|Beyond Components: Subsystems & Hybrids|
The Equivalent Magnetizing Current (EMC) Method for
Biplanar Active and Passive Shim Design
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.
Optimized Longitudinal and Transverse Gradient Coils
with Up to Seven Imaging Regions
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.
Azimuthally Symmetric IBEM Gradient and
Shim Coil Design
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.
Asymmetric Head Gradient Coil for Imaging and
Spectroscopy at 7T
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.
Epoxy Parameters for High Partial Discharge
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.
Experiments in Real-Time MRI with RT-Hawk and Medusa
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.
|Evaluation of a Combined Magnetic
Resonance (MR)/ultra-Wideband (UWB)-Radar Technique
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.
Performance and in Vivo Applications of Simultaneous
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.
Design of a Combined PET and Field-Cycled MRI System
for Small Animal Imaging
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.
Split Cylindrical Gradient Coil for Combined PET-MR
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.