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Purpose: Rapid 2DRF pulse design with subject‐specific B1+ inhomogeneity and B0 off‐resonance compensation at 7 T predicted from convolutional neural networks is presented. Methods: The convolution neural network was trained on half a million single‐channel transmit 2DRF pulses optimized with an optimal control method using artificial 2D targets, B1+ and B0 maps. Predicted pulses were tested in a phantom and in vivo at 7 T with measured B1+ and B0 maps from a high‐resolution gradient echo sequence. Results: Pulse prediction by the trained convolutional neural network was done on the fly during the MR session in approximately 9 ms for multiple hand‐drawn regions of interest and the measured B1+ and B0 maps. Compensation of B1+ inhomogeneity and B0 off‐resonances has been confirmed in the phantom and in vivo experiments. The reconstructed image data agree well with the simulations using the acquired B1+ and B0 maps, and the 2DRF pulse predicted by the convolutional neural networks is as good as the conventional RF pulse obtained by optimal control. Conclusion: The proposed convolutional neural network‐based 2DRF pulse design method predicts 2DRF pulses with an excellent excitation pattern and compensated B1+ and B0 variations at 7 T. The rapid 2DRF pulse prediction (9 ms) enables subject‐specific high‐quality 2DRF pulses without the need to run lengthy optimizations. [ABSTRACT FROM AUTHOR]

Purpose: Some advanced RF pulses, like multidimensional RF pulses, are often long and require substantial computation time because of a number of constraints and requirements, sometimes hampering clinical use. However, the pulses offer opportunities of reduced‐FOV imaging, regional flip‐angle homogenization, and localized spectroscopy, e.g., of hyperpolarized metabolites. Proposed herein is a novel deep learning approach to ultrafast design of multidimensional RF pulses with intention of real‐time pulse updates. Methods: The proposed neural network considers input maps of the desired excitation region of interest and outputs a single‐channel, multidimensional RF pulse. The training library is, e.g., retrieved from a large image database, and the target RF pulses trained upon are calculated with a method of choice. Results: A relatively simple neural network is enough to produce reliable 2D spatial‐selective RF pulses of comparable performance to the teaching method. For binary regions of interest, the training library does not need to be vast; hence, reestablishment of the training library is not necessarily cumbersome. The predicted pulses were tested numerically and experimentally at 3 T. Conclusion: Relatively effortless training of multidimensional RF pulses, based on non‐MRI‐related inputs, but working in an MRI setting still, has been demonstrated. The prediction time of a few milliseconds renders real‐time updates of advanced RF pulses possible. [ABSTRACT FROM AUTHOR]

Purpose: A novel dissolution dynamic nuclear polarization (dDNP) polarizer platform is presented. The polarizer meets a number of key requirements for in vitro, preclinical, and clinical applications. Method: It uses no liquid cryogens, operates in continuous mode, accommodates a wide range of sample sizes up to and including those required for human studies, and is fully automated. Results: It offers a wide operational window both in terms of magnetic field, up to 10.1 T, and temperature, from room temperature down to 1.3 K. The polarizer delivers a 13C liquid state polarization for [1‐13C]pyruvate of 70%. The build‐up time constant in the solid state is approximately 1200 s (20 minutes), allowing a sample throughput of at least one sample per hour including sample loading and dissolution. Conclusion: We confirm the previously reported strong field dependence in the range 3.35 to 6.7 T, but see no further increase in polarization when increasing the magnetic field strength to 10.1 T for [1‐13C]pyruvate and trityl. Using a custom dry magnet, cold head and recondensing, closed‐cycle cooling system, combined with a modular DNP probe, and automation and fluid handling systems, we have designed a unique dDNP system with unrivalled flexibility and performance. [ABSTRACT FROM AUTHOR]

Noninvasive therapeutic cell tracking methods in living animals are important for understanding cell function and fate in connection with cell therapy. Here we report a new particle system based on chitosan-coated poly(lactic-co-glycolic acid) perfluorooctyl bromide (PLGA PFOB) nanoparticles designed for 19 F magnetic resonance imaging (MRI) cell tracking. Chitosan was adsorbed onto the PLGA PFOB nanoparticles through electric interactions, which led to an increase in the hydrodynamic size and a surface charge proportional to the coating weight ratio. Confocal laser scanning microscopy, flow cytometry analysis and 19 F-MRI showed that to achieve the highest labeling efficiency in vitro , the optimal weight ratio of chitosan to the PLGA PFOB nanoparticles was 1:10 for human mesenchymal stem cells (hMSCs) and 1:100 for Raw 264.7 macrophages. In vivo 19 F-MRI showed that 19 F labeled hMSCs remained at the injected site 24 h after injection. Thus, this study validates that chitosan-coated PLGA PFOB nanoparticles have the potential to track cell migration in vivo . [ABSTRACT FROM AUTHOR]

Rheumatoid arthritis (RA) is an autoimmune disease that causes pain and tissue destruction in people worldwide. An accurate diagnosis is paramount in order to develop an effective treatment plan. This study demonstrates that combining near infrared (NIR) imaging and 19F MRI with the injection of labelled nanoparticles provides high diagnostic specificity for RA. The nanoparticles were made from poly(ethylene glycol)-block-poly(lactic-co-glycolic acid) (NP) or PLGA-PEG-Folate (Folate-NP), loaded with perfluorooctyl bromide (PFOB) and indocyanine green (ICG) and evaluated in vitro and in a collagen-induced arthritic (CIA) mouse model. The different particles had a similar size and a spherical shape according to dynamic light scattering (DLS) and transmission electron microscopy (TEM). Based on flow cytometry and 19F MRI analysis, Folate-NP yielded a higher uptake than NP in activated macrophages in vitro. The potential RA-targeting ability of the particles was studied in CIA mice using NIR and 19F MRI analysis. Both NP and Folate-NP accumulated in the RA tissues, where they were visible in NIR and 19F MRI for up to 24 hours. The presence of folate as a targeting ligand significantly improved the NIR signal from inflamed tissue at the early time point (2 hours), but not at later time points. Overall, these results suggest that our nanoparticles can be applied for combined NIR and 19F MRI imaging for improved RA diagnosis. [ABSTRACT FROM AUTHOR]

Contrast agents have been widely used in medicine to enhance contrast in magnetic resonance imaging (MRI). Among them, super paramagnetic iron oxide nanoparticles (SPION) have been reported to have low risk in clinical use. In our study, F127-Folate coated SPION was fabricated in order to efficiently target tumors and provide imaging contrast in MRI. SPION alone have an average core size of 15 nm. After stabilizing with Pluronic F127, the nanoparticles reached a hydrodynamic size of 180 nm and dispersed well in various kinds of media. The F127-Folate coated SPION were shown to specifically target folate receptor expressing cancer cells by flow cytometry analysis, confocal laser scanning microscope, as well as in vitro MRI. Furthermore, in vivo MRI images have shown the enhanced negative contrast from the F127-Folate coated SPION in tumor-bearing mice. In conclusion, our F127-Folate coated SPION have shown great potential as a contrast agent in MRI, as well as in the combination with drug delivery for cancer therapy. [ABSTRACT FROM AUTHOR]