BIA-assessed cellular hydration and muscle performance in youth, adults, and older adults.

BACKGROUND & AIMS: Alterations in body hydration can have an impact on muscle performance, with consequences not only at a sporting level, but on overall health and daily functional competence. Given that the estimation of body water from BIA is based on prediction equations involving assumptions on tissue hydration and body geometry, it is unclear if phase angle (PhA), which is not influenced by assumptions, is a better marker of muscle performance than the BIA estimated parameters of body water. Therefore, the aims of this investigation were to analyze the relationships of BIA-estimated body water compartments with muscle performance among youth, adults, and older adults, and to assess the added value of PhA as a marker of muscle performance. METHODS: BIA assessments were completed on 263 youth (ages 6-17), 249 adults (ages 18-64), and 75 older adults (ages 65+). Muscle performance was assessed by jumping mechanography (power and force) and handgrip strength. Partial correlations were used to compare the degree of association among the BIA measures with muscle performance for each age group, controlling for sex, age, and body weight. RESULTS: TBW, ICW, and PhA were associated with muscle performance at the lower and upper limbs in all age groups (p < 0.05), with the exception of PhA with handgrip strength in adults and older adults and TBW with lower limb total force in the older adults. In youth, the highest associations observed were PhA with lower limb muscle power (r = 0.45, CI:0.35-0.54, p < 0.05) and with handgrip strength (r = 0.42, CI:0.32-0.52, p < 0.05). In adults and older adults, the major associations observed were those of ICW with lower limb muscle power (adults, r = 0.53, CI:0.43-0.61, p < 0.05; older adults, r = 0.52, CI = 0.33-0.67, p < 0.05). ECW had significantly lower associations (p < 0.05) with both lower limb force and power in adults and older adults compared to youth. In the older adults, ECW was negatively associated with lower limb total force (r = -0.24; p < 0.05). CONCLUSIONS: BIA derived hydration parameters may be useful markers of muscle performance in all age groups. In particular, the ICW compartment was a better predictor of muscle performance in adults and older adults compared to youth. In youth, PhA had stronger associations with muscle performance than those of ICW. Thus, phase angle appears to be a useful marker of muscle performance, particularly in youth.

Stay hydrated: basolateral fluids shaping tissues.

During development, embryos perform a mesmerizing choreography, which is crucial for the correct shaping, positioning and function of all organs. The cellular properties powering animal morphogenesis have been the focus of much attention. In contrast, much less consideration has been given to the invisible engine constituted by the intercellular fluid. Cells are immersed in fluid, of which the composition and physical properties have a considerable impact on development. In this review, we revisit recent studies from the perspective of the fluid, focusing on basolateral fluid compartments and taking the early mouse and zebrafish embryos as models. These examples illustrate how the hydration levels of tissues are spatio-temporally controlled and influence embryonic development.

Mechanisms of T2 * anisotropy and gradient echo myelin water imaging.

In MRI, structurally aligned molecular or micro-organization (e.g. axonal fibers) can be a source of substantial signal variations that depend on the structural orientation and the applied magnetic field. This signal anisotropy gives us a unique opportunity to explore information that exists at a resolution several orders of magnitude smaller than that of typical MRI. In this review, one of the signal anisotropies, T2 * anisotropy in white matter, and a related imaging method, gradient echo myelin water imaging (GRE-MWI), are explored. The T2 * anisotropy has been attributed to isotropic and anisotropic magnetic susceptibility of myelin and compartmentalized microstructure of white matter fibers (i.e. axonal, myelin, and extracellular space). The susceptibility and microstructure create magnetic frequency shifts that change with the relative orientation of the fiber and the main magnetic field, generating the T2 * anisotropy. The resulting multi-component magnitude decay and nonlinear phase evolution have been utilized for GRE-MWI, assisting in resolving the signal fraction of the multiple compartments in white matter. The GRE-MWI method has been further improved by signal compensation techniques including physiological noise compensation schemes. The T2 * anisotropy and GRE-MWI provide microstructural information on a voxel (e.g. fiber orientation and tissue composition), and may serve as sensitive biomarkers for microstructural changes in the brain. Copyright © 2016 John Wiley & Sons, Ltd.

Whole-body continuously moving table fat-water MRI with dynamic B0 shimming at 3 Tesla.

PURPOSE: The purpose of this work was to develop a rapid and robust whole-body fat-water MRI (FWMRI) method using a continuously moving table (CMT) with dynamic field corrections at 3 Tesla. METHODS: CMT FWMRI was developed at 3 Tesla with a multiecho golden angle (GA) radial trajectory and dynamic B0 field shimming. Whole-body imaging was performed with 4 echoes and superior-inferior coverage of 1.8 meters without shims in 90 s. 716 axial images were reconstructed with GA profile binning followed by B0 field map generation using fast three-point seeded region growing fat-water separation and slice-specific 0(th) and 1(st) order shim calculation. Slice-specific shims were applied dynamically in a repeated CMT FWMRI scan in the same session. The resulting images were evaluated for field homogeneity improvements and quality of fat-water separation with a whole-image energy optimized algorithm. RESULTS: GA sampling allowed high quality whole-body FWMRI from multiecho CMT data. Dynamic B0 shimming greatly improved field homogeneity in the body and produced high quality water and fat only images as well as fat signal fraction and R2 * relaxivity maps. CONCLUSION: A rapid and robust technique for whole-body fat-water quantification has been developed with CMT MRI with dynamic B0 field correction. Magn Reson Med 76:183-190, 2016. © 2015 Wiley Periodicals, Inc.

Characterization of brown adipose tissue by water-fat separated magnetic resonance imaging.

BACKGROUND: To evaluate the possibility of quantifying brown adipose tissue (BAT) volume and fat concentration with a high resolution, long echo time, dual-echo Dixon imaging protocol. METHODS: A 0.42 mm isotropic resolution water-fat separated MRI protocol was implemented by using the second opposite-phase echo and third in-phase echo. Fat images were calibrated with regard to the intensity of nearby white adipose tissue (WAT) to form relative fat content (RFC) images. To evaluate the ability to measure BAT volume and RFC contrast dynamics, rats were divided into two groups that were kept at 4° or 22°C for 5 days. The rats were then scanned in a 70 cm bore 3.0 Tesla MRI scanner and a human dual energy CT. Interscapular, paraaortal, and perirenal BAT (i/pa/pr-BAT) depots as well as WAT and muscle were segmented in the MRI and CT images. Biopsies were collected from the identified BAT depots. RESULTS: The biopsies confirmed that the three depots identified with the RFC images consisted of BAT. There was a significant linear correlation (P < 0.001) between the measured RFC and the Hounsfield units from DECT. Significantly lower iBAT RFC (P = 0.0064) and significantly larger iBAT and prBAT volumes (P = 0.0017) were observed in the cold stimulated rats. CONCLUSION: The calibrated Dixon images with RFC scaling can depict BAT and be used to measure differences in volume, and fat concentration, induced by cold stimulation. The high correlation between RFC and HU suggests that the fat concentration is the main RFC image contrast mechanism.

Improving chemical shift encoded water-fat separation using object-based information of the magnetic field inhomogeneity.

PURPOSE: The purpose of this work was to improve the robustness of existing chemical shift encoded water-fat separation methods by incorporating object-based information of the B0 field inhomogeneity. THEORY: The primary challenge in water-fat separation is the estimation of phase shifts that arise from B0 field inhomogeneity, which is composed of the background field and susceptibility-induced field. The susceptibility-induced field can be estimated if the susceptibility distribution is known or can be approximated. In this work, the susceptibility distribution is approximated from the source images using the known susceptibility values of water, fat, and air. The field estimate is then demodulated from the source images before water-fat separation. METHODS: Chemical shift encoded source images were acquired in anatomical regions that are prone to water-fat swaps. The images were processed using algorithms from the ISMRM Fat-Water Toolbox, with and without the object-based field map information. The estimates were compared to examine the benefit of using the object-based field map information. RESULTS: Multiple cases are shown in which water-fat swaps were avoided by using the object-based information of the B0 field map. CONCLUSION: Object-based information of the B0 field may improve the robustness of existing chemical shift encoded water-fat separation methods.

Left atrial late gadolinium enhancement with water-fat separation: the importance of phase-encoding order.

PURPOSE: To compare two late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) methods: a Dixon LGE sequence with sequential phase-encoding order, reconstructed using water-fat separation, and standard fat-saturated LGE. MATERIALS AND METHODS: We implemented a dual-echo Dixon LGE method for reconstructing water-only images and compared it to fat-saturated LGE in 12 patients prior to their first pulmonary vein isolation (PVI) procedure. Images were analyzed for quality and fat-suppression. Regions of the left atrium were evaluated by a blinded observer (1 = prominent enhancement, 0 = mild or absent enhancement) on two sets of images (fat-saturated and water-only LGE) and agreement was assessed. RESULTS: Water-only LGE showed a trend toward better fat-suppression (P = 0.06), with a significantly more homogeneous blood pool signal and reduced inflow artifacts (both P < 0.01). Agreement between fat-saturated LGE and water-only methods was found in 84% of regions, significantly correlated by chi-squared test (P < 0.001). The kappa value was 0.52 (moderate). The average number of enhancing segments was higher for fat-saturated LGE than water-only LGE (4.2 ± 2.7 vs. 3.2 ± 2.9, P = 0.03). CONCLUSION: The two-point Dixon LGE technique reduces artifacts due to a centric k-space order. A similar enhancement pattern was observed irrespective of the LGE technique, with more enhancement detected by fat-saturated LGE.

Water/fat-resolved whole-heart Dixon coronary MRA: an initial comparison.

PURPOSE: To improve coronary vessel visualization in whole-heart coronary magnetic resonance angiography (CMRA), fat suppression is typically applied. However, recent studies have shown that cardiac fat can also have diagnostic value. To enhance CMRA image quality by improved fat suppression and to provide additionally fat-only information highly resolved, dual-echo Dixon CMRA approaches have been developed. METHODS: In this pilot study, approved by the institutional review board, 30 patients were investigated comparing whole-heart T1 -weighted dual-echo Dixon CMRA to conventional whole-heart fat-suppressed balanced fast field echo CMRA, integrated into a routine clinical protocol that includes the administration of gadolinium for perfusion and late enhancement measurements. Signal-to-noise-ratio, contrast-to-noise-ratio, and image quality were analyzed. RESULTS: Dual-echo Dixon significantly (P<0.000001) improved image quality compared with conventional fat-suppressed balanced fast field echo CMRA. Signal-to-noise-ratio and contrast-to-noise-ratio were found to be comparable when balanced fast field echo was performed before gadolinium and dual-echo Dixon fast field echo after gadolinium administration. CONCLUSION: Dual-echo Dixon can help to improve whole-heart CMRA image quality significantly. The additional whole-heart fat information delivered by this approach can support a number of new clinical studies addressing the diagnostic and the predictive value of intramyocardial and extramyocardial fatty deposits.

Comparison of cells free in coelomic and water-vascular system of sea cucumber, Apostichopus japonicus.

The sea cucumber, Apostichopus japonicus possesses a variety of cells populating in both the coelomic (cells in the coelomic are called coelomocytes) and water-vascular system. In this study, we compared cells in these two systems of A. japonicus on total cell number, cell types and surface antigens through monoclonal antibodies against coelomocytes. The results demonstrated that the cell types observed in coelomic also could be found in water-vascular system, but the total cell number and percentages of each type were different. The total number of coelomocytes was 2-3 times of that in water-vascular system. Lymphoid cells were numerically dominant in coelomic system, while spherulocytes with pseudopods in water-vascular system. Results of indirect immunofluorescence assay technique showed that both coelomocytes and cells in water-vascular system could be recognized by the corresponding MAbs, and the distribution of its positive signals was not different. In conclusion, cell types and surface antigens in coelomic and water-vascular system were same, but the total cell number and percentages of each type were different. And further researches are needed on whether there are differences in functions of the different composition.

Three-dimensional dixon fat-water separated rapid breathheld imaging of myocardial infarction.

PURPOSE: To develop a breathhold three-dimensional (3D) Dixon technique for fat suppressed imaging of myocardial infarction. MATERIALS AND METHODS: A pulse sequence was developed that uses a radial fan-beam k-space segmentation scheme for efficient coverage of k-space, enabling 3D scans in a single breathhold. The sequence uses a dual-echo bipolar readout to enable Dixon fat-water separation for improved visualization of epicardial and pericardial delayed enhancement. The 3D Dixon method was compared with a conventional 2D fast gradient recalled echo (FGRE) -based technique in 25 patients. RESULTS: Pericardial visualization scores and confidence were higher while overall image quality and artifacts were slightly worse for 3D Dixon compared with 2D FGRE. Robust fat suppression was achieved in 21 of 25 cases using the 3D Dixon method. CONCLUSION: A 3D breathhold method for fat-water separated imaging of myocardial delayed enhancement was developed and validated.

Measurement of interscapular brown adipose tissue of mice in differentially housed temperatures by chemical-shift-encoded water-fat MRI.

PURPOSE: To determine differences in fat-signal fraction (FF) from chemical-shift-encoded water-fat MRI of interscapular BAT in mice housed at different ambient temperatures (Ta ). MATERIALS AND METHODS: C57BL/6J male mice (8 weeks old) were singly housed at 16°C, 23°C, or 30°C (n = 16/group) for 4 weeks. Measures included food intake, body weight (both measured weekly) and body composition (at baseline, 2, and 4 weeks post-thermal exposure); chemical-shift-encoded water-fat MRI was performed on a 9.4 Tesla Bruker magnet with respiratory gating and anesthesia at 4 weeks post-thermal exposure. RESULTS: A significant inverse relationship between food intake and Ta was evidenced (P < 0.0001). Lean mass was similar among groups, while total fat mass was significantly different among groups ([mean ± SE]: 30°C = 5.10 ± 0.19 g; 23°C = 4.18 ± 0.16 g; 16°C = 3.48 ± 0.54 g; P < 0.0001). Mean BAT-FF was positively related to Ta (means: 30°C = 79.4%; 23°C = 61.8%; 16°C = 50.9%; P < 0.0001). CONCLUSION: These cross-sectional results demonstrate that MRI measurement of FF within the interscapular BAT in mice reflects recent functional status of the tissue, with a lower Ta leading to a significantly reduced BAT-FF, indicative of the tissue's involvement in thermogenesis.

Water-fat MRI for assessing changes in bone marrow composition due to radiation and chemotherapy in gynecologic cancer patients.

PURPOSE: To assess the feasibility of using fat-fraction imaging for measuring marrow composition changes over large regions in patients undergoing cancer therapy. MATERIALS AND METHODS: Thirteen women with gynecologic malignancies who were to receive radiation and/or chemotherapy were recruited for this study. Subjects were imaged on a 3T magnetic resonance (MR) scanner at baseline (after surgery but before radiation or chemotherapy), 6 months, and 12 months after treatment. Water-fat imaging was used to generate high-resolution, 3D signal fat fraction (sFF) maps extending from mid-femur to L3. Treatment changes were assessed by measuring marrow sFF in the L4 vertebra, femoral necks, and control tissues. RESULTS: Pretreatment and 6-month scans were compared in nine women. sFF increased significantly in both the L4 vertebral marrow (P = 0.04) and the femoral necks (P = 0.03), while no significant change was observed in control regions. Qualitatively, chemotherapy changes were more uniform in space, whereas the radiation-induced changes were largest in marrow regions inside and close to the target radiation field. CONCLUSION: Water-fat MRI is sensitive to changes in red/yellow marrow composition, and can be used for quantitative and qualitative assessment of treatment-induced marrow damage.

One component? Two components? Three? The effect of including a nonexchanging "free" water component in multicomponent driven equilibrium single pulse observation of T1 and T2.

Quantitative myelin content imaging provides novel and pertinent information related to underlying pathogenetic mechanisms of myelin-related disease or disorders arising from aberrant connectivity. Multicomponent driven equilibrium single pulse observation of T1 and T2 is a time-efficient multicomponent relaxation analysis technique that provides estimates of the myelin water fraction, a surrogate measure of myelin volume. Unfortunately, multicomponent driven equilibrium single pulse observation of T1 and T2 relies on a two water-pool model (myelin-associated water and intra/extracellular water), which is inadequate within partial volume voxels, i.e., containing brain tissue and ventricle or meninges, resulting in myelin water fraction underestimation. To address this, a third, nonexchanging "free-water" component was introduced to the multicomponent driven equilibrium single pulse observation of T1 and T2 model. Numerical simulations and experimental in vivo data show that the model to perform advantageously within partial volume regions while providing robust and reproducible results. It is concluded that this model is preferable for future studies and analysis.

Chemical shift encoded water-fat separation using parallel imaging and compressed sensing.

Chemical shift encoded techniques have received considerable attention recently because they can reliably separate water and fat in the presence of off-resonance. The insensitivity to off-resonance requires that data be acquired at multiple echo times, which increases the scan time as compared to a single echo acquisition. The increased scan time often requires that a compromise be made between the spatial resolution, the volume coverage, and the tolerance to artifacts from subject motion. This work describes a combined parallel imaging and compressed sensing approach for accelerated water-fat separation. In addition, the use of multiscale cubic B-splines for B(0) field map estimation is introduced. The water and fat images and the B(0) field map are estimated via an alternating minimization. Coil sensitivity information is derived from a calculated k-space convolution kernel and l(1)-regularization is imposed on the coil-combined water and fat image estimates. Uniform water-fat separation is demonstrated from retrospectively undersampled data in the liver, brachial plexus, ankle, and knee as well as from a prospectively undersampled acquisition of the knee at 8.6x acceleration.

Recovery of chemical estimates by field inhomogeneity neighborhood error detection (REFINED): fat/water separation at 7 tesla.

PURPOSE: To reduce swaps in fat-water separation methods, a particular issue on 7 Tesla (T) small animal scanners due to field inhomogeneity, using image postprocessing innovations that detect and correct errors in the B0 field map. MATERIALS AND METHODS: Fat-water decompositions and B0 field maps were computed for images of mice acquired on a 7T Bruker BioSpec scanner, using a computationally efficient method for solving the Markov Random Field formulation of the multi-point Dixon model. The B0 field maps were processed with a novel hole-filling method, based on edge strength between regions, and a novel k-means method, based on field-map intensities, which were iteratively applied to automatically detect and reinitialize error regions in the B0 field maps. Errors were manually assessed in the B0 field maps and chemical parameter maps both before and after error correction. RESULTS: Partial swaps were found in 6% of images when processed with FLAWLESS. After REFINED correction, only 0.7% of images contained partial swaps, resulting in an 88% decrease in error rate. Complete swaps were not problematic. CONCLUSION: Ex post facto error correction is a viable supplement to a priori techniques for producing globally smooth B0 field maps, without partial swaps. With our processing pipeline, it is possible to process image volumes rapidly, robustly, and almost automatically.

Time-efficient slab-selective water excitation for 3D MRI.

Spectral-Spatial (SPSP) radiofrequency pulses are simultaneously selective in both the spectral and spatial domains. To selectively excite water spins and exclude fat, the individual subpulses that make up a SPSP pulse must be short (<1 ms at 4 T). A short subpulse duration limits the sharpness of the spatial slabs that can be excited when using a traditional SPSP pulse design approach. In this manuscript, the authors present an algorithm for designing SPSP pulses with substantially reduced maximum B(1) amplitudes and specific absorption rates. The proposed algorithm alternates between iterative design of the radiofrequency waveform for a given gradient shape and minimum-time variable-rate selective excitation reshaping of the gradient waveform. This approach is shown to reduce peak B(1) amplitudes in iteratively designed SPSP pulses by an order of magnitude. Unlike the use of regularization to control peak B(1) or specific absorption rate, the proposed method does not comprise the quality of the excitation profile. To achieve high-quality profiles, it was necessary to design the radiofrequency pulses for a measured rather than ideal gradient waveform. Slab-selective water excitation pulses with durations of 4.1 and 9.2 ms (fractional transition widths of 0.14 and 0.073, respectively) are demonstrated at 4 T.

Myelin water weighted diffusion tensor imaging.

In this study we describe our development and implementation of a magnetization transfer (MT) prepared stimulated-echo diffusion tensor imaging (DTI) technique that can be made sensitive to the microanatomy of myelin tissue. The short echo time (TE) enabled by the stimulated-echo acquisition preserves significant signal from the short T(2) component (myelin water), and the MT preparation further provides differentiating sensitization to this signal. It was found that this combined strategy could provide sufficient sensitivity in our first attempt to image myelin microstructure. Compared to the diffusion tensor derived from the conventional DTI technique, the myelin water weighted (MWW) tensor has the same principal diffusion direction but exhibits a significant increase in fractional anisotropy (FA), which is mainly due to a decrease in radial diffusivity. These findings are consistent with the microstructural organization of the myelin sheaths that wrap around the axons in the white matter and therefore hinder radial diffusion. Given that many white matter diseases (e.g. multiple sclerosis) begin with a degradation of myelin microanatomy but not a loss of myelin content (e.g. loosening of the myelin sheaths), our newly implemented MWW DTI has the potential to lead to improved assessment of myelin pathology and early detection of demyelination.

Identification of brown adipose tissue in mice with fat-water IDEAL-MRI.

PURPOSE: To investigate the feasibility of using IDEAL (Iterative Decomposition with Echo Asymmetry and Least squares estimation) fat-water imaging and the resultant fat fraction metric in detecting brown adipose tissue (BAT) in mice, and in differentiating BAT from white adipose tissue (WAT). MATERIALS AND METHODS: Excised WAT and BAT samples and whole-mice carcasses were imaged with a rapid three-dimensional fat-water IDEAL-SPGR sequence on a 3 Tesla scanner using a single-channel wrist coil. An isotropic voxel size of 0.6 mm was used. Excised samples were also scanned with single-voxel proton spectroscopy. Fat fraction images from IDEAL were reconstructed online using research software, and regions of WAT and BAT were quantified. RESULTS: A broad fat fraction range for BAT was observed (40-80%), in comparison to a tighter and higher WAT range of 90-93%, in both excised tissue samples and in situ. Using the fat fraction metric, the interscapular BAT depot in each carcass could be clearly identified, as well as peri-renal and inguinal depots that exhibited a mixed BAT and WAT phenotype appearance. CONCLUSION: Due to BAT's multi-locular fat distribution and extensive mitochondrial, cytoplasm, and vascular supply, its fat content is significantly less than that of WAT. We have demonstrated that the fat fraction metric from IDEAL-MRI is a sensitive and quantitative approach to noninvasively characterize BAT.

Phase and amplitude correction for multi-echo water-fat separation with bipolar acquisitions.

PURPOSE: To address phase and amplitude errors for multi-point water-fat separation with "bipolar" acquisitions, which efficiently collect all echoes with alternating read-out gradient polarities in one repetition. MATERIALS AND METHODS: With the bipolar acquisitions, eddy currents and other system nonidealities can induce inconsistent phase errors between echoes, disrupting water-fat separation. Previous studies have addressed phase correction in the read-out direction. However, the bipolar acquisitions may be subject to spatially high order phase errors as well as an amplitude modulation in the read-out direction. A method to correct for the 2D phase and amplitude errors is introduced. Low resolution reference data with reversed gradient polarities are collected. From the pair of low-resolution data collected with opposite gradient polarities, the two-dimensional phase errors are estimated and corrected. The pair of data are then combined for water-fat separation. RESULTS: We demonstrate that the proposed method can effectively remove the high order errors with phantom and in vivo experiments, including obliquely oriented scans. CONCLUSION: For bipolar multi-echo acquisitions, uniform water-fat separation can be achieved by removing high order phase errors with the proposed method.

A method for automatic identification of water and fat images from a symmetrically sampled dual-echo Dixon technique.

Sampling water and fat signals symmetrically (i.e., at 0 degrees and 180 degrees relative phase angles) in a dual-echo Dixon technique offers high intrinsic tolerance to phase fluctuations in postprocessing and maximum signal-to-noise performance for the separated water and fat images. However, identification of which image is water and which image is fat after their separation is not possible based on the phase information alone. In this work, we proposed a semiempirical automatic image identification method that is based on the intrinsic asymmetry between the water and fat chemical shift spectra. Specifically, the approximately bimodal feature of the fat spectra and the observation that most in vivo tissues are either predominantly water or predominantly fat are used to construct a spectrum-based algorithm. Additional refinement is accomplished by considering the spatial distribution of the tissues that may have a coexistence of water and fat. The final improved algorithm was tested on a total of 131 three-dimensional patient datasets collected from different scanners and found to yield correct water and fat identification in all datasets.