization with NMR spectroscopic profiling of gut metabolites. For this purpose, sample material was obtained from a 6-week intervention study with ovariectomized (OVX) rats (n = 49) fed with seven different diets varying in calcium content (0.2-6.0 mg/kg) and prebiotic fiber content (0-5.0% w/w). This design ensured a span in (i) calcium available for bone mineralization and (ii) metabolic activity in the gut. After termination of the intervention, longitudinal (T1 ), transverse (T2 ) relaxation, and mechanical bone strength were measured on the excised femur bones. A PLS model with high predictability (Q2 = 0.86, R2 = 0.997) was demonstrated between T2 decay curves and femur mechanical strength. Correlations were established between bone T2 populations and gut short-chain fatty acids. In conclusion, the present dual NMR approach showed strong correlation between T2 relaxation and mechanical strength of the bone, and when metabolic activity in the gut was modulated by inulin, the potential existence of a gut-bone axis was demonstrated.

Evaluating the effect of aging process on the physicochemical characteristics of rice seeds by low field nuclear magnetic resonance and its imaging technique

In-depth investigation of the storability of rice seeds directly relies on the accuracy of the artificial accelerated aging method. In this study, Shennong 265 rice seed samples that underwent a 28 d artificial accelerated aging cycle were monitored by low field nuclear magnetic resonance (LF-NMR) and its imaging technique, the transverse relaxation times and proton density-weighted images of which were acquired at 0, 7, 14, 21 and 28 d during the aging process. Subsequently, the acquired information processed by NMR inversion and corresponding image processing software was combined with results from the standard germination test to describe the physicochemical characteristics of the rice seeds during the aging process. Results suggest that the rate of the T2 decay curve and the T2 relaxation time of the unaged rice seeds are higher than those of the aged rice seeds, and both values increase in positive correlation with the artificial aging duration. In addition, the contents of bound water, free water and total water of the aged seeds are all higher than those of the unaged seeds, although with prolonged aging, the contents of bound water and total water of the rice seeds fluctuates, whilst the content of free water consistently increases. Proton density images of the rice seed samples at different times of the aging process indicate that water distribution inside the seeds is inhomogeneous. Lastly, as aging duration increases, both the germination rate and germination potential of the seeds decrease. This study has determined the physiological and biochemical changes that the seeds undergo during aging, and revealed the relationship between these changes and the viability and vigor of the seeds, thereby providing references for studies on the internal mechanisms of seed deterioration.

Inverse Laplace transform and multiexponential fitting analysis of T2 relaxometry data: a phantom study with aqueous and fat containing samples

BackgroundThe inverse Laplace transform (ILT) is the most widely used method for T2 relaxometry data analysis. This study examines the qualitative agreement of ILT and a proposed multiexponential (Mexp method) regarding the number of T2 components. We performed a feasibility study for the voxelwise characterisation of heterogeneous tissue with T2 relaxometry.MethodsEleven samples of aqueous, fatty and mixed composition were analysed using ILT and Mexp. The phantom was imaged using a 1.5-T system with a single slice T2 relaxometry 25-echo Carr-Purcell-Meiboom-Gill sequence in order to obtain the T2 decay curve with 25 equidistant echo times. The adjusted R2 goodness of fit criterion was used to determine the number of T2 components using the Mexp method on a voxel-based analysis. Comparison of mean and standard deviation of T2 values for both methods was performed by fitting a Gaussian function to the ILT resulting vector.ResultsPhantom results showed pure monoexponential decay for acetone and water and pure biexponential behaviour for corn oil, egg yolk, and 35% fat milk cream, while mixtures of egg whites and yolks as well as milk creams with 12–20% fatty composition exhibit mixed monoexponential and biexponential behaviour at different fractions. The number of T2 components by the Mexp method was compared to the ILT-derived spectrum as ground truth.ConclusionsMexp analysis with the adjusted R2 criterion can be used for the detection of the T2 distribution of aqueous, fatty and mixed samples with the added advantage of voxelwise mapping.

Non-negative least squares computation for in vivo myelin mapping using simulated multi-echo spin-echo T2 decay data.

Multi-compartment T2 mapping has gained particular relevance for the study of myelin water in the brain. As a facilitator of rapid saltatory axonal signal transmission, myelin is a cornerstone indicator of white matter development and function. Regularized non-negative least squares fitting of multi-echo T2 data has been widely employed for the computation of the myelin water fraction (MWF), and the obtained MWF maps have been histopathologically validated. MWF measurements depend upon the quality of the data acquisition, B1+ homogeneity and a range of fitting parameters. In this special issue article, we discuss the relevance of these factors for the accurate computation of multi-compartment T2 and MWF maps. We generated multi-echo spin-echo T2 decay curves following the Carr-Purcell-Meiboom-Gill approach for various myelin concentrations and myelin T2 scenarios by simulating the evolution of the magnetization vector between echoes based on the Bloch equations. We demonstrated that noise and imperfect refocusing flip angles yield systematic underestimations in MWF and intra-/extracellular water geometric mean T2 (gmT2 ). MWF estimates were more stable than myelin water gmT2 time across different settings of the T2 analysis. We observed that the lower limit of the T2 distribution grid should be slightly shorter than TE1 . Both TE1 and the acquisition echo spacing also have to be sufficiently short to capture the rapidly decaying myelin water T2 signal. Among all parameters of interest, the estimated MWF and intra-/extracellular water gmT2 differed by approximately 0.13-4 percentage points and 3-4 ms, respectively, from the true values, with larger deviations observed in the presence of greater B1+ inhomogeneities and at lower signal-to-noise ratio. Tailoring acquisition strategies may allow us to better characterize the T2 distribution, including the myelin water, in vivo.

Ultra-short echo time imaging with multiple echo refocusing for porous media T2 mapping.

T2 relaxation time measurement is a powerful tool to distinguish signal components in porous media. As T2 weighting is generally achieved by spin-echo based methods, it is very challenging to capture very short T2 relaxation time components, approximately 1 ms, with high resolution spatial encoding. It is especially challenging when T2 relaxation times of the other signal components are not known a priori. We propose a method, combining ultrashort echo time (UTE) imaging with multiple spin echo refocusing, to generate a series of images with T2 weighting. The T2 decay curves for each image voxel were extracted, and multiple T2 relaxation components were quantitatively evaluated. The method has been applied to a fast relaxation system, namely, moisture content in wood samples to differentiate cell wall (bound) water and cell cavity (lumen) water.

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.

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.

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.

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.

In vivo proton magnetic resonance spectroscopy of liver metabolites in non-alcoholic fatty liver disease in rats: T2 relaxation times in methylene protons

The aim of this study was to evaluate the transverse relaxation time of methylene resonance as compared to other lipid resonances. The examinations were performed using a 3.0 T scanner with a point-resolved spectroscopy (PRESS) sequence. Lipid relaxation time in a lipid phantom filled with canola oil was estimated with a repetition time (TR) of 6000ms and echo time (TE) of 40–550ms. For in vivo proton magnetic resonance spectroscopy (1H-MRS), eight male Sprague–Dawley rats were given free access to a normal-chow (NC) and another eight male Sprague–Dawley rats were given free access to a high-fat (HF) diet. Both groups drank water ad libitum. T2 measurements in the rats’ livers were conducted at a fixed TR of 6000ms and TE of 40–220ms. Exponential curve fitting quality was calculated through the coefficients of determination (R2). Chemical analyses of the phantom and livers were not performed, but T2 decay curves were acquired. The T2 relaxation time of methylene resonance was estimated as follows: NC rats, 37.1±4.3ms; HF rats, 31.4±1.8ms (p<0.05). The extrapolated M0 values were higher in HF rats than in NC rats (p<0.005). This study of 1H MRS led to sufficient spectral resolution and signal-to-noise ratio differences to characterize the T2 relaxation times of methylene resonance. 1H MRS relaxation times may be useful for quantitative characterization of various liver diseases, including fatty liver disease.

Multicomponent T2 relaxation studies of the avian egg.

To investigate the tissue-like multiexponential T2 signal decays in avian eggs. Transverse relaxation studies of raw, soft-boiled and hard-boiled eggs were performed at 3 Tesla using a three-dimensional Carr-Purcell-Meiboom-Gill imaging sequence. Signal decays over a TE range of 11 to 354 ms were fitted assuming single- and multicomponent signal decays with up to three separately decaying components. Fat saturation was used to facilitate spectral assignment of observed decay components. Egg white, yolk and the centrally located latebra all demonstrate nonmonoexponential T2 decays. Specifically, egg white exhibits two-component decays with intermediate and long T2 times. Meanwhile, yolk and latebra are generally best characterized with triexponential decays, with short, intermediate and very long T2 decay times. Fat saturation revealed that the intermediate component of yolk could be attributed to lipids. Cooking of the egg profoundly altered the decay curves. Avian egg T2 decay curves cover a wide range of decay times. Observed T2 components in yolk and latebra as short as 10 ms, may prove valuable for testing clinical sequences designed to measure short T2 components, such as myelin-associated water in the brain. Thus we propose that the egg can be a versatile and widely available MR transverse relaxation phantom.

How does magnetization transfer influence mcDESPOT results?

A steady-state approach that was termed multicomponent driven equilibrium single pulse observation of T1 and T2 (mcDESPOT) has recently been proposed for myelin water fraction (fM) mapping in brain development and demyelinating diseases. However, fMs estimated by mcDESPOT are significantly higher than myelin water fraction derived from multiecho spin echo T2-decay curve approaches. Magnetization transfer (MT), enhanced by the use of short, relatively high amplitude radiofrequency (RF) pulses in mcDESPOT, may artifactually influence fM maps. Our goal was to investigate the role of MT in mcDESPOT. mcDESPOT data was collected twice from three healthy volunteers using short RF pulses with higher MT effect and long RF pulses with lower MT effect. MR parameters from 11 white and gray regions were compared using a paired student t-test. Whole slice difference images were also compared. MT effects had a substantial influence on the signal generated by the balanced steady-state free procession sequences used in mcDESPOT. However, these MT effects were not clearly evident in the fM values determined by the conventional two-pool mcDESPOT analysis. The signal generated from mcDESPOT is sensitive to MT, but the extracted myelin water fractions are relatively insensitive to changes of MT.

Comparison of myelin water fraction from multiecho T2 decay curve and steady‐state methods

Myelin water fraction is conventionally measured from the T2 decay curve. Recently, a steady-state approach entitled multicomponent-driven equilibrium single pulse observation of T1 /T2 (mcDESPOT) was employed for myelin water fraction mapping. However, no direct comparison between the established multiecho T2 relaxation method and mcDESPOT has been performed. Gradient and spin echo (GRASE) acquired T2 decay curve and mcDESPOT measurements were acquired from 10 healthy volunteers using a 3T MRI. We compared myelin water fraction, transmit radio frequency field (B1 ), and T2 's of intra- and extracellular water obtained from both methods. For all brain regions examined, myelin water fractions from mcDESPOT were significantly higher than those from multiecho GRASE. B1 maps were qualitatively similar between GRASE and mcDESPOT, but multicomponent T2 times were significantly different. To investigate the effect of exchange, mcDESPOT data were analyzed with and without exchange. When exchange was turned off, intra- and extracellular T2 times from mcDESPOT were roughly consistent with GRASE results; however, myelin water fractions derived from mcDESPOT were still significantly higher than those derived from GRASE. Myelin water fraction values derived from mcDESPOT cannot be considered to be equivalent to those derived from T2 decay curve approaches.

In vivo GABA T2 determination with J‐refocused echo time extension at 7 T

A method to measure the T2 relaxation time of GABA with spectral editing techniques is proposed. Spectral editing techniques can be used to unambiguously extract signals of low concentration J-coupled spins such as γ-aminobutyric acid (GABA) from overlapping resonances such as creatine and macromolecules. These sequences, however, generally have fixed and relatively long echo times. Therefore, for the absolute quantification of the edited spectrum, the T2 relaxation time must be taken into account. To measure the T2 relaxation time, the signal intensity has to be obtained at multiple echo times. However, on a coupled spin system such as GABA this is challenging, since the signal intensity of the target resonances is modulated not only by T2 decay but also by the J-coupling, which strongly influences the shapes and amplitudes of the edited signals, depending on the echo time. Here, we propose to refocus the J-modulation of the edited signal at different echo times by using chemical shift selective refocusing. In this way the echo time can be arbitrarily extended while preserving the shape of the edited signal. The method was applied in combination with the MEGA-sLASER editing technique to measure the in vivo T2 relaxation time of GABA (87 ± 11 ms, n = 10) and creatine (109 ± 8 ms, n = 10) at 7 T. The T1 relaxation time of these metabolites in a single subject was also determined (GABA, 1334 ± 158 ms; Cr, 1753 ± 12 ms). The T2 decay curve of coupled spin systems can be sampled in an arbitrary fashion without the need for signal shape correction. Furthermore, the method can be applied with any spectral editing technique. The shortest echo time of the method is limited by the echo time of the spectral editing technique.

T 2 relaxometry measurements in low spatial frequency brain regions differ between fast spin-echo and multiple-echo spin-echo sequences

Dual-echo fast spin-echo (FSE) sequences are used in T2 relaxometry studies of neurological disorders because of shorter clinical scanning times and protocol simplicity. However, FSE sequences have possible spatial frequency-dependent effects, and derived T2 values may include errors that depend on the spatial frequency characteristics of the brain region of interest. Dual-echo FSE and multi-echo spin-echo (MESE) sequences were acquired in nine subjects. The T2 decay curves for FSE and MESE sequences were estimated and percent error maps were generated. T2 error values were obtained along each patient's corticospinal tract (CST). Whole-brain white matter (WM) and gray matter (GM) T2 error values were also obtained. The paired t test was performed to evaluate differences in T2 values in the CST between FSE and MESE sequences. Histograms of error values in CST and in whole-brain WM and GM structures revealed systematic errors in FSE sequences. Significant differences (P < 0.001) in CST T2 values were also observed between FSE and MESE sequences. Our findings indicate that T2 values derived from FSE sequences are prone to large errors, even in low spatial frequency regions such as the CST, when compared to MESE sequences. Future studies should be aware of this limitation of FSE sequences.

T2 relaxation time mapping in phantom and in vivo myocardial studies to investigate optimal method of quantification

Summary Reproducible and accurate T2 measurements are required for the characterization of myocardial tissue, e. g. to distinguish healthy, scar and edematous myocardium. It is the objective of this study to investigate the impact of the fitting algorithm applied for the T2 quantification from data derived from a single-breathhold T2-prepared steady-state free precession (T2p-SSFP) imaging technique. Background In direct comparison to multi spin echo technique, superior performance of T2p-SSFP-based T2 quantification has been reported. In spite of availability of a variety of quantification algorithms, the use of monoexponential model is still the standard for fitting the T2 decay curve. Methods