Ayse Sila Dokumaci¹, Bertrand Pouymayou¹, Roland Kreis¹, and Chris Boesch^1
1Depts. Radiology and Clinical Research, University Bern, Bern, Switzerland

The determination of B1+ in moving organs, in particular in the heart, is a largely unmet problem. Most B1+ mapping sequences are too long and/or cannot be acquired in a (double-) triggered mode. We developed and validated a single-voxel PRESS sequence based on the Bloch-Siegert shift which is largely immune against effects of motion and which can additionally be double-triggered. Measurements in vitro and in the human heart show an excellent performance of the sequence.

Francesco Padormo¹, Aaron T. Hess², Paul Aljabar¹, Peter Jezzard³, Matthew D. Robson², Joseph V. Hajnal^1,4, and Peter J. Koopmans^3
1Division of Imaging Sciences and Biomedical Engineering, King's College London, London, London, United Kingdom, ²Department of Cardiovascular Medicine, University of Oxford, Oxford, United Kingdom, ³FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom,⁴Centre for the Developing Brain, King's College London, London, United Kingdom

Relative B1+ mapping relies on the validity of the SPGR small flip angle approximation. This cannot be guaranteed in the presence of large B1+ dynamic range. Here we present an acquisition and reconstruction scheme which enables relative B1+ mapping in the presence of large dynamic range.

Daniel Brenner¹, Rüdiger Stirnberg¹, Eberhard Daniel Pracht¹, and Tony Stöcker^1,2
1German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany, ²Department of Physics and Astronomy, University of Bonn, Bonn, Germany

Ultra-fast 3DREAM B1 mapping provides a variety of different calibration information, such as B1 and B0 maps as well as an image suitable for normalization of the receive sensitivity. The DREAM FID images also allow direct coregistration to a brain atlas, which facilitates automatic extraction of regional calibration data. The method is well-suited for receive and transmit bias correction of arbitrary imaging data at high field, as demonstrated for MP-RAGE and 3D-EPI acquired at 7T.

Novena A Rangwala¹, Isabel M Dregely¹, Holden H Wu¹, and Kyunghyun Sung^1
1Department of Radiological Sciences, University of California Los Angeles, Los Angeles, CA, United States

Characterizing B1+ distributions accurately is essential in multiparametric quantitative MRI; however, B1+ measurement sequences are additional to quantitative protocols and increase scan duration. This study aimed to characterize the B1+ distribution in the pelvis using a recently proposed reference region variable flip angle (RR-VFA) imaging based technique and compare it with a conventionally available B1+ mapping sequence in the prostate of healthy volunteers. The proposed technique showed B1+ distributions consistent with the conventional B1+ measurement technique, eliminating the need for an additional scan for B1+ correction. Additionally T1 measurements after B1+ correction with the RR-VFA method had significantly lower standard deviations, indicating improved robustness after B1+ correction.

Simon Baudrexel^1,2, Ulrike Noeth², Sarah Reitz^1,2, Johannes Christian Klein^1,2, and Ralf Deichmann^2
1Department of Neurology, Goethe University Frankfurt, Frankfurt am Main, Germany, ²Brain Imaging Center (BIC), Goethe University Frankfurt, Frankfurt am Main, Germany

A technique for direct calculation of the transmitted radio frequency (RF) field (B1⁺) and the receiver sensitivity profile (B1^-) is presented which is based on the acquisition of a standard spoiled gradient echo sequence using two different flip angles (i.e. the variable flip angle method, VFA) without requiring any further measurements. In a sample of 12 healthy subjects, B1⁺ and B1^- maps obtained with the new method were compared with respective maps based on existing techniques, yielding very good agreement throughout the brain with an average absolute deviation of 3%.

Lennart J. Geurts¹, Vincent O. Boer², Tijl A. van der Velden², Peter R. Luijten², Dennis W.J. Klomp², and Jaco J.M. Zwanenburg^2
1Radiology, UMC Utrecht, Utrecht, Utrecht, Netherlands, ²Radiology, UMC Utrecht, Utrecht, Netherlands

This study assessed B0 fluctuations caused by the cardiac cycle using fieldprobes positioned around the headrest in a 7T MRI bore. Six volunteers were included and 2400 field measurements were taken at a 100ms interval. The maximum measured cardiac field fluctuation amplitude was 7.0 nT. On average the cardiac field fluctuation amplitude was 27% of the respiratory field fluctuation. Because fieldprobes were used, there was no confounding influence of pulsatile tissue motion. We conclude that cardiac field fluctuations can be a measurable contributor to B0 instability.

Frédéric Gretsch¹, José P Marques², Rolf Gruetter^1,3, and Daniel Gallichan^1
1CIBM, EPFL, Lausanne, Vaud, Switzerland, ²Dept. of Radiology, University of Lausanne, Vaud, Switzerland, ³Depts. of Radiology, Universities of Lausanne and Geneva, Vaud, Switzerland

We recently showed that fat navigators (FatNavs) can be used for motion correction of head scans, exploiting the natural sparsity of the fat image to allow higher acceleration factors than water images. In this work we investigate the potential of using a dual-echo FatNav to also estimate dynamic changes in the B0-field due to respiration – with the aim of applying the FatNavs to also allow dynamic shimming. Our initial tests indicate that the fat image is suitable for tracking respiration-induced B0 changes – and can do so even at acceleration factors up to 6x9 for the FatNav.

Holger Eggers¹ and Tim Leiner^2
1Philips Research, Hamburg, Germany, ²Department of Radiology, University Medical Center Utrecht, Utrecht, Netherlands

To apply Dixon methods for background suppression in first-pass peripheral angiography, the water-fat separation has to be highly reliable over large field of views. This is difficult to achieve in the lower legs, because large main magnetic field offsets and gradients occassionally arise from poor resonance frequency determination or shimming. An approach based on virtual shimming is proposed in the present work to automatically compensate for such offsets and gradients. It is shown to improve the robustness of the fat suppression in subtractionless first-pass peripheral angiography in demanding cases.

Min-Oh Kim¹ and Dong-Hyun Kim^1
1Electrical and electronic engineering, Yonsei University, Seoul, Seoul, Korea

B1+ inhomogeneity induces different signal modulations spatially, therefore, it needs to be corrected to make the acquired images more reliable. Here, an extremely fast B1 mapping method is proposed to correct B1 inhomogeneity induced image modulation in bSSFP imaging using early transient-state signal.

Catherine J Moran¹, Kristin L Granlund¹, Bragi Sveinsson^1,2, Marcus T Alley¹, Bruce L. Daniel¹, and Brian A Hargreaves^1
1Radiology, Stanford University, Stanford, CA, United States, ²Electrical Engineering, Stanford University, Stanford, CA, United States

The Double Echo Steady State (DESS) sequence has been shown to provide diffusion weighted breast images without the severe distortion of EPI DWI. However, DESS images in the breast demonstrate prominent ghosting artifacts, which, in the low SNR second echo can compromise image quality. We investigated respiration induced B0 in the breasts as the source of this artifact and present initial results of correction of the artifact using a DC navigator.