Hall D Tuesday 13:30-15:30
Anders Niemann1, Samuel Alberg Kock1, Steffen Ringgaard1, Ernst Torben Fründ2, Steffen Ellebæk Petersen, Michael Hasenkam1
1Aarhus University Hospital Skejby, Aarhus N, Denmark; 2Aalborg Hospital, Aarhus University Hospital , Aalborg, Denmark
To generate images suitable for segmentation to be used in CFD simulation of blood flow in fistulas two methods were examined and evaluated. The scans were performed on an in vitro phantom. A mean high steady flow was applied to the inlets of the phantom to simulate the chaotic and turbulent flow in fistulas. Bright blood yielded fast images with excellent image quality except in the fistula chamber, a location with severely turbulent and chaotic flow. Black blood, though slower, yielded excellent image quality everywhere, also in the fistula chamber.
913.
Evaluation of the Thoracic Aorta with Gated CE-MRA: Technical
Feasibility and Comparison with
Ungated Studies
Phillip Young1, Eric Williamson1, Maggie Fung2, David Stanley2, James Glockner1
1Mayo Clinic, Rochester, USA; 2GE Healthcare, Waukesha, Wisconsin, USA
Conventional CE-MRA of the thoracic aorta is limited by motion at the aortic root. We describe our experience with 2 and 4 phase gated CE-MRA sequences, with particular attention to improved visualization of the sinotubular junction, aortic arch vessels, and LCA. Our experience indicates technical feasibility, with markedly improved visualization of the aortic root and proximal coronary arteries resulting from the improved temporal resolution. Prolonged image acquisition and reconstruction times caused limitations in some patients. However, all gated CE-MRA sequences offered improved image quality when compared with prior ungated studies. Gated CE-MRA of the thoracic aorta is a promising technique.
914.
Real Time Self Tracking of Contrast Kinetics for Whole Heart Coronary
Artery Magnetic Resonance
Angiography
Himanshu V. Bhat1, Peng Lai1, Debiao Li1
1Northwestern University, Chicago, Illinois, USA
Contrast enhanced coronary artery magnetic resonance angiography at 3T with slow infusion of contrast agent has recently shown very promising results. In this work a new method for tracking the contrast enhancement during slow infusion of contrast agent is proposed and validated. This method is based on acquiring an extra projection of the heart during imaging and gives an accurate representation of the contrast enhancement. The method is embedded in the high resolution segmented IR-FLASH sequence and has a host of potential applications.
915. Intra-Thoracic Blood Volume Measurement by Contrast Magnetic Resonance Imaging
Massimo Mischi1, Harrie C. M. van den Bosch, Jacques A. den Boer, Jan Verwoerd, Rene` J. Grouls, Cathinka H. Peels, Hendricus H. Korsten
1Eindhoven University of Technology, Eindhoven, Netherlands
The intra-thoracic blood volume (ITBV) is related to the cardiac preload and the left ventricular function. A minimally invasive method for the ITBV measurement by contrast magnetic resonance imaging (MRI) is presented and validated in vitro. The clinical feasibility of the method is also shown. A bolus of a paramagnetic agent is intravenously injected and detected by MRI in the right and left ventricles. The analysis of the measured indicator dilution curves by suitable models, combined with the flow measurement by phase contrast angiography, permits the estimation of the ITBV. The results are accurate and motivate further investigations.
916. 7D Spiral Phase Contrast MRI for the Comprehensive Assessment of Aortic Flow in Mice
Robert L. Janiczek1, Brett R. Blackman1, R. Jack Roy1, Scott T. Acton1, Craig H. Meyer1, Frederick H. Epstein1
1University of Virginia, Charlottesville, Virginia , USA
The ability to assess wall shear stress (WSS) in genetically-engineered mice would enable the investigation of the roles of individual genes in the relationship between WSS and atherosclerosis. The ideal method would cover large regions of the vessel of interest, directly measure WSS, and have high temporal resolution. A 3D stack-of-spirals PC sequence was developed to acquire 7D data of the mouse aorta. High resolution geometry was obtained of the abdominal aorta along with all three-components of velocity throughout systole.
MRA: Continuous Table Movement
Hall D Tuesday 13:30-15:30
971.
Towards Automatic Patient Positioning and Scan Planning Using
Continuously Moving Table Imaging
Peter Koken1, Jochen Keupp1, Sebastian Peter Dries1, Daniel Bystrov1, Peter Börnert1
1Philips Research Europe, Hamburg, Germany
With the increasing number of MRI scan parameters, the operation of a clinical MRI system has become very complex. Improvements in the ease of use of are increasingly important. The idea of this feasibility study is to reduce the operator interaction needed to set up an examination to just selecting the anatomy to be studied by “pushing a single button”. While moving the patient into the MRI magnet, isotropic 3D continuously moving table (CMT) imaging is performed. In parallel, real-time image reconstruction and immediate organ identification is performed using fast image processing. Once the position and extent of the target organ is found, CMT scanning is terminated and the chosen anatomy is automatically positioned in the iso-center. The desired examinations can be started using the automatically derived geometry information without further operator’s interaction.
972.
Continuous Table Movement for Peripheral MRA with Matrix Coils at
3.0T - Comparison to Standard
Step-By-Step MRA
Harald Kramer1, Karin A. Herrmann1, Peter Schmitt2, Michael Zenge2, Christian Glaser1, Maximilian F. Reiser1
1University Hospitals Munich - Grosshadern Campus, Munich, Germany; 2Siemens Medical Solutions, Germany
Because of the well known advantages of magnetic resonance angiography (MRA) like the excellent soft tissue contrast, the lack of ionizing radiation and the possibility of non invasive dynamic imaging, this imaging method established a serious alternative to DSA and CTA. One drawback is the complexity of the exam and the sometimes challenging procedure. One chance to overcome this limitation is the implementation of continuous table movement MRA which shortens and simplifies the entire exam.
973.
Suppression of Image Artifacts Arising from Magnetic Field
Inhomogeneity in Continuous Moving
Table MRI
Yo Taniguchi1, Shinji Kurokawa1, Suguru Yokosawa1, Hisaaki Ochi1, Yoshitaka Bito1
1Hitachi, Ltd., Kokubunji, Japan
Image artifacts and distortions arising from magnetic field inhomogeneity in continuous moving table (CMT) MR images have been investigated using computer simulation. A reconstruction algorithm using phase correction has also been developed from the simulation results, and it was stable in the presence of field inhomogeneity. From the images obtained in phantom experiments it was confirmed that artifacts in the experimental results were similar to those in the simulation results. Furthermore, the artifacts in the images acquired in experiments using both phantoms and volunteers were successfully suppressed by the phase correction technique.
974.
Continuously Moving Table Peripheral CE-MRA (TimCT) on a 1.5 T
Wide-Bore System in an Obese
Population
Florian M. Vogt1, Michael O. Zenge2, Stephan Kannengiesser2, Joerg Barkhausen1, Mark E. Ladd1, Harald H. Quick1
1University Hospital, Essen, Germany; 2Siemens Medical Solutions, Erlangen, Germany
State-of-the-art cylindrical wide-bore MRI scanners provide improved patient comfort for claustrophobic and obese patients. Recently, data acquisition and reconstruction during continuous table movement (TimCT) has been introduced which features 3D coronal slab MRA with centric reordering and increased spatial resolution at the distal end of the large field-of-view. In this study, 5 healthy volunteers and 10 obese patients with known PAOD underwent TimCT CE-MRA. Although examination of the patients on a conventional scanner was impossible because of patient size, moving-table peripheral CE-MRA was successful in all subjects on the wide-bore system. Furthermore, the workflow introduced with TimCT simplified scan planning.
Rita Gouveia Nunes1, Joseph V. Hajnal1, Philip G. Batchelor2, David Atkinson3, David J. Larkman1
1Hammersmith Hospital, Imperial College London, London, UK; 2King's College London, London, UK; 3University College London, London, UK
Continuously moving table approaches allow more efficient acquisition of extended field-of-view images. Unfortunately, as the subject moves through the magnet bore, errors due to imperfections in the B0, gradient and RF fields accumulate leading to severe artefacts. Conventionally, to limit these artefacts, only linear sampling schemes are used and the thickness of the excitation slab reduced. We introduce a generalised method which allows for knowledge of such imperfections to be incorporated into the reconstruction leading to accurate images regardless of the chosen k-space sampling scheme. This flexibility is essential in order to simultaneously acquire multiple images with clinically relevant contrasts.
Hall D Tuesday 13:30-15:30
with T1 Mapping in a Murine Myocardial Infarction Model
Ben Waghorn1, 2, Tiffany Edwards2, Yuhui Yang2, Nathan Yanasak2, Tom Hu2
1Georgia Institute of Technology, Augusta, Georgia, USA; 2Medical College of Georgia, Augusta, Georgia, USA
There is a critical need for non-invasive monitoring of calcium homeostasis in viable myocardial tissue adjacent to necrotic myocardium after myocardial infarction. This study demonstrates that T1 mapping of murine cardiac Manganese-Enhanced MRI can be used to quantify the in-vivo manganese content. Furthermore, the application of this T1 mapping protocol to a myocardial infarction model demonstrates the sensitivity of the technique to delineate regions of the heart with abnormal Mn uptake. This information can potentially be used to estimate salvageable myocardium in a pre-clinical myocardial infarction mouse model.
1021. Optimization of 3-D Tag Sequence and OFM Using a Synthetic Tag Model
Chun Xu1, James J. Pilla1, Gamaliel Isaac2, Aaron Blom1, Joseph H. Gorman1, Robert C. Gorman1, Lawrence Dougherty2
1University of Pennsylvania, Glennolden, Pennsylvania, USA; 2University of Pennsylvania, Philadelphia, Pennsylvania, USA
The aim of this study is to present a novel method of estimating high-resolution 3-D myocardial motion using 3-D tags combined with optical flow method (OFM utilizing a simulation model. A synthetic 3-D tagged cardiac volume was constructed, and deformed by a known systolic flow fields. Prior to phase-to phase pixel displacement estimation, cross correlation coefficient (CC) between the known and estimated flow fields was maximized by adjusting the tag and OFM parameters. This study demonstrates that optimized 3-D OFM combined with 3-D tag sequence has the potential to generate in-vivo myocardial displacement rapidly and accurately.
1022.
Noninvasive Visualization of Myocardial Inflammation Using
Magnetofluorescent Nanoparticle-Contrasted
MRI in Rat Autoimmune Myocarditis
Cheongsoo Park1, Eun Jeong Ahn2, Hyo Eun Park1, Kyuhong Lee1, Tae-Jong Yoon3, Ki-Bae Seung2, Chaejoon Cheong1, Ki Yuk Chang2, Kwan Soo Hong1
1Korea Basic Science Institute, Cheongwon, Republic of Korea; 2the Catholic University, Seoul, Republic of Korea; 3Massachusetts General Hospital, Boston, Massachusetts, USA
Myocarditis is defined as inflammation of the myocardium, mostly caused by viral infection, which leads to autoimmune activation against the host¡¯s own myocardial tissue. Endomyocardial biopsy is still considered to be the gold standard for diagnosing Myocarditis, however it is invasive and low sensitive because of sampling error and high inter-observer variability. Therefore, a novel diagnostic modality to detect the inflammation of myocardium through noninvasive means is needed. Here we investigated whether nanoparticle-contrasted cardiac MRI would be feasible and effective in detecting the status, and discriminating the grade of inflammation in a rat model of experimental autoimmune myocarditis (EAM).
1023.
Cardiac MRI @ 7 Tesla: Initial Experiments in Pigs
Harald H. Quick1, 2, Kai Nassenstein2, Frank Breuckmann2, Stefan Maderwald1, 2, Lena Schäfer2, Mark E. Ladd1, 2, Jörg Barkhausen2
1Erwin L. Hahn Institute for MRI, Essen, Germany; 2University Hospital Essen, Essen, Germany
Cardiac MRI at high field strengths potentially benefits from the increased signal-to-noise ratio (SNR) inherent to high-field MRI. In order to exploit the full SNR potential for cardiac MRI, a number of artifacts and imaging constraints related to the high field strength have to be overcome. The purpose of this study was to perform cardiac MRI in a pig model on a whole-body 7-Tesla MR scanner to evaluate potential advantages and disadvantages specifically associated with cardiac MR imaging at this high field strength.
1024. Cardiac Function in Post-Cardiac Arrest Mice by MRI and Effect of Nitrite Treatment
Stasia Ann Anderson1, Cameron Dezfulian1, Aleksey Alekseyenko1, Mark T. Gladwin1
1National Institutes of Health, Bethesda, Maryland, USA
We examined a mouse model of cardiac arrest by cardiovascular MRI and describe the features of post-arrest cardiac function and the effect of nitrite treatment. We hypothesized that systemic NO2 is depleted during global ischemia (cardiac arrest) and its early repletion could protect the heart from reperfusion injury. Cardiovascular MRI demonstrated the existence and extent of RV dysfunction in a mouse model of cardiac arrest. Systemic nitrite after global ischemia is associated with improved pulmonary blood flow, cardiac function, survival and neurological function in survivors. MRI outcomes indicate RV ejection fraction and contractility are improved by nitrite treatment.
1025. ECG-Gated Cardiac MRI in Mice on a Clinical 3.0T MR Scanner
Jie Huang1, Xiaohai Ma1, 2, Beihua Zhong1, Donna Wang1, Mark DeLano1
1Michigan State University, East Lansing, Michigan, USA; 2Beijing Anzhen Hospital, Beijing, People's Republic of China
Transgenic manipulations in mice are increasingly used to probe genetic and physiological aspects of human cardiovascular physiology. Cardiac MRI in humans is recognized as a robust and accurate method for in vivo assessment of cardiac morphology and function. However, due to the small size and fast rate, cardiac MRI in mice is usually performed on high-field animal scanners significantly limiting the opportunity for cardiac MRI research in mice. In this study we demonstrate the feasibility of performing cardiac MRI in mice with a clinical 3.0T system without the need for an amplifier to detect the R-wave for ECG-gating.
1026.
Cardiovascular Phenotyping of the Mouse Heart Using
4-Dimensional Radial Acquisition and
Liposomal Gd-DTPA
Elizabeth Kathleen Bucholz1, Ketan Ghaghada1, Yi Qi1, Srinivasan Mukundan1, G. Allan Johnson1
1Duke University, Durham, North Carolina, USA
We propose a method for high-throughput cardiovascular phenotyping of the mouse using a 4D radial MRI pulse sequence in conjunction with liposomal Gd-DTPA. To validate the usefulness of the technique, myocardial function was evaluated in a population of 12 mice: 4 C57BL/6J, 4 DBA/2J, and 4 DBA/2J CSQ+. Images were acquired at a resolution of 87x87x348 µm3, with a temporal resolution of 9.6 ms, and 10-12 phases of the heart cycle were captured with a total acquisition time of 16 minutes. Calculation of ejection fraction (EF), end diastolic volume (EDV), and end systolic volume (ESV) were determined to be statistically different for all three populations of mice.
Anna Naumova1, Sarah Fernandes1, 2, Vasily Yarnykh1, Veronica Muskheli1, 2, Chun Yuan1, Charles E. Murry1, 2
1University of Washington, Seattle, Washington, USA; 2Center for Cardiovascular Biology, Institute for Stem Cell and Regenerative Medicine, Seattle, Washington, USA
Cell transplantation using derivatives of embryonic stem cells (ESCs) is a promising therapeutic approach for heart failure. In real clinical practice, the patients with severe heart failure are most in need of cell transplantation therapy. This is the first study to explore restoration effects of hESC-cardiomyocyte transplantation on chronic myocardial infarction. We found that rat cardiac function was moderately improved in one month after cell transplantation into mature infarction. We assume that effect of human cardiomyocyte transplantation to chronic myocardial infarction will become more apparent during a long-term observation, when graft size would reach its functional capability.
1028. An Optical Fiber-Based Gating Device for Cardiac and Abdominal MRI of Small Animals
Adrian Rengle1, Loredana Baboi1, Hervé Saint-Jalmes2, 3, Raphaël Sablong1, Olivier Beuf1
1INSA-Lyon, Université Lyon 1, Villeurbanne, France; 2Faculté de Médecine, Université Rennes 1, Rennes, France; 3Centre Eugène Marquis, Rennes, France
An optical-based device designed to synchronize MRI acquisition on small animals was developed using a transmit-receive pair of optical fibers. Light from a laser diode was focused into the transmit fiber and impinged upon the moving skin. The reflected light was detected by the receive fiber and then carried to a light-voltage amplified photodiode. The output signal was interconnected with a commercial trigger unit. The optical-based signals recorded on mice were correlated with both respiratory and heart motions. Signal amplitudes were large enough to perform an easy adjustment of gating level with good differentiation between cardiac and respiratory signal. The signal was totally unaffected by radiofrequency pulses or currents induced by the magnetic field gradients switching used for imaging. This optical-based gating device was used successfully for dual cardiac and respiratory synchronization for heart and liver examinations of mice at 4.7T. The device developed using thin optical fibers is simple to use and well suitable for small animal MRI using high field strength narrow bore systems.
1029. Cine-MRI vs. 2D-Echocardiography to Measure Left Ventricular Function in Rat Heart in Vivo
Daniel J. Stuckey1, Carolyn A. Carr1, Damian J. Tyler1, Kieran Clarke1
1University of Oxford, Oxford, UK
Two dimensional echocardiography is the most commonly used method for studying cardiac morphology and function in small animals. We have compared 2D-echo with cine-MRI measurements of function in control and infarcted rat hearts and demonstrated strong correlations between the two modalities. However, cine-MRI had greater reproducibility and left ventricular ejection fractions were 12 „b 6% higher when measured using MRI. The accuracy of cine-MRI allows the identification of alterations in heart function that may be missed if using 2D-echo. Therefore, caution should be taken when comparing functional results acquired using short axis 2D-echo vs. cine-MRI.
Arunark Kolipaka1, Kiaran P. McGee1, Anthony J. Romano2, Kevin J. Glaser1, Philip A. Araoz1, Armando Manduca1, Richard L. Ehman1
1Mayo Clinic, Rochester, USA; 2Naval Research Laboratory, Washington, District Of Columbia, USA
Knowledge of the mechanical properties of the myocardium has the potential to provide clinically relevant data for diagnosing a variety of cardiac disease processes. MR elastography (MRE) is a phase-contrast MR-based method for spatially resolving shear stiffness. We propose a new MRE-based model for estimating shear stiffness in a spherical shell geometry using a model of shear wave propagation within a thin spherical shell. This study describes the analysis of MRE-derived estimates of shear modulus using this model in varying thickness shells. This model may find useful applications in the heart, eye and bladder.
Arunark Kolipaka1, Kiaran P. McGee1, Philip A. Araoz1, Richard L. Ehman1
1Mayo Clinic, Rochester, USA
It is appreciated that change to the mechanical properties of the myocardium are associated with a variety of cardiac disease processes. MR elastography (MRE) is a phase-contrast based MR technique capable of quantitating shear stiffness under static imaging conditions. This study describes the use of MRE to measure shear stiffness in a phantom undergoing dynamic volumetric changes. MRE derived measures of shear stiffness are compared to those derived from a pressure-volume derived method for calculating shear modulus of the left ventricle.
Hall D Tuesday 13:30-15:30
of Items/Devices Used in MR Environments
Gregor Schaefers1
1MR:comp GmbH, Gelsenkirchen, Germany
MR safety and image compatibility are internationally recognized as important issues for medical devices. Medical devices and items that can be exposed to an MR environment must be tested on magnetically induced forces, torques, RF heating, induction of voltages and safe functioning as well as MR image artifacts. First standardized test methods were already established. Further standard development is necessary in order to minimize patient risk and guiding device manufacturers in development of MR safe devices as well as supporting the MR user with meaningful experimental results.
1057. Material- And B0-Dependent Scaling of Torque Effects
Roger Luechinger1, Volkert A. Zeijlemaker2, Maarten van Bentem2, Firat Duru3, Peter Boesiger1
1Institute for Biomedical Engineering, University and ETH, Zurich, Switzerland; 2Medtronic Inc., Netherlands; 3University Hospital, Zurich, Switzerland
The scaling with the main magnetic field strength of torque effects on different materials (NdFeB magnet, nickel plate, and Dysprosium sulfate) and on a medical device (Reveal loop recorder) have been investigated. The measurements have been performed at 0.15T, 0.5T, 1T, 1.5T, 3T, and 7T. For ferromagnetic material maximal torque will not change, above its saturation point. Saturation will occur in most ferromagnetic materials in the range of 0.2-1T. Torque on magnets will increase linearly with the main magnetic field strength.
1058. Torque Measurements in MRI Safety Testing
Nikolaus M. Szeverenyi1, Mugdha Thakur2
1SUNY Upstate Medical University, Syracuse, New York, USA; 2Syracuse University, Syracuse, New York, USA
ASMT standard F2213-04 specifies how torque measurements are to be obtained in static magnetic fields using a torque balance, but there exists very little literature from investigators actually using such a device. Instead approximations involving rotation of the ferro-metallic sample on a plastic surface or other qualitative observations are usually employed. We describe the fabrication and use of several modified versions of the ASTM torque balance that will be appreciated by the MRI safety testing community. The origins of this force and its field dependence are also investigated.
1059.
An EEG System with Carbon Wire Electrodes and an
Anti-Polarization Circuit for Simultaneous
EEG-FMRI Recording
Michiro Negishi1, Ilan Laufer1, Mark Abildgaard1, Terry Nixon1, Robert Todd Constable1
1Yale University, New Haven, Connecticut, USA
Simultaneous EEG-fMRI (Electroencephalography-functional Magnetic Resonance Imaging) recording offers high temporal resolution electrophysiological recording and high spatial resolution hemodynamic recording from the same experimental runs. Carbon wire electrodes (not solid electrodes with carbon leads) are suitable for simultaneous EEG-fMRI recording because they cause less radio frequency heating and less susceptibility artifacts than metallic electrodes. However, carbon wire electrodes have not been used widely in human EEG because of the electrode polarization, or imbalance of DC potentials among electrodes. In this study, we developed and evaluated a prototype EEG system with carbon wire electrodes and a pre-amplifier equipped with an anti-polarization mechanism.
1060.
Safety of Localising Intracranial EEG Electrodes Using MRI: A
Comparison Between Head and
Body Coils at 3T
David William Carmichael1, John S. Thornton2, Philip J. Allen2, Louis Lemieux1
1UCL Institute of Neurology, London, UK; 2National Hospital for Neurology and Neurosurgery, London, UK
The safety of post-implantation localisation of intracranial EEG electrodes by MRI was investigated for body and head coils at 3T using a test object with a combination of electrodes simulating a clinical arrangement and a high SAR sequence. For head coil RF-transmission moderate heating was observed (<2ºC) under ‘standard’ conditions, with the external electrode leads (tails) separated, increasing with the tails in electrical contact. Conversely, for body coil RF–transmission, heating was markedly higher (+6.4ºC) with the tails separated. MRI with intracranial EEG electrodes at 3T can be safe, providing SAR is restricted and a head transmit coil is used.
1061.
Estimating Specific Absorption Rate (SAR) During MRI in the
Human Brain with Intracranial EEG
Electrodes Used for Epilepsy
Monitoring: A Preliminary Study Using Finite Integral Technique (FIT)
Modelling
David William Carmichael1, Yan Li2, Andrew McEvoy3, Jeff W. Hand2, 4, Louis Lemieux1
1UCL Institute of Neurology, London, UK; 2Imperial College, London, UK; 3National Hospital for Neurology and Neurosurgery, London, UK; 4Imperial College Healthcare NHS Trust, London, UK
A commercial EM solver was used to model the interaction between an MRI head coil and the human head with a subdural-grid implant used for epilepsy monitoring. The electric field was found to be focused around the implant, with much greater values than seen in the head without the implant. However, when SAR was averaged over both 1g and 10g masses the peak local SAR proximal to the implant increased but the position of maximum local SAR produced (in the sinus region away from the implant) was not altered.
1062. Heating Effects Measured in EEG Electrodes at 3T
Ruth L. O'Gorman1, 2, Laura A. Wherity3, Sophie F. Riches4, Owen G. O'Daly2, Dominic H. ffytche2
1King's College Hospital, London, UK; 2Institute of Psychiatry, London, UK; 3King's College Hospital, UK; 4Institute of Cancer Research, London, UK
The simultaneous acquisition of EEG and fMRI data provides a unique opportunity for investigating cerebral function at high spatial and temporal resolution, but simultaneous EEG-MRI raises several patient safety issues. This study investigated the heating effects from several MRI pulse sequences in EEG electrodes placed in a variety of locations and orientations. A maximum temperature rise of 1.44 ºC was recorded, but the time course of the temperature measurements suggests that greater temperature rises may be likely if high-SAR sequences are applied consecutively. In addition, a large variation in recorded temperature change was observed across different electrode positions and orientations.
1063. Improved RF Safety of Interventional Devices Using Cable Traps
Krishna N. Kurpad1, Erik T. Bieging1, Orhan Unal1, 2
1University of Wisconsin , Madison, USA; 2University of Wisconsin - Madison, Madison, USA
RF safety is a major concern in the design of active tracking and imaging devices for MR guided interventions. In this work, we demonstrate the potential of simple coaxial cable traps in suppressing RF heating to acceptable levels.
1064. Reduction of RF Heating of Interventional Cryoprobes Using Chokes
Sonal Josan1, Ronald Watkins1, Bruce Daniel1, Kim Butts Pauly1
1Stanford University, Stanford, California , USA
In presence of electrically conductive structures, such as implants, wires, or interventional devices, radio-frequency fields used in MRI can cause significant heating of the surrounding tissue. The magnitude of the heat depends on the device geometry, position within the patient, and position relative to the RF coil electric field. These effects have been described for guidewires at 1.5T and higher. The purpose of this work is to show resonant RF heating from a cryoablation device at 0.5T, to determine the safe & worst-case configurations, and demonstrate the use of RF chokes to reduce unwanted currents on the cable that lead to tissue heating.
Hall D Tuesday 13:30-15:30
Kai Kratt1, Ulrike Wallrabe1, Jan G. Korvink1
1University of Freiburg - IMTEK, Freiburg, Germany
We present the development of 3 D solenoidal micro coils for MR analysis based on an automatic wire bonder. By developing a stable and repeatable bond process with insulated wire, micro coils with sub millimeter diameter have been manufactured. The winding process for a single coil takes about 200 ms, whereas the manufacture of a 100 coil array takes less than a minute. Micro coils with 4 windings and inner diameter of 200 µm exhibit an inductance of 12.7 nH and a resistance of 580 mW at 300 MHz. A quality factor of 41 enables high-resolution MRI/NMR.
1099. An Inductively Decoupled Coil Array for Parallel Imaging of Small Animals at 7T
George Carlos do Nascimento1, Fernando Fernandes Paiva1, Afonso C. Silva1
1National Institutes of Health, Bethesda, USA
A two channel small animal coil array for 7T was designed based upon the method of inductive decoupling between the channels. The level ofisolation can be adjusted by adjusting the coupling in the passive transformer.The method shows a very nice immunity to standing waves, cross talking effects and otherparasitic signals in the array channels. The acquired images shows also that the method provides a good signal to noise ratio.
1100. A 4-Channel Transceive Surface Coil Array for Small Animal Imaging at 9.4T
Samuel O. Oduneye1, 2, Ravi S. Menon1, 2
1The University of Western Ontario, London, Canada; 2Robarts Research Institute, London, Canada
As operational frequencies increase linearly with higher static fields, the wavelength approaches the size of the sample being imaged. The resulting standing wave mode deteriorates image homogeneity. With phased array surface coils, the produced B1 field can be tailored to overcome the so called ‘dielectric resonance effect’, high RF power deposition and signal radiation losses. Here we present a novel high field transceive surface coil array for small animal imaging at 9.4T. Additionally, this design allows the coil to be employed for fast parallel imaging techniques while maintaining the high signal to noise ratio inherent advantage of surface coil designs.
Stefan Fischer1, Florian Martin Meise1, Andrea Kronfeld1, Beat Alessandri1, Wolfgang G. Schreiber1
1Mainz University Medical School, Mainz, Germany
Animal models with small animals like rats and mice are common in the research on diseases and its treatment. For those studies the simultaneous examination of multiple small animals is preferable to avoid an overall long scan time for large numbers of animals. A design without shielding, resulting in an inexpensive and simple array construction, allows time effective building of individual coil setups. Theoretically it can be expanded with further elements for multi channel receive systems up to 32 channels, if state-of-the-art scanner technology is used.
1102. Four Channel Array for 9.4T Animal Studies
Christopher Joseph Wargo1, John C. Gore1, Malcolm J. Avison1
1Vanderbilt University, Nashville, Tennessee, USA
Parallel arrays are commonly used in human clinical MR studies due to the benefits they provide. Beyond SNR improvement compared to a volume coil, parallel arrays support rapid imaging methods such as SENSE. The reduced scan time can be used to improve experiment efficiency, increase resolution, or help reduce field-dependent T2* and B0 inhomogeneity blurring and distortion artifacts. To date, parallel imaging has not been widely adapted to animal scanner applications, where advantages for improved performance are sometimes less obvious. We have developed a four channel array intended for 9.4T animal imaging, and evaluated parallel imaging performance in rat brain.
1103. Optimization of Phased Array Coils for Small-Animal MRI at 9.4T
Zhangwei Wang1, Martin Tabbert2, Sven Junge2, Roy E. Gordon2, Qing X. Yang1, Michael B. Smith3, Christopher M. Collins1
1The Pennsylvania State University, Hershey, Pennsylvania, USA; 2BRUKER Biospin GmbH, Ettlingen, Germany; 3Novartis Institutes for BioMedical Research, Inc., Boston, Massachusetts, USA
Animal imaging with phased array coils in high field MRI has become increasingly routine. Mice and rats are among the species most often imaged. To increase the SNR in comparison to existing standard quadrature birdcage coils and an existing phased array coil design, we have performed a numerical analysis and comparison of several proposed array geometries loaded with either a rat head or a mouse body considering the axial B1-homogeneity, B1-sensitivity and g-factor distribution.
1104.
Design of a Highly Sensitive Solenoid-Based RF-Coil for Small
Animal Brain Imaging
Hisaaki OCHI1, Satoshi Minoshima1, Donna J. Cross1, Cecil E. Hayes1
1University of Washington, Seattle, Washington, USA
A highly sensitive solenoid-based RF-coil whose sensitivity distribution is suitable for small animal brain imaging has been designed and fabricated. The designed coil was constructed as a combination of solenoid, Counter-Rotating-Current (CRC), and surface coils. We made a current loop at the top of the CRC coil so that the coupling between CRC and surface coils can be canceled out by adjusting the area of the top loop of the CRC coil. The sensitivity of this coil is 30% or more greater than those of QD birdcage coil and multi-channel phased-array coil of the same size.
1105. 20-Channel Mouse Phased-Array Coil for Clinical 3 Tesla MRI Scanner
Boris Keil1, Lawrence L. Wald2, Graham C. Wiggins2, Christina Triantafyllou3, Florian M. Meise4, Klaus Jochen Klose1, Johannes T. Heverhagen1
1Philipps University, Marburg, Germany; 2A.A. Martinos Center for Biomedical Imaging, MGH Dept. of Radiology, Harvard Medical School, Charlestown, Massachusetts, USA; 3A.A. Martinos Center at McGovern Institute for Brain Research, MIT, Cambridge, Massachusetts, USA; 4Mainz University School, Germany
The purpose of this study was to develop a dedicated 20-channel phased-array coil for mice imaging using a clinical 3 Tesla MRI system. Especially the challenges for the miniature design and the construction of large numbers phased-array mouse coils is presented. A tiny tubular conductors with an inner and outer diameter of 0.8 mm and 1.2 mm respectively was chosen to build all 20 coil elements. The preamplifiers impedance was transformed to a short at the detuning circuits to provide preamplifier decoupling. The small coil geometry shows good decoupling between elements and performs well in SNR.
1106. Multiple-Mouse MRI with Multiple Arrays of Receive Coils (MARCs)
Marc Stephen Ramirez1, James Andrew Bankson1
1The University of Texas M. D. Anderson Cancer Center, Houston, Texas, USA
The efficiency of small-animal MRI studies can be improved by simultaneously scanning multiple animals within a single MRI scanner. To date, this has involved dedicating up to one independent resonator for each animal. In this work, multiple-animal and phased-array technologies were combined to further enhance the imaging efficiency and flexibility of small-animal MRI. Multiple arrays of receive coils (MARCs) were used for accelerated anatomical imaging of two mice in vivo. Reconstructed images from a sensitivity encoding (SENSE) algorithm demonstrate the feasibility of using MARCs to substantially improve the efficiency and reduce the cost of small-animal MRI.
MR Systems, Magnets, Gradients, Shims
Hall D Tuesday 13:30-15:30
Franco Bertora1, Elisa Molinari1, Andrea Viale1
1Italian Institute of Technology, Genova, Italy
Permanent magnet design for MRI has always followed lines that are forcedly different from those employed in designs using superconductors yet, from a basic point of view, the physical principles are the same and a block of permanently magnetized material can be considered as the epitome of ambient temperature superconductivity. When confronted with the problem of designing an open scanner for functional imaging the techniques employed in designing permanent magnets can advantageously be applied to superconducting windings, particularly now that emerging materials such as MgBr2 afford relative ease in the construction of cryogen-free devices.
1149. An Optimised Elliptical Magnet for Deep Surface NMR Imaging
Manola Ciarrocchi1, Angelo Galante1, Vincenzo Di Miccoli2, Marcello Alecci1, Antonello Sotgiu1
1University of L'Aquila, L'Aquila, Italy; 2Itel Telecomunicazioni, Ruvo di Puglia, Italy
Unilateral NMR allows positioning of the sample on the surface of a portable measuring device and this technique has been used for several MRS/MRI applications. However, the open magnet geometry produces a magnetic field with high inhomogeneity, giving rise to reduced relaxation time T2*. MRI applications require a good field homogeneity and increased penetration depth. Unfortunately, most of the unilateral devices present in the literature do not satisfy both these requirements. Here we report the design of a novel elliptical unilateral magnet with improved field homogeneity and penetration along one direction.
1150. Shimming a 0.2 T Permanent Imaging Magnet with Small NdFeB Magnets
David Ian Hoult1, Qunli Deng2, Boguslaw Tomanek2
1National Research Council Institute for Biodiagnostics, Winnipeg, Canada; 2National Research Council Institute for Biodiagnostics, Calgary, Canada
Field shimming (20 ppm over a 30 cm diameter sphere) with small NdFeB magnets on the pole faces of an inexpensive, 0.2 T, permanent imaging magnet is described. Problems overcome included: 950 ppm starting inhomogeneity; drift during field plotting; magnetic moment inconsistency; unknown, induced local pole-face magnetisation; change of magnetisation with magnet inversion, and insufficient convergence of spherical harmonic amplitude with order for magnets close to pole face centres. Keys to success were the modelling of pole face magnetisation by a perpendicular line of magnets and the use of constrained linear programming to maximise the number of shimming magnets.
1151. Characterization of MRI Properties of Human Body Tissues at MicroTesla Magnetic Fields
Byeong-Ho Eom1, Mark Steven Cohen2, Inseob Hahn1, Konstantin I. Penanen1
1California Institute of Technology, Pasadena, California , USA; 2University of California, Los Angeles, Los Angeles, California , USA
Using an imager operating at 170 microTesla we studied the in vivo relaxation characteristics of human tissue and discuss the contrast range and instrument optimizations necessary to provide quality low field imaging
Christoph Barmet1, Nicola De Zanche2, Bertram Wilm2, Klaas P. Pruessmann2
1University and ETH Zürich, Zürich, Switzerland; 2University and ETH Zürich, Switzerland
Magnetic field monitoring with NMR probes is a promising approach but suffers from practical limitations when performed with receive-only probes, relying on external RF excitation. This contribution describes the implementation of a transmit/receive monitoring system, relying on autonomous probeheads equipped with individual RF excitation and RF shielding against MR contamination from the actual imaging experiment. The newly designed probes are found to offer sufficient sensitivity and RF shielding, enabling straightforward monitoring of MRI procedures, as exemplified by initial phantom scans.
1153. Residual Magnetism in MR Suites After Field Rampdown of Superconducting Magnets
Steffen Sammet1, Francisco Aguila1, Regina Maria Koch1, Michael Vincent Knopp1
1The Ohio State University, Columbus, USA
The rampdown of two superconducting clinical magnets, one at 8T and one at 0.7T, was used to evaluate residual magnetization within the MRI suite environments prior, during and after field-rampdown. A controlled rampdown of even an ultrahigh field MR system does not lead to retained magnetic contamination, while forced quenched rampdown of a mid-field system revealed temporary negative remanence.
Silke Maria Lechner1, 2, Adam B. Kerr3, Pekka T. Sipilä1, 2, Rolf F. Schulte1, Dirk Lange1, Florian Wiesinger1
1GE Global Research, Munich, Germany; 2Technical University Munich, Munich, Germany; 3Stanford University, Stanford, USA
Magnetic Field Monitoring (MFM) has been used as k-space trajectory measurement technique, whereupon the calibrated information is used in image reconstruction and result in reduced imaging artifacts like blurring and geometric distortions. This work presents a comparison of MFM with an alternative measurement method commonly used in MR. It is shown that higher image quality and less blurring artifacts are achieved using MFM. The comparison is evaluated in multi shot spiral out and echo-planar imaging sequences and demonstrated to substantially reduce artifacts in both, spiral and EPI. Image entropy is used as a quantitative quality metric.
1155. Gradient Linear System Modeling Using Gradient Characterization
Joseph Y. Cheng1, Borjan Aleksandar Gagoski1, Divya S. Bolar1, Christina Triantafyllou2, 3, Michael Hamm4, Gunnar Krueger5, Elfar Adalsteinsson1
1MIT, Cambridge, Massachusetts, USA; 2Athinoula A. Martinos Imaging Center, McGovern Institute for Brain Research, MIT, Cambridge, Massachusetts, USA; 3Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, MGH, Charlestown, Massachusetts, USA; 4Siemens Medical Solutions, Charlestown, Massachusetts, USA; 5Siemens Medical Solutions, Lausanne, Switzerland
The gradient system is modeled here as a linear time-invariant system, H(f), through a frequency-domain analysis. The model is obtained using a recent gradient characterization technique that combines two previous methods to optimize flexibility, speed, and accuracy. The obtained H(f) generalizes the gradient system to allow for a fast and accurate distortion prediction. As a result, the model will contribute to a robust correction method.
1156. Compensation of Eddy Current by an R-L-C Circuit Model of the Gradient System
Sang Heom Cho1, Pan Ki Kim1, Jong Woo Lim2, Su Yeol Jeon1, Chang Beom Ahn 3
1Kwangwoon University, Seoul, Republic of Korea, 2ISOL Technology
The k-space trajectory is important in the design of spiral pulse sequence as well as in the reconstruction of the image. The real trajectory is, however, usually deviated from the theoretical trajectory obtained from the gradient waveforms due to the eddy currents and non-ideal performances of the gradient systems such as finite bandwidth and slew rate. Such deviations inevitably result in distortions in the reconstructed image. In this paper, we derived an R-L-C circuit model to estimate the real k-space trajectory, by which a significant improvement of reconstruction was achieved at 3 Tesla MRI system.
1157. Reduction of MRI Scanner Acoustic Noise Using a Micro-Perforated Panel Absorber
Michael Li1, Chris K. Mechefske1
1Queen's University, Kingston, Canada
The trend toward higher field strength is worsening the noise problem in MRI. A Boundary Element Method simulation showed that a micro-perforated panel acoustic absorber can significantly reduce MRI noise in the scanner bore. The impedance function of the absorber was used to predict the sound attenuation effect. However, the absorption coefficient functions calculated according to Maa’s theory do not reflect the absorbing effect of a micro-perforated panel absorber in a cylindrical duct such as an MRI scanner bore because the expression of impedance of air gap is based on the assumption of plane waves
1158. Vibration Induced Eddy Current and Its Effect on Image Quality for MRI System
Longzhi Jiang1, Tim Havens2, William Einziger2
1GE Healthcare, Florence , USA; 2GE Healthcare, Florence, USA
During normal operation, MRI systems experience vibration from different external sources, e.g. refrigeration unit, environmental ground vibration and gradient coil pulse. Moving conductors within the MRI system will generate eddy currents, disturbing the homogenous magnetic field and affecting image quality (so called “ghosting”). In this study, vibration induced magnetic field fluctuation was investigated on a system with a single degree of freedom to illustrate the behavior. The methodology was then extended to a 3 dimensional MRI system by using FEM/BEM. Experimentally simulated results are presented, showing general agreement between experimental results and simulation for the 1.5T MRI system.
1159. Control of Gradient Coil Natural Frequency Using a Topology Optimization Technique
Sun Yong Kim1, Il Yong Kim1, Chris K. Mechefske1, Doo Ho Lee2
1Queen's University, Kingston, Canada; 2Dong-eui University, Busan, Republic of Korea
By controlling the natural frequency of the single-winging gradient coil, it is possible to reduce vibration resonant frequency amplitude. The overall noise and vibration of the structure can also be reduced. Viscoelastic damping material is widely used to suppress noise and vibration in industry due to its easy application and economic advantage. A full treatment of the damping material on the gradient coil does not give a maximum damping effect for the structure. The optimum location, thickness and shape of the damping sheets are being determined using topology optimization. This work aims to minimize the level of noise and vibration of the structure.
1160. Phantom Correction of Human Images for Spatial Scaling Errors
Jeff Gunter1, Matt Bernstein2, Bret J. Borowski2, Paula J. Britson1, Chadwick P. Ward2, Clifford R. Jack, Jr. 2
1Mayo Clinic and Foundation, Rochester, Minnesota, USA; 2Mayo Clinic, Rochester, Minnesota, USA
An investigation of the applicability of phantom-derived scanner scaling estimates close-in time human images is presented. Phantom correction reduces human image scaling variability within and across scanners.
1161. Frequency Spectrum of Partial Discharge Events
Derek A. Seeber1, Tony M. Linz2, Bruce D. Collick2, Anthony Mantone1
1GE Healthcare, Florence, South Carolina, USA; 2GE Healthcare, Waukesha, Wisconsin, USA
Each gradient coil, inner and outer, consists of three layers corresponding to the X, Y, and Z-axes of the gradient coil. The inner and outer gradient coils each have two radial spaces between adjacent axes. The radial spacing between adjacent axes is required to reduce the occurrence of “white pixels” and voltage breakdown during an MRI scan. If the “white pixel” performance of the gradient coil can be increased, the radial space savings can be incorporated into an increased patient bore, reduced magnet expenditure, or increased gradient slew rates with higher applied gradient voltages.
1162. Modal Sound Radiation from Finite Cylindrical Shells
Tian Ran Lin1, Peter O'Shea1, Chris K. Mechefske2
1Queensland University of Technology, Brisbane, Australia; 2Queen's University, Kingston, Canada
Modal radiation efficiencies of two fundamental circumferential modes of several different length finite cylindrical shells are studied in this paper. Modal radiation efficiencies of the finite cylinders are found to asymptotically approach those of the corresponding infinite cylindrical shell when the length of the cylinder divided by the circumference modal index (n>1) is more than twice that of the acoustic wavelength. There are two radiation peaks in the modal radiation efficiency attributed to the ring and critical frequencies of the finite cylinder.
1163. Initial Realisation of a Multichannel, Non-Linear PatLoc Gradient Coil
Anna Masako Welz1, Maxim Zaitsev1, Heinrich Lehr2, Gerrit Schultz1, Zhenyu Liu3, Feng Jia3, Hans Post2, Jan Korvink3, Jürgen Hennig1
1University Hospital Freiburg, Freiburg, Germany; 2Bruker BioSpin MRI GmbH, Ettlingen, Germany; 3University Freiburg, Freiburg, Germany
This abstracts presents the initial realisation of image encoding with a multichannel, non-linear PatLoc (parallel imaging in localized gradients) gradient coil and first reconstructed images. Imaging in non-linear, non-bijective magnetic fields has the advantage of faster imaging, or higher resolution especially at the periphery. To conserve some image reconstruction properties, in plane orthogonal gradients were chosen, in radial and circumferential direction. A cylindrical concept was developed for later use as a head gradient set. The first demonstrator is designed for use in an animal system for easier access to the hardware.
1164. Parametrical Optimization of a PatLoc Gradient Coil
zhenyu Liu1, Feng Jia1, Maxim Zaitsev2, Anna Welz2, Gerrit Schultz2, Jan G. Korvink1, Juergen Hennig2
1Dept. of Microsystems Engineering, Laboratory for Simulation, University Freiburg, Freiburg, Germany; 2Dept. of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany
A simple iterative optimization method, instead of the commonly used target field method, is presented to design PatLoc gradient coil. The optimization procedure includes the calculation of the magnetic value using the Biot-Savart method, the determination of the optimal number of conductor should be used, and the corresponding space positions. In order to use the continuous optimization method to optimize the discrete conductors, the continuation method is used to transform the integral design variable to bounded continuous design variable. The optimal solution still keeps the discrete conductor distribution so that the optimized gradient coil can be fabricated without further post-processing.
1165. Shoulder-Slotted Insertable Gradient and Shim Coil Se
Michael Poole1, Dan Green2, Richard Bowtell1
1University of Nottingham, Nottigham, UK; 2Magnex Scientific Ltd., Yarnton, UK
Insert gradient and shim coils designed specifically for head imaging can be made smaller and therefore of lower inductance and resistance as well as capable of producing more intense magnetic fields. Here, an Inverse Boundary Element Method was used to design a cylindrical, shoulder-slotted 3-axis head gradient coil set, also containing 0th and 2nd order shim coils, The shim coils were designed to have low-inductance so as to allow the fast current switching required by dynamic shim updating. The gradient and shim coil set has been constructed and tested at 3T in imaging experiments.
1166. Dynamic Shimming at 7 Tesla
Saikat Sengupta1, Yansong Zhao2, David Foxall2, Piotr Starewicz3, Adam Anderson1, John Gore1, Malcom Avison1
1Vanderbilt University Institute of Imaging Science, Nashville, USA; 2Philips Medical Systems, Inc, USA; 3Resonance Research, Inc, Billerica, USA
We have implemented dynamic shimming on Philips Achieva human 7Tesla system A Real Time Shim System, RTS, (Resonance Research Inc, MA, USA), was used for higher order shim control. Shim corrections were calculated from preacquired fieldmaps. The 1st order corrections were loaded slice wise through the gradient controls and the 2nd order shims were loaded from the RTS system. The static field standard deviations across the brain in all slices were significantly lower with dynamic shimming than with global shimming. This improvement in B0 homogeneity was reflected in reduced signal drop-out and lower image distortion.
1167. Power Versus Inductance: Finite Length Shim Coil Design for High-Field MRI
Parisa Jamali1, Blaine A. Chronik1
1University of Western Ontario, London, Canada
We designed high power, high order shim sets with constrained length using two methods: the minimum inductance method and the minimum power method. While the minimum inductance method gave higher inductive merit and the minimum power method gave higher resistive merit, the percent difference in merits between the two methods was less than six percent. This indicates that we can use the minimum power method for the design of our shim axes.
1168. Local Uni-Planar Gradient Array Design Using Conformal Mapping and Simulated Annealing
Sung M. Moon1, D.N. Ghosh Roy1, K. Craig Goodrich1, J. Rock Hadley1, Dennis L. Parker1
1University of Utah, Salt Lake City, Utah, USA
Many imaging problems, such as breast lesion characterization, can require high spatial and temporal resolution. The improved gradient performance required to achieve high spatial and temporal resolution may be achieved by specially designed local gradient coils such as planar gradient inserts. We present simple and rapid method for design of flat gradient inserts to produce a high strength gradient field and a reasonably uniform imaging region. The planar gradient set is to be placed inside of the imaging bore of the magnet (within the body gradients). For cylindrical gradients, a one dimensional stream function (SF) is used to specify currents on the cylinder surface. For planar gradients, however, this becomes a more complicated two dimensional problem.
1169. Effect of Active Shielding on Zonal Shim Coils for a 31cm Bore 9.4T MR System
Dustin Wesley Haw1, Blaine Alexander Chronik1
1University of Western Ontario, London, Canada
MRI and in-vivo spectroscopy in preclinical applications at very high field (9.4T and above) require improved shimming capabilities. Our goal is to develop and optimize high strength, dynamic shim systems for our 31cm bore 9.4T MR system. It is clear that dynamic shim systems will need to be actively shielded; however, we are interested in investigating how shim performance of shielded shim coils changes as a function of shim order. In all cases the efficiency of unshielded shim coils is better than that of shielded shim coils, as expected. However, the difference decreases considerably with increasing shim order.
1170. MR Imaging Capability of a Field-Cycled MRI/PET Scanner
Kyle Michael Gilbert1, Timothy James Scholl1, Blaine Alexander Chronik1
1The University of Western Ontario, London, Canada
Field-cycled MRI employs two separate, actively controlled resistive magnets to polarize a sample and to provide the magnetic field environment under which data is acquired. A field-cycled MRI system was constructed with a central gap to allow for the inclusion of a PET ring. The SNR and magnetic field homogeneity of the field-cycled MRI system were sacrificed to create a dual-modality scanner. To compensate, a low-pass birdcage coil and a higher order shim set were built, allowing for the acquisition of quality MR images.
1171. From Static to Dynamic: Construction of a B0 Insert for Field-Cycled Contrast in a Clinical MR Scanner
Jamu K. Alford1, Timothy J. Scholl1, William B. Handler1, Brian K. Rutt2, Blaine A. Chronik1
1The University of Western Ontario, London, Canada; 2Robarts Research Institute, London, Canada
To allow field-cycled contrasts in superconducting MR scanners, we have built an actively shielded B0 insert. This insert produces significant magnetic field shifts in the imaging region of clinical MR systems without destabilizing their main field or producing eddy-currents. The insert coil is composed of a powerful primary coil responsible for the B0 field shift and a precisely designed, counter wound, outer shield designed to reduce the insert's fringe field. Design, construction and testing of this unique insert are discussed.
1172. Towards Simultaneous PET and Field-Cycled MRI: Active Shielding for PMT Detectors
Dustin Wesley Haw1, Blaine Alexander Chronik1
1University of Western Ontario, London, Canada
Combined PET and MR scanners are currently under development as a means to obtain specific functional data from PET, registered both temporally and spatially with high-resolution anatomical images from MRI. One approach is to use PET and field-cycled MRI (FCMRI), which uses two separate and dynamically controlled magnets for the polarization and readout phases of MRI, in an interleaved manner. Actively shielded polarizing magnets reduce the magnetic field over the region in which the PMTs would be placed, and allow for extended PET operation during the polarizing phase of FCMRI.
1173. Quantitative Signal and Phase Analysis of a Field-Cycled MRI Scanner
Kyle Michael Gilbert1, Timothy James Scholl1, Jamu Krishna Alford1, Blaine Alexander Chronik1
1The University of Western Ontario, London, Canada
Field-cycled MRI employs two actively controlled electromagnets to polarize a sample and to provide the magnetic field environment during data acquisition. Instabilities in the readout magnet can cause phase errors and image artifacts in the phase-encode direction. The stability of the readout magnet was quantitatively evaluated, along with the expected signal trends. Images were acquired with no visible phase-encode artifacts.
1174. Preliminary Results of CdTe Detector Capabilities Toward MRI-SPECT
Takao Goto1, Yuji Iwadate1, Yoshio Mito2, Tetsuji Tsukamoto1
1GE Yokogawa Medical Systems, Hino-shi, Japan; 2Acrorad co. ltd, Uruma-shi, Japan
Recently there have been new interests in MR Hybrid Systems such as MR-PET and MR-SPECT. CdTe detector has valuable potentials as a new radiation detector and does not need Photo Multiplier. We investigated the interference of MR and CdTe detector toward MR-SPECT realization measuring Enegry Spectra changes, imaging Co-57 point source and scanned MR phantom with Tungsten laminated collimator in both 1.5T and 3T magnetic field. As a result, it is demonstrated that there was no significant effect in working CdTe detector in both 1.5T and 3T and found collimator effect could be avoided to scan specified imaging plane.
1175. Design and Fabrication of a Magnetic Resonance Stage Microscope
Andrey V. Demyanenko1, Julian Michael Tyszka1
1California Institute of Technology, Pasadena, California , USA
A uniplanar geometry analogous to an inverted stage optical microscope is proposed for high resolution MR imaging which addresses many of the limitations of conventional volume gradient and RF coil designs, particularly restrictions on medium volume and physical access when imaging small organisms such as developing embryos or thin tissue explants. The stage microscope geometry provides unhindered access to the sample from above, encouraging the future integration of optical imaging equipment with MR microscopy.
1176. Multiple Mouse Imaging of 16 Live Mice
Jonathan Eric Bishop1, Shoshana Spring1, Jun Dazai1, Brige Paul Chugh1, Sharon Portnoy1, Steven Suddarth, G Ronald Morris, R Mark Henkelman1
1Hospital for Sick Children, Toronto, Canada
Preliminary results for fully parallel imaging of 16 live mice are presented. The technique scales well and provides a significant increase in throughput compared to single mouse imaging.
1177.
Development of a Compact Whole Hand MRI System for Diagnosis
of Rheumatoid Arthritis Using a 0.3 T
Permanent Magnet
Shinya Handa1, Katsumi Kose1, Tomoyuki Haishi2
1University of Tsukuba, Tsukuba, Japan; 2MRTechonology Inc., Tsukuba, Japan
A compact whole hand MRI system for diagnosis of rheumatoid arthritis (RA) was developed using a 0.3 T permanent magnet and a locally shielded RF probe. The total system was installed in a 1.5 m ´ 2.0 m open space. Because the T1 weighted 3D images showed 1.6 times SNR advantage over those obtained with a 0.21 T permanent magnet previously reported, we concluded that our new system can be used for evaluation RA with reduced examination time or higher spatial resolution in the same examination time.
Hall D Tuesday 13:30-15:30
Leslie Ying1, Jinhua Sheng1
1University of Wisconsin - Milwaukee, Milwaukee, Wisconsin, USA
JSENSE formulates parallel imaging as a nonlinear problem to estimate the coil sensitivities and the desired images simultaneously. The existing algorithm solves the problem by iterative alternating minimization, which requires quite a few self calibration data for an accurate initial sensitivity estimation. In this abstract, we propose to use variable projection method to solve the nonlinear optimization problem. This method requires very few self calibration data because it converges to an optimal solution regardless of the initial value. The proposed method has been tested on a set of simulation data and demonstrated promising results.
1260. Automatic Coil Selection for SENSE Imaging with Large Coil Arrays
Mariya Doneva1, Peter Börnert2
1University of Luebeck, Luebeck, Germany; 2Philips Research Europe, Hamburg, Germany
The use of a large number of coil elements for parallel imaging allows improved imaging performance and increased SNR but can lead to memory storage problems and increased reconstruction times. We present an efficient approach for coil selection, based on singular value decomposition (SVD), applicable to massively parallel SENSE imaging. The SVD-based coil selection can be used instead of manual coil selection in conventional scan planning and is especially useful in planning double oblique SENSE scans. It is also applicable to real-time or interventional imaging, where the selection could be performed locally enabling dynamical coil switch during image acquisition.
1261. A Comparison of Reconstruction Techniques for Non-Uniformly Sampled 3D Parallel Imaging
Zhikui Xiao1, 2, William Scott Hoge2, R. V. Mulkern, 23, Guangshu Hu1, Walid E. Kyriakos2, 3
1Tsinghua University, Beijing, People's Republic of China; 2Brigham and Women's Hospital, Boston, Massachusetts, USA; 3Children's Hospital, Boston, Massachusetts, USA
In this abstract, we explore a specific non-uniform sampling scheme for 3D imaging on a rectilinear grid. We show that high-quality images can be reconstructed by 2D-SPACE RIP and 2D-GRAPPA-Operator. To evaluate the proposed sampling method and reconstruction schemes, results from a phantom study and in-vivo 3D human data are shown. Overall, fewer artifacts can be seen in the 2D-SPACE RIP reconstructions.
1262. Accelerating Acquisition in Spiral Imaging
Ajit Devaraj1, Jim Pipe1
1St. Joseph's Hospital and Medical Center, Phoenix, Arizona , USA
Most pr