Lieke van den Wildenberg¹, Quincy van Houtum¹, Wybe van der Kemp¹, Catalina Arteaga de Castro¹, Alex Bhogal¹, Paul Chang², Sahar Nassirpour², and Dennis Klomp^1
1Radiology Department, UMC Utrecht, Utrecht, Netherlands, ²MR Shim GmbH, Reutlingen, Germany

Maximizing shim performance, particularly for larger organs such as the liver, is crucial at ultra-high field MRI due to the increased sensitivity to B₀ field inhomogeneity. The conventional shimming in most MRI systems at ultra-high field, provides insufficient correction. However, by combining the available 2^nd order spherical harmonic fields with an external array of 16 local shim coils, the magnetic field homogeneity in the liver is improved by as much as 44%.

Xinqiang Yan^1,2
1Vanderbilt University Institute of Imaging Science, Nashville, TN, United States, ²Department of Radiology and Radilogical Science, Vanderbilt University Medical Center, Nashville, TN, United States

Multiple coils shimming technology has been demonstrated as a promising approach to reduce the B₀ inhomogeneity in MRI. However, strong coupling arises when local DC coils are placed close to the imaging area and RF coils. To solve this problem, we proposed a novel local DC shim coil that has little effect on the RF coils, which we called "RF transparent" DC coil. This concept was validated by EM simulation, bench test, and MR experiments. The RF transparent concept will bring much more freedoms to DC coil design (such as many turn and irregular shaped). 

Bruno Pinho-Meneses¹, Jason Stockmann^2,3, Edouard Chazel¹, Paul-François Gapais¹, Eric Giacomini¹, Franck Mauconduit¹, Alexandre Vignaud¹, Michel Luong⁴, and Alexis Amadon^1
1Université Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France, ²Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, ³Harvard Medical School, Boston, MA, United States, ⁴Université Paris-Saclay, CEA, Institut de Recherche sur les Lois Fondamentales de l'Univers, Gif-sur-Yvette, France

A Singular Value Decomposition based Multi-Coil Array for B₀ shimming of the human brain was designed from a database of 100 δB₀ fieldmaps. An optimized 2-layer 36-channel MCA design was obtained and constructed. The system was characterized and measured fieldmaps were used for comparison to expected performance from ideal simulated fields. The static whole-brain and dynamic slice-wise shimming was validated in-vivo and assessed with GRE and EPI acquisitions at 7 Tesla.

Paul Chang¹, Sahar Nassirpour¹, Kaizad Rustomji², Elodie Georget², Ingmar Voogt³, Aidin Haghnejad³, Evita Wiegers⁴, Jannie Wijnen⁴, and Dennis Klomp^4
1MR Shim GmbH, Reutlingen, Germany, ²Multiwave Imaging, Marseille, France, ³WaveTronica, Utrecht, Netherlands, ⁴UMC Utrecht, Utrecht, Netherlands

Increased B0 inhomogeneity at ultra-high fields continues to pose a challenge for many MR applications. Local arrays of shim coils offer a complimentary way of reducing the local inhomogeneities. In this study, practical design considerations for a combined RF/B0 shim 7T head coil were assessed. Numerical simulations were used to find the optimal size and distance of the shim coils relative to Rx loops. These results were then verified in a bench test. Finally, having these considerations in mind, it was shown that by optimizing the arrangement of the shim coils improved B0 homogeneity can be achieved.

Vincent O. Boer¹, Jan Ole Pedersen², Hørður Andreasen³, Sadri Güler^1,4, Vitaliy Zhurbenko³, Jason Stockmann⁵, Irena Zivkovic⁶, and Esben Thade Petersen^1,4
1Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital, Hvidovre, Denmark, ²Philips Healthcare, Copenhagen, Denmark, ³Department of Electrical Engineering, Technical University of Denmark, Kongens Lyngby, Denmark, ⁴Section for Magnetic Resonance, DTU Health Tech, Technical University of Denmark, Kongens Lyngby, Denmark, ⁵Athinoula A Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, ⁶Electrical Engineering department, Technical University of Eindhoven, Eindhoven, Netherlands

Shielded coaxial RF coils show very low coupling between elements, and are ideal for building transmit-receive arrays. In this work we extended a 6 element transceive array with B₀ shim capabilities. 

Fardad Michael Serry¹, Junzhou Chen^1,2, Anthony G Christodoulou^1,2, Yuheng Huang^1,2, Fei Han³, Won Bae^4,5, Christine Chung^4,5, Richard Handlin¹, John Stager¹, Matthew Dausch¹, Yubin Cai¹, Yujie Shan¹, Yucen Liu¹, Yibin Xie¹, Xiaoming Bi³, Rohan Dharmakumar^1,2, Zhaoyang Fan^1,6, Debiao Li^1,2, Hsin-Jung Yang¹, and Hui Han^1
1Biomedical Imaging Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA, United States, ²Department of Bioengineering, UCLA, Los Angeles, CA, United States, ³Siemens Medical Solutions USA, Inc., Los Angeles, CA, United States, ⁴University of California, San Diego, San Diego, CA, United States, ⁵VA Medical Center, San Diego, CA, United States, ⁶University of Southern California Department of Radiology, Los Angeles, CA, United States

Metal artifact image degradation can interfere with tissue status assessment. Metal artifact reduction pulse sequences, mainly spin-echo based, and scanner B0-shimming can mitigate the artifacts. We have tested in a metal hip prosthesis phantom improving shimming locally with a novel technology that integrates separate but co-planar RF receive and shim arrays, expanding the freedom to position shim coils and shape B0, independently of the RF coil geometry and pulse sequence. Metal-induced signal-void artifact was reduced in GRE scans, revealing up to 50% additional area around the prosthesis. The sequence-agnostic technology may help improve MRI near metal prostheses and interventional devices.

Alexandre D'Astous¹, Ryan Topfer¹, Gaspard Cereza¹, Eva Alonso-Ortiz¹, Lincoln Craven-Brightman², Jason Stockmann^2,3, and Julien Cohen-Adad^1,4
1NeuroPoly Lab, Institute of Biomedical Engineering, Ecole Polytechnique, Montreal, QC, Canada, ²Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ³Harvard Medical School, Boston, MA, United States, ⁴Functional Neuroimaging Unit, Centre de recherche de l'Institut universitaire de gériatrie de Montréal, Montreal, QC, Canada

As MRI static fields get increasingly stronger, reducing $$$B_0$$$ inhomogeneities becomes more important but also challenging. When standard active shimming on commercial systems is insufficient for researchers’ needs, alternative approaches such as external shim or hybrid AC/DC coils can be used. However, in order to perform advanced shimming experiments, a proper software ecosystem is required and there is currently no open-source solution for transparent and reproducible shimming experiments. Here we introduce the Shimming Toolbox (https://shimming-toolbox.org), an open-source software package for performing and prototyping static, dynamic and realtime $$$B_0$$$ shimming experiments.

Richard W. Bowtell¹, Michael Packer ², Peter Hobson ², James Leggett¹, Niall Holmes¹, Paul Glover ¹, Matthew Brookes¹, and Mark Fromhold^2
1Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham, United Kingdom, ²School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom

Cylindrical shields formed from material of high permeability are commonly used in providing low-magnetic field environments for experimental research. Cylindrical coils are often sited inside such shields to produce controlled patterns of field variation, but interaction of the coils with the mu-metal distorts the fields. Here we show how to analytically calculate the fields that are produced by simple coils inside a finite-length, cylindrical mu-metal shield with end-caps, and report experimental measurements on two different coils (loop and saddle), demonstrating excellent agreement with the theory.  Optimal spacings of Helmholtz-type coils inside finite-length shields are also derived using the analytic expressions.

Terence W. Nixon¹, Yanning Liu¹, Henk M. DeFeyter¹, Scott McIntyre¹, and Robin A. de Graaf^1
1Yale University, New Haven, CT, United States

Deuterium metabolic imaging (DMI) is a powerful new method to supplement the anatomical and functional information of MRI with a metabolic component. A reduction in overall scan time by interleaving MRI and DMI is clinically relevant, whereas research applications can benefit from complimentary information obtained through interleaved acquisition. Because most MR scanners only allow acquisition of one frequency, additional hardware is required to enable interleaved acquisition. Here we present hardware for the upconversion of 2H data into the 1H receive path and present a solution to achieve effective phase and frequency locking.

Baosong Wu¹, Sajad Hosseinnezhadian², Yonghyun Ha², Kartiga Selvaganesan², Charles Rogers III², Kasey Hancock², Gigi Galiana², and R. Todd Constable^2
1Department of Radiology and Biomedical Imaging, Yale School of Medicine, NEW HAVEN, CT, United States, ²Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, United States

This work presents the feasibility of Bloch-Siegert (BS) frequency encoding for magnetic resonance (MR) applications requiring a simultaneous transmit and receive system. RF frequency encoding technique is referred to receiving MR signal while existing one offset-field radiation, which can be considered as a radio frequency interference(RFI). A prototype was built demonstrating first MR experiment and preliminary data using this method. Our system is currently a research technology with the goal of generating a low-field and point-of-care medical imaging system using novel RF encoding. 

Yonghyun Ha¹, Kartiga Selvaganesan¹, Baosong Wu¹, Kasey Hancock¹, Charles Rogers III¹, Sajad Hosseinnezhadian¹, Gigi Galiana¹, and R. Todd Constable^1
1Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, United States

The response times of RF coils in MRI are long when operating at low B₀ field, making it difficult to achieve the desired pulse shape in the coil. Compensation pulses are shown that were optimized using a series of square pulses. Both the duration and amplitude of the compensation elements were calculated with Q-factor which was calculated from the ring-down time measured using a sniffer coil. The SNRs of the echo signal acquired using compensated pulse was compared with those of signal obtained with uncompensated pulses and showed significant improvements of 51.5%.

Yonghyun Ha¹, Kartiga Selvaganesan¹, Sajad Hosseinnezhadian¹, Baosong Wu¹, Kasey Hancock¹, Gigi Galiana¹, and R. Todd Constable^1
1Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, United States

For gradient-free RF spatial encoding, MR image based B₁ mapping methods cannot be used due to the absence of gradient coils. However, it is important to get a B₁ map particularly if Bloch-Siegert shift encoding is used. In this work, a method to automatically measure the amplitude of B₁ field is introduced. Three perpendicular pickup loops were used to measure the B₁ field in three orthogonal axes simultaneously. The position of the pickup loops was controlled by 3D printer, and the peak-to-peak voltage of the coupled signal was automatically saved using PC oscilloscope.

Matthew A. McCready¹, William B. Handler¹, Francisco Martinez^2,3, Timothy J. Scholl^2,3, and Blaine A. Chronik^1,2
1Physics and Astronomy, Western University, London, ON, Canada, ²Medical Biophysics, Western University, London, ON, Canada, ³Robarts Research Institute, Western University, London, ON, Canada

Delta relaxation enhanced magnetic resonance (dreMR) is a field-shifting quantitative molecular imaging method. The dreMR method may be used to produce images with signal proportional to concentration of contrast agents with longitudinal relaxivity dispersion. Here we find that field inhomogeneities and ramping periods, which were previously ignored, cause significant errors in dreMR images. These errors include apparent non-zero signal from dispersion-free tissue, and apparent change in signal due to contrast agents. We show that these effects can be mitigated by use of an improved homogeneity design method, and increased slew rates.

Samson Lecurieux Lafayette¹ and Claude Fermon^1
1SPEC - CEA Saclay - Université Paris Saclay, Saclay, France

Classic high field MRI is a powerful tool in healthcare. However, it is an expensive and complex installation and it might be useful to supply a less convenient device adapted to a lot of usage not requiring high field potential. We have developed a very low field MRI working at between 1mT and 10mT. Main static field is providing by a water-cooled resistive magnet. In order to achieve an iso spatial resolution of 2mm in a reasonably short time of acquisition, we have worked on adapted sequences including compressed sensing and optimized detection with parallel acquisition.

Robert Kowal¹, Enrico Pannicke², Marcus Prier¹, Ralf Vick², Georg Rose³, and Oliver Speck^1
1Department of Biomedical Magnetic Resonance, Otto von Guericke University, Magdeburg, Germany, ²Chair of Electromagnetic Compatibility, Otto von Guericke University, Magdeburg, Germany, ³Chair in Healthcare Telematics and Medical Engineering, Otto von Guericke University, Magdeburg, Germany

The SNR-performance of a low-field (0.26T) Tabletop-MRI-system was experimentally compared to a high-field (3T) clinical scanner. The SNR of simple FID sequences were evaluated for RF-units with identical coil and sample geometries as well as T/R-switch designs. The SNR was calculated from time signals and put into perspective to compute the relative SNR-performance of the Tabletop-system which was measured at 11.3%. Additional compensations for several differing experimental conditions were carried out. The full comparison suggests limiting factors in the equivalent measurement in the clinical scanner which can result in more SNR loss than expected.

Zhenhua Shen¹, Xuchen Zhu¹, Shihong Han¹, Fuyi Fang¹, Wei Luo¹, Shao Che¹, Zidong Wei¹, Jinguang Zong¹, Yongquan Ye², Bo Li¹, Shuheng Zhang¹, Anthony Vu², Weiguo Zhang², and Guobin Li^1
1United Imaging Healthcare, Shanghai, China, ²UIH America, Inc., Houston, TX, United States

For the first time, routine clinical body imaging with large FOV on a whole-body 5T MRI system is demonstrated. With multi-channel RF parallel transmission hardware architecture and static RF shimming techniques, the uniformity of the RF transmission field is shown to be well controlled for imaging quality guarantee. Preliminary results show great promise for body imaging at 5T.

Sebastian Walter Rieger¹, Karla Miller¹, Peter Jezzard¹, and Wenchuan Wu^1
1Wellcome Centre for Integrative Neuroimaging, University of Oxford, Oxford, United Kingdom

In post mortem MRI, the absence of body temperature autoregulation can lead to significant local heating in the sample from RF absorption and heat from the environment. This can interfere with scanning (such as diffusion measurements) and in unfixed samples, accelerate tissue decomposition. In this work, a temperature control system is presented which enables prolonged scanning of post mortem samples at a stable temperature while preserving tissue.

Jean-Lynce GNANAGO^1,2,3,4,5,6, Tony GERGES^1,2,3,4,5,6, Laura Chastagnier^{1,2,4,6,7,8,9,10}, Emma Petiot^{2,4,6,7,8,9,10}, Vincent SEMET^1,2,4,5,6, Philippe Lombard^1,2,3,4,5,6, Christophe Marquette^{1,2,4,6,7,8,9,10}, Michel Cabrera^1,2,3,4,5,6, and Simon Auguste Lambert^{1,2,3,4,5,6
1}Université Claude Bernard Lyon 1, VILLEURBANNE, France, ²INSA LYON, VILLEURBANNE, France, ³Ecole Centrale Lyon, Ecully, France, ⁴CNRS, VILLEURBANNE, France, ⁵AMPERE UMR 5005, VILLEURBANNE, France, ⁶Université de Lyon, VILLEURBANNE, France, ⁷3d.FAB, VILLEURBANNE, France, ⁸CPE Lyon, VILLEURBANNE, France, ⁹ICBMS, VILLEURBANNE, France, ¹⁰UMR 5246, VILLEURBANNE, France

Tissue engineering for regenerative medecine is a growing field which faces structural and functional challenges at different scales. Real-time quantitative 3D characterization of tissues both in vitro and in vivo would help biologists assessing their methods. Magnetic Resonance Imaging (MRI) offers the possibility to perform such characterization non-invasively. We propose here a 7T MRI coil integrated within a perfusion tissue engineering bioreactor to perform tissue assessments throughout its growth. The MRI bioreactor is built using 3D printing and plastronics. This works resulted in a successful observation of a bioprinted tissue with a 75 µm in plane resolution.

Farah Mushtaha^1,2, Tristan K. Kuehn^1,3, Omar El-Deeb⁴, Seyed A. Rohani³, Luke W. Helpard³, Hanif Ladak^2,3,5, Amanda Moehring⁶, Corey A. Baron^1,2,3,7, and Ali R. Khan^1,2,3,7
1Robarts Research Institute, London, ON, Canada, ²Medical Biophysics, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada, ³School of Biomedical Engineering, Western University, London, ON, Canada, ⁴Neuroscience, Western University, London, ON, Canada, ⁵Department of Electrical and Computer Engineering, Western University, London, ON, Canada, ⁶Biology, Western University, London, ON, Canada, ⁷The Brain and Mind Institute, Western University, London, ON, Canada

Validating diffusion MRI (dMRI) representations and models of brain tissue is challenging because there is no reference ground-truth for in vivo scans. We investigate the microstructural characteristics of 3D printed axon-mimetic (3AM) phantoms as a dMRI validation tool using fluorescence microscopy and phase-contrast micro computed tomography (micro-CT). Both microscopy and micro-CT yielded pore diameters of ~ 8 μm. We constructed a 2-compartment microstructural model using microscopy and micro-CT data to simulate 3AM dMRI scans, and compared the observed metrics from in-vivo scans and simulation data.

Rona Shaharabani¹, Shir Filo¹, Oshrat Shtangel¹, and Aviv Mezer^1
1The Edmond and Lily Safra Center for Brain Science, The Hebrew University of Jerusalem, Jerusalem, Israel, Jerusalem, Israel

Neurodegenerative diseases such as Alzheimer, Parkinson, and Multiple sclerosis are often linked to abnormal changes in lipids and iron. Lipids are the main components of any membrane, including myelin, and iron is an essential brain’s trophic. The interaction of lipids and iron with water protons is considered to be a major contributor to the brain’s MRI signals. Here we examine the combined effects of the iron and lipid compositions on quantitative MRI parameters using a novel phantom system. We quantitatively characterize the R2* dependence on lipid and iron concentrations.