Novel & Early High Field Human Imaging

Friday 16 May 2014

Yuehui Tao¹, Aaron T. Hess¹, Graeme A. Keith¹, Christopher T. Rodgers¹, Alexander Liu¹, Jane M. Francis¹, Stefan Neubauer¹, and Matthew D. Robson^1
1University of Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, Oxford, United Kingdom

First-pass myocardial perfusion imaging is used clinically but would benefit from improvements, which might be expected at 7T due to higher SNR and longer T1. But major implementation challenges at 7T are found owing to the large B0&B1 variations across the heart, low peak B1, and SAR restrictions that make uniform saturation extremely difficult to achieve. We propose a train of four HS8 pulses for saturation in first-pass myocardial perfusion imaging at 7T, and compare it with previously proposed solutions in simulation and in-vivo experiments. We also present the first series of human first-pass myocardial perfusion images at 7T.

Sebastian Schmitter¹, Susanne Schnell², Kamil Ugurbil¹, Michael Markl², and Pierre-Francois van de Moortele^1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, ²Department of Radiology, Northwestern University, Chicago, IL, United States

There is growing interest in using time-resolved 3D phase-contrast MRI with three-directional velocity encoding (4D flow MRI) for the assessment of aortic hemodynamics. Previous studies investigating intracranial 3D blood flow have shown that 4D flow MRI directly benefits from ultra-high fields (i.e.≥7T). However, at 7T short RF wavelength can result in areas void of transmit B1 (B1+), especially in the torso, requiring multi-channel B1+ methods. Here, we demonstrate successful 4D flow imaging in the entire thoracic aorta at 7T. Two critical methodological components are investigated: 1) dynamically applied multiple B1+ shim settings through the acquisition and 2) kt-Grappa acceleration.

Stephan Gruber¹, Lenka Minarikova¹, Katja Pinker-Domenig², Olgica Zaric¹, Marek Chmelik¹, Thomas Helbich², Pascal Baltzer², Roland Boubela¹, Wolfgang Bogner¹, and Siegfried Trattnig^1
1High Field MR Centre, Medical University of Vienna, Vienna, Austria, ²Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria

Dynamic contrast-enhanced MRI is an important tool for detection and characterization of breast lesions. With the availability of high field systems for clinical routine (3T) and research (7T) increased SNR and spatial resolution may improve diagnostic accuracy for breast MRI. To test the feasibility of breast MRI at 3T and 7T specificity, sensitivity and SNR were calculated in 24 patients. In addition B1-maps were measured at 3T and 7T in five healthy subjects.

Katharina Fuchs¹, Jan Rieger^1,2, Andreas Graessl¹, and Thoralf Niendorf^1,3
1Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany, ²MRI.TOOLS GmbH, Berlin, Germany,³Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max-Delbrueck Center, Berlin, Germany

Diffusion-weighted imaging (DWI) of the orbit is an emerging MRI application to provide guidance during diagnostic assessment and treatment of ophthalmological diseases. The standard approach for DWI is EPI. EPI is prone to severe geometric distortions, especially at high and ultrahigh magnetic fields. Realizing these constraints and the potential of ocular DWI, this work uses diffusion sensitized multi-shot RARE for ophthalmic MRI. This technique affords distortion free diffusion weighted images of the orbit, which is demonstrated in in-vivo images in healthy volunteers.

Xiufeng Li¹, Dingxin Wang², Steen Moeller¹, Kamil Ugurbil¹, and Gregory J Metzger^1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, ²Siemens Medical Solutions USA Inc, Minneapolis, MN, United States

Due to various challenges, there exist only few arterial spin labeling imaging studies at 7T, and most mainly focused on superior brain region. Recently, Multi-Band (MB) imaging, as a novel method reducing MRI time with increased spatial or temporal resolution, was applied at 3T using FAIR. Here, the feasibility of applying MB EPI pCASL for whole brain perfusion imaging at 7T has been explored and demonstrated with passive B1 and 3rd B0 shimming optimization, showing that up to 10 times acceleration can be achieved for MB EPI in pCASL imaging with acceptable data quality for assessing perfusion.

Eberhard Daniel Pracht¹, Daniel Brenner¹, Alard Roebroeck², and Tony Stöcker^1
1German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany, ²Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Netherlands

Gray matter imaging is an important technique for cortical lesion detection in neurological disorders, such as epilepsy and Alzheimer's. It is increasingly performed utilizing the DIR sequence. The aim of this project was to optimize the DIR Turbo-Spin-Echo (TSE) sequence for ultra-high field application to benefit from the overall SNR gain at high field. Therefore typical high field issues such as B0 /B1 inhomogeneities and SAR limitations had to be addressed. Furthermore an efficient fat suppression technique had to be implemented to enhance image quality significantly.

Lirong Yan¹, Xinyuan Miao², Rui Wang², Robert Smith¹, Songlin Yu¹, Hee Kwon Song³, Yan Zhuo², and Danny JJ Wang^1
1University of California Los Angeles, Los Angeles, CA, United States, ²Institute of Biophysics, Chinese Academy of Sciences, Beijing, China, ³University of Pennsylvania, Philadelphia, United States

In this study, a fast non-contrast enhanced time-resolved 4-D dynamic MRA (dMRA) using 3D stack of stars golden angle acquisition was developed for 7T. Compared to the standard Cartesian-based non-contrast dMRA, the golden angle radial-based dMRA provides the advantages of shorter scan time (less than half of the scan time) and improved delineation of distal arteries. Preliminary data on an arterio-venous malformation shows the potential clinical utility of this radial-based dMRA technique at 7T.

Kejia Cai^1,2, Hari Hariharan¹, Anup Singh¹, Mohammad Haris^1,3, Kevin D'Aquilla¹, Ravi Prakash Reddy Nanga¹, Feliks Kogan¹, and Ravinder Reddy^1
1Radiology, University of Pennsylvania, Philadelphia, PA, United States, ²CMRR 3T Research Program, Radiology, University of Illinois at Chicago, Illinois, IL, United States, ³Sidra Medical and Research Center, Doha, Qatar, United States

Glutamate (Glu) is the primary neurotransmitter responsible for excitatory synaptic transmission in the central nervous system. Excessive Glu in the synaptic space can trigger a toxic cascade leading to neuronal death, which has been implicated in a wide range of neurological and psychiatric disorders. GluCEST, an imaging technique that utilizes the chemical exchange saturation effect of Glu has been exploited for mapping single-slice Glu in brain and spinal cord at the ultra-high field 7T. However, 3D GluCEST mapping may be necessary to localize Glu abnormalities in a large brain volume. The purpose of this study is to extend the 2D GluCEST for 3D imaging. A turbo acquisition method has been investigated and optimized for scan time efficiency.

Rafael O'Halloran¹, Eric Aboussouan¹, Murat Aksoy¹, Eric Peterson¹, and Roland Bammer^1
1Radiology, Stanford University, Stanford, CA, United States

Diffusion-weighted MRI at 7T using conventional techniques is challenging due to short T2 relaxation times, high SAR, and increased susceptibility artifacts compared to lower field strengths. The diffusion-weighted steady state free precession sequence (DW-SSFP) appears well-suited as a means to address these challenges at 7T due to decreases T2-sensitivity, lower SAR burden, and potentially lower sensitivity to susceptibility artifacts as compared to spin-echo-prepared, diffusion-weighted EPI. In this work we compare EPI images acquired at 3T to DW-SSFP images acquired at 3T and 7T in 2 healthy human subjects.

An T. Vu¹, Edward Auerbach¹, Christophe Lenglet¹, Steen Moeller¹, Julien Sein¹, Pierre-Francois Van de Moortele¹, Kamil Ugurbil¹, and Essa Yacoub^1
1University of Minnesota, CMRR, Minneapolis, MN, United States

Mapping the structural connectivity in healthy adults for the Human Connectome Project requires high quality, high resolution, multiband (MB)-accelerated whole brain diffusion MRI (dMRI). Higher fields provide higher SNR and the opportunity to acquire at higher resolution, but at the cost of increased B1+ inhomogeneity (resulting in signal loss in regions such as the cerebellum and temporal lobe) and SAR (limiting our ability reduce TR or accelerate). This abstract describes the steps we have taken to facilitate high resolution, whole brain dMRI at 7T, enabling cortical layer specific anisotropy and FA previously only seen in ex-vivo human studies.