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Scaling MPI imaging hardware to image a human head presents challenges for the primary drive and receive coils. The larger imaging volume necessitates increased inductance, power delivery, and large physical sizes. Here, we present human-head scale drive and receive solenoid coils in a split gradiometer configuration designed for a mechanically-rotating field-free line MPI system. The design efficiency allows for 8mT drive fields (at ���26 kHz) from the water-cooled drive coil using an amplifier providing 21 A RMS and ���120 V RMS into the drive filter. The geometric decoupling between the drive and Rx coil of the gradiometer pair is -52 dB., International Journal on Magnetic Particle Imaging, Vol 8 No 1 Suppl 1 (2022)

We present the fabrication and characterization of a shift coil assembly designed for a rotating permanent magnet FFL human fMPI imager. The realized system consists of two sets of inner and outer coils (���racetracks���), each driven by an independent amplifier. Hollow conductors and a highly parallel water-cooling circuit provide heat removal during operation. The measured electrical characteristics of the coils (Rinner = 310 mOhms, Linner = 26 mH, Router = 399 mOhms, Louter =41 mH, M = 22.6 mH) match simulated values well, and field efficiency measurements demonstrate ability to shift a 1.03 T/m FFL over a 20 cm FOV within driving capabilities of the amplifier system (field efficiency = 0.215 mT/A)., International Journal on Magnetic Particle Imaging, Vol 8 No 1 Suppl 1 (2022)

A two-dimensional MPI acquisition allows signal from SPIONs outside the intended 2D imaging plane to interfere destructively with that from SPIONs in the desired slice, creating unwanted artifacts in the reconstructed image. We address this "side-lobe" signal interference with a Side Lobe Informed Center Extraction (SLICE) reconstruction, which utilizes a projection-space 3D forward model of the detected harmonics. The developed method reduces the out-of-plane interference artifacts in the 2D image reconstruction without the need to change the simplified acquisition schemes or hardware of the gradiometer detection based FFL system, for example by adding true 3D encoding which would interfere with the goal of fast, International Journal on Magnetic Particle Imaging, Vol 8 No 1 Suppl 1 (2022)

PURPOSE: To test an integrated “AC/DC” array approach at 7 Tesla, where B(0) inhomogeneity poses an obstacle for functional imaging, diffusion-weighted MRI, MR spectroscopy, and other applications. METHODS: A close-fitting 7T 31-channel brain array was constructed and tested using combined Rx and ΔB(0) shim channels driven by a set of rapidly-switchable current amplifiers. The coil was compared to a shape-matched 31-channel reference receive-only array for RF safety, signal-to-noise ratio (SNR), and inter-element noise correlation. We characterize the coil array’s ability to provide global and dynamic (slice-optimized) shimming using ΔB(0) field maps and echo planar imaging (EPI) acquisitions. RESULTS: The SNR and average noise correlation were equivalent to the 31ch reference array. Global and slice-optimized shimming provide 11% and 40% improvements respectively compared to baseline 2(nd)-order spherical harmonic shimming. Birdcage transmit coil efficiency was similar for the reference and AC/DC array setups. CONCLUSION: Adding ΔB(0) shim capability to a 31ch 7T receive array can significantly boost 7T brain B(0) homogeneity without sacrificing the array’s RF performance, potentially improving ultra-high field neuroimaging applications that are vulnerable to off-resonance effects.

Silicones are industrially important polymers characterized by a wide spectrum of chemical and physical properties with a number of important applications including automotive components, construction materials, isolating parts in electronic devices, flexible electronics, and medical products. Development of additive manufacturing methods for silicones enable production of complex and custom designed shapes and structures at both the micro- and macro-scale, economically feasible. In general, such materials can be fabricated using stereolithographic, extrusion-based, or inkjet printing techniques, in which silicones are polymerized using either photo- or heat-initiators. Silicones can also be crosslinked based on chemical reactions. Although this approach is supposedly the simplest, it has not been widely applied in additive manufacturing, as suitable technology for mixing and curing reactive inks without clogging nozzles has not be developed yet. To address this issue, a new 3D printer, that enables the fabrication of highly reactive and low viscous materials, has been developed and tested experimentally. The proposed fabrication method involves the ejection of two reactive droplets simultaneously from individual dispensers, merging and mixing them in free space outside the nozzle followed by deposition of the merged drop in a patterned format on a substrate. It was shown that the printing process is robust and stable more than 4 hours and it can be used on demand. By incorporating an XYZ positioner, it was possible to deposit droplets in an overlapping fashion to print any programmable shape featuring homogeneous structure, with a small number of pores. Moreover, due to the almost instantaneous reaction between two components (< 10s), the fabrication of very high aspect ratio (AR > 50) objects is possible. Lastly, the presented method can be easily adapted to print in free space without the use of support materials. Thesis Master of Applied Science (MASc)