Signe Johanna Vannesjo¹, Benjamin Dietrich¹, Christoph Barmet¹, Bertram J Wilm¹, David O Brunner¹, and Klaas P Pruessmann^1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Dynamic use of higher-order shims to improve static B0, puts increasing demands on characterization of shim field dynamics and requires pre-emphasis implementations to counteract eddy current effects. Measurements of the shim impulse response function (SIRF), using a dynamic field camera, and rectangular test functions, have previously been shown to provide detailed information on shim responses. Here, frequency-sweeped test pulses are implemented for wide bandwidth coverage and increased sensitivity of the SIRF measurements. It is shown that SIRFs thus measured could form a basis for digital pre-emphasis, enabling a flat frequency response and fast shim settling after a switching event.

Vincent Oltman Boer¹, Mariska P. Luttje¹, Alex A. Bhogal¹, Giel Mens², Hans Hoogduin¹, Peter R. Luijten¹, and Dennis W.J. Klomp^1
1Radiology, UMC Utrecht, Utrecht, Utrecht, Netherlands, ²Philips Medical Solutions, Best, Netherlands

Real-time control of the shim fields will allow for compensation of B₀ field variations in the human body caused by breathing, cardiac pulsation, non-voluntarily motion, scanner drift etc. In this work the feasibility of real-time measurement and updating of the shim fields is examined and applied to real-time measurement and correction of the B₀ field in the human breast at 7T.

Julian Maclaren¹, Brian S. Armstrong², Robb T. Barrows², K. A. Danishad³, Thomas Ernst⁴, Colin L. Foster², Kazim Gumus⁴, Michael Herbst¹, Ilja Y. Kadashevich³, Todd P. Kusik², Qiaotian Li², Cris Lovell-Smith¹, Tom Prieto⁵, Peter Schulze³, Oliver Speck³, Daniel Stucht³, and Maxim Zaitsev^1
1Dept. of Radiology, University Medical Center, Freiburg, Germany, ²Electrical Engineering, University of Wisconsin-Milwaukee, ³Biomedical Magnetic Resonance, Otto-von-Guericke University, Magdeburg, ⁴Dept. of Medicine, University of Hawaii, ⁵Dept. of Neurology, Medical College of Wisconsin

This work describes the design, construction and testing of an MR-compatible in-bore camera capable of measuring head motion with a precision of around 10 micrometres. The system is used to quantify cardiac and breathing-related head motion in normal subjects during simultaneous MR imaging.

Muhammad E.H. Chowdhury¹, Karen J Mullinger¹, and Richard W Bowtell^1
1SPMMRC, School of Physics and Astronomy, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

Large artefacts due to switched gradients, cardiac pulsation and head movement compromise EEG data quality during simultaneous EEG-fMRI. Artefacts are often corrected using average artefact subtraction (AAS), but small movements significantly hinder the performance of AAS. Here we attenuate the artefacts by subtracting the signal from a reference layer, which has a similar conductivity to tissue and carries a set of electrodes and leads that precisely overlay those attached to the scalp. In experiments on a phantom and human subject undergoing small movements, we demonstrate that Reference Layer Artefact Subtraction (RLAS) outperforms AAS in reduction of gradient and movement artefacts.

Geron A. Bindseil¹, William B. Handler¹, and Blaine A. Chronik^1,2
1Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada, ²Robarts Research Institute, University of Western Ontario, London, Ontario, Canada

In simultaneous PET-MRI, the RF coil is located within the PET ring. Many RF coils consist of a symmetrical arrangement of discrete highly attenuating components: solder and capacitors. The authors investigated the effect of a birdcage RF coil on PET image artifacts and noise through a comprehensive Monte Carlo simulation utilizing the commercial reconstruction software of the small-animal system modeled. Attenuation-corrected PET images from simulations with and without an RF coil were compared. The RF coil case had 40% higher scatter fraction, 25% higher noise and artifacts. RF coils having discrete components in the PET FOV should be designed carefully.

Christian Würslin¹, Holger Schmidt^1,2, Petros Martirosian¹, Lars Stegger³, and Nina Schwenzer^1
1Dept. of Diagnostic and Interventional Radiology, University Hospital Tübingen, D-72076 Tübingen, Germany, ²Department of Preclinical Imaging and Radiopharmacy, University Hospital Tübingen, Tübingen, Germany, ³Clinic und Polyclinic of Nuklear Medicine, University Hospital Münster, Münster, Germany

To compensate for respiratory motion artefacts in PET images while maintaining full SNR using simultaneously acquired MR images. Three patients underwent simultaneous thoracic/abdominal PET/MR examination. PET data were acquired in listmode. Simultaneous MR acquisition yielded navigator data and 2D-multislice data (each slice acquired 12x). Slices were sorted into consistent blocks of anatomic information at different respiratory states. Blocks were co-registered using non-rigid registration yielding respiration-induced tissue deformation fields. PET data were gated and reconstructed. Then, PET images were aligned using the deformation fields and summed up to obtain the final images. Corrected PET images showed sharper edges at similar SNR.

Mark Jason Hamamura¹, Seunghoon Ha¹, Werner W Roeck¹, James Hugg², Dirk Meier³, Bradley E Patt², and Orhan Nalcioglu^1,4
1Tu & Yuen Center for Functional Onco-Imaging, University of California, Irvine, CA, United States, ²Gamma Medica, Inc., Northridge, CA, United States,³Gamma Medica, Inc., Fornebu, Norway, ⁴Department of Cogno-Mechatronics Engineering, Pusan National University, Pusan, Korea, Republic of

The integration of small-bore MRI and SPECT systems for back-to-back multimodality imaging has previously been limited to magnetic field strengths of only 0.1 T. Through the use of CZT-based nuclear radiation detectors, we have integrated SPECT with a 7 T MRI system for small-animal imaging. Co-registered MR and SPECT images of a mouse injected with ^99mTc were acquired using this combined system.

Victoria Bull¹, John Civale¹, Ian Rivens¹, David J Collins², Gail ter Haar¹, and Martin O Leach^2
1Department of Radiotherapy and Imaging, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Sutton, Surrey, United Kingdom, ²CR-UK and EPSRC Cancer Imaging Centre, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Sutton, Surrey, United Kingdom

Although MRI is considered the gold standard for HIFU treatment guidance, it lacks the ability to interrogate blood flow and monitor cavitation during treatments. A hybrid MR-ultrasound (MR-US) imaging system has shown promise as an improved technique, allowing real-time Doppler ultrasound and B-mode cavitation detection to be performed simultaneously with MR thermometry. A comparative study of truly simultaneous MR-US thermometry has also been conducted, showing good correlation between measurements of temperature change. The appearance of cavitation correlated with fluctuations in MR thermometry, and colour Doppler added dynamic information to MR angiographs. This system is a strong candidate for clinical use.

David O. Brunner¹, Benjamin E. Dietrich¹, Matteo Pavan¹, and Klaas P. Pruessmann^1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Zurich, Switzerland

Concurrent RF transmission and reception would be beneficial for many applications in NMR such as imaging of short T₂-samples. Since the isolation achieved by decoupling of transmit and receive paths is typically not sufficient neither robust, the sideband excitation approach is applied to isolate the excitation pulse from the retrieved data. In conjunction with a custom excitation chain and spectrometer, images have been acquired using the SWIFT sequence with continuous excitation and reception. RF transmitter infidelities are captured by a real-time monitoring of the RF chain allowing reconstructing the data on the excitation pulse as measured in the coil.

Zhipeng Cao¹, Giuseppe Carluccio², Joshua Park³, Sukhoon Oh⁴, Zhang-Hee Cho³, and Christopher M. Collins^4
1Bioengineering, Penn State University, Hershey, PA, United States, ²Electrical Engineering, The University of Illinois at Chicago, Chicago, IL, United States,³Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Korea, Republic of, ⁴Radiology, Penn State University, Hershey, PA, United States

The feasibility of human head imaging at 14T is explored using a Bloch-based MRI simulator that considers realistic B0, B1, and E1 distributions, including multiple transmit and receive channels. Field inhomogeneity, image SNR and SAR in the human head with and without RF shimming are examined at 3T, 7T, and 14T. The results showed a dramatic increase of image SNR from 3T to 14T, with a more subtle SAR increase, especially from 7T to 14T.