ISMRM 23rd Annual Meeting & Exhibition • 30 May - 05 June 2015 • Toronto, Ontario, Canada

Scientific Session • System Monitoring & Correction

Tuesday 2 June 2015

Room 718 A

16:00 - 18:00


Seung-Kyun Lee, Ph.D., Maxim Zaitsev, Ph.D.

16:00 0489.   Motion-insensitive sequence for single-voxel determination of B1+ by Bloch-Siegert shift in moving organs including the human heart
Ayse Sila Dokumaci1, Bertrand Pouymayou1, Roland Kreis1, and Chris Boesch1
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.

16:12 0490.   Large Dynamic Range Relative B1+ Mapping
Francesco Padormo1, Aaron T. Hess2, Paul Aljabar1, Peter Jezzard3, Matthew D. Robson2, Joseph V. Hajnal1,4, and Peter J. Koopmans3
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.

16:24 0491.   
Rapid MRI System Calibration using 3DREAM
Daniel Brenner1, Rüdiger Stirnberg1, Eberhard Daniel Pracht1, and Tony Stöcker1,2
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.

16:36 0492.   Validation of Variable Flip Angle Imaging-Based Simultaneous B1+ and T1 Mapping in the Prostate at 3T
Novena A Rangwala1, Isabel M Dregely1, Holden H Wu1, and Kyunghyun Sung1
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.

16:48 0493.   Direct calculation of B1+ and B1- from two point variable flip angle data for quantitative T1 and PD mapping
Simon Baudrexel1,2, Ulrike Noeth2, Sarah Reitz1,2, Johannes Christian Klein1,2, and Ralf Deichmann2
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%.

17:00 0494.   B0 changes around the head induced by the cardiac cycle at 7T
Lennart J. Geurts1, Vincent O. Boer2, Tijl A. van der Velden2, Peter R. Luijten2, Dennis W.J. Klomp2, and Jaco J.M. Zwanenburg2
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.

17:12 0495.   
Investigating the potential of highly accelerated FatNavs for dynamic shimming
Frédéric Gretsch1, José P Marques2, Rolf Gruetter1,3, and Daniel Gallichan1
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.

17:24 0496.   Automatic Virtual Shimming for Robust Fat Suppression in Subtractionless First-Pass Peripheral Angiography
Holger Eggers1 and Tim Leiner2
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.

17:36 0497.   Fast B1 inhomogeneity correction in bSSFP imaging using transient-state signal
Min-Oh Kim1 and Dong-Hyun Kim1
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.

17:48 0498.   Respiration Induced B0 Variation in Double Echo Steady State Imaging (DESS) in the Breast
Catherine J Moran1, Kristin L Granlund1, Bragi Sveinsson1,2, Marcus T Alley1, Bruce L. Daniel1, and Brian A Hargreaves1
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.