Aris van Ieperen^1,2, Chantal Tax^1,3, Dennis Klomp¹, Bas Vermulst², Jeroen Siero^1,4, Joost van Straalen⁵, Martijn Heintges⁵, and Edwin Versteeg^1
1Radiology, University Medical Center Utrecht, Utrecht, Netherlands, ²Electromechanics & Power Electronics, Eindhoven University of Technology, Eindhoven, Netherlands, ³CUBRIC, School of Physics and Astronomy, Cardiff University, Cardiff, United Kingdom, ⁴Spinoza Centre for Neuroimaging, Amsterdam, Netherlands, ⁵Prodrive Technologies B.V., Son, Netherlands

For high-resolution diffusion-MRI, strong gradients combined with fast readout are desired. In this study, we propose a gradient system architecture for such strong gradients and fast readouts without nerve stimulation by implementing a filter topology that allows for both low and high frequency gradient waveforms. Two gradient inserts with different specifications are realized and two proposed modulation strategies are implemented in the amplifier firmware. Field measurements demonstrated the desired dual-mode capability of the system. With one gradient insert, a gradient amplitude of 300 mT/m and slew rates well above 10.000 T/m/s can be reached with only 500A&330V as amplifier output.

Manouchehr Takrimi¹ and Ergin Atalar^2
1National Magnetic Resonance Research Center, Bilkent University, Ankara, Turkey, ²Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey

A z-gradient array coil equipped with a tunable shield array is proposed to achieve multiple imaging volumes that can be shifted along the coil axis. This is achieved by a set of independently tunable power amplifiers that feed the array elements. The proposed array dynamically provides a proper shield for the main array in which its magnetic profile can be adjusted on the fly. Five multiple-region magnetic profiles are simulated to demonstrate the flexibility of the proposed array: (a) a double-gradient profile; (b) shifted version of (a); (c) highly linear double-gradient profile without shielding; (d) triple-gradient profile; (e) quintuple-gradient profile.

Mathias Davids^1,2,3, Livia Vendramini¹, Natalie Ferris^4,5, Valerie Klein^1,3, Bastien Guerin^1,2, and Lawrence L. Wald^1,2,5
1Martinos Center for Biomedical Imaging, Charlestown, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Heidelberg, Germany, ⁴Harvard Graduate Program in Biophysics, Harvard University, Cambridge, MA, United States, ⁵Harvard-MIT Division of Health Sciences and Technology, Boston, MA, United States

We describe the process of designing and analyzing two body gradient coils with and without PNS optimization suitable for prototype construction and experimental validation. The optimized coil achieves a 51% increase in PNS thresholds at a 15% inductance penalty. Both coils are construction-ready (single continuous wire path) and have realistic and matched design characteristics (actively shielded, torque/force balanced, high field linearity in 40 cm ROL). We are in the process of constructing coil prototypes, with the ultimate goal of experimentally validating their PNS differences.

H. Douglas Morris¹, Nastaren Abad², Radhika Madhavan³, Chitresh Bhushan², Ante Zhu², Luca Marinelli², Eric Fiveland², J Kevin DeMarco^4,5, Robert S Shih^4,5, Maureen Hood^4,5, Gail Kohls⁴, Kimbra Kenny⁴, Tom K F Foo², and Vincent B Ho^4,5
1Radiology and Radiological Sciences, Uniform Services University of the Health Sciences, Bethesda, MD, United States, ²GE Global Research, Niskayuna, NY, United States, ³GE Healthcare, Niskayuna, NY, United States, ⁴Walter Reed National Military Medical Center, Bethesda, MD, United States, ⁵Uniform Services University of the Health Sciences, Bethesda, MD, United States

Comparisons of the multi-shell DWI is described for the USU/GE MAGNUS 3T head-only gradient system and a clinical whole-body GE MR750 3T magnet system. The advantages of high-performance gradients are shown in analysis outcomes of dMRI metrics.  Direct comparison is made between identical diffusion pulse sequences and system optimized sequences for each platform.  The shorter TE and high-gradient strength of MAGNUS enhance SNR and diffusion imaging response. 

Nicolas Boulant¹, Cécile Lerman¹, Lionel Quettier², Olivier Dubois², Frédéric Molinié², Peter Dietz³, and Guy Aubert^2
1University Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif sur Yvette, France, ²University Paris-Saclay, CEA, Irfu, Gif sur Yvette, France, ³Siemens Healthcare GmbH, Erlangen, Germany

The whole-body Iseult 11.7T CEA magnet has delivered its first images after nearly 20 years of research and development. Before reaching this long-waited step, a gradient coil–magnet interaction test campaign was run for several months at 3T, 7T, 10.2T and 11.7T on the same identical system. It included acoustics, vibrations, magnet safety system voltage and power deposition in the He bath measurements. Some vibration results versus field strength are presented here. Vibration amplitudes are shown to increase less than with B0 field strength.

Paulina Šiurytė¹, Joao Tourais¹, and Sebastian Weingärtner^1
1Imaging Physics, TU Delft, Delft, Netherlands

 Acoustic noise in MRI is a main source of patient anxiety, with noise levels reaching up to 130 dB. In this work, a low-cost solution is proposed, combining active noise cancelling and direct sequence noise prediction from the scanner gradient inputs. The prediction is based on the linearity between gradient coil input derivative and corresponding acoustic noise. A proposed Predictive Noise Cancelling demonstrated an in-bore noise reduction up to 10 dB despite the system imperfections.

Alex C Barksdale^1,2, Clarissa Cooley¹, and Lawrence Wald^1
1MGH, Charlestown, MA, United States, ²MIT, Cambridge, MA, United States

Mid-field (0.5T) MRI is an attractive alternative to higher field strengths for improved cost, accessibility and patient comfort. Magnet length is a major determinant of patient comfort/acceptance but is constrained by escalating wire costs. We present a mid-field magnet design using rare-earth permanent magnets to supplement solenoidal superconducting windings, enabling shorter bore lengths than superconducting windings alone. The optimization problem is formulated and solved using linear programming. For a given superconducting wire length, we demonstrate that adding rare-earth materials can reduce bore lengths by 10% using <250kg of rare-earth material for a 5ppm, 0.5T B0 specification over a 450mm DSV.

Nicolas Arango¹, Jacob White¹, and Elfar Adalsteinsson^1,2
1Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ²Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA, United States

For a rigidly positioned ∆B₀ shim coil, calibration is a one-time process of acquiring high resolution ∆B₀ fields. For subject-specific shim coil position, this approach is too slow. We propose a fast magnetostatic inverse approach for subject-specific calibration by only acquiring few, low resolution fieldmaps each with several active shim coils. Our simulation study, which included a noise model and a measured ∆B 0 test case, suggests a scan-time reduction of afactor of 170, reducing calibration time from over an hour to less than a minute with negligible impact on shim quality.

Dion Thomas¹, Freya Harrison², Alice Little^1,3, Alex King¹, Annabel Jain Sorby-Adams⁴, Shieak Tzeng², Renee Turner⁴, and Sergei Obruchkov^1
1Victoria University of Wellington, Wellington, New Zealand, ²University of Otago, Wellington, New Zealand, ³The University of Auckland, Auckland, New Zealand, ⁴The University of Adelaide, Adelaide, Australia

A custom built single sided magnetic resonance system, generates an external region of homogeneous B0 = 0.2T field, a sweet spot, from which signal can be detected. The device is capable of relaxometry, diffusion and perfusion measurements and was used to continuously monitor progress of an MCA occlusion in a ovine sheep stroke model.  The data from the device was compared to image data acquired on a clinical 3T MRI system.

Isabellle Saniour¹, Fraser J.L. Robb², Victor Taracila², James Shin¹, Vishwas Mishra¹, Rena Fukuda¹, Jana Vincent², Henning U. Voss¹, Michael G. Kaplitt³, J. Levi Chazen¹, and Simone Angela Winkler ^1
1Department of Radiology, Weill Cornell Medicine, New York, NY, United States, ²GE Healthcare, Aurora, OH, United States, ³Department of Neurological Surgery, Weill Cornell Medicine, New York, NY, United States

Transcranial MRgFUS has been successfully used to treat a variety of neurodegenerative diseases. However, body coil brain image quality is poor, and a low-signal band artifact may occur in some regions due to RF wave reflections. Further, acoustic coil transparency has not been addressed extensively to date. In this work, we simulate a 10-channel coil design that can significantly increase the SNR by a factor of 20 over the body coil and thus indirectly improve the signal at the region of interests. Acoustic simulations/experiments exhibit transparency of the FUS-Flex coil as high as 97% at 650 kHz.