Hall D Monday 14:00-16:00
906. In Vivo Transit Time MR-Measurements of Pulse Wave Velocity in the Murine Aorta at 17.6 Tesla
Marco Parczyk1,
Volker Herold1, Gert Klug1, Thomas Schulze-Till1,
Wolfgang Bauer1, Eberhard Rommel1, Peter Jakob1
1University of Wuerzburg, Wuerzburg, Germany
Aortic stiffness increases in an early state of arteriosclerosis, assessable by pulse wave velocity (PWV) MR-measurements. Up to now only studies in larger animals and humans have been reported in literature. The feasibility of in vivo PWV MR-measurements by two non-invasive MR-imaging techniques is presented. Because pulse wave and flow velocities are similar to velocities in humans, but dimensions are about 20-times smaller, the challenges in this project were especially the high temporal and spatial resolutions needed.
907. In Vivo Measurement of
Local Pulse-Wave Velocity in Mice with MRI at 17.6 T
Volker Herold1, Gert Klug1, Marco
Parczyk1, Christian Ziener1, Thomas Weber1,
Susanta Sarkar2, Wolfgang Rudof Bauer1, Eberhard Rommel1,
Peter Michael Jakob1
1University of Wuerzburg, Wuerzburg, Germany; 2GlaxoSmithKline (GSK), King of Prussia, Pennsylvania, USA
Pulse wave velocity (PWV) is an important parameter for the evaluation of the arterial stiffness and cardiovascular risk. Several diseases such as hypertension and arteriosclerosis are associated with vascular remodeling and arterial stiffening. Mouse models of human diseases are increasingly used to investigate patho-physiological mechanisms of the cardiovascular system. A non invasive method is presented to assess local PWV in the ascending and descending aorta of mice with MR-Microscopy at 17.6 T. The results demonstrated the feasibility of high field MR microscopy to quantify local pulse wave velocity as a measure of local aortic stiffness.
908. Carotid Wall Shear Rate
Measured with Spiral Fourier Velocity Encoding
Joao Luiz Azevedo de Carvalho1, Jon Fredrik
Nielsen1, Krishna S. Nayak1
1University of Southern California, Los Angeles, California , USA
Fourier velocity encoding (FVE) has been proposed as a method for non-invasively measuring fluid shear rate and hence vascular wall shear stress, an important factor implicated in atherogenesis. The scan-time of 2DFT FVE is prohibitively long for clinical use, but the recently introduced spiral FVE method shows promise as it is substantially faster. In this work, we investigate the feasibility of using spiral FVE for estimating shear rates near the carotid artery walls in clinically practical scan times. We present: (1) a phantom validation of spiral FVE against high-resolution 2DFT phase contrast; (2) evaluation of resolution requirements; (3) in vivo demonstration.
909. Intracranial Compliance
and Pressure Measurement Based on MR Flow Quantification and Brain
Circulation Model Circuit: Sensitivity to Hyperventilation and Hydrocephalus
Kagayaki Kuroda1, Kosuke Maruhashi1,
Moyuru Ohya1, Masatoshi Honda2, Hideki Atsumi3,
Koichi Oshio4, Mitsunori Matsumae3
1Tokai University, Hiratsuka, Japan; 2Tokai University Hospital, Isehara, Japan; 3Tokai University, Isehara, Japan; 4Keio University, Shinanomachi, Japan
A noninvasive technique to evaluate brain compliance index (BCI) and intracranical pressure index (ICPI) based on MR flow quantification and an inverse analysis of brain-circulation-equivalent electrical circuits was developed. The technique was applied to healthy volunteers (N = 6) with normal breathing and hyperventilation during scanning. The BCI significantly decrease with hyperventilation in 5 volunteers. The technique was also applied to patients (N = 3) with hydrocephalus. Both BCI and ICPI were significantly lower in those patients than in the normal volunteers. These results indicated that the technique is sensitive to the change or abnormality of the brain physical properties.
910. Compliance and Anatomy
of the Neo-Aorta in Children with Hypoplastic Left Heart Syndrome (HLHS)
Michael Helle1,
2, Inga Voges1, Michael Jerosch-Herold2,
Christopher Hart1, Traudel Hansen1, Hans-Heiner Kramer1,
Carsten Rickers1
1Christian-Albrechts-Universität, Kiel, Germany; 2Brigham & Women's Hospital, Boston, USA
The purpose of this study was to assess aortic anatomy and aortic compliance (AC) in children with hypoplastic left heart syndrome (HLHS) using cardiac MRI at 3 Tesla.Cine MRI and contrast enhanced time-resolved MR-angiography were performed in all patients for measuring selected diameters of the neo-aorta and for a selected determination of the AC.Diameters of the aortic root, the ascending aorta and the aortic arch were significantly increased. We found a significant smaller aortic isthmus in children with HLHS, whereas the dimensions of the descending aorta were not significantly changed. AC was decreased in the ascending aorta as well as the aortic arch.
Aurélien F.
Stalder1, Max F. Russe1, Alex Frydrychowicz1,
Jelena Bock1, Jürgen Hennig1, Michael Markl1
1University Hospital Freiburg, Freiburg, Germany
The purpose of this work was the development of an optimized quantitative analysis method in order to derive flow and wall parameters from CINE phase contrast (PC) MR data. The data analysis strategy combines “Green’s theorem” and B-spline interpolation with their finite difference property to provide an optimal quantification of several blood flow and vessel wall parameters. Calculation of the local blood flow velocity derivatives onto the vessel contour using B-spline interpolation allowed a direct and reliable estimate of time-resolved segmental WSS vectors independent of any restrictive global assumptions regarding the flow profile.
Hall D Monday 14:00-16:00
946. The Effect of Lipid
Core Position on Carotid Fibrous Cap Stress Levels
Samuel Alberg
Kock1, Jens Vinge Nygaard, Anders K. Niemann1, Anette
Klærke, William Paaske, Erling Falk, Won Yong Kim1
1Aarhus University Hospital Skejby, Aarhus N, Denmark
To determine if not only the size of atherosclerotic lipid cores, but also their position influence carotid fibrous cap stress levels, three computational models of a carotid bifurcation with varying lipid core placement were created using geometry based on MRI scans of a patient with a high-grade stenosis. Computational fluid structure interaction simulations were performed on the models revealing proximally based lipid cores to exhibit far greater stress levels than both distally and centrally located lipid cores. Computational analyses may yield valuable additional information concerning fibrous cap stress levels which may support current methods of diagnostics.
947. Ultra-Short TE Imaging
Protocol for Detection of Aortic Calcification
Daniel A.
Herzka1, Reza Nezafat2, Juergen Rahmer3,
Warren J. Manning2, Peter Boernert3
1Philips Research North America, Briarcliff Manor, New York, USA; 2Beth Israel Deaconess Harvard Medical School, Boston, Massachusetts, USA; 3Philips Research Europe, Hamburg, Germany
Ultra-short TE sequences are advantageous because they can capture signal from tissues with short T2, while preventing signal loss from sources of artifact such as off-resonance and susceptibility boundaries. We optimized a UTE protocol for visualization of calcified atherosclerotic lesions in vivo in human aortas. The protocol was tested on volunteers and a patient with known atherosclerosis. UTE yielded images with calcium deposits clearly co-localized with atherosclerotic lesions observed with black-blood FSE, and made possible detection of calcification on the luminal side of the aorta. These preliminary results indicate that calcium imaging with MR is feasible and worth further investigation.
948. Signal Features of the
Atherosclerotic Plaque at 3.0T Versus 1.5T: Impact on Automatic Classification
William Sean
Kerwin1, Fei Liu1, Hunter Underhill1, Vasily
Yarnykh1, Chun Yuan1
1University of Washington, Seattle, Washington, USA
We evaluated signal differences between 1.5T and 3T MRI of carotid atherosclerotic plaque using an automatic classifier. Despite being trained on only 1.5T data, subjects scanned at both field strengths yielded highly similar classification results for the presence and average areas of calcification, lipid-rich core, hemorrhage, and fibrous tissue. These results suggest that signal properties are sufficiently similar at 3T relative to 1.5T that classifier performance is not significantly affected.
949. Long Segment Dark Blood
Carotid Artery Imaging with Pencil-Beam-Excitation and Diffusion
Preparation at
3T
Axel Bornstedt1,
Peter Bernhardt1, Vinzenz Hombach1, Markus Kunze1,
Jochen Spiess1, Nico Merkle1, Volker Rasche1
1Uniklinik Ulm, Ulm, Germany
Robust long segment (~150 mm) 3D dark blood vessel visualisation of the carotid arteries at 3T is accomplished with pencil beam excitation and diffusion prepared gradient echo imaging.
Venkatesh Mani1, Hamza El Aidi1,
Mark Woodward1, Paul Muntner1, Silvia H. Aguiar1,
Karen Beth Weinshelbaum1, Hiroaki Taniguchi1, John E.
Postley2, Valentin Fuster1, Zahi A. Fayad1
1Mount Sinai School of Medicine, New York, New York, USA; 2Columbia University, New York, New York, USA
The purpose of this study was to evaluate if MRI plaque burden measures in conjunction with traditional risk factors improve predictive capacity for cardiovascular disease (mCVD) and may therefore be useful in pre identification of patients at risk for cardiovascular disease. MR measures of plaque burden were obtained from 296 patients and ROC curves were used to determine predictive capacity of MR derived parameters for predicting mCVD. Combining MR parameters with traditional risk factors provided highest retrospective predictive capacity for mCVD.
James Qiupeng Zhan1, Alan R. Moody2,
General Leung2, Radhakrishnan Ravikumar2, Susan Crisp2
1Sunnybrook Health Sciences Centre, Toronto , Canada; 2Sunnybrook Health Sciences Centre, Toronto, Canada
A study was conducted to measure carotid artery intraplaque haemorrhage (IPH) volume over time using Magnetic Resonance Direct Thrombus Imaging (MRDTI) and correlate it with the occurrence of prior ipsilateral ischemic events. Patients who received multiple MRDTI scans and were diagnosed with complicated plaque were classified as either symptomatic (having previous events) or asymptomatic. Two trained observers analyzed the MRDTI data and determined IPH volumes. The intra-and inter-reader coefficients of variation were 6.2% and 8.2%, with correlation coefficients of 0.987 and 0.972. Relative mean change in IPH volume was 86.31±266.44% for asymptomatic patients and 10.23±54.87 % for symptomatic patients (P<0.01).
952. Improvements in Spatial
Resolution Using a Novel 8-Element Carotid Phased Array Coil at 3T
Niranjan Balu1, Vasily Yarnykh1,
Cecil Hayes1, Joshua Scholnick1, Dongxiang Xu1,
Baocheng Chu1, Chun Yuan1
1University of Washington, Seattle, USA
Carotid plaque imaging demands high SNR and high resolution. While current four-element phased array (PA) coils provide adequate SNR over a limited FOV, PA coils with additional elements can improve SNR and coverage. Using a novel eight-element PA (8PA) coil , upto 60% improvement in SNR and CNR were observed with a high-resolution (0.63mm in-plane) protocol. An ultra-high resolution (0.27mm in-plane) T1w black-blood quadruple inversion recovery sequence was implemented to assess the resolution improvement made possible by the 8PA coil. The 8PA coil enabled ultra-high resolution imaging with SNR improvements greater than 1.35 times with better vessel wall delineation.
Kevin DeMarco1, Xiaohai Ma1, John
Brooks1, David Zhu1, Vasily Yarnykh2
1Michigan State University, East Lansing, Michigan, USA; 2University of Washington, Seattle, Washington, USA
Contrast-enhanced T1 weighted images (CE T1WI) demonstrate lipid rich necrotic core (LR-NC) with higher contrast-to-noise ratio (CNR) at 1.5T using gadodiamide. This study extends in vivo carotid plaque imaging to 3T and evaluates the effect of post-injection time on appearance of LR-NC using gadobenate dimeglumine by comparing CNR of LR-NC at 5 and 10 minutes after contrast injection in 43 outpatients with carotid stenosis. LR-NC CNR was similar at both time points, but with higher signal-to-noise ratio at 10 minutes. LR-NC volume measurement at both time points employing automated algorithm in MRI-PlaqueView is under investigation as is comparison with histology.
954. Magnetic Resonance
Intraplaque Hemorrhage is Associated with Cerebrovascular Outcomes in
Asymptomatic Male Patients with Non-Severe Stenosis
Navneet Singh1, Alan R. Moody1,
General Leung1, Ravikumar Radhakrishnan1, James Zhan1,
Robert Magissano1
1Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Canada
Intraplaque hemorrhage (IPH) is an emerging marker of plaque instability. We investigated the correlation of MR detected IPH to cerebrovascular outcomes in a group of asymptomatic males with non-severe stenosis. A GE 1.5T MR and an 8 channel neurovascular coil array (USA Instruments, USA) using a 3D T1-weighted, fat-suppressed spoiled gradient echo sequence was used. The group with IPH (n=30) had six events (2 strokes, 1 amF, 3 TIAs) compared to no events in the MR IPH negative group (n=47) (RR = 9.60, 95%CI 1.21 to 75.9, p=0.0320).
955. Fibrous Cap Projection
Length: A Better Biomarker of Plaque Vulnerability Than Lipid Core Size
Dongxiang Xu1, Niranjan Balu1,
Hunter R. Underhill1, Jianming Cai2, Chun Yuan1
1University of Washington, Seattle, Washington, USA; 2Chinese PLA General Hospital, Beijing, USA
Atherosclerotic disease has become one of the leading causes of death and major disability in the United States. In the past years, with the rapid development of using high resolution magnetic resonance imaging (MRI) technology in assessing atherosclerotic components, more and more evidences have shown that plaque composition is the decisive factor determining plaque vulnerability. Cai et al[1] using gadolinium-based contrast enhanced MRI showed that post contrast T1-weighted images can provide accurate quantitative measurements of the intact fibrous cap (FC) in advanced carotid atherosclerotic plaques in vivo. Based on this observation, an automatic FC detection method was developed and validated in our previous research [2]. In this study, we further explore lesion index Normalized Fibrous cap Projection Length Index (NFPLI). Our preliminary trial result has shown its more predictive power in plaque vulnerability than other plaque measurements.
956. Rapid 3D Vessel Wall
Imaging at 3T: Optimization of Diffusion
Preparation and Comparison to Other
Protocols
Mahender K.
Makhijani1, Gerald S. Pohost2, Krishna S. Nayak1
1University of Southern California, Los Angeles, California , USA; 2University of Southern California, USA
Multi-contrast high-resolution imaging is used to characterize carotid plaque components. Standard multi-slice methods have long scan times and are not suited for plaque quantitation. Diffusion preparation has been recently proposed as a means for blood suppression in 3D vessel wall imaging. We characterize the tradeoffs of this approach when applied in conjunction with DIR and evaluate its performance at 3T in-vivo for bilateral carotid imaging and compare it with standard protocols and 3D SSFP approach. Cardiac gated 3D carotid vessel-wall datasets with 0.5x0.5x2.5 mm3 resolution over a 16x3.2x5cm3 FOV, and vessel wall CNR > 18, were obtained in 100 seconds
Radhakrishnan Ravikumar1, Alan R. Moody1,
General Leung1, James Q. Zhang1, Peter N. Burns1,
Susan Crisp1, Marilyn Robertson Horton1, Robert Maggisano1
1Sunnybrook Health Sciences Centre, Toronto, Canada
Plaque neovascularity, in addition to nurturing plaque growth can also be a causative factor for intraplaque hemorrhage thus predisposing the patient to increased risk of cerebrovascular events. Contrast enhanced ultrasound has been effectively used in identifying plaque neovascularity. The main purpose of this study was to see whether contrast enhanced MRI can help identify neovessels within the plaque and to compare the MR findings with contrast ultrasound findings. Delayed enhancement uptake patterns visualised on MR correlated well with neovascularity positive areas detected on contrast ultrasound.
958. High-Resolution T1- And
T2-Weighted Black Blood Inner Volume 3D Fast Spin Echo Imaging for
Characterizing Vessel Wall Components in Vivo
Dimitris Mitsouras1, Robert V. Mulkern1,
2, Christopher D. Owens1, Tianxi Cai3, Amanda G.
Whitmore1, Hale Ersoy1, Michael S. Conte1,
Mark A. Creager1, Frank J. Rybicki1
1Harvard Medical School & Brigham And Women's Hospital, Boston, Massachusetts, USA; 2Children's Hospital, Boston, Massachusetts, USA; 3Harvard School of Public Health, Boston, Massachusetts, USA
Saphenous vein femoral-popliteal bypass graft imaging using a high spatial resolution (0.312mm in-plane) black-blood inner-volume 3DFSE sequence in 14 subjects revealed significantly larger wall area measured from T1W than T2W images (median ratio 1.52, median difference 5.45mm2, P<0.001). This significant difference was due to an increased outer wall boundary. T2 relaxometry of two specimens revealed shorter T2 values in an outer vs. an inner wall layer, accounting for the in vivo finding of differing areas measured from different contrast weightings. Correlative histology attributed the shorter T2 in the outer layer to collagen-rich fibrous tissue vs. myofibroblasts embedded in proteoglycan-rich matrix.
959. Gender Differences in
Aortic Wall Thickness Regression by Magnetic Resonance Imaging (MRI) and Its
Association to HDL Profile: The Plaque Follow Up Study by the National
Institute of Aging (NIA)
Gustavo Khattar Godoy1, Veronica R.S Fernandes1,
Hossein Bahrami1, Christopher Sibley1, Ilan Gottlieb1,
David A. Bluemke1, Joao A.C Lima1
1Johns Hopkins University, Baltimore, USA
The aim of the study was to assess the relationship between changes in aortic wall thickness measured by MRI with lipid profile and gender,of 114 participants of a randomized clinical trial using lipid-lowering drugs for 2 years.Were analized 3 segments of the thoracic aorta (ascending,arch and descending),using a double inversion recovery black blood fast spin-eco sequence with ECG-gating and T1-Weighted post-gadolinium.Were found a significant lower rate reduction of the aortic thickness in men when compared to women.Greater HDL levels were related to a decrease in ascending aortic wall thickness ,after adjustments for variables.
960. Quantitative Comparison
of Carotid Plaque Composition Between 1.5 and 3.0T Field-Strengths
Hunter R. Underhill1, Vasily L. Yarnykh1,
Thomas S. Hatsukami1, Jinnan Wang1, Niranjan Balu1,
Cecil Hayes1, Minako Oikawa1, Wei Yu1,
Dongxiang Xu1, Baocheng Chu1, Bradley T. Wyman2,
Nayak L. Polissar3, Chun Yuan1
1University of Washington, Seattle, USA; 2Pfizer, Groton, USA; 3The Mountain-Whisper-Light Statistical Consulting, Seattle, USA
We sought to assess the effects of field-strength on the quantification of carotid atherosclerotic disease. Participants with 16-79% carotid stenosis underwent high-resolution carotid MRI at both 1.5T and 3.0T. There was strong agreement between field-strengths in quantitative measurements of plaque morphology and detection of plaque components. However, the increased magnetic susceptibility of calcification and a stronger effect of paramagnetic ferric iron in hemorrhage at 3.0T may introduce a quantitative bias in measurements of these components. As such, 3.0T imaging may improve the detection of calcification, but more sensitive imaging techniques may need to be used for hemorrhage evaluation at 3.0T.
Jinnan Wang1, 2, Vasily L. Yarnykh1,
Baocheng Chu1, Chun Yuan1
1University of Washington, Seattle, Washington, USA
In this study, an improved version of motion sensitization driven equilibrium (iMSDE) sequence was proposed for carotid artery vessel wall imaging. By adding a new refocusing pulse, the iMSDE sequence is less sensitive to the B1 inhomogeneity at high field strength. Both phantom test and in vivo imaging has demonstrated that iMSDE sequence can dramatically increase signal level, when comparing with traditional MSDE sequence, without losing flow suppression efficiency.
962. High-Resolution
Ultra-Short TE Imaging of Ex Vivo
Human Carotid Plaques Correlates with CT
Daniel A.
Herzka1, Juergen Rahmer2, Reza Nezafat3, Ray
Chan1, Wei Liu1, Peter Boernert2
1Philips Research North America, Briarcliff Manor, New York, USA; 2Philips Research Europe, Hamburg, Germany; 3Beth Israel Deaconess Harvard Medical School, Boston, Massachusetts, USA
Ultra-short TE (UTE) sequences have the advantage that they are able to capture signal components with very short T2. We investigate the use of single and multi-echo UTE sequences for the detection of calcium deposits in ex vivo human carotid samples with known atherosclerosis. UTE images correlated significantly with high-resolution CTs but with better soft-tissue contrast. Though low in intensity, the signal from calcifications is detectable with UTE MRI and may be complementary to current multicontrast atherosclerotic tissue characterization approaches. Further work is required to assess the feasibility of these acquisitions in vivo.
Glenda Sibylle van Bochove1, Leonie E M Paulis1,
Dolf Segers2, Willem J M Mulder3, Rob Krams4,
Gustav J. Strijkers1, Klaas Nicolay1
1Eindhoven University of Technology, Eindhoven, Netherlands; 2Erasmus Medical Center, Rotterdam, Netherlands; 3Mount Sinai School of Medicine, New York, New York, USA; 4Imperial College London, London, UK
Recently, a mouse model has become available where both stable and vulnerable atherosclerotic plaque phenotypes are induced by the placement of a tapered cast around the right carotid artery of apoE-/- mice. The aim was to evaluate the contrast generated in these plaques by injection of Gd3+ liposomes and Gd3+-micelles to obtain insight in plaque permeability. Both stable and vulnerable plaques appeared non-permeable for liposomes, while accumulation of micelles was observed in both lesion types. Therefore, liposomes are a good candidate for targeting endothelial markers and micelles may also be suitable for targeting factors inside the atherosclerotic plaque.
964. Molecular Imaging of
Atherosclerosis Using PEG-Micelles Targeted by an ApoE Derived Peptide
Eik Leupold1, Esad Vucic2, Willem
Mulder2, Margitta Dathe1, Zahi Adel Fayad2
1Leibniz Institute of Molecular Pharmacology (FMP), Berlin, Germany; 2Mount Sinai School of Medicine, New York, USA
We use Gadolinium labeled PEG-micelles as contrast agents for MRI with ApoE knockout mice as atherosclerosis models. Targeting is achieved by an ApoE derived peptide (A2). The PEG-micelles consist of maleimide-PEG-DPPE, Gd-DTPA-BSA and rhodamine-DPPE. The micelles are produced by lipid-film hydration and A2 is coupled via maleimide/sulfhydryle conjugation.The micelles are 18nm in diameter and have a high stability. In vivo application (50mmol Gd/kg) results in a high, long lasting enhancement of atherosclerotic plaque in MRI using a 9.4T system. The maximum enhancement of 129±46% is reached at 24h, compared to 30±15% in mice treated with control PEG-micelles. Confocal microscopy was performed on sections taken from the thoracic aorta. A co-localization of A2 PEG micelles with macrophages in atherosclerotic plaques could be shown.A2 modified PEG-micelles containing Gd are a new contrast agent that is excellently suited for the MRI based diagnosis of atherosclerosis.
965. Comparison of Synthetic
HDL Contrast Agents for Atherosclerosis Imaging
David Peter Cormode1, Rohith Chandrasekar2,
Karen C. Briley-Saebo1, Alessandra Barazza1, Willem J.
Mulder1, Edward A. Fisher3, Zahi Adel Fayad1
1Mount Sinai School of Medicine, New York, USA; 2The Cooper Union for the Advancement in Science and Art, New York, USA; 3New York University, New York, USA
We have previously reported a macrophage specific MRI contrast agent based on HDL. To make this agent more versatile, we have formed Gd-labeled, synthetic HDL using a 37 or 18 amino acid peptide that mimics apoA-I, the main protein constituent of HDL. The effectiveness of these peptide-agents for detecting macrophages in the abdominal aorta of apoE knockout mice is assessed via MRI studies. Targeting to macrophages is confirmed by confocal microscopy. In addition, the biodistribution and pharmacokinetics are reported and the therapeutic properties of these particles in terms of removing cholesterol from macrophages are investigated.
966. Imaging Vasulcar Injury
Using a Novel Gadolinium-Based Contrast Agent
Pauliina Lehtolainen1, Manfred
Junemann-ramirez, Panagiotis Kyrtatos1, Anthony N. Price1,
Kenjiro Ikuta2, Yoshiki Katayama2, John F. Martin, Mark
F. Lythgoe
1 Institute of Child Health and Department of Medicine, University College London, London, UK; 2Kyushu University,, Fukuoka, Japan
The vasculature is one of the most promising targets for a site -specific MRI strategy, as the diagnosis of vascular disease in its early stages is essential to a successful treatment intervention. Here we report on an endothelial-lesion specific contrast agent, evans-blue chelated gadolinium (EB-DTPA-Gd) for imaging the vascular damage and regeneration of vascular wall. Vascular injury generated by angioplasty was clearly distinguished by EB-DTPA-Gd accumulation by T1-weighted MR images using 9.4T scanner.
967. Comparison of
Gadofluorine M and Gd-DTPA Relaxivities for Quantitation and Characterization
of
Atherosclerotic Plaque in Mouse at 11.7T
Haiying Tang1, Richard Kennan1,
Ching H. Chang1, Bernd Misselwitz2, Donna Suresch1,
Dan Zhou1, Brett Connally1, Michael Klimas1,
Donald S. Williams1, Richard Hargreaves1, Haiying Liu1
1Merck Research Laboratories, Rahway, New Jersey, USA; 2Bayer Schering Pharma AG, Berlin, Germany
Recent advances in MRI technology and novel imaging contrast agents have made MRI an important imaging modality for detecting and characterizing atherosclerosis. Gadofluorine M has been reported to target the extracellular matrix of plaque, and is an important marker of plaque staging. Comparisons of relaxivities and dose response in plaque are made between Gd-DTPA and Gadofluorine M at 11.7 Tesla. The results confirm that Gadofluorine M greatly helps in the identification and quantitation of plaque burden in major arteries of mouse model of atherosclerosis with improved sensitivity and efficiency, and may provide better characterization of plaque components at different stages.
968. Imaging of Macrophage
Infiltration in an Abdominal Aortic Aneurysm Mouse Model
Gregory Harrison Turner1, Alan R. Olzinski1,
Roberta E. Bernard1, Karpagam Aravindhan1, Heather W.
Karr1, Robert N. Willette1, Peter J. Gough1,
Beat M. Jucker1
1GlaxoSmithKline, King of Prussia, Pennsylvania, USA
Abdominal aortic aneurysms result from a vascular inflammatory process involving macrophage recruitment. Abdominal aortic aneurysms (AAA) can be consistently produced in hyperlipidimic ApoE-/- mice by continuous infusion of Angiotensin-II (Ang-II). Administration of USPIO was used as an imaging biomarker for the distribution of macrophage within an aneurysm. These results demonstrate the feasibility of using a USPIO contrast agent as a surrogate for acute inflammatory processes in the aorta of ApoE-/- mice.
969. GdAAZTA-C17 (Q=2)
Labeled High Density Lipoproteins (HDL) for the in Vivo Detection of
Atherosclerotic Plaque
Karen Briley-Saebo1, Simonetta Geninatti2,
David Cormode1, Alessandra Barazza1, Wei Chen1,
Edward Fisher3, Silvio Aime2, Zahi A. Fayad1
1Mount Sinai School of medicine, New York, USA; 2University of Torino, Torino, Italy; 3New York University, New York, USA
To increase CNR and reduce the dose administered, high relaxivity gadolinium chelates with two water exchange sites (q=2) were integrated into high-density lipoproteins (HDL). The q=2 HDL adduct was characterized relative to GdDTPA-DMPE (q=1) HDL, and the MR efficacy evaluated in mouse models of atherosclerosis. The results indicate that the q=2 lipid integrates into the lipid core. The q=1 lipid, however, formed a micelle that interacted with the surface. Similar MR arterial enhancement was observed after administration of 0.048 mmol Gd/Kg q=1 HDL and 0.018 mmol/Kg q=2 HDL. The q=2 HDL adduct may allow for low dose detection of atherosclerosis.
970. Characterization of an in Vivo Model of Atherosclerosis Using Histological and MRI TechniquesStephanie Elaine GarWai Chiu1, Alan R. Moody1,
James Qiupeng Zhan1, Radhakrishnan Ravikumar1, General
Leung1
1Sunnybrook Health Sciences Centre, Toronto, Canada
Intraplaque hemorrhage and plaque neovascularization are recognized as contributors to atherosclerotic plaque vulnerability, but current animal models do not consistently or spontaneously produce these types of lesions. As a first step towards building upon the commonly used hypercholesterolemic rabbit model, a low dose of recombinant human vascular endothelial growth factor (rhVEGF) was administered to a group of rabbits. These injections have been shown to increase both intramural endothelial cell and macrophage density in hypercholesterolemic rabbits. MRI using both an intravascular and an extravascular contrast agent was performed on the rabbits in an attempt to detect these changes non-invasively.
Hall D Monday 14:00-16:00
Sequence: Scope of Applications
Magalie Viallon1, Jean-Noël Hyacinthe1, Dominique Didier1, Pierre Croisille2
1Hopital Universitaire de Genève, GENEVA, Switzerland; 2Hopital Cardiologique Louis Pradel, LYON, France
T1 or T2 weighted TSE and T1 SE dark blood (DB) MR imaging (eventually combined with fat saturation (FS) or inversion recovery(IR)) are involved to characterize pathologies like DAVD, tumours, sarcoïdosis, myocarditis, to determine the area-at-risk in acute myocardium infarction (MI) or to detail cardiac morphology in congenital disease. But Dark-blood TSE methods are subject to artifacts (signal loss due to incoherent cardiac motion from RR length changes), resolution is restricted by the breathhold duration and remain low. In free breathing paediatric patients TSE DB techniques is dramatically hindered by the respiratory motion. PROPELLER then BLADE were new encoding strategies implemented to correct for intra and inter scan motion in brain morphological acquisition and offer a solution in uncooperative patients (Parkinson, stroke or Alzheimer diseases). We investigate here the capabilities of BLADE to circumvent motion sensitivity in DB cardiac morphology imaging and improve image quality.
Yuesong Yang1, Ram Vijayaraghavan1, Jay Detsky1, John J. Graham1, Warren Foltz1, Alexander Dick1, Graham A. Wright1
1Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Canada
Right ventricular (RV) myocardial infarction and dysfunction are independent indicators of poor prognosis in patients with acute myocardial infarction (AMI). Conventional DE-MRI has a limited role in the detection of the RV involvement in reperfused MI due to the thinned RV wall and pericardial fat tissue. We hypothesize that a T2-weighted cardiac MR technique with fat saturation is a better method to identify RV involvement in the acute stage of MI, and that the DE-MRI technique based on IR-prepared SSFP is a better technique to demonstrate RV involvement in the chronic stage of MI.
1010. Optimization of T2 and T2* Measurement in Myocardium at 3.0 T
Jared Guthrie Cobb1, 2, Huairen Zeng2, 3, Cynthia Paschal2
1Vanderbilt University , Nashville, Tennessee, USA; 2Vanderbilt University, Nashville, Tennessee, USA; 3Vanderbilt University Medical Center, Nashville, Tennessee, USA
High field clinical scanners are increasingly available to researchers and clinicians and possess a significant SNR advantage over 1.5T scanners. New accelerated imaging techniques designed to optimize spatial and temporal acquisition may allow researchers to detect subtle changes in myocardial tissue, including changes that may be indicators of differences in oxygen utilization such as variations in T2 and T2*. In pursuit of this goal, we developed optimized breath hold scans to measure T2 and T2* in the myocardial septum at 3.0T.
1011. Single-Shot SSFP for Imaging of Edematous Myocardium in Patients
Jordin D. Green1, 2, James Reavley Clarke2, Matthias G. Friedrich2
1Siemens Medical Solutions, Calgary, Canada; 2University of Calgary, Calgary, Canada
Cardiovascular MR can be used to visualize myocardial edema, a characteristic of patients with acute myocardial infarcts, but can be challenging in difficult patients. SSFP is T2/T1-weighted in the steady state with high imaging efficiency. The purpose of this study was to demonstrate the feasibility of using single-shot SSFP to image myocardial edema. The study was conducted in six patients. Results were compared to a conventional T2-weighted STIR sequence. Of the 32 myocardial segments positive for edema according to the STIR sequence, 24 were positive using SSFP. Of the 52 negative for edema according to STIR, 45 were negative using SSFP.
Myra Sabene Cocker1, Oliver Strohm1, Jordin Daniel Green, 12, Steven M. Shea3, Hassan Abdel-Aty1, Matthias G. Friedrich1
1Libin Cardiovascular Institute at the University of Calgary, Calgary, Canada; 2Siemens Medical Solutions, Calgary, Canada; 3Siemens Corporate Research Inc., Baltimore, Maryland, USA
AASPIR (Asymmetric Adiabatic Spectral Inversion Recovery) was compared with STIR (Short T1 Inversion Recovery) for T2-weighted cardiovascular magnetic resonance (CMR) imaging of global and regional myocardial edema. Our findings support the implementation of AASPIR instead of STIR to visualize myocardial edema, as AASPIR allows for increased SNR and improved image quality.
1013.
T2* Measurements in Myocardial Iron Overload: Comparison of
Error Models on Optimized
Analysis Protocol
Marco Borri1
1University of Turin, Turin, Italy
Iron-induced heart failure is the main cause of death in transfusion-dependent anemia. In the presence of tissue iron, the shortening of the relaxation time constant T2* is used for detection of cardiac iron. It has been shown that patients with short T2* - corresponding with myocardial iron loading - have greater risk of systolic dysfunction. T2* measurements are performed with standardized protocols. An error estimation would help the clinical comparison of T2* measurements, especially in single patient’s follow-up. In this work an optimized analysis protocol is indicated and five different error models are compared.
1014. Comparing Myocardial T2* and T2 Measurements in Thalassemia Patients
Taigang He1, Peter D. Gatehouse1, Gillian C. Smith1, Raad H. Mohiaddin1, Dudley J. Pennell1, David N. Firmin1
1Royal Brompton Hospital and Imperial College London, London, UK
The aim of this study is to compare myocardial T2* and T2 measurements in vivo in order to establish the relationship between them. In total 137 thalassemia patients were scanned on a 1.5T MRI scanner. It indicates that T2* of 20ms is a useful indicator to identify patient with cardiac iron. It also demonstrates that mmyocardial T2* measurement correlated linearly with T2 measurement in TM patients with iron overload. These findings suggests that both T2* and T2 measurements can be used for assessment of iron overload in the heart for transfusion dependent diseases such as thalassemia.
1015. Multi-Spiral MRI for Cardiac T2-Star DeterminationPhilipp Ehses1, Nicole Seiberlich1, Peter Nordbeck1, Florian Fidler2, Peter Michael Jakob1, 2, Wolfgang Rudolf Bauer1
1University of Würzburg, Würzburg, Germany; 2Research Center Magnetic-Resonance-Bavaria, Würzburg, Germany
Cardiovascular T2* magnetic resonance imaging is a valuable tool in the diagnosis of heart disease. In this work, a multi-spiral method for cardiac T2* determination is presented. A multi-spiral sequence is one that acquires each spiral arm multiple times after an excitation in order to generate multiple T2* contrasts. The spiral trajectory was chosen because it inherently refocuses motion- and flow-induced phase errors, which can be beneficial for cardiac applications.
1016. Postmortem Insitu MRI as an Adjunct to Autopsy for the Diagnosis of Myocardial Infarction
Christian Jackowski1, 2, Marcel Warntjes1, 3, Anders Persson1, Michael Thali2, Johan Berge4
1University of Linköping, Linköping, Sweden; 2University of Bern, Bern, Switzerland; 3Division of Clinical Physiology, University of Linköping, Linköping, Sweden; 4Department of Forensic Medicine, Linköping, Sweden
Autopsy diagnosis of myocardial infarction (MI) is still challenging because many lethal ischemic events do not lead to visible myocardial alterations. In these cases the lack of survival time prohibits myocardial reactions after ischemia, such as edema and inflammatory responses. Postmortem non-contrast enhanced insitu MRI (pm-MRI) may support the diagnosis of peracute MI. Being extremely sensitive to water distribution alterations within the myocardial tissue pm-MRI can accurately visualize areas of decreased micro-circulation. The extent of the ischemia is shown by a lowered signal in T2-weighted and proton density weighted images that have been optimized for the post-mortem conditions. As pm-MRI also reliably demonstrates acute, subacute and chronic infarction it might even serve as an alternative in cases in which traditional autopsy is refused for different reasons.
Kyle Stephan McCommis1, Ioannis Koktzoglou2, Haosen Zhang1, Debiao Li2, Robert J. Gropler1, Jie Zheng1
1Washington University School of Medicine, St. Louis, Missouri, USA; 2Northwestern University, Chicago, Illinois, USA
Double-inversion-recovery (DIR) and diffusion-weighted (DW) prepared T2 images were obtained to determine the myocardial oxygen extraction fraction (OEF) in stenotic canines. These T2 and hyperemic OEF values were determined in the left-anterior descending (LAD) stenosis-subtended region and the remote normal left-circumflex (LCX) region. No significant T2 or OEF differences were found between the two methods. However, the DW technique shows better image quality and OEF accuracy when irregular EKG-triggering or arrhythmias occurs.
1018. Myocardial Iron Distribution in Thalassemia: An in Vivo Study with Black Blood T2* Imaging
Taigang He1, Peter D. Gatehouse1, Dudley J. Pennell1, David N. Firmin1
1Royal Brompton Hospital and Imperial College London, London, UK
A black blood T2* technique was employed to investigate myocardial iron distribution in 55 thalassemia patients. The study was conducted on a 1.5T MRI scanner. Images were obtained in the mid-ventricular with 8 echo times and compared for each patient. This is the first in vivo study to demonstrate that myocardial iron deposition is uneven and dominantly in the epimyocardial region in iron overloaded thalassemia patients. This finding agrees well with previously published autopsy reports. These data suggest that T2* measurements in-vivo should use large transmural regions of interest.
1019. Longitudinal Analysis of Heart and Liver Iron in Thalassemia Major
Leila Noetzli1, Nilesh Ghugre1, Thomas Coates1, John Wood1
1Childrens Hospital Los Angeles, Los Angeles, California , USA
The relationship between heart and liver iron in patients with thalassemia major has been complex and ambiguous. There has been evidence of high liver iron being associated with high heart iron, but there seems to be no correlation between the two at any given time. To address this issue, we retrospectively analyzed patients who had three or more MRIs to estimate their liver and heart iron. Through this longitudinal analysis, we found that the majority of patient’s hepatic iron concentration (HIC) versus cardiac R2* trajectories follow a counterclockwise hysteresis loop. In particular, heart iron lags with respect to liver iron. This finding is helpful to understand the complex relationship between heart and liver iron movement.
Hall D Monday 14:00-16:00
Zhangwei Wang1, Timothy J. Mosher1, Christopher M. Collins1
1Penn State University, Hershey, Pennsylvania, USA
Little information has been published regarding the SAR distributions in extremities using dedicated extremity coils. This has led to gross extrapolations from data calculated for other parts of the body, such as the head, to determine operating limits in extremity imaging. Here we evaluate what RF power levels can be used in imaging of the human knee with a dedicated extremity coil without exceeding IEC or FDA limits on SAR or temperature.
1046. SAR Evaluation of 7.0 Tesla Perfusion Imaging with Arterial Spin Labeling Coil
Shumin Wang1, Hellmut Merkle1, Lalith Talagala1
1LFMI/NINDS/NIH, Bethesda, Maryland, USA
We examined the safety of neck labeling coils at 7.0 Tesla by using both numerical simulations and experimental data. This study combines the SAR contribution of a CASL neck labeling coil during RF labeling and that of a volume transmit coil during image acquisition. Results indicate that CASL perfusion with a neck labeling coil will be possible at even higher fields without exceeding the SAR guidelines.
1047. 9.4 T RF Heating: In Vivo Thermoregulatory Temperature Response in Porcine Models
Devashish Shrivastava1, Robert Schlentz1, Jeramy Kulesa1, Lance DelaBarre1, Carl Snyder1, Timothy Hanson1, J. Thomas Vaughan1
1University of Minnesota, Minnesota, USA
In vivo thermoregulatory response to RF heating at 9.4 T was studied by measuring temperatures in the heads of eight human-sized porcine models. Temperatures were measured in the scalp and brain by fluoroptic thermometry. Continuous wave RF power was delivered for 2.5-3.4 hours to four anesthetized animals. A four loop head coil was used, which was tuned to 400 MHz. The SAR was maintained close to 3 W/kg. Sham RF was delivered to the other four anesthetized animals to understand the effect of anesthesia on temperatures. Run-away heating response was seen in three out of four RF heated animals.
1048. Proton Resonance Frequency Shift Based NMR Thermometry for Ultra-High Field RF Safety Appl
Devashish Shrivastava1, Lance DelaBarre1, Shalom Michaeli1, Carl Snyder1, Timothy Hanson1, J. Thomas Vaughan1
1University of Minnesota, Minnesota, USA
The relative variation in the slopes of proton resonance frequency shift related phase changes was studied over 34.6 and 40.6 C in a non-perfused porcine brain at 7 T. This was done to develop an MR thermometry technique with sub-degree celsius accuracy to measure RF heating in porcine models at ultra-high fields. The phase-change slope varied between (-0.01 ppm/ C) and (-0.015 ppm/ C) in the porcine brain.
1049. Subjective Acceptance of 7T: Initial Experience in the First 210 Subjects
Jens Matthias Theysohn1, 2, Stefan Maderwald1, 2, Oliver Kraff1, 2, Christoph Moenninghoff1, 2, Wolfgang P. Becker1, 2, Patrick Kokulinsky1, 2, Michael Forsting1, 2, Mark E. Ladd1, 2, Susanne C. Ladd1, 2
1University Duisburg-Essen, Essen, Germany; 2University Hospital Essen, Essen, Germany
The introduction of ultra high field MRI systems for clinical human imaging leads to a raised consciousness regarding subjective patient acceptance and appearance of side-effects. We present our data collected from the first 210 human subjects undergoing a 7T MRI examination. Following the examination, potential sources of discomfort and side effects were rated on a 10-point scale and documented. General acceptance was high and side-effects tolerable. We believe that the willingness to undergo such an examination will be even higher if medical benefit for the individual is expected. No critical situation occurred.
1050. Lowering the Imager Significantly Reduces the Field Exposure of MRI Occupational Workers
Adnan Trakic1, Hua Wang1, Feng Liu1, Hector Sanchez Lopez1, Ewald Weber1, Stuart Crozier1
1The University of Queensland, Brisbane, Australia
In MRI, healthcare workers can be exposed to strong static and time-varying magnetic fields outside the imager, which can lead to the stimulation of electric fields in the body. Tissue of the central and peripheral nervous system (CPNS) in the head and torso is particularly susceptible. Reported is a simple solution that can notably reduce the head/trunk exposure of MRI operators to both static and low-frequency magnetic fields. The numerical results indicate that the upper body CPNS exposure can be reduced by factors of up to 50 or more, when the scanner is lowered by 1 m in height relative to the normal operator position.
1051. Simple Analytical Equation of the Induced E-Field
Esra Abaci1, Emre Kopanoglu1, Vakur Behcet Erturk1, Ergin Atalar1
1Bilkent University, Ankara, Turkey
During MRI, due to the time varying magnetic field, electric field is induced. To derive simplified expression of induced E-field in a cylindrical homogenous volume with radius ρ 0 and conductivity s the gradient fields are assumed to be uniform. The analytical E-field expression is simplified using low frequency based assumptions. The result satisfies the expected conditions, e.g. the divergence of E-field is zero and also it is in line with our intuitive understanding on what E field should be. With this simplified expression, electric field behavior inside the body can easily be defined without an additional computational work.
1052. Induced Magnetic Forces in the Human Head During MRI Procedures: A Group Analysis
Ruiliang Wang1, Dardo Tomasi1, Gene-Jack Wang1, Elisabeth C. Caparelli1, Rita Z. Goldstein1, Nora D. Volkow2, Joanna S. Fowler1
1Brookhaven National Laboratory, Upton, USA; 2National Institutes of Health, Bethesda, USA
Understanding the complex distribution of magnetic field gradients and the induced magnetic forces in human head during magnetic resonance imaging is an important safety issue, particularly for high filed MRI. The magnetic force acting on biological tissues that are exposed to an external magnetic field is proportional to tissue susceptibility and the spatial distribution of the static magnetic field. The aim of this work was to map the magnetic force acting on biological tissues of the human head when the subject’s heads are placed in the homogeneous magnetic field of an MRI scanner for a group of healthy subjects
1053. Tailoring of Gradient Coils for Numerical Exposure Evaluations Based on Experimentally Measured B-Field
Feng Liu1, Adnan Trakic1, Hector Sanchez Lopez1, Ewald Weber1, Stuart Crozier1
1The University of Queensland, Brisbane, Australia
Assessment of MRI worker exposures to pulsed magnetic fields produced by gradient coils has recently attracted a lot of awareness in the field of occupational health and safety. To accurately model the exposures, a full three-dimensional distribution of the magnetic field in the vicinity of the magnet end is required. Unfortunately, for many MRI installations, the coil pattern that generates this magnetic field is often not provided by the manufacturer. A method is presented in which the prediction of a current distribution that generates a nearly identical magnetic field pattern is constrained by a number of experimentally measured magnetic field sample points outside the gradient set of interest. The method takes into consideration other important descriptors such as field uniformity in the working volume, gradient coil geometry, driving current, gradient strength, active shielding etc. To demonstrate the application of the method, current density and matching magnetic field distributions of x- and z-axis gradient coils are derived. This enables robust, accurate evaluations of exposures of tissue-equivalent numerical worker models without pre-knowledge of gradient coil patterns.
1054.
Tissue-Mimicking Phantoms for a Combined Magnetic Resonance (MR)/ultra-Wideband
(UWB)
Radar Technique
Florian Thiel1, Florian Schubert1, Werner Hoffmann1, Frank Seifert1
1Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany
Our research is aimed towards the synergetic technological development of ultra-broadband (UWB) sounding combined with magnetic-resonance imaging (MRI), to access innovative fields of application such as the imaging of cardiac blood vessels and heart beat monitoring, accurate modelling of electromagnetic wave propagation through heterogeneous, malignant and benign, biological tissue for high-field MRI, and fast and precise identification and localisation of breast cancer. As our first step towards this ambitious aim we report on moveable multilayer tissue-like phantoms specifically designed for testing and development of a UWB-MRI combination setup.
Florian Fidler1, Toni Hippmann2, Marcus Warmuth3, Philipp Ehses4, Peter Nordbeck3, Michael T. Friedrich5, Wolfgang Geistert5, Walter Kullmann2, Peter Michael Jakob, 14, Wolgang Rudolf Bauer3
1Research Center Magnetic-Resonance-Bavaria, Würzburg, Germany; 2Fachhochschule Würzburg-Schweinfurt, Schweinfurt, Germany; 3University Hospital Würzburg, Würzburg, Germany; 4University of Würzburg, Würzburg, Germany; 5Biotronik GmbH & Co. KG, Berlin, Germany
The understanding of heating effects in MRI, especially in patients with medical implants, is one of the most important issues in MRI safety. Local electric fields are known as the cause of implant heating, but these are in general not accessible. The vast majority of the electric field is induced from eddy currents generated by the high frequency magnetic B1-field. The purpose of this work was to give a quantitative comparison of SAR maps and therefore heating results on different MRI systems and a simulation based on the knowledge of the B1-field.
Hall D Monday 14:00-16:00
Xu Chu1, Juan Sabate2, Yudong Zhu2
1GE Global Research Center, Shanghai, People's Republic of China; 2GE Global Research Center, Niskayuna, New York, USA
Current variation in a transmit coil due to load change can be substantial in a setup using a conventional RF power amplifier. The capability of a newly developed ultra-low output impedance RF power amplifier in suppressing such current variation is explored. The new amplifier, when connected to drive a transmit coil with L-type input-matching network, acts approximately as a current source, suppressing current variation due to load change and/or EM coupling. Meanwhile, the output-matching network of the MOSFET transforms the input impedance of the coil into the optimum load of the MOSFET, hence maximizing the available output power.
Adam Martin Winchell1, 2, Ralf Berthold Loeffler1, Yong Zhang1, Ruitian Song1, Kathleen J. Helton1, Lawrence L. Wald3, Claudia Maria Hillenbrand1
1St. Jude Children's Research Hospital, Memphis, Tennessee, USA; 2University of Memphis and UTHSC Joint Biomedical Engineering Program, Memphis, Tennessee, USA; 3Massachusetts General Hospital, Charlestown, Massachusetts, USA
A complete territorial brain perfusion system was developed using three independent surface-coils for the left, right carotid and vertebral arteries. Three independent trigger signals controlled by the sequence program gated a single external RF pulse to apply flow-driven adiabatic spin inversion for imaging. This low cost approach was demonstrated in both phantom and volunteer measurements. The volunteer measurements produced well-defined and localized territorial perfusion images which correspond with expected normal physiological conditions.
1091. RF Current Source Development for Parallel Transmit Arrays Using a High Power MOSFET
WonJe Lee1, Eddy B. Boskamp, Thomas M. Grist, Krishna N. Kurpad
1Uinversity of Wisconsin-Madison, Madison, USA
RF current source technology is gaining ground in parallel transmit arrays in order for B1 field pattern and local SAR control in high fields. In this work we present a RF current source development using a high power MOSFET by means of driven current amplitude and suppression of current induced by a neighboring element. Experimental results demonstrate improved craven current efficiency and reliability against load impedance changes. Simultaneously, current induced by a neighboring element is suppressed by a factor of 17 dB at the closest loop to loop distance by shunting the output capacitance of the chosen MOSFET.
1092. Design of a Strip Transmit Coil/Array for Low Field Open MR
Bing Wu1, 2, Jun Gao1, Jiabin Yao1, Cunli Zhang1, Xiaoliang Zhang2, 3
1GE Healthcare, Beijing, People's Republic of China; 2UCSF, San Francisco, California , USA; 3UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco & Berkeley, California , USA
RF coils with microstrip transmission line structure have shown the advantages for high and ultrahigh field MRI due to the excellent high frequency performance. In this work, we explore the feasibility of transmit body coil or coil array design using microstrip design technique for low-field open MR applications. Result shows that the proposed microstrip transmit (Tx) coil or parallel transmit array appears to be more compact and efficient than the conventional saddle-type transmit coils.
1093. An 8 Channel TX-RX Head Array for Improved SNR at 3T
Frank Resmer1, Markus Klarhöfer2, Titus Lanz1
1Rapid Biomedical GmbH, Rimpar, Germany; 2University of Basel, Basel, Switzerland
The design of an 8 channel TX-RX Array for 3T is described. It provides an SNR comparable to a volume coil of similar dimensions. Sufficient decoupling between elements is vital with TX-RX arrays. So far TX-RX arrays have been built with strip lines or gap designs to decouple individual elements. These approaches provide good intrinsic decoupling but also reduce the coil sensitivity. The coil presented here uses a conventional design with a capacitive decoupling network and so combines a high SNR with good element decoupling.
1094. Efficiency of a 3T Whole Body 16 Channel TEM Transmit Array
Ed Boskamp1, Scott Lindsay1, Patrick Gross2, Hans-Peter Fautz2, Mika Vogel2, John Lorbiecki1, Yudong Zhu3
1GE Healthcare, Waukesha, Wisconsin, USA; 2GE Research, Munich, Germany; 3GE Research, Niskayuna, New York, USA
A 3T whole body 16 channel TEM style transmit array was built and compared to an 8 loop whole body transmit array. The new 16 channel version has an efficiency of 0.231 uT /ãW of B+1 in the center of the coil when driven in an emulated homogeneous birdcage mode. The new array displays lower temperature than the 8 loop design. This array is connected to an 8 channel transmit chain. Each channel is sending power via splitter to 2 rungs, which can be opposite (180 degree phase difference) or neighboring (22.5 degree phase difference)
1095. 7 Tesla Localized RF Excitation/Reception Using a Highly Coupled Coil and Without B1 Measurements
Tamer S. Ibrahim1, YiK-Kiong Hue1, Lin Tang2
1University of Pittsburgh, Pittsburgh, Pennsylvania, USA; 2University of Oklahoma, Norman, Oklahoma, USA
The presented results demonstrate that by properly modeling the load, transmit/receive array, and the excitation/reception scheme, an RF power-controlled B1 shimming can be 1) guided with simulations that require a minimum of computational time required (seconds) and 2) efficiently implemented without any B1 measurements. Localized excitation/reception is demonstrated using a 7T system.
1096.
Evaluation of a Phase Shifting Matrix for Body Coil B1+
Shimming in a Dielectric Phantom
Elisabeth Beermann1, Patrick Gross2
1GE Healthcare, Solingen, Germany; 2GE Global Research, Munich, Germany
One challenges in high field MRI is the B1-field inhomogeneity due to particular patient RF permittivity. This results in artifacts in the MR images and thus can compromise their diagnostic value. RF shimming and parallel transmit offer a potential solution to this challenge. In order to interface an 8-channel system with a 16-channel transverse-electromagnetic (TEM) body-array, the use of a phase shifting or Butler matrix was investigated and B1 shimming in a dielectric phantom was performed. The results for a dielectric phantom thus indicate that the advantages of using a phase shifting matrix are similar to those in a non-dielectric phantom previously published.
1097. Preamp-Like Decoupling and Amplitude Modulation in CMCD Amplifiers for Transmit Arrays
Jeremiah Aaron Heilman1, Natalia Gudino, Matthew J. Riffe, Markus Vester2, Mark A. Griswold
1Case Western Reserve University, Cleveland, Ohio, USA; 2Siemens Medical Solutions, Erlangen, Germany
Development of current-mode class-D amplifier, including improvements for amplitude modulation, greater efficiency, and decoupling.
Hall D Monday 14:00-16:00
1130. A Simple Vector Modulator Approach to Phase and Amplitude Control for B1 Shimming
Ke Feng1, Xiaojun Chen1, William A. Grissom2, Douglas C. Noll2, Mary Preston McDougall1, Steven M. Wright1
1Texas A&M University, College Station, Texas, USA; 2University of Michigan, Ann Arbor, Michigan, USA
B1 shimming is an alternative approach to Transmit SENSE as a method of compensating for full-wave effects at high fields. In order to perform B1 shimming, independent amplitude and phase control of the overall RF pulse is required for each element or input port of a multi-port coil. Digital attenuators and phase shifters with sufficient resolution are quite expensive. This paper presents an inexpensive alternative which combines a vector modulator with digital potentiometers to realize a simple and scalable system to control an array for B1 shimming. In addition, by replacing the digital potentiometers with more expensive fast digital-to-analog boards, the system is capable of full modulation for transmit SENSE.
1131. RF Switching Matrix Enables 128 Channel Architecture and Dynamic Element-To-Receiver Routing
Yuan Ma1, Jennifer A. Black1, Vanish K. Dabra1, William Peterson1
1GE Healthcare, Waukesha, Wisconsin, USA
A high linearity, low-noise radio frequency switching matrix has been created to enable 128-channel architecture and dynamic element-to-receiver routing. This was accomplished using RF simulation tools, careful component selection, and programmable intelligence control.
1132. A Wire-Free, Radio-Frequency, Shielded Projection Window for MRI Suites
David Ian Hoult1, Patricia Gervai1, Uta Sboto-Frankenstein1
1National Research Council Institute for Biodiagnostics, Winnipeg, Canada
The investigation by fMRI of neural mechanisms associated with visual stimuli is now relatively common. However, the absence of high-quality, wire-free projection windows in MRI suites, particularly at the back of the magnet, often forces investigators to place video projectors inside the shielded room. This poses potential hazards including the risk of projector malfunction and over-heating. Thus a salt-solution window with good optical properties is proposed as a solution to this problem.
Adrian Rengle1, Hélène Ratiney1, Adriana Bucur1, Sophie Cavassila1, Olivier Beuf1
1INSA-Lyon, Université Lyon 1, Villeurbanne, France
In the field of small animal imaging, the interest for phased-array coil imaging is growing but high field MR experimental systems with multiple receiver channels are still rare and the upgrade of existing systems is relatively expensive. In this work, a standard 4.7T Bruker Biospec Avan