A Platform Integrating Acquisition, Reconstruction, Visualization, and Manipulator Control Modules for MRI-Guided Interventions.

This work presents a platform that integrates a customized MRI data acquisition scheme with reconstruction and three-dimensional (3D) visualization modules along with a module for controlling an MRI-compatible robotic device to facilitate the performance of robot-assisted, MRI-guided interventional procedures. Using dynamically-acquired MRI data, the computational framework of the platform generates and updates a 3D model representing the area of the procedure (AoP). To image structures of interest in the AoP that do not reside inside the same or parallel slices, the MRI acquisition scheme was modified to collect a multi-slice set of intraoblique to each other slices; which are termed composing slices. Moreover, this approach interleaves the collection of the composing slices so the same k-space segments of all slices are collected during similar time instances. This time matching of the k-space segments results in spatial matching of the imaged objects in the individual composing slices. The composing slices were used to generate and update the 3D model of the AoP. The MRI acquisition scheme was evaluated with computer simulations and experimental studies. Computer simulations demonstrated that k-space segmentation and time-matched interleaved acquisition of these segments provide spatial matching of the structures imaged with composing slices. Experimental studies used the platform to image the maneuvering of an MRI-compatible manipulator that carried tubing filled with MRI contrast agent. In vivo experimental studies to image the abdomen and contrast enhanced heart on free-breathing subjects without cardiac triggering demonstrated spatial matching of imaged anatomies in the composing planes. The described interventional MRI framework could assist in performing real-time MRI-guided interventions.

Multispectral diffusion-weighted imaging near metal implants.

PURPOSE: The need for diffusion-weighted-imaging (DWI) near metallic implants is becoming increasingly relevant for a variety of clinical diagnostic applications. Conventional DWI methods are significantly hindered by metal-induced image artifacts. A novel approach relying on multispectral susceptibility artifact reduction techniques is presented to address this unmet need. METHODS: DWI near metal implants is achieved through a combination of several advanced MRI acquisition technologies. Previously described approaches to Carr-Purcell-Meiboom-Gill spin-echo train DWI sequences using the periodically rotated overlapping parallel lines with enhanced reconstruction are combined with multispectral-imaging metal artifact reduction principles to provide DWI with substantially reduced artifact levels. The presented methods are applied to limited sets of slices over areas of sarcoma risk near six implanted devices. RESULTS: Using the presented methods, DWI assessment without bulk image distortions is demonstrated in the immediate vicinity of metallic interfaces. In one subject, the apparent diffusion coefficient was reduced in a region of suspected sarcoma directly adjacent to fixation hardware. CONCLUSIONS: An initial demonstration of minimal-artifact multispectral DWI in the near vicinity of metallic hardware is described and successfully demonstrated on clinical subjects. Magn Reson Med 79:987-993, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Flexible longitudinal magnetization contrast in spectrally overlapped 3D-MSI metal artifact reduction sequences: Technical considerations and clinical impact.

PURPOSE: It has previously been demonstrated that increased overlap of spectral bins in three-dimensional multispectral imaging techniques (3D-MSI) can aid in reducing residual artifacts near metal implants. However, increasing spectral overlap also necessitates consideration of saturation effects for species with long T1 values. Here, an interleaved spectral bin acquisition strategy is presented for overlapping 3D-MSI that allows for flexible choice of repetition times while simultaneously addressing these cross talk concerns. METHODS: A phantom imaging experiment is used to illustrate the amplified effect of cross talk on 3D-MSI acquisitions. A methodological approach to address cross talk across a variety of prescribed repetition times is then described. Using the presented principles, a clinical subject with a total hip replacement was imaged to generate T1, proton density, and short-tau inversion recovery contrasts. In addition, a fracture instrumentation case was imaged pre- and postcontrast using T1-weighted spectrally overlapped 3D-MSI. RESULTS: Phantom results demonstrate that conventional spectral interleaving approaches can generate unwanted signal characteristics in heavily overlapped 3D-MSI. Clinical images using the presented methods successfully demonstrate T1, proton density, and inversion recovery image contrasts using heavily overlapped 3D-MSI. CONCLUSIONS: Through automated management of spectral bin distributions across multiple interleaves, a variety of longitudinal magnetization contrasts can efficiently be acquired without any clinically relevant cross-talk impact using heavily overlapped 3D-MSI.

Evidence for the growing importance of Eurasian local source to PAHs in the Arctic central basin.

Polycyclic aromatic hydrocarbons (PAHs) are traditionally considered to enter the Arctic Ocean through long-range transport. Arctic warming, especially sea ice retreat, will certainly increase the contribution from local source (such as river input and ice melting). However, this hypothesis remains poorly constrained for lack of quantitative evidence. Here PAHs in surface seawater (67°N-89°N, 152°E-177°E) and sea ice (82°N-89°N) were collected in the western Arctic in 2010. Dissolved concentrations of 15 PAHs (Σ15PAHs) in surface layer ice (26.2 to 49.8 ng/L) were one order of magnitude higher than the underlying seawater. The content of dissolved Σ15PAHs was significantly higher in the marginal ice zone than those in the Chukchi Sea shelf, and the dissolved Σ15PAHs concentration differed by nearly an order of magnitude in two closely adjacent sections in the basin area, which both showed high fraction of river water and sea ice meltwater. This pattern could be explained by the different local inputs from Eurasia and North America. This scenario was further visualized by ice back trajectories capturing significantly higher PAH signals from the Eurasian margin than those from North America and stable oxygen isotopic data finding a positive correlation of PAH levels with the fractions of river runoff and ice-melting water coming from the Eurasia. The PAHs budget of the Arctic Ocean was also dominated by local sources (river and ice melting) as inputs (76 %) and volatilization as outputs (47 %). This study reveals the importance of Eurasian local inputs in supplying PAHs to the central Arctic Ocean. Those processes, which have not been well recognized for PAHs previously, are expected to increase and will undermine global efforts to reduce exposure by remobilizing PAHs stored in permafrost and ice.

Application of combined physicochemical and biological processes for enhanced treatment of avermectin fermentation wastewater.

This paper aimed at developing the enhanced biological treatment processes for treating avermectin fermentation wastewater (AFW). After UASB treatment and chemical coagulation, the pretreated AFW was subsequently flowed into a rCAA reactor (reactor with repeated coupling of aerobes and anaerobes using macroporous carriers) system for further pollutant degradation and excess sludge reduction. By the treatment with chemical coagulation, COD, total nitrogen and total phosphorus concentration of treated AFW were eliminated to 550-700 mg/L, 130-160 mg/L and 1 mg/L, respectively, and the dark color of the wastewater was greatly bleached. After this decolorized wastewater was treated by the following rCAA bioreactor, the COD could be reduced to around 200-300 mg/L, while the further decrease of COD less than 200 mg/L was difficult. The Biolog analysis and OUR test for the water treated by rCAA bioreactor demonstrated that the effluent from chemical coagulation contained some unknown compounds with low biodegradability and would simplify the microbial community in the subsequent rCAA reactor.

Dynamic imaging of contrast-enhanced coronary vessels with a magnetization prepared rotated stripe keyhole acquisition.

PURPOSE: To evaluate dynamic coronary imaging based on a magnetization prepared contrast-enhanced (CE) rotated stripe keyhole acquisition scheme. MATERIALS AND METHODS: Background suppression of long T(1) tissue was used so that the k-space would be selectively dominated by the contribution of the CE vessel. The phase-encoding axis was then adjusted parallel to the long axis of the vessel to sample the significant power spectrum of the vessel. The performance of this approach was evaluated by means of computer simulations and experimental studies on phantoms and a pig model instrumented with an intracoronary catheter for infusion of contrast media. RESULTS: Computer simulations and phantom studies demonstrated that by rotating the gradient axes to match the k-space pattern of the frequency spectrum, one can reduce the keyhole band to 20% of the full k-space while preserving the structure's lumen width and sharpness. In vivo studies validated those findings, and dynamic angiograms of the CE coronary arteries were obtained as rapidly as 140 msec per image, with an in-plane spatial resolution of 1.5 mm. CONCLUSION: With efficient background suppression, a rotated stripes keyhole acquisition can efficiently acquire the significant k-space of a CE vessel, and provide improved vessel definition with a reduced acquisition matrices scheme.

Fast magnetization-driven preparation for imaging of contrast-enhanced coronary arteries during intra-arterial injection of contrast agent.

PURPOSE: To implement a short-duration magnetization preparation sequence, which consists of a saturation followed by multiple inversion pulses, for imaging of short-T1 species and suppression of long-T1 species. MATERIALS AND METHODS: Computer optimizations were performed to derive preparation schemes that 1) suppress long-T1 background species with T1>or=250 msec, 2) maximize the MZ of contrast-enhanced (CE) structures with T1250 msec, and about a 30% reduction for 20 msec