Applications of New Hardware Systems
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Monday 7 May 2012
Room 210-211  16:30 - 18:30 Moderators: Christoph Barmet, Paul R. Harvey

16:30 0142.   
Measurement and pre-emphasis of shim responses using frequency sweeps
Signe Johanna Vannesjo1, Benjamin Dietrich1, Christoph Barmet1, Bertram J Wilm1, David O Brunner1, and Klaas P Pruessmann1
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.

16:42 0143.   
Real-time shim compensation in the human breast
Vincent Oltman Boer1, Mariska P. Luttje1, Alex A. Bhogal1, Giel Mens2, Hans Hoogduin1, Peter R. Luijten1, and Dennis W.J. Klomp1
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.

16:54 0144.   Measurement of microscopic head motion during brain imaging
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 Zaitsev1
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.

17:06 0145.   
Reference Layer Artefact Subtraction (RLAS): A novel method of minimizing EEG artefacts during simultaneous fMRI.
Muhammad E.H. Chowdhury1, Karen J Mullinger1, and Richard W Bowtell1
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.

17:18 0146.   
Discrete RF Coil Components Introduce Significant Noise and Artifacts into PET Images in Combined PET-MRI Systems
Geron A. Bindseil1, William B. Handler1, and Blaine A. Chronik1,2
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.

17:30 0147.   MR-based Compensation of Respiratory Motion Artifacts of In-Vivo PET Images Acquired on a Simultaneous Whole-Body MR/PET System
Christian Würslin1, Holger Schmidt1,2, Petros Martirosian1, Lars Stegger3, and Nina Schwenzer1
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.

17:42 0148.   Integrated 7T MRI and SPECT Systems for Small-Animal Imaging
Mark Jason Hamamura1, Seunghoon Ha1, Werner W Roeck1, James Hugg2, Dirk Meier3, Bradley E Patt2, and Orhan Nalcioglu1,4
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.

17:54 0149.   
Hybrid magnetic resonance and ultrasound (MR-US) imaging as a novel method of High Intensity Focused Ultrasound treatment guidance and monitoring
Victoria Bull1, John Civale1, Ian Rivens1, David J Collins2, Gail ter Haar1, and Martin O Leach2
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.

18:06 0150.   
MRI with Sideband Excitation: Application to Continuous SWIFT
David O. Brunner1, Benjamin E. Dietrich1, Matteo Pavan1, and Klaas P. Pruessmann1
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.

18:18 0151.   
Bloch Simulation of Human MR Imaging at 14T
Zhipeng Cao1, Giuseppe Carluccio2, Joshua Park3, Sukhoon Oh4, Zhang-Hee Cho3, and Christopher M. Collins4
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.