Echo Acquisition Research Articles

A Novel Approach of Using Selected Unconventional Geodesic Methods of Estimation on VTS Areas

The Vessel Traffic Service (VTS) systems belong to the fundamental tools used in ensuring a high level of safety across sea basins with heavy traffic, where the presence of navigational hazards poses a great risk of collision or a ship running aground. In order to determine the mutual location of ships, VTS systems obtain information from different facilities, such as coastal radar stations, AIS, and vision systems. Fixing a ship’s position is always accompanied by a degree of error, but the degree of error depends on the specific position fixing system used. In order to increase the accuracy of position fixing in VTS systems, the authors propose the use of contemporary geodetic methods. The article presents the theoretical fundamentals of two unconventional geodesic methods of estimation: M estimation and Msplit(q)estimation and the authors’ own proposal of their application in VTS systems. The article concludes with a test verifying theoretical assumptions, performed with the use of a computer application allowing position fixing with the use of selected robust adjustment methods. Furthermore, an example is presented of Msplit(q)estimation as used for the acquisition of low-signal radar echoes, which in VTS systems are not automatically identified for tracking. The level of the echo signal makes it difficult for a VTS controller to separate these objects from typical radar noise and interference.

Normal values and test-retest variability of stimulated-echo diffusion tensor imaging and fat fraction measurements in the muscle.

To assess the test-retest variability of both diffusion parameters and fat fraction (FF) estimates in normal muscle, and to assess differences in normal values between muscles in the thigh. 29 healthy volunteers (mean age 37 years, range 20-60 years, 17/29 males) completed the study. Magnetic resonance images of the mid-thigh were acquired using a stimulated echo acquisition mode-echoplanar imaging (STEAM-EPI) imaging sequence, to assess diffusion, and 2-point Dixon imaging, to assess FF. Imaging was repeated in 19 participants after a 30 min interval in order to assess test-retest variability of the measurements. Intraclass correlation coefficients (ICCs) for test-retest variability were 0.99 [95% confidence interval, (CI): 0.98, 1] for FF, 0.94 (95% CI: 0.84, 0.97) for mean diffusivity and 0.89 (95% CI: 0.74, 0.96) for fractional anisotropy (FA). FF was higher in the hamstrings than the quadriceps by a mean difference of 1.81% (95% CI:1.63, 2.00)%, p < 0.001. Mean diffusivity was significantly lower in the hamstrings than the quadriceps (0.26 (0.13, 0.39) x10-3 mm2s-1, p < 0.001) whereas fractional anisotropy was significantly higher in the hamstrings relative to the quadriceps with a mean difference of 0.063 (0.05, 0.07), p < 0.001. This study has shown excellent test-retest, variability in MR-based FF and diffusion measurements and demonstrated significant differences in these measures between hamstrings and quadriceps in the healthy thigh. Test-retest variability is excellent for STEAM-EPI diffusion and 2-point Dixon-based FF measurements in the healthy muscle. Inter- and intraobserver variability were excellent for region of interest placement for STEAM-EPI diffusion and 2-point Dixon-based FF measurements in the healthy muscle. There are significant differences in FF and diffusion measurements between the hamstrings and quadriceps in the normal muscle.

Susceptibility-based MR Imaging of Nitinol Stent.

Conventional MR techniques have difficulty to accurately localize the stent position and access the stent restenosis because of the effects of susceptibility and radiofrequency (RF) shielding artifacts caused by stent mesh. Previous studies have demonstrated that a susceptibility-based positive contrast MR method exhibits excellent efficacy for visualizing MR compatible metal devices by taking advantage of their high magnetic susceptibility. However, the method is not evaluated in the visualization of stents. Therefore, the purpose of this study is to prospectively assess whether the susceptibility-based positive contrast method can be used to visualize the nitinol stents, with the comparison of two typical MR positive contrast techniques, i.e., susceptibility gradient mapping using the original resolution (SUMO) and the gradient echo acquisition for super-paramagnetic particles with positive contrast (GRASP). The experiment results showed that the susceptibility-based method provided better visualization and more precise localization of the stent than SUMO and GRASP.

Decreased water T2 in fatty infiltrated skeletal muscles of patients with neuromuscular diseases.

Quantitative imaging techniques are emerging in the field of magnetic resonance imaging of neuromuscular diseases (NMD). T2 of water (T2w ) is considered an important imaging marker to assess acute and chronic alterations of the muscle fibers, being generally interpreted as an indicator for "disease activity" in the muscle tissue. To validate the accuracy and robustness of quantitative imaging methods, 1 H magnetic resonance spectroscopy (MRS) can be used as a gold standard. The purpose of the present work was to investigate T2w of remaining muscle tissue in regions of higher proton density fat fraction (PDFF) in 40 patients with defined NMD using multi-TE single-voxel 1 H MRS. Patients underwent MR measurements on a 3T system to perform a multi-TE single-voxel stimulated echo acquisition method (STEAM) MRS (TE=11/15/20/25(/35) ms) in regions of healthy, edematous and fatty thigh muscle tissue. Muscle regions for MRS were selected based on T2 -weighted water and fat images of a two-echo 2D Dixon TSE. MRS results were confined to regions with qualitatively defined remaining muscle tissue without edema and high fat content, based on visual grading of the imaging data. The results showed decreased T2w values with increasing PDFF with R2 =0.45 (p<10-3 ) (linear fit) and with R2 =0.51 (exponential fit). The observed dependence of T2w on PDFF should be considered when using T2w as a marker in NMD imaging and when performing single-voxel MRS for T2w in regions enclosing edematous, nonedematous and fatty infiltrated muscle tissue.

Central nervous system vasculopathy caused by Fabry disease: a case report

BackgroundFabry disease is rare, and the diagnosis is often delayed. Here, we describe a case of Fabry disease resulting in vasculopathy of the central nervous system. Magnetic resonance (MR) black-blood sequence (three-dimensional T1 volumetric isotropic turbo spin echo acquisition), with the unique advantage of imaging the vascular wall, facilitated a clear identification of the vasculopathy.Case presentationA 27-year-old man visited our hospital for the treatment of “ double vision 6d.” After a series of examinations, the patient was diagnosed with Fabry disease, which caused vasculopathy of the central nervous system. Subsequently, the patient was treated with corticosteroids and his symptoms were attenuated. Two months after the initial treatment, the initial lesion in the vascular vessel disappeared, however, a new lesion appeared. Similarly, four months after the initial treatment, although the previous lesion disappeared, a new lesion appeared.ConclusionsThis case highlights that clinicians should use MR black-blood sequence scan in a timely manner in case of young patients with migratory lesions of brain. In case of detection of a vascular lesion in combination with other systemic lesions, the possibility of Fabry disease should be considered.

Effects Of Downhill Running On Muscle MRI T2 In Young mdx Mice

Previous studies have demonstrated that downhill treadmill running causes skeletal muscle damage that can be detected with magnetic resonance transverse relaxation time (T2) in adult dystrophic mice (mdx). However, young mdx mice (under 12 weeks of age) are characterized by a peak inflammatory phase with greater heterogeneity among muscles, potentially making it more difficult to detect T2 changes. PURPOSE: To determine whether muscle damage following downhill running can be detected in young mdx mice using proton magnetic resonance imaging (MRI) and spectroscopy (MRS). METHODS: C57BL/10ScSn-DMDmdx (mdx, n=5) and wild-type C57BL/10ScSn (controls, n=5) male mice of 6-9 weeks of age performed downhill running on a treadmill (14% grade at 8-12m/min for 45-60 min). MRI/MRS was conducted prior to and 24 hours following running in the mice hindlimbs. T2-weighted, multiple-slice, single spin-echo MR axial images were acquired (TR 2s, TE 14/40 ms, 12 slices) from the hindlimbs. MRI T2 values were calculated on a pixel-by-pixel basis for the anterior compartment (AC), posterior compartment (PC), and the deep medial region between the tibia and fibula (MC). In addition, single voxel 1H-MRS data were acquired from the soleus and gastrocnemius using stimulated echo acquisition mode (STEAM; TR 9 s, 32 TE’s exponentially spaced: 5-288 ms, 4 phase cycles) with a 4.7 T Varian/Agilent MR system. RESULTS: At baseline, T2 was elevated (p<0.05) in mdx mice (26.8±1.2ms) compared to controls (24.8±0.9 ms). Following downhill running, the mdx mice had elevated (p<0.05) T2 values compared to baseline when a composite of the compartments were compared (Pre: 26.8±1.2ms; Post: 28.8±1.4 ms). The MC was typically (80%) the most affected hindlimb region in the mdx mice. Similarly, 1H-MRS derived T2 values were increased (p=0.05) in a composite measure of the soleus and gastrocnemius after downhill running (29.8±4.2ms) in mdx compared to before downhill running (26.4±2.8ms). There were no significant changes in T2 in control mice after performing the downhill running protocol. CONCLUSIONS: Overall, our findings support the use of downhill running combined with MR T2 measures as a valuable approach for testing potential therapeutic interventions in young dystrophic mice. Funding Source: NIH (NIAMS) R01 AR070101.

A New Single-Pass SAR Interferometry Technique with a Single-Antenna for Terrain Height Measurements

One of the prospective research topics in radar remote sensing technology is the methodology for designing an optimal radar system for high-precision two-dimensional and three-dimensional image acquisition of the Earth’s surface with minimal hardware requirements. In this study, we propose a single-pass interferometric synthetic aperture radar (SAR) imaging technique with only a single antenna for the estimation of the terrain height. This technique enabled us to obtain terrain height information in one flight of the carrier, on which only one receiving antenna was mounted. This single-antenna single-pass interferometry required a squint angle look geometry and additional image synthesis processing. The limiting accuracy of the terrain height measurement was approximately 1.5 times lower than that of the conventional two-pass mode and required a longer baseline than two-pass interferometry to have an equivalent accuracy performance. This imaging method could overcome the temporal decorrelation problem of two-pass interferometry due to a short time gap in the radar echo acquisitions during two sub-aperture intervals. We compared the accuracy performance of the terrain height measurements of our method with the conventional two-pass interferometry. This comparison was carried out at various spectral bandwidths, degrees of surface roughness, and baseline lengths. We validated our idea with numerical simulations of a digital elevation map, and showed real extracted data of the terrain heights in the Astrakhan and Volga regions of the Russian Federation, obtained from airborne SAR with our single-antenna single-pass interferometry technique.

In situ monitoring of lipid droplet release from biopolymer microgels under simulated gastric conditions using magnetic resonance imaging and spectroscopy.

Functional foods are being designed to breakdown in the human gut in a controlled fashion so as to regulate blood nutrient profiles, hormone release, energy intake, and bioavailability. Biopolymer microgels, small spherical beads made from proteins and/or polysaccharides, are a promising tool that can be used to modulate the gastrointestinal behavior of food components. In this study, lipid droplets were loaded into microgels fabricated from either alginate or carrageenan using an injection-gelation method. The lipid-loaded microgels were then incubated in simulated gastric juices and the impact of biopolymer type on the release of the lipid droplets was observed. Optical microscopy and turbidity measurements showed that lipid droplet release occurred more rapidly for the carrageenan microgels, which was attributed to their partial disruption in the gastric fluids. In contrast, lipid droplet release was relatively slow from the alginate microgels because they remained intact. We also showed that magnetic resonance imaging (MRI) could be used for in situ monitoring of carrageenan microgel disruption and lipid droplet release under simulated stomach conditions. This method was based on quantifying the local lipid levels using T1 images and the magnetic resonance spectroscopy. A water-selected VIBE sequence was optimized for obtaining the T1 images and a stimulated echo acquisition mode (STEAM) sequence was selected for obtaining the MR spectra. The MRI method may be particularly useful for in vivo studies of the behavior of filled microgels.

Novel Calibrated Short TR Recovery (CaSTRR) Method for Brain-Blood Partition Coefficient Correction Enhances Gray-White Matter Contrast in Blood Flow Measurements in Mice.

The goal of the study was to develop a novel, rapid Calibrated Short TR Recovery (CaSTRR) method to measure the brain-blood partition coefficient (BBPC) in mice. The BBPC is necessary for quantifying cerebral blood flow (CBF) using tracer-based techniques like arterial spin labeling (ASL), but previous techniques required prohibitively long acquisition times so a constant BBPC equal to 0.9 mL/g is typically used regardless of studied species, condition, or disease. An accelerated method of BBPC correction could improve regional specificity in CBF maps particularly in white matter. Male C57Bl/6N mice (n = 8) were scanned at 7T using CaSTRR to measure BBPC determine regional variability. This technique employs phase-spoiled gradient echo acquisitions with varying repetition times (TRs) to estimate proton density in the brain and a blood sample. Proton density weighted images are then calibrated to a series of phantoms with known concentrations of deuterium to determine BBPC. Pseudo-continuous ASL was also acquired to quantify CBF with and without empirical BBPC correction. Using the CaSTRR technique we demonstrate that, in mice, white matter has a significantly lower BBPC (BBPCwhite = 0.93 ± 0.05 mL/g) than cortical gray matter (BBPCgray = 0.99 ± 0.04 mL/g, p = 0.03), and that when voxel-wise BBPC correction is performed on CBF maps the observed difference in perfusion between gray and white matter is improved by as much as 14%. Our results suggest that BBPC correction is feasible and could be particularly important in future studies of perfusion in white matter pathologies.

Volume Isotropic Turbo Spin Echo Acquisition Magnetic Resonance Imaging Pulse Sequence in Assessment of Temporomandibular Disorders

Background: Magnetic resonance imaging is the chief imaging modality used in assessment of temporomandibular disorders.Aim of the study: This study aimed to investigate the validity of Volume ISotropic Turbo spin echo Acquisition (VISTA) pulse sequence in the assessment of temporomandibular disorders.Subjects and Methods: Fifteen patients with temporomandibular joint related complaints performed MRI bilaterally using VISTA proton density and two-dimensional proton density turbo spin echo pulse sequences. Four-point scale was used to assess the clarity of articular disc position, disc morphology, cortical bone delineation, and overall image quality of both tested techniques. Besides, the final diagnosis of each case was obtained.Results: The main and standard deviation of traditionally used 2D proton density images in determination of disc position, disc morphology, delineation of cortical bone and overall image quality were (2.57± 0.49), (2.37± 0.60), (2.8± 0.4), (2.57± 0.49), respectively. While those for VISTA images were (1.8± 0.4), (1.53± 0.72), (2.1± 0.60), (1.7± 0.64) with the same order. The final diagnosis was similar in both techniques in 25 cases out of 30.Conclusion: Volume ISotropic Turbo Spin Echo Acquisition (VISTA) magnetic resonance pulse sequence could reveal the temporomandibular joint related structures, but with less image quality than that of traditionally used two-dimensional proton density images.

Improved signal-to-noise ratio in EPI sequences with highly asymmetric spin echo and highly asymmetric STEAM preparations (HASE-EPI and HASTEAM-EPI).

Alternative versions of echo-planar imaging (EPI) sequences with standard spin echo (SE) or stimulated echo acquisition mode (STEAM) preparations are proposed, allowing for improved signal-to-noise ratio (SNR), especially in high-resolution imaging. The suitability of the proposed sequences, dubbed "highly asymmetric SE-EPI" (HASE-EPI) and "highly asymmetric STEAM-EPI" (HASTEAM-EPI), is tested in vivo, for anatomical imaging with [Formula: see text] weighting and diffusion-weighted imaging (DWI). In HASE-EPI and HASTEAM-EPI, echo formation occurs prior to the EPI readout, rather than at k-space centre as in standard SE-EPI and STEAM-EPI. This allows for a constant preparation period, independent of the spatial resolution. The proposed sequences are compared to their standard counterparts, via simulations and experimentally via in vivo anatomical imaging and DWI. HASE-EPI and HASTEAM-EPI yield SNR improvements for large matrix sizes and fully sampled EPI readout. Simulations and in vivo results show a signal gain in HASE-EPI versus SE-EPI or HASTEAM-EPI versus STEAM-EPI for white and gray matter, particularly for higher spatial resolution with full readout in anatomical imaging and DWI. However, simulations also show that in the case of very long EPI-readout trains, HASE-EPI and HASTEAM-EPI are more prone to pixel broadening due to relaxation effects. In contrast to commonly used SE-EPI or STEAM-EPI, the proposed sequences facilitate the acquisition of anatomical imaging and DWI data with improved SNR, especially for full EPI readouts. However, the applicability of HASE-EPI and HASTEAM-EPI should be carefully assessed: while signal gains are less pronounced when using parallel imaging and/or reduced matrix sizes, there may be pixel broadening for very long EPI-readout trains.

Magnitude-intrinsic water-fat ambiguity can be resolved with multipeak fat modeling and a multipoint search method.

PurposeTo develop a postprocessing algorithm for multiecho chemical‐shift encoded water–fat separation that estimates proton density fat fraction (PDFF) maps over the full dynamic range (0‐100%) using multipeak fat modeling and multipoint search optimization. To assess its accuracy, reproducibility, and agreement with state‐of‐the‐art complex‐based methods, and to evaluate its robustness to artefacts in abdominal PDFF maps.MethodsWe introduce MAGO (MAGnitude‐Only), a magnitude‐based reconstruction that embodies multipeak liver fat spectral modeling and multipoint optimization, and which is compatible with asymmetric echo acquisitions. MAGO is assessed first for accuracy and reproducibility on publicly available phantom data. Then, MAGO is applied to N = 178 UK Biobank cases, in which its liver PDFF measures are compared using Bland‐Altman analysis with those from a version of the hybrid iterative decomposition of water and fat with echo asymmetry and least squares estimation (IDEAL) algorithm, LiverMultiScan IDEAL (LMS IDEAL, Perspectum Diagnostics Ltd, Oxford, UK). Finally, MAGO is tested on a succession of high field challenging cases for which LMS IDEAL generated artefacts in the PDFF maps.ResultsPhantom data showed accurate, reproducible MAGO PDFF values across manufacturers, field strengths, and acquisition protocols. Moreover, we report excellent agreement between MAGO and LMS IDEAL for 6‐echo, 1.5 tesla human acquisitions (bias = −0.02% PDFF, 95% confidence interval = ±0.13% PDFF). When tested on 12‐echo, 3 tesla cases from different manufacturers, MAGO was shown to be more robust to artefacts compared to LMS IDEAL.ConclusionMAGO resolves the water–fat ambiguity over the entire fat fraction dynamic range without compromising accuracy, therefore enabling robust PDFF estimation where phase data is inaccessible or unreliable and complex‐based and hybrid methods fail.

Proton MR spectroscopy in the breast: Technical innovations and clinical applications.

Proton magnetic resonance spectroscopy (MRS) is a promising noninvasive diagnostic technique for investigation of breast cancer metabolism. Spectroscopic imaging data may be obtained following contrast-enhanced MRI by applying the point-resolved spectroscopy sequence (PRESS) or the stimulated echo acquisition mode (STEAM) sequence from the MR voxel encompassing the breast lesion. Total choline signal (tCho) measured in vivo using either a qualitative or quantitative approach has been used as a diagnostic test in the workup of malignant breast lesions. In addition to tCho metabolites, other relevant metabolites, including multiple lipids, can be detected and monitored. MRS has been heavily investigated as an adjunct to morphologic and dynamic MRI to improve diagnostic accuracy in breast cancer, obviating unnecessary benign biopsies. Besides its use in the staging of breast cancer, other promising applications have been recently investigated, including the assessment of treatment response and therapy monitoring. This review provides guidance on spectroscopic acquisition and quantification methods and highlights current and evolving clinical applications of proton MRS. Level of Evidence 5 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2019.

Fast Padé transform for increasing the signal to noise ratio of spectra provided by STEAM pulse sequence.

There are two routine pulse-sequences for single voxel spectroscopy (SVS), point resolved spectroscopy (PRESS) and stimulated echo acquisition mode (STEAM). Although STEAM has several advantages in comparison to PRESS, signal/noise ratio (SNR) superiority of PRESS makes it the first choice for SVS. Application of fast Padé transform (FPT) instead of Fast Furrier transform (FFT) might increase the SNR of the signal produced by STEAM pulse-sequence and therefore allows the benefits of its advantages. We aimed to evaluate and compare the noise root mean square (RMS) and SNR provided by STEAM pulse-sequence using both FPT and FFT. A gelatin-based phantom was constructed in a 19-cm acrylic cylinder. The phantom had two normal/tumoral parts. The SVS was performed using a 3T MRI scanner. STEAM pulse-sequence were used with the following parameters: TR = 2000ms, TM = 10ms, and three TEs of 20, 135 and 270ms with two data-points of 1024 and 512 and voxel-size of 1cm3. The raw data were extracted and processed using both FFT and FPT estimators to produce the spectrum. The noise RMS and SNR of Cho and Cr metabolites were assessed. According to the results, noise RMS of spectra provided by FPT were decreased between 3619.01-14252.94% in comparison to FFT (p< 0.00001). The SNR of Cr1 and Cho peaks of the spectra provided by FPT were increased more than 96.80 and 97.18, respectively (0.00006 <p< 0.02). The difference of noise RMS's provided by FPT are thousands percent less than FFT. This enormous decrease in noise provides a good increase of SNR. While the range of Cr1 and Cho SNR by FFT are between 41.55-120.32 the range of SNRs of these peaks provided by FPT are between 1719.99-9744.79, which implies a significant difference between the efficiency of FPT and FFT. This study showed that application of FPT in comparison to FFT can increase the spectra SNR and so that its usage can be helpful during the application of STEAM pulse-sequence which results in lower SNR in comparison to PRESS pulse-sequence. Thus, we should make use of the advantages of STEAM pulse-sequence.

High-dimensionality undersampled patch-based reconstruction (HD-PROST) for accelerated multi-contrast MRI.

PurposeTo develop a new high‐dimensionality undersampled patch‐based reconstruction (HD‐PROST) for highly accelerated 2D and 3D multi‐contrast MRI.MethodsHD‐PROST jointly reconstructs multi‐contrast MR images by exploiting the highly redundant information, on a local and non‐local scale, and the strong correlation shared between the multiple contrast images. This is achieved by enforcing multi‐dimensional low‐rank in the undersampled images. 2D magnetic resonance fingerprinting (MRF) phantom and in vivo brain acquisitions were performed to evaluate the performance of HD‐PROST for highly accelerated simultaneous T1 and T2 mapping. Additional in vivo experiments for reconstructing multiple undersampled 3D magnetization transfer (MT)‐weighted images were conducted to illustrate the impact of HD‐PROST for high‐resolution multi‐contrast 3D imaging.ResultsIn the 2D MRF phantom study, HD‐PROST provided accurate and precise estimation of the T1 and T2 values in comparison to gold standard spin echo acquisitions. HD‐PROST achieved good quality maps for the in vivo 2D MRF experiments in comparison to conventional low‐rank inversion reconstruction. T1 and T2 values of white matter and gray matter were in good agreement with those reported in the literature for MRF acquisitions with reduced number of time point images (500 time point images, ~2.5 s scan time). For in vivo MT‐weighted 3D acquisitions (6 different contrasts), HD‐PROST achieved similar image quality than the fully sampled reference image for an undersampling factor of 6.5‐fold.ConclusionHD‐PROST enables multi‐contrast 2D and 3D MR images in a short acquisition time without compromising image quality. Ultimately, this technique may increase the potential of conventional parameter mapping.

A black-blood ultra-short echo time (UTE) sequence for 3D isotropic resolution imaging of the lungs.

Ultra-short echo time MRI is a promising alternative to chest CT for cystic fibrosis patients. Black-blood imaging in particular could help discern small-sized anomalies, such as mucoid plugging, which may otherwise be confused with neighboring blood vessels, particularly when contrast agent is not used. We, therefore, implemented and tested an ultra-short echo time sequence with black-blood preparation. Additionally, this sequence may also be used to generate bright-blood angiograms. Using this sequence, data was acquired during free breathing in 10 healthy volunteers to obtain respiratory-motion-resolved 3D volumes covering the entire thorax with an isotropic resolution of (1 mm)3 . The magnitude of signal suppression relative to a bright-blood reference acquisition was quantified and compared with that obtained with a turbo-spin echo (TSE) acquisition. Bright-blood angiograms were also generated by subtraction. Finally, an initial feasibility assessment was performed in 2 cystic fibrosis patients, and images were visually compared with contrast-enhanced images and with CT data. Black-blood preparation significantly decreased the average normalized signal intensity in the vessel lumen (-66%; P < 0.001). Similarly, blood signal was significantly lowered (-60%; P = 0.001) compared with the TSE acquisition. In patients, mucoid plugging could be emphasized in the black-blood datasets. An intercostal artery could also be visualized in the subtraction angiograms. Black-blood free-breathing ultra-short echo time imaging was successfully implemented and motion-resolved full volumetric coverage of the lungs with high spatial resolution was achieved, while obtaining an angiogram without contrast agent injection. Encouraging initial results in patients prompt further investigations in a larger cohort.

Effect of triglyceride glycerol CH signal on olefinic resonance quantification with proton magnetic resonance spectroscopy at 3 T

The in-vivo Magnetic Resonance Spectroscopy (MRS) techniques STimulated Echo Acquisition Mode (STEAM) and Point RESolved Spectroscopy (PRESS) are used to assess fat unsaturation levels in human adipose tissue by measuring the olefinic proton resonance at ≈5.4 ppm. At clinical field strengths, the resonance is overlapped by that of the triglyceride glycerol CH proton at ≈5.2 ppm. In the presented work, olefinic resonance contamination by that of the glycerol CH proton for STEAM and PRESS as a function of echo time (TE) is assessed at 3 T. MRS spectra were acquired from the triglyceride tricaprylin (contains glycerol but no olefinic protons), and from free oleic acid (contains olefinic but no glycerol protons) using STEAM (TE of 20 to 300 ms, mixing time of 20 ms) and PRESS (TE of 40 to 300 ms), with TE increments of 10 ms. Estimated olefinic signal contamination by the glycerol CH resonance was evaluated for short-TE (STEAM with TE of 20 ms and PRESS with TE of 40 ms) for human adipose tissue based on a literature composition and using the spectra acquired for tricaprylin and oleic acid. Contaminations of ≈20% for STEAM with a TE = 20 ms and ≈13% for PRESS with a TE = 40 ms were obtained. Glycerol CH contributions to the olefinic resonance was also estimated for eight oils in a similar manner. High-resolution in-vitro 16.5 T Nuclear Magnetic Resonance (NMR) spectra of the oils suggest that in the absence of significant T2 relaxation and J-coupling effects, 9 to 17% (depending on unsaturated fatty acid content) of the olefinic signal is attributable to the glycerol CH proton. The signal yield responses of the glycerol CH and the olefinic protons as a function of TE indicate that a TE of 90 ms for STEAM and a TE of 200 ms for PRESS are suitable for quantification of the olefinic resonance with minimal impact from the glycerol CH resonance. Signal area yields relative to those obtained with short-TE were 30% and 29% for the olefinic resonance and 4% and 5% for the glycerol resonance for STEAM with a TE of 90 ms and PRESS with a TE of 200 ms, respectively. The efficacy of the timings was verified in vivo on tibial bone marrow.

Association of bone mineral density and fat fraction with magnetic susceptibility in inflamed trabecular bone.

PurposeTo evaluate the relationship between bone mineral density (BMD) and magnetic susceptibility, and between proton density fat fraction and susceptibility, in inflamed trabecular bone.MethodsTwo different phantoms modeling the fat fraction (FF) and BMD values of healthy bone marrow and disease states were scanned using a multiecho gradient echo acquisition at 3T. After correction for fat‐water chemical shift, susceptibility mapping was performed, and susceptibility measurements were compared with BMD and FF values using linear regression. Patients with spondyloarthritis were scanned using the same protocol, and susceptibility values were calculated in areas of inflamed bone (edema) and fat metaplasia, both before and after accounting for the contribution of fat to the total susceptibility.ResultsSusceptibility values in the phantoms were accurately described by a 2D linear function, with a negative correlation between BMD and susceptibility and a positive correlation between FF and susceptibility (adjusted R2 = 0.77; P = 3·10−5). In patients, significant differences in susceptibility were observed between fat metaplasia and normal marrow, but these differences were eliminated by removing the fat contribution to the total susceptibility.ConclusionsBMD and proton density fat fraction both influence the total susceptibility of bone marrow and failure to account for the fat contribution could lead to errors in BMD quantification. We propose a method for removing the fat contribution from the total susceptibility, based on the observed linear relationship between susceptibility and FF. In inflamed bone, the overall increase in susceptibility in areas of fat metaplasia is at least partly due to increased fat content.

An Improved Forward-Looking Sonar 3D Visualization Scheme of Underwater Objects

This paper presents an improved scheme for forward-looking sonar (FLS) visualization, including an echo acquisition method, a global threshold based on local outlier factor and a reconstruction method. Based on the model of line target in the shallow water, the paper presents an echo acquisition method with impulse response convolution and ray tracing, and considering the reverberation. Then, a transform matrix is presented for the coordinate transformation to obtain the point cloud. After that, the paper presents the global threshold based on local outlier factor (LOF) method to solving the problem of noise sensitivity in the global thresholding. Finally, the paper presents a novel reconstruction method, including the coarse step via random sample consensus (RANSC) and the refined step via Power crust. Both simulation and experimental results show that the scheme in this paper produced superior result compared with the state-of the art.

Parental Acquisition of Echocardiographic Images in Pediatric Heart Transplant Patients Using a Handheld Device: A Pilot Telehealth Study

Pediatric heart transplant patients (PedHtx) require frequent monitoring by echocardiography (echo); however, they often live far from hospitals with pediatric echo services, resulting in urgent/emergent transfers to specialized institutions. Our primary objective was to evaluate the feasibility of parental acquisition of echo images to assess left ventricular (LV) systolic function in PedHtx using a handheld echo device. Secondary objectives included retesting for skill maintenance and in patients with decreased LV systolic function. During a routine clinic visit, parents received 1-hour training with a handheld echo device to acquire images in parasternal short-axis and apical views. Parents recorded images on their children at training completion and 24hours later at home. An independent echocardiographer assessed clinic, training, and home echos for LV systolic function. Fifteen PedHtx (mean age of 12.6years of age; range, 4.1-16.7) were enrolled. All parents could acquire home images adequate for qualitative assessment of LV systolic function with no discrepancy compared with clinical echos. LV ejection fraction (LVEF) could be calculated (5/6 area-length method) in 86% of training and 43% of home echos with <10% difference in LVEF measurements between home and clinic echos. Five parents repeated home echos >12months later. All home echos were adequate for qualitative assessment of LV systolic function (LVEF measurable in two). Additionally, five heart failure patients with decreased LV systolic function (mean age of 8.6years; range 1.9-15.1) were enrolled. All home echos were adequate for qualitative assessment of LV systolic function (LVEF measurable in one). Our results suggest that parental home echo acquisition using a handheld echo device is feasible and adequate for qualitative assessment of LV systolic function in PedHtx. However, quantitative assessment of LV systolic function, especially in patients with dysfunction, and retention of the skill set without additional training are suboptimal.