Andre van der Kouwe¹, Hongbae Jeong¹, Zinong Yang², Donald Straney¹, Robert Frost¹, Laura Lewis², and Giorgio Bonmassar^1
1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ²Department of Biomedical Engineering, Boston University, Boston, MA, United States

We introduce a new EEG net, which will allow clinicians to monitor EEG while tracking head motion for correction. Motion during MRI limits patient scans, especially of children and patients with seizures. The MotoNet was built using PTF, embedding EEG/motion sensor pairs on opposite sides in one circuit. MRI safety studies at 3T confirmed maximum heating below 1ºC. EEG/motion measurements were made with a standard commercial EEG system. Using a custom MRI sequence with spatial localization gradients only, we showed that the signal on each channel was highly correlated with motion, allowing for electrode positioning and motion tracking.

Casper Beijst¹, Woutjan Branderhorst¹, Jan Lagendijk¹, Bjoern Weissler^2,3, David Schug^2,3, Florian Mueller², Harald Radermacher², Martino Borgo⁴, Wout Schuth⁴, Jurgen Mollink⁵, Govaert Borst⁵, Marc Verheyen⁵, Frank van Duin⁴, Dennis Klomp¹, Hugo de Jong¹, and Volkmar Schulz^2,3
1UMC Utrecht, Utrecht, Netherlands, ²Rheinisch-Westfaelische Technische Hochschule, Aachen, Germany, ³Hyperion Hybrid Imaging Systems, Aachen, Germany, ⁴Futura Composites, Heerhugowaard, Netherlands, ⁵Philips Medical Systems, Best, Netherlands

The Unity 1.5T MR-linac has clinically been introduced to provide stereotactic precision for moving targets. We are now developing an integrated 1.5T MRI/PET system with identical MRI performance for planning of MR-linac treatments. The system offers 70 cm bore size and includes PET detectors mounted in the gap of a split gradient coil. Recently, the first ring of PET detectors was installed. We performed extensive interference tests and acquired the first simultaneous images using a brain phantom. Our vision is that the combination of MR-linac with MRI/PET will allow the use of PET information for stereotactic radiation therapy guidance.

Felix Krüger¹, Christoph Stefan Aigner¹, Sebastian Dietrich¹, Kerstin Hammernik^2,3, and Sebastian Schmitter^1,4,5
1Physikalisch-Technische Bundesanstalt, Braunschweig and Berlin, Germany, ²Technical University of Munich, Munich, Germany, ³Imperial College London, London, United Kingdom, ⁴Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ⁵Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

In this work, we estimate relative 2D B₁⁺-maps from initial localizer scans using deep learning at 7T. We investigate 7 UNets and MultiResUNets architectures to estimate complex, channel-wise, relative 2D B₁⁺-maps of 8 transmit channels from a single gradient echo localizer obtained with 32 receive channels. The networks are evaluated in 5 unseen volunteers not included in the training library by comparing the prediction with the acquired relative B₁⁺-maps using different evaluation metrics for homogeneous B₁⁺ phase shimming. Our approach saves additional B₁⁺-mapping scans, and, hence, overcomes long calibration times in the human body at 7T.

Qi Liu¹, Hoang (Mark) Nguyen^1,2, Xucheng Zhu³, Xiaohui Zhai³, Bo Li³, Jian Xu¹, and Weiguo Zhang^1
1UIH America, Inc., Houston, TX, United States, ²Department of Computer Science and Electrical Engineering, University of Missouri at Kansas City, Kansas City, MO, United States, ³United Imaging Healthcare, Shanghai, China

A versatile, practical, and effective gradient trajectory correction technique that considers gradient system nonlinearity is proposed using deep learning. Its performance was validated on phantoms and human subjects and demonstrated superior quality than the conventional techniques.

Reza Babaloo¹, Ege Aydin¹, and Ergin Atalar^1,2
1Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, ²National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey

The MRI gradient system heating changes its characteristics, and without a feedback system, the gradient waveform distorts resulting image artifacts. The primary effect of temperature rise in the gradient coil winding is the increase in the coil resistance. Feedforward based controllers, preferable in gradient array systems and multi-coil designs, use a linear time-invariant model. However, the gradient heating makes the system time-variant. To address this issue, we propose predicting gradient coil thermal variation using the thermal differential equation and updating feedforward controller parameters continuously.

Zhe Wu¹, Alexander Jaffray², Johanna Vannesjo³, Kamil Uludag^4,5, and Lars Kasper^1
1Techna Institute, University Health Network, Toronto, ON, Canada, ²UBC MRI Research Center, University of British Columbia, Vancouver, BC, Canada, ³Department of Physics, Norwegian University of Science and Technology, Trondheim, Norway, ⁴Techna Institute & Koerner Scientist in MR Imaging, University Health Network, Toronto, ON, Canada, ⁵Biomedical Engineering, Center for Neuroscience Imaging Research, Institute for Basic Science, Sungkyunkwan University, Suwon, Korea, Republic of

This study investigated the long-term stability of GIRF within an eight-month period, together with the benefits of an optimized GIRF acquisition protocol. These studies provide insight into mechanisms of image quality degrading and potentially lead to improved image quality control, generalizable to arbitrary imaging sequences.

Hannes Dillinger¹ and Sebastian Kozerke^1
1ETH and University Zurich, Zurich, Switzerland

This work highlights the mechanically resonant behaviour of MRI gradient systems when excited with an oscillating gradient, e.g. echo planar readout. Results demonstrate that a beat phenomenon can be observed in the signal phase with a frequency dependent on readout bandwidth and mechanical resonances of the system. Insights of the beat source are derived theoretically and validated experimentally. Data confirms that the beat phenomenon results in increased blurring in phase encoding direction leading to suggestions for system optimization in order to reduce the impact of the beat phenomenon.

Edwin Versteeg¹, Mark van Uden², Luke van der Hofstad², Kevin Bax², Martino Borgo^2,3, Wout Schuth³, Jeroen Siero^1,4, Mark Gosselink¹, and Dennis Klomp^1
1Radiology, University Medical Center Utrecht, Utrecht, Netherlands, ²Tesla Dynamic Coils, Zaltbommel, Netherlands, ³Futura Composites, Heerhugowaard, Netherlands, ⁴Spinoza Centre for Neuroimaging, Amsterdam, Netherlands

The sound level in MRI can be lowered by using a silent gradient axis that adds extra soundless encoding. In this work, we present the field characteristics and first images for a silent gradient designed for a clinical 3 Tesla system. This silent gradient featured a built-in 32-channel receive coil and weighs 21 kg. The gradient field could be oscillated at 23.5 kHz and featured a linear region of 20 cm. The coil had limited interactions with the transmit B1 field and did not affect B1 homogeneity, which was showcased in phantom and in-vivo images.

Sebastian Theilenberg¹, Yun Shang¹, Chathura Kumaragamage², Scott McIntyre², Terence W. Nixon², Robin A. de Graaf², and Christoph Juchem^1,3
1Department of Biomedical Engineering, Columbia University, New York, NY, United States, ²Department of Radiology and Biomedical Engineering, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, CT, United States, ³Department of Radiology, Columbia University Medical Center, New York, NY, United States

As part of a multi-center effort to design and build an accessible 1.5 T head-only MRI scanner (NIH U01EB025153, PI M. Garwood), we designed and constructed a prototype multi-coil array fitting the limited available space and capable of generating linear and non-linear image encoding fields as well as strong concomitant localized B₀ shim fields. Here, we describe the construction process, and present system characteristics as well as experimental validation of its field generation capabilities utilizing a conventional 4 T MRI scanner.

Lucia Navarro de Lara^1,2, Jason Stockmann^1,2, Boris Keil³, Azma Mareyam¹, Mohammad Daneshzand^1,2, Larry Wald^1,2, and Aapo Nummenmaa^1,2
1Martinos Center - MGH, Charlestown, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³Institute of Medical Physics and Radiation Protection, Technische Hochschule Mittelhessen, Giessen, Germany

Multichannel Transcranial Magnetic Stimulation is an emerging technology for non-invasive stimulation of the human brain. Combining this technique with fMRI offers the unique benefits of studying the causal relationships between the cortical and subcortical nodes of large-scale brain networks. For this reason a whole head 28-channel RF coil array was developed to be integrated with the first 3-axis-TMS multichannel system. We have analyzed how the SNR of the constructed array changes when placing the stimulation units. Additionally, we compared the SNR/g-factor maps with commercial available 32/20-channel RF coils. The results show that the RF coil is performing as expected.

Gaël Saïb¹, Sherry Huang², Emily Long¹, S. Lalith Talagala³, Hellmut Merkle¹, Alan P. Koretsky¹, and Natalia Gudino^1
1NINDS/LFMI, National Institutes of Health, Bethesda, MD, United States, ²Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States, ³NINDS/NMRF, National Institutes of Health, Bethesda, MD, United States

Continuous arterial spin labeling using a separate neck labeling coil is an attractive approach for imaging perfusion at 7T. This approach is hindered by specialize hardware including a labeling coil and a separate amplifier located outside the magnet room. On-coil amplifiers have demonstrated higher RF power efficiency with minimal cable loss and patient-coil interaction. This work shows that a separate labeling coil using on-coil amplification can be used for flow driven adiabatic inversion in a flow phantom suggesting that it may provide a suitable approach to simplify the hardware package required as well as to improve CASL studies at 7T.

Xiaoping Wu¹, Andrea Grant¹, Xiaodong Ma¹, Edward Auerbach¹, Jerahmie Ladder¹, Alireza Sadeghi-Tarakameh¹, Yigitcan Eryaman¹, Russell Lagore¹, Nader Tavaf², Pierre‐Francois Van de Moortele¹, Gregor Adriany¹, and Kamil Ugurbil^1
1CMRR, Radiology, University of Minnesota, Minneapolis, MN, United States, ²3M, Minneapolis, MN, United States

Susceptibility-weighted imaging (SWI) and quantitative susceptibility mapping (QSM) have been shown to provide unique contrasts that can be used to study pathophysiologic changes of tissue magnetic susceptibility in various brain diseases. As magnetic susceptibility effects increase with the main field strength, there has been a rapidly growing interest in performing SWI and QSM at ultrahigh field (UHF) (7 Tesla and above). The aim of this study was to demonstrate how the use of the UHF of 10.5 Tesla may promote SWI and QSM of the human brain.