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Prog #

Hector Sanchez Lopez¹, Feng Liu¹, Adnan Trakic¹, Ewald Weber¹, Stuart Crozier¹

¹University of Queensland, Brisbane, Australia

This paper presents a new method for biplanar active and passive shim design using an Equivalent Magnetizing Current (EMC) method.  The EMC induced by the rotational component of the magnetization is equivalent to that of the stream function (SF) and hence the SF is proportional to the magnetization. Using this approach, the magnetic field generated by a magnetized disk of finite thickness is related directly to the SF and hence no intermediate step to transform the current density into SF is required. Optionally, instead of a current pattern, a set of iron pieces can be employed so that the magnetized shims can be placed at equally spaced contours of the magnetization-stream function (MSF). The MSF is expressed as a sum of orthogonal functions of the azimuthal angle and shim domain radius and so it is tailored in the source domain in order to generate a particular magnetic field harmonic or a combination of these inside the DSV. The method is validated using known examples and the potential to generate new solutions is demonstrated.

Joshua Thomas de Bever¹, ², Blaine Alexander Chronik²

¹University of Utah, Salt Lake City, USA; ²University of Western Ontario, London, Canada

Imaging of mice using MRI is a critical part of studies investigating the genetics behind human diseases such as cancer, atherosclerosis, and cardiac disease. It can take multiple hours to image a single mouse, and the number of mice required to properly complete a large experiment can be on the order of tens of thousands. A gradient coil insert with multiple imaging regions would allow significant increases in throughput while maintaining gradient strengths required for high performance imaging. This abstract presents the results of a systematic computer simulation design study of multiple-imaging-region (MIR) gradient coils. The parameter space has been mapped for both Longitudinal and Transverse gradients with one, two, three, four, five, and seven imaging regions.

Michael Stephen Poole¹, Richard Bowtell¹

¹University of Nottingham, Nottingham, UK

Many coil systems required for MRI have a high degree of symmetry with the coils often being wound on a "surface of revolution" about the main field direction and the desired field variation generally has a known simple azimuthal dependence of the form cos(m φ) or sin(m φ). Incorporation of this a priori knowledge of the symmetry into the IBEM framework reduces the number of elements and consequently the computational effort and memory requirements. Here we demonstrate this by designing an insert head gradient formed from an array of annuli and a biradial ZX shim coil.

Dan Green¹, Simon Pittard¹, Robin A. de Graaf², Terence W. Nixon², Hoby P. Hetherington²

¹Varian, Inc., Yarnton, UK; ²MRRC, Yale University, New Haven, Connecticut, USA

Many fast imaging and spectroscopy sequences are difficult at high field as they are very sensitive to magnetic field inhomogeneities. Greater importance is being placed on shimming the subject, with a number of studies outlining the required shim specifications, and the development of methods such as dynamic shimming. Here a new head-only asymmetric gradient set is described, featuring water-cooled active shims up to 3rd order, which are inductively and capacitively decoupled from the main gradients. A large patient bore (42cm) allows use of noise insulation and a variety of array coils.

Derek A. Seeber¹, Anthony Mantone¹, Weijun Yin²

¹GE Healthcare, Florence, South Carolina, USA; ²GE Research, Niskayuna, New York, USA

The epoxy is an integral component for both mechanical support and electrical performance.  Epoxy manufactures typically specify parameters describing the viscosity, glass transition temperature (Tg), thermal expansion (CTE), tensile, modulus, elongation, dielectric constant and dissipation factor. As a PDIV performance parameter is not specified by the manufactures of epoxy systems, a method must be developed to use the epoxy manufacture’s properties to ensure high PDIV for an MRI gradient coil.

Pascal Stang¹, Juan Santos¹, John Pauly¹, Greig Scott¹

¹Stanford University, Stanford, California , USA

Real-time MR imaging places substantial performance demands on console hardware, interface buses, and reconstruction software.  Moreover, user interfaces and software must integrate tightly with the scanner to allow instantaneous changes to the pulse sequence.  We present a real-time MRI receiver system based on the Medusa console and RT-Hawk control and reconstruction software.  Using the system, we demonstrate real-time cardiac imaging at 50 frames per second.  System limitations and bottlenecks are explored in the context of real-time operation, including the throughput and latency of Medusa’s USB 2.0 data transport.

Florian Thiel¹, Werner Hoffmann¹, Frank Wojcik¹, Mathias Hein², Jürgen Sachs², Ulrich Schwarz², Marko Helbig², Frank Seifert¹

¹Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany; ²TU Ilmenau, Germany

This research aims at the synergetic use of ultra-wideband (UWB)-Radar technologies combined with magnetic resonance imaging (MRI), to gain complementary information, e.g. to accelerate cardiac MR imaging or to measure the electromagnetic wave propagation through heterogeneous, malignant and benign, biological tissue more accurately. We propose the multi-modal combination of MR and UWB-Radar for improved functional diagnosis and imaging.

Hans F. Wehrl¹, M S. Judenhofer¹, M Becker², G Reischl¹, H J. Machulla¹, C D. Claussen¹, B J. Pichler¹

¹University of Tuebingen, Tuebingen, Germany; ²Bruker BioSpin MRI GmbH, Ettlingen, Germany

The combination of PET and MRI for simultaneous imaging paves the way for dual functional imaging. A small animal PET/MR system operating inside a 7 Tesla MR scanner is presented. An evaluation of the performance of a combined PET/MR system is given. In vivo studies in oncology, cardiology and brain perfusion have been performed in mouse models. In contrast to PET/CT the data from an integrated PET/MR system can be acquired simultaneously and thus, they can be temporally matched.

Geron Andre Bindseil¹, William Bradfield Handler¹, Timothy James Scholl¹, Kyle Michael Gilbert¹, Hao Peng², Blaine Alexander Chronik¹

¹University of Western Ontario, London, Canada; ²Stanford University, Stanford, USA

There is great interest in combining anatomical and functional imaging systems. Current approaches to PET/MRI either change PET to make it compatible with conventional MRI or change MRI to make it compatible with conventional PET. An approach of the latter kind is investigated and the design of a PET/Field-cycled MRI (FCMRI) system using the Siemens Inveon small-animal PET is proposed. Advantages of PET/FCMRI over other PET/MRI approaches for small-animal preclinical imaging are explored.

Dan Green¹, Simon Pittard¹, Michael Poole², Richard William Bowtell², Rob C. Hawkes³, Alun J. Lucas³, T Adrian Carpenter³

¹Varian, Inc., Yarnton, UK; ²University of Nottingham, Nottingham, UK; ³University of Cambridge, Cambridge, UK

One approach to simultaneous PET-MR is to place a PET ring in the gap of a split imaging magnet. In order to minimize interference between the MR and PET detection the gradient coils must also be split whilst retaining access to the imaging region. Here an Inverse Boundary Element Method (IBEM) is used to design actively-shielded cylindrical gradients with substantial central gaps. A full three-axis set has been designed, built and tested.