Chris A. Cocosco¹, Daniel Gallichan¹, Andrew J. Dewdney², Gerrit Schultz¹, Anna M. Welz¹, Walter R.T. Witschey¹, Hans Weber¹, Juergen Hennig¹, and Maxim Zaitsev^1
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg (i.Br.), B.W., Germany, ²Siemens Healthcare Imaging, Erlangen, Germany

We report on the first in-vivo results with a prototype PatLoc gradient insert coil designed for human head imaging on a clinical 3T scanner. We found imaging volunteers with this PatLoc non-linear spatial encoding system to be safe, feasible, and to deliver locally improved image resolution. We also report on new evaluation measurements regarding the safety of this insert coil for human head imaging, including the simultaneous use of four in-plane gradient encoding fields, which is the object of current investigation.

Seung-Kyun Lee¹, Lorne Hofstetter¹, and Ileana Hancu^1
1GE Global Research, Niskayuna, NY, United States

We show that bilateral breast shimming can be significantly improved by employing local shim coils. A pair of Helmholtz-like coils compensate for the left-right B0 field difference, on the order of 100 Hz, caused by the inherently asymmetric positioning of heart and lungs.

Christoph Juchem¹, Terence W Nixon¹, Scott McIntyre¹, Vincent O Boer², Douglas L Rothman¹, and Robin A de Graaf^1
1MR Research Center, Yale University, New Haven, CT, United States, ²Department of Radiology, UMC, Utrecht, Netherlands

A novel technique for the magnetic field homogenization of the human brain is presented in which shim fields are synthesized by a combination of non-orthogonal basis fields from a set of individually driven, generic coils. First experimental results of dynamic multi-coil (DMC) shimming at 7 Tesla are shown to outperform state-of-the-art zero-to-third order spherical harmonic dynamic shim updating (SH-DSU)

Jason Peter Stockmann¹, Gigi Galiana², Leo Tam¹, Terry Nixon³, and Robert Todd Constable^1,2
1Biomedical Engineering, Yale University, New Haven, CT, United States, ²Diagnostic Radiology, Yale University, New Haven, CT, United States, ³Diagnostic Radiology, Yale University, New Have, CT, United States

We show the first single-channel, axial-plane O-Space images made using a custom, actively-shielded 12-cm Z2 quadratic gradient insert on a Siemens 3T human scanner. Gradient calibration via field mapping is described. Eddy currents are measured using two different methods and are found in each case to be negligible. Image reconstruction is performed using the entire encoding matrix with the Kaczmarz algorithm (also known as the algebraic reconstruction technique). As compared with images acquired using radial k-space trajectories, O-Space images show comparable resolution but reduced artifact levels owing to the less coherent point spread function of the quadratic field's curvilinear frequency isocontours.

Saikat Sengupta^1,2, Malcolm Avison^2,3, John Gore^2,3, and Edward Brian Welch^2,3
1Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, United States, ²Vanderbilt University Institute of Imaging Science, Nashville, United States,³Radiology and Radiological Sciences, Vanderbilt University, Nashville, United States

We present advances in a prospective software compensation method of higher order shim induced eddy currents in multislice Dynamic Bo Shimming (DS). The method based on steady state generation of eddy fields requires no hardware eddy current compensation, subject specific prescanning or shim shielding. Results of application to 2nd and 3rd order DS in single shot EPI are presented demonstrating correction of distortions, ghosting and signal loss. The model of correction is modified to include static interaction between shims and invariability with time between shim switches is demonstrated.

Johanna Vannesjö¹, Ariane Fillmer¹, Christoph Barmet¹, Peter Boesiger¹, Anke Henning¹, and Klaas Paul Pruessmann^1
1Institute for Biomedical Technology, University and ETH Zurich, Zurich, Switzerland

With the use of dynamic shimming higher demands are put on shim systems, regarding switching speed and dynamic characteristics. This calls for a fast and reliable method to comprehensively characterize the dynamic properties of the shims. Here we have investigated the use of shim impulse response functions (SIRF), as probed with a suitable set of input pulses and measurements of the field responses with a dynamic field camera. It was shown that the SIRF measurements could reveal different dynamic features of the shims, which may prove useful for system diagnostics and pre-emphasis setting.

Michael Stephen Poole¹, Hector Sanchez Lopez¹, Shin-ichi Urayama², Hitohsi Kitaguchi³, Osamu Ozaki⁴, and Stuart Crozier^1
1ITEE, University of Queensland, Brisbane, QLD, Australia, ²Human Brain Research Center, Kyoto University Graduate School of Medicine, Kyoto, Japan, ³National Institute for Materials Science, Tsukuba, Japan, ⁴Kobe Steel Ltd., Kobe, Japan

A new method is presented for simulating the eddy currents induced in magnet cryostat structures by switching gradient coils. Multiple thick cryostat layers are modelled accurately using the network method. Fourier decomposed basis-functions in z and  allow the 3D simulation of eddy currents from X, Y, Z or any other coils. Simulations are applied to the cryostat of a HTS magnet currently under construction.

Leo K Tam¹, Jason P Stockmann¹, Gigi Galiana², and Robert Todd Constable^1
1Biomedical Engineering, Yale University, New Haven, Connecticut, United States, ²Diagnostic Radiology & Neurosurgery, Yale University, New Haven, Connecticut

Previous research has demonstrated the utility of non-linear magnetic gradients such as the Z2 or C2 and S2 spherical harmonics for highly accelerated parallel imaging. In the present work, a systematic study of gradients shapes that are used in higher order gradients is performed via the Null Space Imaging (NSI) method, a technique based on designing gradients complementary to receiver coils. All combinations of spherical harmonics through the fourth order and additional combinations such as ones focused on orthogonal gradients (eg. C2 and S2 together with linears) were considered, in total 21 combinations. Simulations demonstrate that an optimal second order gradient set is composed of linear gradients and the second order in-plane gradients (C2, S2, and Z2) for NSI imaging at fixed sampling bandwidth.

Alice Borceto¹, andrea Viale¹, Franco Bertora¹, Leonardo Bertora², and Richard Bowtell^3
1Robotics,Brain and Cognitive Science, Italian Institute of Technology, Genoa, GE, Italy, ²Paramed Medical system, Genoa, (GE), Italy, ³Sir Peter Mansfield Magnetic Resonace Center, University of Nottingham, Nottingham, United Kingdom

The performances of an unshielded gradient system can be heavily affected by the presence of an iron yoke, increasing the non-linearity and non-uniformity of the field in the region of interest. This departure from ideal performance causes image distortions. It is therefore important to study the interaction between unshielded gradient coils and the iron yoke. Here, three different techniques for modelling the effect of iron (mirror coils, boundary element method and full finite element simulation) are presented and the results compared. Among the three the boundary element method offers the best compromise between accuracy and calculation time.

Jesse Bellec¹, Chen-Yi Liu¹, Scott B King², and Christopher Paul Bidinosti^1,3
1Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba, Canada, ²MR Technology, NRC Institute for Biodiagnostics, Winnipeg, Manitoba, Canada, ³Physics, University of Winnipeg, Winnipeg, Manitoba, Canada

Transmit array spatial encoding (TRASE) [1] is a novel gradient-free imaging technique relying on Tx RF phase gradients to spatially encode the transverse magnetization. Ideal phase gradients have a strong-uniform magnitude and strong-linear phase gradient over a large volume. To optimize TRASE MRI, a target field approach has been used to determine current distributions that produce linear phase gradients and uniform magnitude, but over limited volumes. A horizontal-B0 z-phase gradient design resembles initial spiral birdcage designs, suggesting that the approach is suitable for TRASE optimization.