Andreas Graessl

Max-Delbrück-Centrum für Molekulare Medizin, Berlín, Berlin, Germany

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Publications (25)70.55 Total impact

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    ABSTRACT: The objective of this study was to document and review advances and groundbreaking progress in cardiac and body MR at ultrahigh fields (UHF, B0 ≥ 7.0 T) with the goal to attract talent, clinical adopters, collaborations and resources to the biomedical and diagnostic imaging communities. This review surveys traits, advantages and challenges of cardiac and body MR at 7.0 T. The considerations run the gamut from technical advances to clinical opportunities. Key concepts, emerging technologies, practical considerations, frontier applications and future directions of UHF body and cardiac MR are provided. Examples of UHF cardiac and body imaging strategies are demonstrated. Their added value over the kindred counterparts at lower fields is explored along with an outline of research promises. The achievements of cardiac and body UHF-MR are powerful motivators and enablers, since extra speed, signal and imaging capabilities may be invested to overcome the fundamental constraints that continue to hamper traditional cardiac and body MR applications. If practical obstacles, concomitant physics effects and technical impediments can be overcome in equal measure, sophisticated cardiac and body UHF-MR will help to open the door to new MRI and MRS approaches for basic research and clinical science, with the lessons learned at 7.0 T being transferred into broad clinical use including diagnostics and therapy guiding at lower fields. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.
    NMR in Biomedicine 02/2015; DOI:10.1002/nbm.3268 · 3.56 Impact Factor
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    ABSTRACT: This study examines the subjective acceptance during UHF-CMR in a cohort of healthy volunteers who underwent a cardiac MR examination at 7.0T. Within a period of two-and-a-half years (January 2012 to June 2014) a total of 165 healthy volunteers (41 female, 124 male) without any known history of cardiac disease underwent UHF-CMR. For the assessment of the subjective acceptance a questionnaire was used to examine the participants experience prior, during and after the UHF-CMR examination. For this purpose, subjects were asked to respond to the questionnaire in an exit interview held immediately after the completion of the UHF-CMR examination under supervision of a study nurse to ensure accurate understanding of the questions. All questions were answered with "yes" or "no" including space for additional comments. Transient muscular contraction was documented in 12.7% of the questionnaires. Muscular contraction was reported to occur only during periods of scanning with the magnetic field gradients being rapidly switched. Dizziness during the study was reported by 12.7% of the subjects. Taste of metal was reported by 10.1% of the study population. Light flashes were reported by 3.6% of the entire cohort. 13% of the subjects reported side effects/observations which were not explicitly listed in the questionnaire but covered by the question about other side effects. No severe side effects as vomiting or syncope after scanning occurred. No increase in heart rate was observed during the UHF-CMR exam versus the baseline clinical examination. This study adds to the literature by detailing the subjective acceptance of cardiovascular magnetic resonance imaging examinations at a magnetic field strength of 7.0T. Cardiac MR examinations at 7.0T are well tolerated by healthy subjects. Broader observational and multi-center studies including patient cohorts with cardiac diseases are required to gain further insights into the subjective acceptance of UHF-CMR examinations.
    PLoS ONE 01/2015; 10(1). DOI:10.1371/journal.pone.0117095 · 3.53 Impact Factor
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    ABSTRACT: This study is designed to examine the feasibility of diffusion-sensitized multishot split-echo rapid acquisition with relaxation enhancement (RARE) for diffusion-weighted ophthalmic imaging free of geometric distortions at 3.0 and 7.0 T in healthy volunteers and patients with intraocular masses. A diffusion-sensitized multishot split-echo RARE (ms-RARE) variant is proposed as an alternative imaging strategy for diffusion-weighted imaging. It is compared with standard single-shot echo planar imaging (EPI) and readout-segmented EPI in terms of geometric distortions in a structure phantom as well as in vivo at 3.0 and 7.0 T. To quantify geometric distortions, center of gravity analysis was carried out. Apparent diffusion coefficient (ADC) mapping in a diffusion phantom was performed to verify the diffusion sensitization within ms-RARE. An in vivo feasibility study in healthy volunteers (n = 10; mean age, 31 ± 7 years; mean body mass index, 22.6 ± 1.7 kg/m) was conducted at 3.0 and 7.0 T to evaluate clinical feasibility of ms-RARE. As a precursor to a broader clinical study, patients (n = 6; mean age, 55 ± 12 years; mean body mass index, 27.5 ± 4.7 kg/m) with an uveal melanoma and/or retinal detachment were examined at 3.0 and 7.0 T. In 1 case, the diseased eye was enucleated as part of the therapy and imaged afterward with magnetic resonance microscopy at 9.4 T. Macrophotography and histological investigation was carried out. For qualitative assessment of the image distortion, 3 independent readers reviewed and scored ms-RARE in vivo images for all subjects in a blinded reading session. Statistical significance in the difference of the scores (a) obtained for the pooled ms-RARE data with b = 0 and 300 s/mm and (b) for the 3 readers was analyzed using the nonparametric Mann-Whitney test. The assessment of geometric integrity in phantom imaging revealed the ability of ms-RARE to produce distortion-free images. Unlike ms-RARE, modest displacements (2.3 ± 1.4 pixels) from the fast low angle shot imaging reference were observed for readout-segmented EPI, which were aggravated for single-shot EPI (8.3 ± 5.7 pixels). These observations were confirmed in the in vivo feasibility study including distortion-free diffusion-weighted ophthalmic images with a 0.5 × 0.5 × 5 mm spatial resolution at 3.0 T and as good as 0.2 × 0.2 × 2 mm at 7.0 T. The latter represents a factor of 40 enhancement in spatial resolution versus clinical protocols recently reported for diffusion-weighted imaging of the eye at 1.5 T. Mean ADC values within the vitreous body were (2.91 ± 0.14) × 10 mm/s at 3.0 T and (2.93 ± 0.41) × 10 mm/s at 7.0 T. Patient data showed severe retinal detachment in the anatomical images. Whereas the tumor remained undetected in T1-weighted and T2-weighted imaging at 3.0/7.0 T, in vivo ADC mapping using ms-RARE revealed the presence of a uveal melanoma with a significant contrast versus the surrounding subretinal hemorrhage. This observation was confirmed by high-resolution ex vivo magnetic resonance microscopy and histology. Qualitative analysis of image distortion in ms-RARE images obtained for all subjects yielded a mean ± SD image quality score of 1.06 ± 0.25 for b = 0 s/mm and of 1.17 ± 0.49 for b = 300 s/mm. No significant interreader differences were observed for ms-RARE with a diffusion sensitization of b = 0 s/mm and 300 s/mm. This work demonstrates the capability of diffusion-sensitized ms-RARE to acquire high-contrast, high-spatial resolution, distortion-free images of the eye and the orbit at 3.0 and 7.0 T. Geometric distortions that are observed for EPI-based imaging approaches even at lower field strengths are offset by fast spin-echo-based imaging techniques. The benefits of this improvement can be translated into the assessment of spatial arrangements of the eye segments and their masses with the ultimate goal to provide guidance during diagnostic treatment of ophthalmological diseases.
    Investigative Radiology 01/2015; DOI:10.1097/RLI.0000000000000129 · 4.45 Impact Factor
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    ABSTRACT: This review documents technical progress in ophthalmic magnetic resonance imaging (MRI) at ultrahigh fields (UHF, B0 ≥ 7.0 T). The review surveys frontier applications of UHF-MRI tailored for high spatial resolution in vivo imaging of the eye, orbit and optic nerve. Early examples of clinical ophthalmic UHF-MRI including the assessment of melanoma of the choroid membrane and the characterisation of intraocular masses are demonstrated. A concluding section ventures a glance beyond the horizon and explores research promises along with future directions of ophthalmic UHF-MRI.
    Klinische Monatsblätter für Augenheilkunde 12/2014; 231(12):1187-1195. DOI:10.1055/s-0034-1383365 · 0.70 Impact Factor
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    ABSTRACT: Imaging of the human eye in vivo at 7 Tesla is an advanced magnetic resonance imaging application and not yet part of routine clinical practice. However, ultra highfield magnetic resonance imaging of the human eye provides benefits for in vivo evaluation of anatomy and morphology in sub-millimeter spatial resolution for today's clinical science and for future clinical applications. To this end the purpose of the study was to examine the applicability of a 6 channel transceiver radiofrequency coil array in conjunction with an optoacoustic triggering regime for imaging of the orbital and intracranial structures at 7 Tesla in vivo. Magnetic resonance imaging was performed in 7 healthy volunteers (3 female/4 male) with T1-weighted 3D fast low angle shot and 2D T2-weighted rapid acquisition with refocused echoes sequences. The six-channel coil array supports high spatial resolution imaging with an in plane resolution of 0.25 x 0.28 mm. This facilitates the depiction of anatomical details of the eye, the orbit, the optic nerve and the optical nerve sheath. Motion related artifacts could be eliminated using optoacoustic triggering regime. Our results underline the benefits of multi-element transceiver RF coil array technology and trigger protocols tailored for MRI eye applications in vivo.
    Experimental Eye Research 06/2014; DOI:10.1016/j.exer.2014.05.017. · 3.02 Impact Factor
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    ABSTRACT: Imaging of the human eye in vivo at 7 Tesla is an advanced magnetic resonance imaging application and not yet part of routine clinical practice. However, ultra highfield magnetic resonance imaging of the human eye provides benefits for in vivo evaluation of anatomy and morphology in sub-millimeter spatial resolution for today's clinical science and for future clinical applications. To this end the purpose of the study was to examine the applicability of a 6 channel transceiver radiofrequency coil array in conjunction with an optoacoustic triggering regime for imaging of the orbital and intracranial structures at 7 Tesla in vivo. Magnetic resonance imaging was performed in 7 healthy volunteers (3 female/4 male) with T1-weighted 3D fast low angle shot and 2D T2-weighted rapid acquisition with refocused echoes sequences. The six-channel coil array supports high spatial resolution imaging with an in plane resolution of 0.25 x 0.28 mm. This facilitates the depiction of anatomical details of the eye, the orbit, the optic nerve and the optical nerve sheath. Motion related artifacts could be eliminated using optoacoustic triggering regime. Our results underline the benefits of multi-element transceiver RF coil array technology and trigger protocols tailored for MRI eye applications in vivo.
    Experimental Eye Research 06/2014; 125. DOI:10.1016/j.exer.2014.05.017 · 3.02 Impact Factor
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    ABSTRACT: Hintergrund: Die Ultra-Hochfeld-MRT (UHF-MRT) bei 7 Tesla stellt ein vielversprechendes Bildgebungsverfahren für die ophthalmologische Forschung und zukünftig auch zur Diagnostik und Differenzierung von Raumforderungen dar. Durch das höhere Signal-zu-Rausch-Verhältnis im Vergleich zu geringeren Magnetfeldstärken verfügt diese Technik über Entwicklungspotenzial hinsichtlich einer räumlich hochaufgelösten, ophthalmologischen Tumordiagnostik und der Untersuchung von Läsionen des Sehnervens. Die physikalisch bedingten, längeren Echo- und Repetitions-Zeiten und die daraus resultierenden, längeren Scanzeiten führen in der Praxis jedoch häufig zu vermehrten Bewegungsartefakten. Die Minimierung dieser Artefakte ist daher eine wesentliche Herausforderung bei der UHF-MRT am Auge. Ziel der Untersuchung war die Etablierung von Bildgebungsprotokollen mit Blickfixierungstrigger zur Reduzierung von Bewegungsartefakten bei der in vivo 7 Tesla MR-Bildgebung. Methodik: An Probanden (n = 17) wurden verschiedene MR-Bildgebungssequenzen (T1w 3D Flash, 2D T2w Turbo Spin Echo) mit einem 7 Tesla MRT und einem speziellen Triggerprotokoll durchgeführt. Dazu schauten die Probanden über eine Spiegelvorrichtung auf ein außerhalb des MRT-Scanners positioniertes Target. Auf dieses wurde eine Animation projiziert, die die Probanden für ca. 3 Sekunden fixieren mussten. Der Lidschluss und die Bewegung der Augen waren dabei nur in einer Pause, welche in die Animation eingebaut wurde, erlaubt. Während der Pause wurde die Datenaufnahme der MR-Sequenz jeweils für den gleichen Zeitraum unterbrochen und mit jedem Start der Blickfixierung fortgesetzt. Ergebnisse: Die Studie zeigt, dass das entwickelte MR-Protokoll mit einer sequenziell getriggerten Datenakquisition die Qualität der MR-Bildgebung bei 7T deutlich verbessert. Das Protokoll ermöglicht in vivo MR-Untersuchungen von Bulbus und Orbita mit einer räumlichen Auflösung von bis zu (0,2 x 0,2 x 1) mm und deutlich reduzierten Bewegungsartefakten. Schlussfolgerungen: Die UHF-MRT ermöglicht die hochauflösende, verzerrungsfreie morphologische Darstellung von Auge und Orbita im µm-Bereich. Die Technologie besitzt damit das Potenzial für klinische Anwendungen hinsichtlich verbesserter Tumordiagnostik und Bilgebung von Läsionen des Sehnervens.
    64. Tagung der Vereinigung Norddeutscher Augenärzte, Warnemünde; 05/2014
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    ABSTRACT: This study was designed to examine the feasibility of ophthalmic magnetic resonance imaging (MRI) at 7.0 T using a local 6-channel transmit/receive radiofrequency (RF) coil array in healthy volunteers and patients with intraocular masses. A novel 6-element transceiver RF coil array that makes uses of loop elements and that is customized for eye imaging at 7.0 T is proposed. Considerations influencing the RF coil design and the characteristics of the proposed RF coil array are presented. Numerical electromagnetic field simulations were conducted to enhance the RF coil characteristics. Specific absorption rate simulations and a thorough assessment of RF power deposition were performed to meet the safety requirements. Phantom experiments were carried out to validate the electromagnetic field simulations and to assess the real performance of the proposed transceiver array. Certified approval for clinical studies was provided by a local notified body before the in vivo studies. The suitability of the RF coil to image the human eye, optical nerve, and orbit was examined in an in vivo feasibility study including (a) 3-dimensional (3D) gradient echo (GRE) imaging, (b) inversion recovery 3D GRE imaging, and (c) 2D T2-weighted fast spin-echo imaging. For this purpose, healthy adult volunteers (n = 17; mean age, 34 ± 11 years) and patients with intraocular masses (uveal melanoma, n = 5; mean age, 57 ± 6 years) were investigated. All subjects tolerated all examinations well with no relevant adverse events. The 6-channel coil array supports high-resolution 3D GRE imaging with a spatial resolution as good as 0.2 × 0.2 × 1.0 mm, which facilitates the depiction of anatomical details of the eye. Rather, uniform signal intensity across the eye was found. A mean signal-to-noise ratio of approximately 35 was found for the lens, whereas the vitreous humor showed a signal-to-noise ratio of approximately 30. The lens-vitreous humor contrast-to-noise ratio was 8, which allows good differentiation between the lens and the vitreous compartment. Inversion recovery prepared 3D GRE imaging using a spatial resolution of 0.4 × 0.4 × 1.0 mm was found to be feasible. T2-weighted 2D fast spin-echo imaging with the proposed RF coil afforded a spatial resolution of 0.25 × 0.25 × 0.7 mm. This work provides valuable information on the feasibility of ophthalmic MRI at 7.0 T using a dedicated 6-channel transceiver coil array that supports the acquisition of high-contrast, high-spatial resolution images in healthy volunteers and patients with intraocular masses. The results underscore the challenges of ocular imaging at 7.0 T and demonstrate that these issues can be offset by using tailored RF coil hardware. The benefits of such improvements would be in positive alignment with explorations that are designed to examine the potential of MRI for the assessment of spatial arrangements of the eye segments and their masses with the ultimate goal to provide imaging means for guiding treatment decisions in ophthalmological diseases.
    Investigative radiology 03/2014; DOI:10.1097/RLI.0000000000000049 · 4.85 Impact Factor
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    ABSTRACT: A combination of magnetic resonance images with real-time high-resolution ultrasound known as fusion imaging may improve ophthalmologic examination. This study was undertaken to evaluate the feasibility of orbital high-field magnetic resonance and real-time colour Doppler ultrasound image fusion and navigation. This case study, performed between April and June 2013, included one healthy man (age, 47 years) and two patients (one woman, 57 years; one man, 67 years) with choroidal melanomas. All cases underwent 7.0-T magnetic resonance imaging using a custom-made ocular imaging surface coil. The Digital Imaging and Communications in Medicine volume data set was then loaded into the ultrasound system for manual registration of the live ultrasound image and fusion imaging examination. Data registration, matching and then volume navigation were feasible in all cases. Fusion imaging provided real-time imaging capabilities and high tissue contrast of choroidal tumour and optic nerve. It also allowed adding a real-time colour Doppler signal on magnetic resonance images for assessment of vasculature of tumour and retrobulbar structures. The combination of orbital high-field magnetic resonance and colour Doppler ultrasound image fusion and navigation is feasible. Multimodal fusion imaging promises to foster assessment and monitoring of choroidal melanoma and optic nerve disorders. • Orbital magnetic resonance and colour Doppler ultrasound real-time fusion imaging is feasible • Fusion imaging combines the spatial and temporal resolution advantages of each modality • Magnetic resonance and ultrasound fusion imaging improves assessment of choroidal melanoma vascularisation.
    European Radiology 02/2014; 24(5). DOI:10.1007/s00330-014-3101-5 · 4.34 Impact Factor
  • Experimental Eye Research 01/2014; 125:89–94. · 3.02 Impact Factor
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    Proc. Intl. Soc. Mag. Reson. Med.; 01/2014
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    ABSTRACT: To design and evaluate a modular transceiver coil array with 32 independent channels for cardiac MRI at 7.0T. The modular coil array comprises eight independent building blocks, each containing four transceiver loop elements. Numerical simulations were used for B1 (+) field homogenization and radiofrequency (RF) safety validation. RF characteristics were examined in a phantom study. The array's suitability for accelerated high spatial resolution two-dimensional (2D) FLASH CINE imaging of the heart was examined in a volunteer study. Transmission field adjustments and RF characteristics were found to be suitable for the volunteer study. The signal-to-noise intrinsic to 7.0T together with the coil performance afforded a spatial resolution of 1.1 × 1.1 × 2.5 mm(3) for 2D CINE FLASH MRI, which is by a factor of 6 superior to standardized CINE protocols used in clinical practice at 1.5T. The 32-channel transceiver array supports one-dimensional acceleration factors of up to R = 4 without impairing image quality significantly. The modular 32-channel transceiver cardiac array supports accelerated and high spatial resolution cardiac MRI. The array is compatible with multichannel transmission and provides a technological basis for future clinical assessment of parallel transmission techniques at 7.0T. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 07/2013; DOI:10.1002/mrm.24903 · 3.40 Impact Factor
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    ISMRM 2013, Melbourne; 05/2013
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    ABSTRACT: This work demonstrates the feasibility of a hybrid radiofrequency (RF) applicator that supports magnetic resonance (MR) imaging and MR controlled targeted RF heating at ultrahigh magnetic fields (B0≥7.0T). For this purpose a virtual and an experimental configuration of an 8-channel transmit/receive (TX/RX) hybrid RF applicator was designed. For TX/RX bow tie antenna electric dipoles were employed. Electromagnetic field simulations (EMF) were performed to study RF heating versus RF wavelength (frequency range: 64 MHz (1.5T) to 600 MHz (14.0T)). The experimental version of the applicator was implemented at B0 = 7.0T. The applicators feasibility for targeted RF heating was evaluated in EMF simulations and in phantom studies. Temperature co-simulations were conducted in phantoms and in a human voxel model. Our results demonstrate that higher frequencies afford a reduction in the size of specific absorption rate (SAR) hotspots. At 7T (298 MHz) the hybrid applicator yielded a 50% iso-contour SAR (iso-SAR-50%) hotspot with a diameter of 43 mm. At 600 MHz an iso-SAR-50% hotspot of 26 mm in diameter was observed. RF power deposition per RF input power was found to increase with B0 which makes targeted RF heating more efficient at higher frequencies. The applicator was capable of generating deep-seated temperature hotspots in phantoms. The feasibility of 2D steering of a SAR/temperature hotspot to a target location was demonstrated by the induction of a focal temperature increase (ΔT = 8.1 K) in an off-center region of the phantom. Temperature simulations in the human brain performed at 298 MHz showed a maximum temperature increase to 48.6C for a deep-seated hotspot in the brain with a size of (19×23×32)mm(3) iso-temperature-90%. The hybrid applicator provided imaging capabilities that facilitate high spatial resolution brain MRI. To conclude, this study outlines the technical underpinnings and demonstrates the basic feasibility of an 8-channel hybrid TX/RX applicator that supports MR imaging, MR thermometry and targeted RF heating in one device.
    PLoS ONE 04/2013; 8(4):e61661. DOI:10.1371/journal.pone.0061661 · 3.53 Impact Factor
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    ABSTRACT: BACKGROUND: Functional and morphologic assessment of the right ventricle (RV) is of clinical importance. Cardiovascular magnetic resonance (CMR) at 1.5T has become gold standard for RV chamber quantification and assessment of even small wall motion abnormalities, but tissue analysis is still hampered by limited spatial resolution. CMR at 7T promises increased resolution, but is technically challenging. We examined the feasibility of cine imaging at 7T to assess the RV. METHODS: Nine healthy volunteers underwent CMR at 7T using a 16-element TX/RX coil and acoustic cardiac gating. 1.5T served as gold standard. At 1.5T, steady-state free-precession (SSFP) cine imaging with voxel size (1.2x1.2x6) mm3 was used; at 7T, fast gradient echo (FGRE) with voxel size (1.2x1.2x6) mm3 and (1.3x1.3x4) mm3 were applied. RV dimensions (RVEDV, RVESV), RV mass and RV function (RVEF) were quantified in transverse slices. Overall image quality, image contrast and image homogeneity were assessed in transverse and sagittal views. RESULTS: All scans provided diagnostic image quality. Overall image quality and image contrast of transverse RV views were rated equally for SSFP at 1.5T and FGRE at 7T with voxel size (1.3x1.3x4)mm3. FGRE at 7T provided significantly lower image homogeneity compared to SSFP at 1.5T. RVEDV, RVESV, RVEF and RVM did not differ significantly and agreed close between SSFP at 1.5T and FGRE at 7T (p=0.5850; p=0.5462; p=0.2789; p=0.0743). FGRE at 7T with voxel size (1.3x1.3x4) mm3 tended to overestimate RV volumes compared to SSFP at 1.5T (mean difference of RVEDV 8.2+/-9.3ml) and to FGRE at 7T with voxel size (1.2x1.2x6) mm3 (mean difference of RVEDV 9.3+/-8.6ml). CONCLUSIONS: FGRE cine imaging of the RV at 7T was feasible and provided good image quality. RV dimensions and function were comparable to SSFP at 1.5T as gold standard.
    Journal of Cardiovascular Magnetic Resonance 03/2013; 15(1):23. DOI:10.1186/1532-429X-15-23 · 4.44 Impact Factor
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    Journal of Cardiovascular Magnetic Resonance 01/2013; 15(1). DOI:10.1186/1532-429X-15-S1-W14 · 4.44 Impact Factor
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    Journal of Cardiovascular Magnetic Resonance 01/2013; 15(1). DOI:10.1186/1532-429X-15-S1-W2 · 4.44 Impact Factor
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    Journal of Cardiovascular Magnetic Resonance 01/2013; 15(1). DOI:10.1186/1532-429X-15-S1-W24 · 4.44 Impact Factor
  • ISMRM, Salt Lake City; 01/2013
  • ISMRM, Salt Lake City; 01/2013