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Calcium sulfate is an established carrier for localized drug delivery, but a means to non‐invasively measure drug release, which would improve our understanding of localized delivery, remains an unmet need. We aim to quantitatively estimate the diffusion‐controlled release of small molecules loaded into a calcium sulfate carrier through a gadobutrol‐based contrast agent, which acts as a surrogate small molecule. A central cylindrical core made of calcium sulfate, either alone or within a metal scaffold, is loaded with contrast agents that release into agar. Multi‐echo scans are acquired at multiple time points over 4 weeks and processed into R2* and quantitative susceptibility mapping (QSM) maps. Mean R2* values are fit to a known drug delivery model, which are then compared with the decrease in core QSM. Fitting R2* measurements of calcium sulfate core while constraining constants to a drug release model results in an R2‐value of 0.991, yielding a diffusion constant of 4.59 × 10−11 m2 s−1. Incorporating the carrier within a metal scaffold results in a slower release. QSM shows the resulting loss of susceptibility in the non‐metal core but is unreliable around metal. R2* characterizes the released gadobutrol, and QSM detects the resulting decrease in core susceptibility. The addition of a porous metal scaffold slows the release of gadobutrol, as expected. [ABSTRACT FROM AUTHOR]

Research on the interfacial instability of two‐phase systems can help in gaining a better understanding of various hydrodynamic instabilities in nature. However, owing to the nonlinear and complex spatiotemporal dynamics of the unstable interface, the instability is challenging to control and suppress. This paper presents a novel interfacial instability of the magnetic microswarm induced by the competition between the destabilizing effect of magnetic field and the stabilizing effect of acoustic field. The physics underlying this novel phenomenon is discussed by analyzing the contributions of the external fields. Unlike previous studies, this study demonstrates that the instability is independent of the interfacial force or diffusion effect and can persist without dissipation over time. The manipulation of the unstable interface is further achieved by adjusting the configuration of the magneto‐acoustic system. This approach can be used in thermal encoding metamaterials and has great potential applications in systems where the instability is detrimental. [ABSTRACT FROM AUTHOR]

Purpose: To demonstrate for the first time the feasibility of performing prospective motion correction using spherical navigators (SNAVs). Methods: SNAVs were interleaved in a 3D FLASH sequence with an additional short baseline scan (6.8 s) for fast rotation estimation. Assessment of SNAV‐based prospective motion correction was performed in six volunteers. Participant motion was guided using randomly generated stepwise prompts as well as prompts derived from real motion cases. Experiments were performed on a 3 T MRI scanner using a 32‐channel head coil. Results: When optimized for real‐time application, SNAV‐based motion estimates were computed in 25.8 ± 1.3 ms. Phantom‐based quantification of rotation and translation accuracy indicated mean absolute errors of 0.10 ± 0.09° and 0.25 ± 0.14 mm, respectively. Implementing SNAV‐based motion estimates for prospective motion correction led to a clear improvement in image quality with minimal increase in scan time (<5%). Conclusion: Optimization of SNAV processing for real‐time application enables prospective motion correction with low latency and minimal scan time requirements. [ABSTRACT FROM AUTHOR]

Purpose: 3D‐printed porous metal scaffolds are a promising emerging technology in orthopedic implant design. Compared to solid metal implants, porous metal implants have lower magnetic susceptibility values, which have a direct impact on imaging time and image quality. The purpose of this study is to determine the relationship between porosity and effective susceptibility through quantitative estimates informed by comparing coregistered scanned and simulated field maps. Methods: Five porous scaffold cylinders were designed and 3D‐printed in titanium alloy (Ti‐6Al‐4V) with nominal porosities ranging from 60% to 90% using a cellular sheet‐based gyroid design. The effective susceptibility of each cylinder was estimated by comparing acquired B0 field maps against simulations of a solid cylinder of varying assigned magnetic susceptibility, where the orientation and volume of interest of the simulations was informed by a custom alignment phantom. Results: Magnitude images and field maps showed obvious decreases in artifact size and field inhomogeneity with increasing porosity. The effective susceptibility was found to be linearly correlated with porosity (R2 = 0.9993). The extrapolated 100% porous (no metal) magnetic susceptibility was −9.9 ppm, closely matching the expected value of pure water (−9 ppm), indicating a reliable estimation of susceptibility. Conclusion: Effective susceptibility of porous metal scaffolds is linearly correlated with porosity. Highly porous implants have sufficiently low effective susceptibilities to be more amenable to routine imaging with MRI. [ABSTRACT FROM AUTHOR]

Purpose The conventional two-point (2pt) Dixon technique explicitly estimates B0 map by performing phase unwrapping. When signal loss, phase singularity, artifacts, or spatially isolated regions corrupt the measured phase images, this unwrapping-based technique will face difficulty. This work aims to improve the reliability of B0 mapping by performing unwrapping error correction. Method To detect the unwrapping-caused phase errors, we determined a magnitude-based fat/water mask and used it as reference to identify pixels being mismatched by the phase-based mask, which was derived from the B0-corrected phase term of the Hermitian product between echoes. Then, we corrected the afore-determined phase error on a region-by-region basis. We tested the developed method with nine patients' data, and the results were compared with a well-established region-growing technique. Results By adding the step to correct unwrapping-caused error, we improved the robustness of B0 mapping, resulting in better fat-water separation when compared with the conventional 2pt and the phasor-based region-growing techniques. Conclusion We showed the feasibility of B0 mapping with bipolar 2pt human cardiac data. The software is freely available to the scientific community. Magn Reson Med 78:1862-1869, 2017. © 2016 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

Purpose: To implement and optimize a new approach for susceptibility-weighted image (SWI) generation from multi-echo multi-channel image data and compare its performance against optimized traditional SWI pipelines.Materials and Methods: Five healthy volunteers were imaged at 7 Tesla. The inter-echo-variance (IEV) channel combination, which uses the variance of the local frequency shift at multiple echo times as a weighting factor during channel combination, was used to calculate multi-echo local phase shift maps. Linear phase masks were combined with the magnitude to generate IEV-SWI. The performance of the IEV-SWI pipeline was compared with that of two accepted SWI pipelines-channel combination followed by (i) Homodyne filtering (HPH-SWI) and (ii) unwrapping and high-pass filtering (SVD-SWI). The filtering steps of each pipeline were optimized. Contrast-to-noise ratio was used as the comparison metric. Qualitative assessment of artifact and vessel conspicuity was performed and processing time of pipelines was evaluated.Results: The optimized IEV-SWI pipeline (σ = 7 mm) resulted in continuous vessel visibility throughout the brain. IEV-SWI had significantly higher contrast compared with HPH-SWI and SVD-SWI (P < 0.001, Friedman nonparametric test). Residual background fields and phase wraps in HPH-SWI and SVD-SWI corrupted the vessel signal and/or generated vessel-mimicking artifact. Optimized implementation of the IEV-SWI pipeline processed a six-echo 16-channel dataset in under 10 min.Conclusion: IEV-SWI benefits from channel-by-channel processing of phase data and results in high contrast images with an optimal balance between contrast and background noise removal, thereby presenting evidence of importance of the order in which postprocessing techniques are applied for multi-channel SWI generation.Level Of Evidence: 2 J. Magn. Reson. Imaging 2017;45:1113-1124. [ABSTRACT FROM AUTHOR]

Two 2D wavy hexagonal hexahydroxyl cyclotricatechylene (CTC) based COFs, CTC-COF-2 and CTC-COF-3 were synthesized through solvothermal reaction. The bowl-shaped conformation caused CTC skeletons packed in a columnar manner with the same oriented units, thus forming an undulated structure. The gas adsorption properties of CTC-COFs were investigated, which show the potential application abilities in hydrogen storage of CTC-COFs. The introduction of pyrene into CTC-COF-3 makes it a potential semiconducting π-conjugated material. [ABSTRACT FROM AUTHOR]

Purpose: To develop and evaluate a tool for accurate, reproducible, and programmable motion control of imaging phantoms for use in motion sensitive magnetic resonance imaging (MRI) applications. Methods: In this paper, the authors introduce a compact linear motion stage that is made of nonmagnetic material and is actuated with an ultrasonic motor. The stage can be positioned at arbitrary positions and orientations inside the scanner bore to move, push, or pull arbitrary phantoms. Using optical trackers, measuring microscopes, and navigators, the accuracy of the stage in motion control was evaluated. Also, the effect of the stage on image signal-to-noise ratio (SNR), artifacts, and B0 field homogeneity was evaluated. Results: The error of the stage in reaching fixed positions was 0.025±0.021 mm. In execution of dynamic motion profiles, the worst-case normalized root mean squared error was below 7% (for frequencies below 0.33 Hz). Experiments demonstrated that the stage did not introduce artifacts nor did it degrade the image SNR. The effect of the stage on the B0 field was less than 2 ppm. Conclusions: The results of the experiments indicate that the proposed system is MRI-compatible and can create reliable and reproducible motion that may be used for validation and assessment of motion related MRI applications. [ABSTRACT FROM AUTHOR]

Purpose To develop and evaluate a multiecho phase-unwrapping-based B0 mapping method. Methods The proposed method estimates a B0 map by Non-Iterative Correction of phase-Errors (B0-NICE). The B0-NICE method generates an initial B0 map from a 'pseudo in-phase' data set by introducing a bias frequency shift to the multipeak fat model, followed by correcting the phase errors using both phase and magnitude information. The performance of the B0-NICE method was evaluated with all data cases from the 2012 ISMRM Challenge. Results The B0 field estimates from B0-NICE were compared with those generated by GlObally Optimal Surface Estimation (GOOSE). In the presence of large B0 inhomogeneity, the B0-NICE method was able to generate more realistic B0 maps from multiecho data, compared with GOOSE. Accurate estimation of fat-fraction (FF) map was also achieved using the proposed algorithm. Conclusion The primary finding of the present study is that accurate FF and B0 maps are achievable if magnitude data is processed independently and used to correct phase errors existing in B0 maps generated by phase unwrapping. The B0-NICE software is freely available to the scientific community. Magn Reson Med 74:1177-1188, 2015. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Purpose To develop and evaluate a local frequency shift (LFS) mapping method specifically designed for multi-echo acquisitions and multi-channel receive coils. Methods The proposed method uses the pixel-by-pixel inter-echo variance (IEV) as a weighting factor during channel-combination. Five healthy volunteers were scanned at 7 T. The IEV-weighted method was quantitatively compared to established (adaptive and Hermitian product) channel-combination methods with respect to IEV of LFS over the entire brain. Results In all experiments, the IEV-weighted method generated LFS maps free of artifacts caused by unwrapping errors. Based on measurements of the inter-echo frequency variance throughout the whole brain, the IEV-weighted method produced the lowest variation and the best contrast at the edge of the brain. Conclusion The primary finding of the present study is that accurate LFS maps are achievable if the data from each channel is processed independently prior to combination followed by a weighted combination using IEV as the weighting term. The software is freely available to the scientific community. Magn Reson Med 73:1654-1661, 2015. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Macrocyclic CTV-Br3 reacted with the linear benzene-1,4-diboronic acid and 1,4-diethynylbenzene via Suzuki and Sonogashira-Hagihara coupling reactions producing the rigid porous materials CTV-CMP-1 and CTV-CMP-2. The porous materials have good thermal and chemical stability. The Brunauer-Emmet-Teller specific surface areas of CTV-CMP-1 and CTV-CMP-2 are 314 and 218 cm2·g−1, respectively. Physical properties of the porous materials were investigated, CTV-CMP-1 showed moderate hydrogen adsorption about 0.81 wt% at 1.13 bar while CTV-CMP-2 showed lower hydrogen adsorption about 0.51 wt%. These materials are analogs to activated carbons which could be potentially used in gas separation and organic compound adsorption. [ABSTRACT FROM AUTHOR]

We present a new intervention-based phase unwrapping algorithm, which solves the inherent integration-path-dependent problem (typically resulting in streaks), by using a 2D recursive orthogonal referring (PUROR) approach. The streaks were removed by three consecutive procedures: intra-image phase unwrapping, inter-image cross-referring a 'good-strip,' and cross-referring line segments. The application of these procedures results in streak-free 2D phase images. The phase inconsistencies across slices in a 3D image were removed using a hybrid 3D PUROR algorithm: the two step approach involves stacking the individual slices, by using the mean phase values of each slice, then applying the 2D PUROR algorithm to reformatted 2D images that include the slice direction. The described approach was tested with in vivo multislice phase images acquired in the axial, sagittal, and coronal orientation. The results of the unwrapped phase volume recovered using the PUROR algorithm have equivalent quality to that achieved by using established methods, but the PUROR algorithm is about two orders of magnitude faster (between 1 and 5 s per 256 × 256 slice; independent of slice orientation and echo time). Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Until now, only one-dimensional navigator-echo techniques have been implemented with multielement RF coils. For the multidimensional navigator echoes, which extract six-degree of freedom motion information from the raw k-space data, an efficient raw data combination approach is needed. In this work, three combination approaches, including summation of the complex raw data, summation following phase alignment, and summation of the squares of the k-space magnitude profiles, were evaluated with the spherical navigator echoes (SNAV) technique. In vivo brain imaging experiments were used to quantify accuracy and precision and demonstrated that SNAVs acquired with an eight-channel head coil can determine the rotation and translation in range up to 10° and 20 mm with subdegree and submillimeter accuracy, respectively. Results from a 3D brain volume realignment experiment showed excellent agreement between baseline images and SNAV-aligned follow-up volumes. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Spherical navigator echoes have been shown to determine rigid-body rotation and translation simultaneously. Following the determination of rotation, translations are determined from the phase change between the baseline and transformed spherical navigator echoes. Because the measured phase change is limited in the interval (−π, π), a phase-unwrapping algorithm is required to recover the true phase change in absolute values. The unwrapping algorithm presented in this article is based on a priori information about the true translation-induced phase-change function. The algorithm is verified using simulation and in vivo experiments, and the accuracy and precision of translation determination are evaluated. Specifically, the effects of background and off-resonance-induced phase noise are explored. When the proposed phase-unwrapping algorithm was used, translations up to 15 mm were measured, with accuracy better than 5%; for translations up to 40 mm, an error of approximately 10% was observed. Magn Reson Med, 2010. © 2009 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]