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Bluemink JJ, Raaijmakers AJE, Koning W, Andreychenko A, Rivera DS, Luijten PR, Klomp DWJ, van den Berg CAT. Dielectric waveguides for ultrahigh field magnetic resonance imaging. Magn Reson Med 2015; 76:1314-24. [DOI: 10.1002/mrm.26007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Revised: 09/11/2015] [Accepted: 09/12/2015] [Indexed: 11/09/2022]
Affiliation(s)
- Johanna J. Bluemink
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Alexander J. E. Raaijmakers
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Wouter Koning
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Anna Andreychenko
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Debra S. Rivera
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Peter R. Luijten
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Dennis W. J. Klomp
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Cornelis A. T. van den Berg
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
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Spicher N, Maderwald S, Ladd ME, Kukuk M. Heart rate monitoring in ultra-high-field MRI using frequency information obtained from video signals of the human skin compared to electrocardiography and pulse oximetry. CURRENT DIRECTIONS IN BIOMEDICAL ENGINEERING 2015. [DOI: 10.1515/cdbme-2015-0018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
AbstractVideos of the human skin contain subtle color variations associated with the blood volume pulse. This remote photoplethysmography signal can be used for heart rate monitoring and represents an alternative to signals obtained from contact-based hardware. We developed an algorithm that estimates the heart rate in real-time from photoplethysmography signals and evaluate its performance in the context of ultra-high-field magnetic resonance imaging. We compare its accuracy to heart rate values estimated from electrocardiography and finger pulse oximetry triggers, obtained from MR vendor-provided hardware. For eight subjects, two experiments are conducted with the patient table outside and inside a 7 Tesla scanner. During both 5 min setups, heart rates from the algorithm and contact-based methods are stored. Their comparison suggests technical feasibility of the contactless method but that it is inferior in accuracy compared to contact-based hardware and that low heart rates (≤50 beats per minute) and adequate illumination are major challenges for practical feasibility.
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Affiliation(s)
- Nicolai Spicher
- 1Department of Computer Science, University of Applied Sciences and Arts Dortmund, 44227 Dortmund, Germany
| | - Stefan Maderwald
- 2Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, 45141 Essen, Germany
| | - Mark E. Ladd
- 3Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, 45141 Essen, Germany and Division of Medical Physics in Radiology, German Cancer Research Center, 69120 Heidelberg, Germany
| | - Markus Kukuk
- 1Department of Computer Science, University of Applied Sciences and Arts Dortmund, 44227 Dortmund, Germany
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Oezerdem C, Winter L, Graessl A, Paul K, Els A, Weinberger O, Rieger J, Kuehne A, Dieringer M, Hezel F, Voit D, Frahm J, Niendorf T. 16-channel bow tie antenna transceiver array for cardiac MR at 7.0 tesla. Magn Reson Med 2015; 75:2553-65. [PMID: 26183320 DOI: 10.1002/mrm.25840] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Revised: 05/22/2015] [Accepted: 06/20/2015] [Indexed: 02/03/2023]
Abstract
PURPOSE To design, evaluate, and apply a bow tie antenna transceiver radiofrequency (RF) coil array tailored for cardiac MRI at 7.0 Tesla (T). METHODS The radiofrequency (RF) coil array comprises 16 building blocks each containing a bow tie shaped λ/2-dipole antenna. Numerical simulations were used for transmission field homogenization and RF safety validation. RF characteristics were examined in a phantom study. The array's suitability for high spatial resolution two-dimensional (2D) CINE imaging and for real time imaging of the heart was examined in a volunteer study. RESULTS The arrays transmission fields and RF characteristics are suitable for cardiac MRI at 7.0T. The coil performance afforded a spatial resolution as good as (0.8 × 0.8 × 2.5) mm(3) for segmented 2D CINE MRI at 7.0T which is by a factor of 12 superior versus standardized protocols used in clinical practice at 1.5T. The proposed transceiver array supports 1D acceleration factors of up to R = 6 without impairing image quality significantly. CONCLUSION The 16-channel bow tie antenna transceiver 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 7.0 Tesla. Magn Reson Med 75:2553-2565, 2016. © 2015 Wiley Periodicals, Inc.
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Affiliation(s)
- Celal Oezerdem
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Lukas Winter
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Andreas Graessl
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Katharina Paul
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Antje Els
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Oliver Weinberger
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | | | | | - Matthias Dieringer
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Berlin, Germany
| | - Fabian Hezel
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Dirk Voit
- Biomedizinische NMR Forschungs GmbH am Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany
| | - Jens Frahm
- Biomedizinische NMR Forschungs GmbH am Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Göttingen, Germany
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Berlin, Germany
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Hess AT, Bissell MM, Ntusi NAB, Lewis AJM, Tunnicliffe EM, Greiser A, Stalder AF, Francis JM, Myerson SG, Neubauer S, Robson MD. Aortic 4D flow: quantification of signal-to-noise ratio as a function of field strength and contrast enhancement for 1.5T, 3T, and 7T. Magn Reson Med 2015; 73:1864-71. [PMID: 24934930 DOI: 10.1002/mrm.25317] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Revised: 04/28/2014] [Accepted: 05/22/2014] [Indexed: 01/10/2023]
Abstract
PURPOSE To investigate for the first time the feasibility of aortic four-dimensional (4D) flow at 7T, both contrast enhanced (CE) and non-CE. To quantify the signal-to-noise ratio (SNR) in aortic 4D flow as a function of field strength and CE with gadobenate dimeglumine (MultiHance). METHODS Six healthy male volunteers were scanned at 1.5T, 3T, and 7T with both non-CE and CE acquisitions. Temporal SNR was calculated. Flip angle optimization for CE 4D flow was carried out using Bloch simulations that were validated against in vivo measurements. RESULTS The 7T provided 2.2 times the SNR of 3T while 3T provided 1.7 times the SNR of 1.5T in non-CE acquisitions in the descending aorta. The SNR gains achieved by CE were 1.8-fold at 1.5T, 1.7-fold at 3T, and 1.4-fold at 7T, respectively. CONCLUSION The 7T provides a new tool to explore aortic 4D flow, yielding higher SNR that can be used to push the boundaries of acceleration and resolution. Field strength and contrast enhancement at all fields provide significant improvements in SNR.
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Affiliation(s)
- Aaron T Hess
- University of Oxford Centre for Clinical Magnetic Resonance Research, Division of Cardiovascular Medicine, Radcliffe Department of Medicine, Oxford, United Kingdom
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High spatial resolution coronary magnetic resonance angiography at 7 T: comparison with low spatial resolution bright blood imaging. Invest Radiol 2014; 49:326-30. [PMID: 24637588 DOI: 10.1097/rli.0000000000000047] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES The aim of this study was to compare bright blood high spatial resolution (HR) coronary magnetic resonance angiography (MRA) with low spatial resolution (LR) bright blood coronary MRA at 7 T. MATERIALS AND METHODS Twenty-four healthy volunteers underwent navigator-gated 3-dimensional imaging of the right coronary artery at 7 T using 2 sequences: HR bright blood and LR bright blood. Image postprocessing involved newly developed multiplanar reformatting to straighten the right coronary artery. Image quality was determined by vessel edge sharpness, signal-to-noise ratio, contrast-to-noise ratio, visible vessel length, and vessel diameter. RESULTS Vessel edge sharpness was statistically significantly higher in HR as compared with LR (0.57 ± 0.1 vs 0.46 ± 0.06; P < 0.001), at the cost of lower signal-to-noise ratio (HR, 32.9 ± 11.0 vs LR, 112.5 ± 48.9; P < 0.001) and contrast-to-noise ratio (HR, 17.9 ± 7.4 vs LR, 50.5 ± 26.1; P < 0.001). Visible vessel length and vessel diameter were similar for both sequences (P > 0.05). CONCLUSIONS High spatial resolution bright blood coronary MRA at 7 T is feasible and improves vessel edge sharpness as compared with LR bright blood imaging.
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Schmitter S, Wu X, Uğurbil K, Van de Moortele PF. Design of parallel transmission radiofrequency pulses robust against respiration in cardiac MRI at 7 Tesla. Magn Reson Med 2014; 74:1291-305. [PMID: 25411131 DOI: 10.1002/mrm.25512] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 09/15/2014] [Accepted: 10/13/2014] [Indexed: 12/18/2022]
Abstract
PURPOSE Two-spoke parallel transmission (pTX) radiofrequency (RF) pulses have been demonstrated in cardiac MRI at 7T. However, current pulse designs rely on a single set of B1(+)/B0 maps that may not be valid for subsequent scans acquired at another phase of the respiration cycle because of organ displacement. Such mismatches may yield severe excitation profile degradation. METHODS B1(+)/B0 maps were obtained, using 16 transmit channels at 7T, at three breath-hold positions: exhale, half-inhale, and inhale. Standard and robust RF pulses were designed using maps obtained at exhale only, and at multiple respiratory positions, respectively. Excitation patterns were analyzed for all positions using Bloch simulations. Flip-angle homogeneity was compared in vivo in cardiac CINE acquisitions. RESULTS Standard one- and two-spoke pTX RF pulses are sensitive to breath-hold position, primarily due to B1(+) alterations, with high dependency on excitation trajectory for two spokes. In vivo excitation inhomogeneity varied from nRMSE = 8.2% (exhale) up to 32.5% (inhale) with the standard design; much more stable results were obtained with the robust design with nRMSE = 9.1% (exhale) and 10.6% (inhale). CONCLUSION A new pTX RF pulse design robust against respiration induced variations of B1(+)/B0 maps is demonstrated and is expected to have a positive impact on cardiac MRI in breath-hold, free-breathing, and real-time acquisitions.
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Affiliation(s)
- Sebastian Schmitter
- University of Minnesota, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Xiaoping Wu
- University of Minnesota, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Kâmil Uğurbil
- University of Minnesota, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
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Keith GA, Rodgers CT, Hess AT, Snyder CJ, Vaughan JT, Robson MD. Automated tuning of an eight-channel cardiac transceive array at 7 tesla using piezoelectric actuators. Magn Reson Med 2014; 73:2390-7. [PMID: 24986525 PMCID: PMC4245186 DOI: 10.1002/mrm.25356] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Revised: 05/21/2014] [Accepted: 06/17/2014] [Indexed: 11/22/2022]
Abstract
Purpose Ultra-high field (UHF) MR scanning in the body requires novel coil designs due to B1 field inhomogeneities. In the transverse electromagnetic field (TEM) design, maximum B1 transmit power can only be achieved if each individual transmit element is tuned and matched for different coil loads, which requires a considerable amount of valuable scanner time. Methods An integrated system for autotuning a multichannel parallel transmit (pTx) cardiac TEM array was devised, using piezoelectric actuators, power monitoring equipment and control software. The reproducibility and performance of the system were tested and the power responses of the coil elements were profiled. An automated optimization method was devised and evaluated. Results The time required to tune an eight-element pTx cardiac RF array was reduced from a mean of 30 min to less than 10 min with the use of this system. Conclusion Piezoelectric actuators are an attractive means of tuning RF coil arrays to yield more efficient B1 transmission into the subject. An automated mechanism for tuning these elements provides a practical solution for cardiac imaging at UHF, bringing this technology closer to clinical use. Magn Reson Med 73:2390–2397, 2015. © 2014 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Graeme A Keith
- Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Christopher T Rodgers
- Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Aaron T Hess
- Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Carl J Snyder
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - J Thomas Vaughan
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Matthew D Robson
- Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
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Aussenhofer SA, Webb AG. An eight-channel transmit/receive array of TE01 mode high permittivity ceramic resonators for human imaging at 7T. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 243:122-129. [PMID: 24818565 DOI: 10.1016/j.jmr.2014.04.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Revised: 03/31/2014] [Accepted: 04/03/2014] [Indexed: 06/03/2023]
Abstract
This study describes the design, construction and operation of a new type of transmit/receive array using ceramic resonators operating in a transverse electromagnetic (TE) mode. Single element function and performance at 298.1MHz (7T) are analyzed and compared to a lumped element design loop coil with comparable geometry. The results show that ceramic resonators working in the TE01δ mode configuration produce similar efficiency, defined as the transmit magnetic field (B1(+)) per square root of the specific absorption rate (SAR), to conventional surface coils. An array consisting of eight ceramic elements was then designed to operate in transmit/receive mode. This array was driven via power/phase splitters by two independent transmit channels and functional cardiac images were produced from a number of healthy volunteers.
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Affiliation(s)
- S A Aussenhofer
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - A G Webb
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
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Abstract
Since the introduction of 4 T human systems in three academic laboratories circa 1990, rapid progress in imaging and spectroscopy studies in humans at 4 T and animal model systems at 9.4 T have led to the introduction of 7 T and higher magnetic fields for human investigation at about the turn of the century. Work conducted on these platforms has demonstrated the existence of significant advantages in SNR and biological information content at these ultrahigh fields, as well as the presence of numerous challenges. Primary difference from lower fields is the deviation from the near field regime; at the frequencies corresponding to hydrogen resonance conditions at ultrahigh fields, the RF is characterized by attenuated traveling waves in the human body, which leads to image nonuniformities for a given sample-coil configuration because of interferences. These nonuniformities were considered detrimental to the progress of imaging at high field strengths. However, they are advantageous for parallel imaging for signal reception and parallel transmission, two critical technologies that account, to a large extend, for the success of ultrahigh fields. With these technologies, and improvements in instrumentation and imaging methods, ultrahigh fields have provided unprecedented gains in imaging of brain function and anatomy, and started to make inroads into investigation of the human torso and extremities. As extensive as they are, these gains still constitute a prelude to what is to come given the increasingly larger effort committed to ultrahigh field research and development of ever better instrumentation and techniques.
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Wu X, Schmitter S, Auerbach EJ, Uğurbil K, Van de Moortele PF. Mitigating transmit B 1 inhomogeneity in the liver at 7T using multi-spoke parallel transmit RF pulse design. Quant Imaging Med Surg 2014; 4:4-10. [PMID: 24649429 DOI: 10.3978/j.issn.2223-4292.2014.02.06] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2014] [Accepted: 02/26/2014] [Indexed: 11/14/2022]
Abstract
In this work, the use of multi-spoke slice-selective parallel transmit (pTX) RF pulse was explored to address B 1+ inhomogeneity in the largest transverse section of the liver at 7T. The impact of the number of spokes was specifically investigated, considering RF pulses consisting of 2, 3 and 4 spokes, as well as single-spoke RF pulses corresponding to static B 1 shimming. Healthy volunteers were imaged on a whole body MR scanner equipped with an eight-channel transmit system. A robust and fast transmit B 1 (B 1+) estimation method was employed to obtain the eight-channel B 1+ maps within a single breath hold. Gradient echo (GRE) images of the liver were acquired using the four different RF pulses and the results were compared. The use of static B 1 shimming (i.e., 1-spoke RF pulse) resulted in partial improvement but significant signal dropouts were still observed in the target region. By comparison, the use of multi-spoke pTX RF pulse design gave rise to much improved excitation homogeneity without signal dropouts. These results demonstrate the effectiveness of multi-spoke pTX RF pulse design in B 1+ homogenization for liver magnetic resonance imaging (MRI) at 7T. The current findings at 7T may have implications for body imaging applications in clinical settings at 3T where B 1+ inhomogeneities are also known for degrading image quality in the torso.
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Affiliation(s)
- Xiaoping Wu
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Sebastian Schmitter
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Edward J Auerbach
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Pierre-François Van de Moortele
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
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Kraff O, Fischer A, Nagel AM, Mönninghoff C, Ladd ME. MRI at 7 Tesla and above: demonstrated and potential capabilities. J Magn Reson Imaging 2014; 41:13-33. [PMID: 24478137 DOI: 10.1002/jmri.24573] [Citation(s) in RCA: 126] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2013] [Accepted: 01/03/2014] [Indexed: 12/29/2022] Open
Abstract
With more than 40 installed MR systems worldwide operating at 7 Tesla or higher, ultra-high-field (UHF) imaging has been established as a platform for clinically oriented research in recent years. Along with technical developments that, in part, have also been successfully transferred to lower field strengths, MR imaging and spectroscopy at UHF have demonstrated capabilities and potentials for clinical diagnostics in a variety of studies. In terms of applications, this overview article focuses on already achieved advantages for in vivo imaging, i.e., in imaging the brain and joints of the musculoskeletal system, but also considers developments in body imaging, which is particularly challenging. Furthermore, new applications for clinical diagnostics such as X-nuclei imaging and spectroscopy, which only really become feasible at ultra-high magnetic fields, will be presented.
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Affiliation(s)
- Oliver Kraff
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
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Johst S, Orzada S, Fischer A, Schäfer LC, Nassenstein K, Umutlu L, Lauenstein TC, Ladd ME, Maderwald S. Sequence comparison for non-enhanced MRA of the lower extremity arteries at 7 Tesla. PLoS One 2014; 9:e86274. [PMID: 24454963 PMCID: PMC3894206 DOI: 10.1371/journal.pone.0086274] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2013] [Accepted: 12/10/2013] [Indexed: 11/18/2022] Open
Abstract
In this study three sequences for non-contrast-enhanced MRA of the lower extremity arteries at 7T were compared. Cardiac triggering was used with the aim to reduce signal variations in the arteries. Two fast single-shot 2D sequences, a modified Ultrafast Spoiled Gradient Echo (UGRE) sequence and a variant of the Quiescent-Interval Single-Shot (QISS) sequence were triggered via phonocardiogram and compared in volunteer examinations to a non-triggered 2D gradient echo (GRE) sequence. For image acquisition, a 16-channel transmit/receive coil and a manually positionable AngioSURF table were used. To tackle B1 inhomogeneities at 7T, Time-Interleaved Acquisition of Modes (TIAMO) was integrated in GRE and UGRE. To compare the three sequences quantitatively, a vessel-to-background ratio (VBR) was measured in all volunteers and stations. In conclusion, cardiac triggering was able to suppress flow artifacts satisfactorily. The modified UGRE showed only moderate image artifacts. Averaged over all volunteers and stations, GRE reached a VBR of 4.18±0.05, UGRE 5.20±0.06, and QISS 2.72±0.03. Using cardiac triggering and TIAMO imaging technique was essential to perform non-enhanced MRA of the lower extremities vessels at 7T. The modified UGRE performed best, as observed artifacts were only moderate and the highest average VBR was reached.
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Affiliation(s)
- Sören Johst
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital, University Duisburg-Essen, Essen, Germany
- * E-mail:
| | - Stephan Orzada
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital, University Duisburg-Essen, Essen, Germany
| | - Anja Fischer
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital, University Duisburg-Essen, Essen, Germany
| | - Lena C. Schäfer
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital, University Duisburg-Essen, Essen, Germany
| | - Kai Nassenstein
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital, University Duisburg-Essen, Essen, Germany
| | - Lale Umutlu
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital, University Duisburg-Essen, Essen, Germany
| | - Thomas C. Lauenstein
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital, University Duisburg-Essen, Essen, Germany
| | - Mark E. Ladd
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital, University Duisburg-Essen, Essen, Germany
| | - Stefan Maderwald
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
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Niendorf T, Schulz-Menger J. [Cardiovascular ultrahigh field magnetic resonance imaging : challenges, technical solutions and opportunities]. Radiologe 2014; 53:422-8. [PMID: 23613023 DOI: 10.1007/s00117-012-2348-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
CLINICAL/METHODICAL ISSUE This involves high spatial resolution cardiac imaging with ultrahigh magnetic fields (7 T) and clinically acceptable image quality. STANDARD RADIOLOGICAL METHODS Cardiovascular magnetic resonance imaging (MRI) at a field strength of 1.5 T using a spatial resolution of (2 × 2 × 6-8) mm(3). METHODICAL INNOVATIONS Cardiac MRI at ultrahigh field strength makes use of multitransmit/receive radiofrequency (RF) technology and development of novel technology that utilizes the traits of ultrahigh field MRI. PERFORMANCE Enhanced spatial resolution which is superior by a factor of 6-10 to what can be achieved by current clinical cardiac MRI. The relative spatial resolution (pixels per anatomical structure) comes close to what can be accomplished by current cardiac MRI in small rodents. ACHIEVEMENTS Feasibility studies demonstrate the gain in spatial resolution at 7.0 T due to the sensitivity advantage inherent to ultrahigh magnetic fields. PRACTICAL RECOMMENDATIONS Please stay tuned and please put further weight behind the solution of the remaining technical problems of cardiac MRI at 7.0 T.
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Affiliation(s)
- T Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrück Centrum für Molekulare Medizin, Robert-Rössle-Str. 10, 13125, Berlin, Deutschland.
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Uğurbil K, Xu J, Auerbach EJ, Moeller S, Vu AT, Duarte-Carvajalino JM, Lenglet C, Wu X, Schmitter S, Van de Moortele PF, Strupp J, Sapiro G, De Martino F, Wang D, Harel N, Garwood M, Chen L, Feinberg DA, Smith SM, Miller KL, Sotiropoulos SN, Jbabdi S, Andersson JLR, Behrens TEJ, Glasser MF, Van Essen DC, Yacoub E. Pushing spatial and temporal resolution for functional and diffusion MRI in the Human Connectome Project. Neuroimage 2013; 80:80-104. [PMID: 23702417 PMCID: PMC3740184 DOI: 10.1016/j.neuroimage.2013.05.012] [Citation(s) in RCA: 572] [Impact Index Per Article: 52.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Revised: 05/05/2013] [Accepted: 05/07/2013] [Indexed: 12/21/2022] Open
Abstract
The Human Connectome Project (HCP) relies primarily on three complementary magnetic resonance (MR) methods. These are: 1) resting state functional MR imaging (rfMRI) which uses correlations in the temporal fluctuations in an fMRI time series to deduce 'functional connectivity'; 2) diffusion imaging (dMRI), which provides the input for tractography algorithms used for the reconstruction of the complex axonal fiber architecture; and 3) task based fMRI (tfMRI), which is employed to identify functional parcellation in the human brain in order to assist analyses of data obtained with the first two methods. We describe technical improvements and optimization of these methods as well as instrumental choices that impact speed of acquisition of fMRI and dMRI images at 3T, leading to whole brain coverage with 2 mm isotropic resolution in 0.7 s for fMRI, and 1.25 mm isotropic resolution dMRI data for tractography analysis with three-fold reduction in total dMRI data acquisition time. Ongoing technical developments and optimization for acquisition of similar data at 7 T magnetic field are also presented, targeting higher spatial resolution, enhanced specificity of functional imaging signals, mitigation of the inhomogeneous radio frequency (RF) fields, and reduced power deposition. Results demonstrate that overall, these approaches represent a significant advance in MR imaging of the human brain to investigate brain function and structure.
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Affiliation(s)
- Kamil Uğurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA.
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66
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Rodgers CT, Piechnik SK, DelaBarre LJ, Van de Moortele PF, Snyder CJ, Neubauer S, Robson MD, Vaughan JT. Inversion recovery at 7 T in the human myocardium: measurement of T(1), inversion efficiency and B(1) (+). Magn Reson Med 2013; 70:1038-46. [PMID: 23197329 PMCID: PMC4134266 DOI: 10.1002/mrm.24548] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Revised: 09/17/2012] [Accepted: 10/10/2012] [Indexed: 12/17/2022]
Abstract
At clinical MRI field strengths (1.5 and 3 T), quantitative maps of the longitudinal relaxation time T1 of the myocardium reveal diseased tissue without requiring contrast agents. Cardiac T1 maps can be measured by Look-Locker inversion recovery sequences such as ShMOLLI at 1.5 and 3 T. Cardiovascular MRI at a field strength of 7 T has recently become feasible, but doubts have remained as to whether magnetization inversion is possible in the heart due to subject heating and technical limitations. This work extends the repertoire of 7 T cardiovascular MRI by implementing an adiabatic inversion pulse optimized for use in the heart at 7 T. A "ShMOLLI+IE" adaptation of the ShMOLLI pulse sequence has been introduced together with new postprocessing that accounts for the possibility of incomplete magnetization inversion. These methods were validated in phantoms and then used in a study of six healthy volunteers to determine the degree of magnetization inversion and the T1 of normal myocardium at 7 T within a 22-heartbeat breathhold. Using a scanner with 16 × 1 kW radiofrequency outputs, inversion efficiencies ranging from -0.79 to -0.83 (intrasegment means; perfect 180° would give -1) were attainable across the myocardium. The myocardial T1 was 1925 ± 48 ms (mean ± standard deviation).
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Affiliation(s)
- Christopher T. Rodgers
- Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, Level 0, John Radcliffe Hospital, Oxford, OX3 9DU, UK
| | - Stefan K. Piechnik
- Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, Level 0, John Radcliffe Hospital, Oxford, OX3 9DU, UK
| | - Lance J. DelaBarre
- Center for Magnetic Resonance Research, University of Minnesota, 2021 Sixth Street SE, Minneapolis, MN 55455, USA
| | | | - Carl J. Snyder
- Center for Magnetic Resonance Research, University of Minnesota, 2021 Sixth Street SE, Minneapolis, MN 55455, USA
| | - Stefan Neubauer
- Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, Level 0, John Radcliffe Hospital, Oxford, OX3 9DU, UK
| | - Matthew D. Robson
- Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, Level 0, John Radcliffe Hospital, Oxford, OX3 9DU, UK
| | - J. Thomas Vaughan
- Center for Magnetic Resonance Research, University of Minnesota, 2021 Sixth Street SE, Minneapolis, MN 55455, USA
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67
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Schmitter S, DelaBarre L, Wu X, Greiser A, Wang D, Auerbach EJ, Vaughan JT, Uğurbil K, Van de Moortele PF. Cardiac imaging at 7 Tesla: Single- and two-spoke radiofrequency pulse design with 16-channel parallel excitation. Magn Reson Med 2013; 70:1210-9. [PMID: 24038314 DOI: 10.1002/mrm.24935] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2013] [Revised: 07/05/2013] [Accepted: 08/04/2013] [Indexed: 01/12/2023]
Abstract
PURPOSE Higher signal to noise ratio (SNR) and improved contrast have been demonstrated at ultra-high magnetic fields (≥7 Tesla [T]) in multiple targets, often with multi-channel transmit methods to address the deleterious impact on tissue contrast due to spatial variations in B1 (+) profiles. When imaging the heart at 7T, however, respiratory and cardiac motion, as well as B0 inhomogeneity, greatly increase the methodological challenge. In this study we compare two-spoke parallel transmit (pTX) RF pulses with static B1 (+) shimming in cardiac imaging at 7T. METHODS Using a 16-channel pTX system, slice-selective two-spoke pTX pulses and static B1 (+) shimming were applied in cardiac CINE imaging. B1 (+) and B0 mapping required modified cardiac triggered sequences. Excitation homogeneity and RF energy were compared in different imaging orientations. RESULTS Two-spoke pulses provide higher excitation homogeneity than B1 (+) shimming, especially in the more challenging posterior region of the heart. The peak value of channel-wise RF energy was reduced, allowing for a higher flip angle, hence increased tissue contrast. Image quality with two-spoke excitation proved to be stable throughout the entire cardiac cycle. CONCLUSION Two-spoke pTX excitation has been successfully demonstrated in the human heart at 7T, with improved image quality and reduced RF pulse energy when compared with B1 (+) shimming.
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Affiliation(s)
- Sebastian Schmitter
- University of Minnesota, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
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68
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Graessl A, Renz W, Hezel F, Dieringer MA, Winter L, Oezerdem C, Rieger J, Kellman P, Santoro D, Lindel TD, Frauenrath T, Pfeiffer H, Niendorf T. Modular 32-channel transceiver coil array for cardiac MRI at 7.0T. Magn Reson Med 2013; 72:276-90. [PMID: 23904404 DOI: 10.1002/mrm.24903] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2013] [Revised: 06/27/2013] [Accepted: 07/02/2013] [Indexed: 01/18/2023]
Abstract
PURPOSE To design and evaluate a modular transceiver coil array with 32 independent channels for cardiac MRI at 7.0T. METHODS 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. RESULTS 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. CONCLUSION 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.
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Affiliation(s)
- Andreas Graessl
- Berlin Ultrahigh Field Facility, Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
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69
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Carpenter JP, Patel AR, Fernandes JL. Highlights of the 16th annual scientific sessions of the Society for Cardiovascular Magnetic Resonance. J Cardiovasc Magn Reson 2013; 15:60. [PMID: 23870663 PMCID: PMC3726510 DOI: 10.1186/1532-429x-15-60] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2013] [Accepted: 06/13/2013] [Indexed: 12/25/2022] Open
Abstract
The 16th Annual Scientific Sessions of the Society for Cardiovascular Magnetic Resonance (SCMR) took place in San Francisco, USA at the end of January 2013. With a faculty of experts from across the world, this congress provided a wealth of insight into cutting-edge research and technological development. This review article intends to provide a highlight of what represented the most significant advances in the field of cardiovascular magnetic resonance (CMR) during this year's meeting.
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70
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Detailing magnetic field strength dependence and segmental artifact distribution of myocardial effective transverse relaxation rate at 1.5, 3.0, and 7.0 T. Magn Reson Med 2013; 71:2224-30. [DOI: 10.1002/mrm.24856] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Revised: 06/04/2013] [Accepted: 06/05/2013] [Indexed: 12/12/2022]
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71
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Wu X, Schmitter S, Auerbach EJ, Moeller S, Uğurbil K, Van de Moortele PF. Simultaneous multislice multiband parallel radiofrequency excitation with independent slice-specific transmit B1 homogenization. Magn Reson Med 2013; 70:630-8. [PMID: 23801410 DOI: 10.1002/mrm.24828] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Revised: 04/12/2013] [Accepted: 05/08/2013] [Indexed: 11/10/2022]
Abstract
PURPOSE To develop a new parallel transmit (pTx) pulse design for simultaneous multiband (MB) excitation in order to tackle simultaneously the problems of transmit B1 (B1+) inhomogeneity and total radiofrequency (RF) power, so as to allow for optimal RF excitation when using MB pulses for slice acceleration for high and ultrahigh field MRI. METHODS With the proposed approach, each of the bands that are simultaneously excited is subject to a band-specific set of B1 complex shim weights. The method was validated in the human brain at 7T using a 16-channel pTx system and was compared to conventional MB pulses operating in the circularly polarized (CP) mode. Further numerical simulations based on measured B1 maps were conducted. RESULTS The new method improved B1+ homogeneity by 60% when keeping the total RF power constant and reduced total RF power by 72% when keeping the excitation fidelity constant, as compared to the conventional CP mode. CONCLUSION A new pTx pulse design formalism is introduced targeting slice-specific B1+ homogenization in MB excitation while constraining total RF power. These pulses lead to significantly improved slice-wise B1+ uniformity and/or largely reduced total RF power, as compared to the conventionally employed MB pulses applied in the CP mode.
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Affiliation(s)
- Xiaoping Wu
- University of Minnesota, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
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72
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Niendorf T, Graessl A, Thalhammer C, Dieringer MA, Kraus O, Santoro D, Fuchs K, Hezel F, Waiczies S, Ittermann B, Winter L. Progress and promises of human cardiac magnetic resonance at ultrahigh fields: a physics perspective. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 229:208-22. [PMID: 23290625 DOI: 10.1016/j.jmr.2012.11.015] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2012] [Revised: 11/16/2012] [Accepted: 11/16/2012] [Indexed: 05/12/2023]
Abstract
A growing number of reports eloquently speak about explorations into cardiac magnetic resonance (CMR) at ultrahigh magnetic fields (B0≥7.0 T). Realizing the progress, promises and challenges of ultrahigh field (UHF) CMR this perspective outlines current trends in enabling MR technology tailored for cardiac MR in the short wavelength regime. For this purpose many channel radiofrequency (RF) technology concepts are outlined. Basic principles of mapping and shimming of transmission fields including RF power deposition considerations are presented. Explorations motivated by the safe operation of UHF-CMR even in the presence of conductive implants are described together with the physics, numerical simulations and experiments, all of which detailing antenna effects and RF heating induced by intracoronary stents at 7.0 T. Early applications of CMR at 7.0 T and their clinical implications for explorations into cardiovascular diseases are explored including assessment of cardiac function, myocardial tissue characterization, MR angiography of large and small vessels as well as heteronuclear MR of the heart and the skin. A concluding section ventures a glance beyond the horizon and explores future directions. The goal here is not to be comprehensive but to inspire the biomedical and diagnostic imaging communities to throw further weight behind the solution of the many remaining unsolved problems and technical obstacles of UHF-CMR with the goal to transfer MR physics driven methodological advancements into extra clinical value.
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Affiliation(s)
- Thoralf Niendorf
- Berlin Ultrahigh Field Facility, Max-Delbrueck Center for Molecular Medicine, Berlin, Germany.
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73
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Károlyi M, Seifarth H, Liew G, Schlett CL, Maurovich-Horvat P, Stolzmann P, Dai G, Huang S, Goergen CJ, Nakano M, Otsuka F, Virmani R, Hoffmann U, Sosnovik DE. Classification of coronary atherosclerotic plaques ex vivo with T1, T2, and ultrashort echo time CMR. JACC Cardiovasc Imaging 2013; 6:466-74. [PMID: 23498670 PMCID: PMC3661771 DOI: 10.1016/j.jcmg.2012.09.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2012] [Revised: 09/04/2012] [Accepted: 09/06/2012] [Indexed: 11/23/2022]
Abstract
OBJECTIVES This study sought to determine whether the classification of human coronary atherosclerotic plaques with T1, T2, and ultrashort echo time (UTE) cardiac magnetic resonance (CMR) would correlate well with atherosclerotic plaque classification by histology. BACKGROUND CMR has been extensively used to classify carotid plaque, but its ability to characterize coronary plaque remains unknown. In addition, the detection of plaque calcification by CMR remains challenging. Here, we used T1, T2, and UTE CMR to evaluate atherosclerotic plaques in fixed post-mortem human coronary arteries. We hypothesized that the combination of T1, T2, and UTE CMR would allow both calcified and lipid-rich coronary plaques to be accurately detected. METHODS Twenty-eight plaques from human donor hearts with proven coronary artery disease were imaged at 9.4-T with a T1-weighted 3-dimensional fast low-angle shot (FLASH) sequence (250-μm resolution), a T2-weighted rapid acquisition with refocused echoes (RARE) sequence (in-plane resolution 0.156 mm), and an UTE sequence (300-μm resolution). Plaques showing selective hypointensity on T2-weighted CMR were classified as lipid-rich. Areas of hypointensity on the T1-weighted images, but not the UTE images, were classified as calcified. Hyperintensity on the T1-weighted and UTE images was classified as hemorrhage. Following CMR, histological characterization of the plaques was performed with a pentachrome stain and established American Heart Association criteria. RESULTS CMR showed high sensitivity and specificity for the detection of calcification (100% and 90%, respectively) and lipid-rich necrotic cores (90% and 75%, respectively). Only 2 lipid-rich foci were missed by CMR, both of which were extremely small. Overall, CMR-based classification of plaque was in complete agreement with the histological classification in 22 of 28 cases (weighted κ = 0.6945, p < 0.0001). CONCLUSIONS The utilization of UTE CMR allows plaque calcification in the coronary arteries to be robustly detected. High-resolution CMR with T1, T2, and UTE contrast enables accurate classification of human coronary atherosclerotic plaque.
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Affiliation(s)
- Mihály Károlyi
- Cardiac MR/PET/CT Program, Massachusetts General Hospital, Harvard Medical School, Boston, USA
| | - Harald Seifarth
- Cardiac MR/PET/CT Program, Massachusetts General Hospital, Harvard Medical School, Boston, USA
| | - Gary Liew
- Cardiac MR/PET/CT Program, Massachusetts General Hospital, Harvard Medical School, Boston, USA
| | - Christopher L. Schlett
- Cardiac MR/PET/CT Program, Massachusetts General Hospital, Harvard Medical School, Boston, USA
| | - Pál Maurovich-Horvat
- Cardiac MR/PET/CT Program, Massachusetts General Hospital, Harvard Medical School, Boston, USA
| | - Paul Stolzmann
- Cardiac MR/PET/CT Program, Massachusetts General Hospital, Harvard Medical School, Boston, USA
| | - Guangping Dai
- Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, USA
| | - Shuning Huang
- Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, USA
| | - Craig J. Goergen
- Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, USA
| | | | | | | | - Udo Hoffmann
- Cardiac MR/PET/CT Program, Massachusetts General Hospital, Harvard Medical School, Boston, USA
| | - David E. Sosnovik
- Cardiac MR/PET/CT Program, Massachusetts General Hospital, Harvard Medical School, Boston, USA
- Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, USA
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74
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von Knobelsdorff-Brenkenhoff F, Tkachenko V, Winter L, Rieger J, Thalhammer C, Hezel F, Graessl A, Dieringer MA, Niendorf T, Schulz-Menger J. Assessment of the right ventricle with cardiovascular magnetic resonance at 7 Tesla. J Cardiovasc Magn Reson 2013; 15:23. [PMID: 23497030 PMCID: PMC3621368 DOI: 10.1186/1532-429x-15-23] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Accepted: 03/06/2013] [Indexed: 02/06/2023] Open
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 (1.2 x 1.2 x 6) mm3 was used; at 7T, fast gradient echo (FGRE) with voxel size (1.2 x 1.2 x 6) mm3 and (1.3 x 1.3 x 4) mm3 were applied. RV dimensions (RVEDV, RVESV), RV mass (RVM) 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 (1.3 x 1.3 x 4)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 (1.3 x 1.3 x 4) mm3 tended to overestimate RV volumes compared to SSFP at 1.5T (mean difference of RVEDV 8.2 ± 9.3 ml) and to FGRE at 7T with voxel size (1.2 x 1.2 x 6) mm3 (mean difference of RVEDV 9.3 ± 8.6 ml). 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.
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Affiliation(s)
- Florian von Knobelsdorff-Brenkenhoff
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max-Delbrueck Center for Molecular Medicine, HELIOS Klinikum Berlin Buch, Department of Cardiology and Nephrology, Berlin, Germany
| | - Valeriy Tkachenko
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max-Delbrueck Center for Molecular Medicine, HELIOS Klinikum Berlin Buch, Department of Cardiology and Nephrology, Berlin, Germany
| | - Lukas Winter
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Jan Rieger
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Christof Thalhammer
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Fabian Hezel
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Andreas Graessl
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Matthias A Dieringer
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max-Delbrueck Center for Molecular Medicine, HELIOS Klinikum Berlin Buch, Department of Cardiology and Nephrology, Berlin, Germany
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Jeanette Schulz-Menger
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max-Delbrueck Center for Molecular Medicine, HELIOS Klinikum Berlin Buch, Department of Cardiology and Nephrology, Berlin, Germany
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den Hartog AG, Bovens SM, Koning W, Hendrikse J, Pasterkamp G, Moll FL, de Borst GJ. PLACD-7T Study: Atherosclerotic Carotid Plaque Components Correlated with Cerebral Damage at 7 Tesla Magnetic Resonance Imaging. Curr Cardiol Rev 2012; 7:28-34. [PMID: 22294972 PMCID: PMC3131713 DOI: 10.2174/157340311795677743] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/2010] [Revised: 10/16/2010] [Accepted: 01/07/2011] [Indexed: 11/22/2022] Open
Abstract
Introduction: In patients with carotid artery stenosis histological plaque composition is associated with plaque stability and with presenting symptomatology. Preferentially, plaque vulnerability should be taken into account in pre-operative work-up of patients with severe carotid artery stenosis. However, currently no appropriate and conclusive (non-) invasive technique to differentiate between the high and low risk carotid artery plaque in vivo is available. We propose that 7 Tesla human high resolution MRI scanning will visualize carotid plaque characteristics more precisely and will enable correlation of these specific components with cerebral damage. Study objective: The aim of the PlaCD-7T study is 1: to correlate 7T imaging with carotid plaque histology (gold standard); and 2: to correlate plaque characteristics with cerebral damage ((clinically silent) cerebral (micro) infarcts or bleeds) on 7 Tesla high resolution (HR) MRI. Design: We propose a single center prospective study for either symptomatic or asymptomatic patients with haemodynamic significant (70%) stenosis of at least one of the carotid arteries. The Athero-Express (AE) biobank histological analysis will be derived according to standard protocol. Patients included in the AE and our prospective study will undergo a pre-operative 7 Tesla HR-MRI scan of both the head and neck area. Discussion: We hypothesize that the 7 Tesla MRI scanner will allow early identification of high risk carotid plaques being associated with micro infarcted cerebral areas, and will thus be able to identify patients with a high risk of periprocedural stroke, by identification of surrogate measures of increased cardiovascular risk.
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Affiliation(s)
- A G den Hartog
- Departments of Vascular Surgery, Utrecht, the Netherlands, Interuniversity Cardiology Institute of the Netherlands (ICIN), Utrecht, The Netherlands
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76
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Thalhammer C, Renz W, Winter L, Hezel F, Rieger J, Pfeiffer H, Graessl A, Seifert F, Hoffmann W, von Knobelsdorff-Brenkenhoff F, Tkachenko V, Schulz-Menger J, Kellman P, Niendorf T. Two-dimensional sixteen channel transmit/receive coil array for cardiac MRI at 7.0 T: design, evaluation, and application. J Magn Reson Imaging 2012; 36:847-57. [PMID: 22706727 PMCID: PMC3445730 DOI: 10.1002/jmri.23724] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2012] [Accepted: 05/07/2012] [Indexed: 12/17/2022] Open
Abstract
PURPOSE To design, evaluate, and apply a 2D 16-channel transmit/receive (TX/RX) coil array tailored for cardiac magnetic resonance imaging (MRI) at 7.0 T. MATERIALS AND METHODS The cardiac coil array consists of two sections each using eight elements arranged in a 2 × 4 array. Radiofrequency (RF) safety was validated by specific absorption rate (SAR) simulations. Cardiac imaging was performed using 2D CINE FLASH imaging, T 2 mapping, and fat-water separation imaging. The characteristics of the coil array were analyzed including parallel imaging performance, left ventricular chamber quantification, and overall image quality. RESULTS RF characteristics were found to be appropriate for all subjects included in the study. The SAR values derived from the simulations fall well within the limits of legal guidelines. The baseline signal-to-noise ratio (SNR) advantage at 7.0 T was put to use to acquire 2D CINE images of the heart with a very high spatial resolution of (1 × 1 × 4) mm(3) . The proposed coil array supports 1D acceleration factors of up to R = 4 without significantly impairing image quality. CONCLUSION The 16-channel TX/RX coil has the capability to acquire high contrast and high spatial resolution images of the heart at 7.0 T.
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Affiliation(s)
- Christof Thalhammer
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Wolfgang Renz
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
- Siemens Healthcare, Erlangen, Germany
| | - Lukas Winter
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Fabian Hezel
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Jan Rieger
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
- MRI.TOOLS GmbH, Berlin, Germany
| | - Harald Pfeiffer
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
- Physikalische-Technische Bundesanstalt (PTB), Germany
| | - Andreas Graessl
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Frank Seifert
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
- Physikalische-Technische Bundesanstalt (PTB), Germany
| | - Werner Hoffmann
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
- Physikalische-Technische Bundesanstalt (PTB), Germany
| | - Florian von Knobelsdorff-Brenkenhoff
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
- HELIOS Klinikum Berlin-Buch, Dept. of Cardiology and Nephrology, Berlin, Germany
- Experimental and Clinical Research Center (ECRC), Charité - University Medicine Campus Berlin Buch, Berlin, Germany
| | - Valeriy Tkachenko
- HELIOS Klinikum Berlin-Buch, Dept. of Cardiology and Nephrology, Berlin, Germany
- Experimental and Clinical Research Center (ECRC), Charité - University Medicine Campus Berlin Buch, Berlin, Germany
| | - Jeanette Schulz-Menger
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
- HELIOS Klinikum Berlin-Buch, Dept. of Cardiology and Nephrology, Berlin, Germany
- Experimental and Clinical Research Center (ECRC), Charité - University Medicine Campus Berlin Buch, Berlin, Germany
| | - Peter Kellman
- Laboratory of Cardiac Energetics, National Institutes of Health/NHLBI, Bethesda, MD, USA
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
- MRI.TOOLS GmbH, Berlin, Germany
- Experimental and Clinical Research Center (ECRC), Charité - University Medicine Campus Berlin Buch, Berlin, Germany
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77
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Ellermann J, Goerke U, Morgan P, Ugurbil K, Tian J, Schmitter S, Vaughan T, Van De Moortele PF. Simultaneous bilateral hip joint imaging at 7 Tesla using fast transmit B₁ shimming methods and multichannel transmission - a feasibility study. NMR IN BIOMEDICINE 2012; 25:1202-8. [PMID: 22311346 PMCID: PMC3419302 DOI: 10.1002/nbm.2779] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2011] [Revised: 12/13/2011] [Accepted: 12/16/2011] [Indexed: 05/04/2023]
Abstract
The objective of this study was to demonstrate the feasibility of simultaneous bilateral hip imaging at 7 Tesla. Hip joint MRI becomes clinically critical since recent advances have made hip arthroscopy an efficacious approach to treat a variety of early hip diseases. The success of these treatments requires a reliable and accurate diagnosis of intraarticular abnormalities at an early stage. Articular cartilage assessment is especially important to guide surgical decisions but is difficult to achieve with current MR methods. Because of gains in tissue contrast and spatial resolution reported at ultra high magnetic fields, there are strong expectations that imaging the hip joint at 7 Tesla will improve diagnostic accuracy. Furthermore, there is growing evidence that the majority of these hip abnormalities occur bilaterally, emphasizing the need for bilateral imaging. However, obtaining high quality images in the human torso, in particular of both hips simultaneously, must overcome a major challenge arising from the damped traveling wave behaviour of RF waves at 7 Tesla that leads to severe inhomogeneities in transmit B1 (B(1) (+) ) phase and magnitude, typically resulting in areas of low signal and contrast, and consequently impairing use for clinical applications. To overcome this problem, a 16-channel stripline transceiver RF coil was used, together with a B1 shimming algorithm aiming at maximizing B(1) (+) in six regions of interest over the hips that were identified on axial scout images. Our successful results demonstrate that this approach effectively reduces inhomogeneities observed before B1 shimming and provides high joint tissue contrast in both hips while reducing the required RF power. Critical to this success was a fast small flip angle B(1) (+) calibration scan that permitted the computation of subject-specific B1 shimming solutions, a necessary step to account for large spatial variations in B(1) (+) phase observed in different subjects.
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Affiliation(s)
- J Ellermann
- University of Minnesota Medical Center, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, USA.
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78
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Comparison of three multichannel transmit/receive radiofrequency coil configurations for anatomic and functional cardiac MRI at 7.0T: implications for clinical imaging. Eur Radiol 2012; 22:2211-20. [PMID: 22653280 DOI: 10.1007/s00330-012-2487-1] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Revised: 04/06/2012] [Accepted: 04/10/2012] [Indexed: 12/17/2022]
Abstract
OBJECTIVES To implement, examine, and compare three multichannel transmit/receive coil configurations for cardiovascular MR (CMR) at 7T. METHODS Three radiofrequency transmit-receive (TX/RX) coils with 4-, 8-, and 16-coil elements were used. Ten healthy volunteers (seven males, age 28 ± 4 years) underwent CMR at 7T. For all three RX/TX coils, 2D CINE FLASH images of the heart were acquired. Cardiac chamber quantification, signal-to-noise ratio (SNR) analysis, parallel imaging performance assessment, and image quality scoring were performed. RESULTS Mean total examination time was 29 ± 5 min. All images obtained with the 8- and 16-channel coils were diagnostic. No significant difference in ejection fraction (EF) (P > 0.09) or left ventricular mass (LVM) (P > 0.31) was observed between the coils. The 8- and 16-channel arrays yielded a higher mean SNR in the septum versus the 4-channel coil. The lowest geometry factors were found for the 16-channel coil (mean ± SD 2.3 ± 0.5 for R = 4). Image quality was rated significantly higher (P < 0.04) for the 16-channel coil versus the 8- and 4-channel coils. CONCLUSIONS All three coil configurations are suitable for CMR at 7.0T under routine circumstances. A larger number of coil elements enhances image quality and parallel imaging performance but does not impact the accuracy of cardiac chamber quantification. KEY POINTS • Cardiac chamber quantification using 7.0T magnetic resonance imaging is feasible. • Examination times for cardiac chamber quantification at 7.0T match current clinical practice. • Multichannel transceiver RF technology facilitates improved image quality and parallel imaging performance. • Increasing the number of RF channels does not influence cardiac chamber quantification.
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79
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Umutlu L, Forsting M, Ladd ME. Ultrahigh-field magnetic resonance imaging: the clinical potential for anatomy, pathogenesis, diagnosis and treatment planning in neck and spine disease. Neuroimaging Clin N Am 2012; 22:363-71, xii. [PMID: 22548937 DOI: 10.1016/j.nic.2012.02.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An increase of the magnetic field strength to ultrahigh-field yields advantageous as well as disadvantageous changes in physical effects. The beneficial increase in signal/noise ratio can be leveraged into higher spatiotemporal resolution, and an exacerbation of artifacts can impede ultrahigh-field imaging. With the successful introduction of intracranial and musculoskeletal imaging at 7 T, recent advances in coil design have created opportunities for further applications of ultrahigh-field magnetic resonance (MR) imaging in other parts of the body. Initial studies in 7 T neck and spine MR imaging have revealed promising insights and new challenges, demanding further research and methodological optimization.
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Affiliation(s)
- Lale Umutlu
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Hufelandstr. 55, D-45122 Essen, Germany.
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80
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Moser E, Stahlberg F, Ladd ME, Trattnig S. 7-T MR--from research to clinical applications? NMR IN BIOMEDICINE 2012; 25:695-716. [PMID: 22102481 DOI: 10.1002/nbm.1794] [Citation(s) in RCA: 143] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Revised: 08/25/2011] [Accepted: 08/31/2011] [Indexed: 05/31/2023]
Abstract
Over 20,000 MR systems are currently installed worldwide and, although the majority operate at magnetic fields of 1.5 T and below (i.e. about 70%), experience with 3-T (in high-field clinical diagnostic imaging and research) and 7-T (research only) human MR scanners points to a future in functional and metabolic MR diagnostics. Complementary to previous studies, this review attempts to provide an overview of ultrahigh-field MR research with special emphasis on emerging clinical applications at 7 T. We provide a short summary of the technical development and the current status of installed MR systems. The advantages and challenges of ultrahigh-field MRI and MRS are discussed with special emphasis on radiofrequency inhomogeneity, relaxation times, signal-to-noise improvements, susceptibility effects, chemical shifts, specific absorption rate and other safety issues. In terms of applications, we focus on the topics most likely to gain significantly from 7-T MR, i.e. brain imaging and spectroscopy and musculoskeletal imaging, but also body imaging, which is particularly challenging. Examples are given to demonstrate the advantages of susceptibility-weighted imaging, time-of-flight MR angiography, high-resolution functional MRI, (1)H and (31)P MRSI in the human brain, sodium and functional imaging of cartilage and the first results (and artefacts) using an eight-channel body array, suggesting future areas of research that should be intensified in order to fully explore the potential of 7-T MR systems for use in clinical diagnosis.
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Affiliation(s)
- Ewald Moser
- Centre for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
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81
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Metzger GJ, Auerbach EJ, Akgun C, Simonson J, Bi X, Uğurbil K, van de Moortele PF. Dynamically applied B1+ shimming solutions for non-contrast enhanced renal angiography at 7.0 Tesla. Magn Reson Med 2012; 69:114-26. [PMID: 22442056 DOI: 10.1002/mrm.24237] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2011] [Revised: 01/13/2012] [Accepted: 02/10/2012] [Indexed: 11/10/2022]
Abstract
The purpose of this study was to detail a strategy for performing non-contrast enhanced renal magnetic resonance angiography studies at 7.0 T. It is demonstrated that with proper B1+ management, these studies can be successfully performed at ultrahigh field within local specific absorption rate constraints. An inversion prepared gradient echo acquisition, standard for non-contrast renal magnetic resonance angiography studies, required radiofrequency pulse specific B 1+ shimming solutions to be dynamically applied to address the field dependent increases in both B(0) and B1+ inhomogeneity as well as to accommodate limitation in available power. By using more efficient B1+ shimming solutions for the inversion preparation and more homogeneous solutions for the excitation, high quality images of the renal arteries were obtained without venous and background signal artifacts while working within hardware and safety constraints. Finite difference time domain simulations confirmed in vivo measurements with respect to B1+ distributions and homogeneity for the range of shimming strategies used and allowed the calculation of peak local specific absorption rate values normalized by input power and B1+. Increasing B1+ homogeneity was accompanied by decreasing local specific absorption rate per Watt and increasing maximum local specific absorption rate per [B1+](2), which must be considered, along with body size and respiratory rate, when finalizing acquisition parameters for a given individual.
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Affiliation(s)
- Gregory J Metzger
- Department of Radiology, Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota 55455, USA
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82
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Detailing the use of magnetohydrodynamic effects for synchronization of MRI with the cardiac cycle: A feasibility study. J Magn Reson Imaging 2012; 36:364-72. [DOI: 10.1002/jmri.23634] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Accepted: 02/09/2012] [Indexed: 11/07/2022] Open
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83
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The road to functional imaging and ultrahigh fields. Neuroimage 2012; 62:726-35. [PMID: 22333670 DOI: 10.1016/j.neuroimage.2012.01.134] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Revised: 01/24/2012] [Accepted: 01/30/2012] [Indexed: 11/23/2022] Open
Abstract
The Center for Magnetic Resonance (CMRR) at the University of Minnesota was one of the laboratories where the work that simultaneously and independently introduced functional magnetic resonance imaging (fMRI) of human brain activity was carried out. However, unlike other laboratories pursuing fMRI at the time, our work was performed at 4T magnetic field and coincided with the effort to push human magnetic resonance imaging to field strength significantly beyond 1.5T which was the high-end standard of the time. The human fMRI experiments performed in CMRR were planned between two colleagues who had known each other and had worked together previously in Bell Laboratories, namely Seiji Ogawa and myself, immediately after the Blood Oxygenation Level Dependent (BOLD) contrast was developed by Seiji. We were waiting for our first human system, a 4T system, to arrive in order to attempt at imaging brain activity in the human brain and these were the first experiments we performed on the 4T instrument in CMRR when it became marginally operational. This was a prelude to a subsequent systematic push we initiated for exploiting higher magnetic fields to improve the accuracy and sensitivity of fMRI maps, first going to 9.4T for animal model studies and subsequently developing a 7T human system for the first time. Steady improvements in high field instrumentation and ever expanding armamentarium of image acquisition and engineering solutions to challenges posed by ultrahigh fields have brought fMRI to submillimeter resolution in the whole brain at 7T, the scale necessary to reach cortical columns and laminar differentiation in the whole brain. The solutions that emerged in response to technological challenges posed by 7T also propagated and continues to propagate to lower field clinical systems, a major advantage of the ultrahigh fields effort that is underappreciated. Further improvements at 7T are inevitable. Further translation of these improvements to lower field clinical systems to achieve new capabilities and to magnetic fields significantly higher than 7T to enable human imaging is inescapable.
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84
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Suttie JJ, Delabarre L, Pitcher A, van de Moortele PF, Dass S, Snyder CJ, Francis JM, Metzger GJ, Weale P, Ugurbil K, Neubauer S, Robson M, Vaughan T. 7 Tesla (T) human cardiovascular magnetic resonance imaging using FLASH and SSFP to assess cardiac function: validation against 1.5 T and 3 T. NMR IN BIOMEDICINE 2012; 25:27-34. [PMID: 21774009 PMCID: PMC3440016 DOI: 10.1002/nbm.1708] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2010] [Revised: 12/02/2010] [Accepted: 02/15/2011] [Indexed: 05/04/2023]
Abstract
We report the first comparison of cardiovascular magnetic resonance imaging (CMR) at 1.5 T, 3 T and 7 T field strengths using steady state free precession (SSFP) and fast low angle shot (FLASH) cine sequences. Cardiac volumes and mass measurements were assessed for feasibility, reproducibility and validity at each given field strength using FLASH and SSFP sequences. Ten healthy volunteers underwent retrospectively electrocardiogram (ECG) gated CMR at 1.5 T, 3 T and 7 T using FLASH and SSFP sequences. B1 and B0 shimming and frequency scouts were used to optimise image quality. Cardiac volume and mass measurements were not significantly affected by field strength when using the same imaging sequence (P > 0.05 for all parameters at 1.5 T, 3 T and 7 T). SSFP imaging returned larger end diastolic and end systolic volumes and smaller left ventricular masses than FLASH imaging at 7 T, and at the lower field strengths (P < 0.05 for each parameter). However, univariate general linear model analysis with fixed effects for sequence and field strengths found an interaction between imaging sequence and field strength (P = 0.03), with a smaller difference in volumes and mass measurements between SSFP and FLASH imaging at 7 T than 1.5 T and 3 T. SSFP and FLASH cine imaging at 7 T is technically feasible and provides valid assessment of cardiac volumes and mass compared with CMR imaging at 1.5 T and 3 T field strengths.
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Affiliation(s)
- J J Suttie
- Department of Cardiovascular Medicine, University of Oxford, Centre for Clinical Magnetic Resonance Research, Oxford, UK.
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85
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Snyder CJ, Delabarre L, Moeller S, Tian J, Akgun C, Van de Moortele PF, Bolan PJ, Ugurbil K, Vaughan JT, Metzger GJ. Comparison between eight- and sixteen-channel TEM transceive arrays for body imaging at 7 T. Magn Reson Med 2011; 67:954-64. [PMID: 22102483 DOI: 10.1002/mrm.23070] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2010] [Revised: 06/02/2011] [Accepted: 06/06/2011] [Indexed: 11/05/2022]
Abstract
Eight- and sixteen-channel transceive stripline/TEM body arrays were compared at 7 T (297 MHz) both in simulation and experiment. Despite previous demonstrations of similar arrays for use in body applications, a quantitative comparison of the two configurations has not been undertaken to date. Results were obtained on a male pelvis for assessing transmit, signal to noise ratio, and parallel imaging performance and to evaluate local power deposition versus transmit B(1) (B(1) (+) ). All measurements and simulations were conducted after performing local B(1) (+) phase shimming in the region of the prostate. Despite the additional challenges of decoupling immediately adjacent coils, the sixteen-channel array demonstrated improved or nearly equivalent performance to the eight-channel array based on the evaluation criteria. Experimentally, transmit performance and signal to noise ratio were 22% higher for the sixteen-channel array while significantly increased reduction factors were achievable in the left-right direction for parallel imaging. Finite difference time domain simulations demonstrated similar results with respect to transmit and parallel imaging performance, however, a higher transmit efficiency advantage of 33% was predicted. Simulations at both 3 and 7 T verified the expected parallel imaging improvements with increasing field strength and showed that, for a specific B(1) (+) shimming strategy used, the sixteen-channel array exhibited lower local and global specific absorption rate for a given B(1) (+) .
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Affiliation(s)
- C J Snyder
- Department of Radiology, University of Minnesota, Minneapolis, MN, USA
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86
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Gräßl A, Winter L, Thalhammer C, Renz W, Kellman P, Martin C, von Knobelsdorff-Brenkenhoff F, Tkachenko V, Schulz-Menger J, Niendorf T. Design, evaluation and application of an eight channel transmit/receive coil array for cardiac MRI at 7.0 T. Eur J Radiol 2011; 82:752-9. [PMID: 21920683 DOI: 10.1016/j.ejrad.2011.08.002] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2011] [Accepted: 08/03/2011] [Indexed: 12/18/2022]
Abstract
The objective of this work is to design, examine and apply an eight channel transmit/receive coil array tailored for cardiac magnetic resonance imaging at 7.0 T that provides image quality suitable for clinical use, patient comfort, and ease of use. The cardiac coil array was designed to consist of a planar posterior section and a modestly curved anterior section. For radio frequency (RF) safety validation, numerical computations of the electromagnetic field (EMF) and the specific absorption rate (SAR) distribution were conducted. In vivo cardiac imaging was performed using a 2D CINE FLASH technique. For signal-to-noise ratio (SNR) assessment reconstructed images were scaled in SNR units. The parallel imaging capabilities of the coil were examined using GRAPPA and SENSE reconstruction with reduction factors of up to R=4. The assessment of the RF characteristics yielded a maximum noise correlation of 0.33. The baseline SNR advantage at 7.0 T was put to use to acquire 2D CINE images of the heart with a spatial resolution of 1 mm × 1 mm × 4 mm. The coil array supports 1D acceleration factors of up to R=3 without impairing image quality significantly. For un-accelerated 2D CINE FLASH acquisitions the results revealed an SNR of approximately 140 for the left ventricular blood pool. Blood/myocardium contrast was found to be approximately 90 for un-accelerated 2D CINE FLASH acquisitions. The proposed 8 channel cardiac transceiver surface coil has the capability to acquire high contrast, high spatial and temporal resolution in vivo images of the heart at 7.0 T.
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Affiliation(s)
- Andreas Gräßl
- Berlin Ultrahigh Field Facility, Max-Delbrueck-Center for Molecular Medicine, Robert-Roessle-Strasse 10, 13125 Berlin, Germany.
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87
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88
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Raaijmakers AJE, Ipek O, Klomp DWJ, Possanzini C, Harvey PR, Lagendijk JJW, van den Berg CAT. Design of a radiative surface coil array element at 7 T: The single-side adapted dipole antenna. Magn Reson Med 2011; 66:1488-97. [DOI: 10.1002/mrm.22886] [Citation(s) in RCA: 187] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Revised: 01/28/2011] [Accepted: 01/30/2011] [Indexed: 11/10/2022]
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89
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Wright AC, Lemdiasov R, Connick TJ, Bhagat YA, Magland JF, Song HK, Toddes SP, Ludwig R, Wehrli FW. Helmholtz-pair transmit coil with integrated receive array for high-resolution MRI of trabecular bone in the distal tibia at 7T. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 210:113-22. [PMID: 21402488 PMCID: PMC3085966 DOI: 10.1016/j.jmr.2011.02.019] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2010] [Revised: 12/31/2010] [Accepted: 02/18/2011] [Indexed: 05/17/2023]
Abstract
A Helmholtz-pair local transmit RF coil with an integrated four-element receive array RF coil and foot immobilization platform was designed and constructed for imaging the distal tibia in a whole-body 7T MRI scanner. Simulations and measurements of the B(1) field distribution of the transmit coil are described, along with SAR considerations for operation at 7T. Results of imaging the trabecular bone of three volunteers at 1.5T, 3T and 7T are presented, using identical 1.5T and 3T versions of the 7T four-element receive array. The spatially registered images reveal improved visibility for individual trabeculae and show average gains in SNR of 2.8× and 4.9× for imaging at 7T compared to 3T and 1.5T, respectively. The results thus display an approximately linear dependence of SNR with field strength and enable the practical utility of 7T scanners for micro-MRI of trabecular bone.
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Affiliation(s)
- Alexander C Wright
- Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, PA, USA.
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90
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Kraff O, Bitz AK, Breyer T, Kruszona S, Maderwald S, Brote I, Gizewski ER, Ladd ME, Quick HH. A Transmit/Receive Radiofrequency Array for Imaging the Carotid Arteries at 7 Tesla. Invest Radiol 2011; 46:246-54. [DOI: 10.1097/rli.0b013e318206cee4] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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91
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Brandts A, Westenberg JJM, Versluis MJ, Kroft LJM, Smith NB, Webb AG, de Roos A. Quantitative assessment of left ventricular function in humans at 7 T. Magn Reson Med 2011; 64:1471-7. [PMID: 20593368 DOI: 10.1002/mrm.22529] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The purpose of this study was to determine the ability of 7 T cardiac magnetic resonance imaging (MRI) to quantitatively assess left ventricular volumes, mass, and function from cine short-axis series and left ventricular diastolic filling from velocity-encoded MRI in 10 healthy volunteers. As comparative "gold standard," the corresponding measures obtained at 1.5 T were taken. Left ventricular volumes, function, and mass were obtained by manual image segmentation. Trans-mitral flow graphs were obtained from 2D one-directional through-plane velocity-encoded MRI planned at the mitral valve in end-systole. Imaging at 7 T MRI was successful in 80% of the examinations. Assessment of left ventricular volumes, function, and mass at 7 T showed good agreement with 1.5 T (no significant differences between variables describing volumes, function, and mass with intraclass correlation coefficients ranging from 0.77 to 0.96). Trans-mitral stroke volume and the ratio between early and atrial peak filling rate showed strong agreement at both field strengths (no significant differences between stroke volumes and filling ratios with intraclass correlation coefficients 0.92 for stroke volumes and 0.77 for peak filling ratios). In conclusion, this study shows that assessing left ventricular volumes, function, and flow is feasible at 7 T MRI and that standardized MRI protocols provide similar quantitative results when compared with 1.5 T MRI.
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Affiliation(s)
- Anne Brandts
- Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
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92
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Orzada S, Bitz AK, Schäfer LC, Ladd SC, Ladd ME, Maderwald S. Open design eight-channel transmit/receive coil for high-resolution and real-time ankle imaging at 7 T. Med Phys 2011; 38:1162-7. [DOI: 10.1118/1.3553399] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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93
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Dieringer MA, Renz W, Lindel T, Seifert F, Frauenrath T, von Knobelsdorff-Brenkenhoff F, Waiczies H, Hoffmann W, Rieger J, Pfeiffer H, Ittermann B, Schulz-Menger J, Niendorf T. Design and application of a four-channel transmit/receive surface coil for functional cardiac imaging at 7T. J Magn Reson Imaging 2011; 33:736-41. [DOI: 10.1002/jmri.22451] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2010] [Accepted: 11/10/2010] [Indexed: 11/12/2022] Open
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Frauenrath T, Hezel F, Renz W, d'Orth TDG, Dieringer M, von Knobelsdorff-Brenkenhoff F, Prothmann M, Menger JS, Niendorf T. Acoustic cardiac triggering: a practical solution for synchronization and gating of cardiovascular magnetic resonance at 7 Tesla. J Cardiovasc Magn Reson 2010; 12:67. [PMID: 21080933 PMCID: PMC2998500 DOI: 10.1186/1532-429x-12-67] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2010] [Accepted: 11/16/2010] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND To demonstrate the applicability of acoustic cardiac triggering (ACT) for imaging of the heart at ultrahigh magnetic fields (7.0 T) by comparing phonocardiogram, conventional vector electrocardiogram (ECG) and traditional pulse oximetry (POX) triggered 2D CINE acquisitions together with (i) a qualitative image quality analysis, (ii) an assessment of the left ventricular function parameter and (iii) an examination of trigger reliability and trigger detection variance derived from the signal waveforms. RESULTS ECG was susceptible to severe distortions at 7.0 T. POX and ACT provided waveforms free of interferences from electromagnetic fields or from magneto-hydrodynamic effects. Frequent R-wave mis-registration occurred in ECG-triggered acquisitions with a failure rate of up to 30% resulting in cardiac motion induced artifacts. ACT and POX triggering produced images free of cardiac motion artefacts. ECG showed a severe jitter in the R-wave detection. POX also showed a trigger jitter of approximately Δt = 72 ms which is equivalent to two cardiac phases. ACT showed a jitter of approximately Δt = 5 ms only. ECG waveforms revealed a standard deviation for the cardiac trigger offset larger than that observed for ACT or POX waveforms.Image quality assessment showed that ACT substantially improved image quality as compared to ECG (image quality score at end-diastole: ECG = 1.7 ± 0.5, ACT = 2.4 ± 0.5, p = 0.04) while the comparison between ECG vs. POX gated acquisitions showed no significant differences in image quality (image quality score: ECG = 1.7 ± 0.5, POX = 2.0 ± 0.5, p = 0.34). CONCLUSIONS The applicability of acoustic triggering for cardiac CINE imaging at 7.0 T was demonstrated. ACT's trigger reliability and fidelity are superior to that of ECG and POX. ACT promises to be beneficial for cardiovascular magnetic resonance at ultra-high field strengths including 7.0 T.
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Affiliation(s)
- Tobias Frauenrath
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Fabian Hezel
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Wolfgang Renz
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- Siemens Healthcare, Erlangen, Germany
| | - Thibaut de Geyer d'Orth
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Matthias Dieringer
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- Working Group on Cardiovascular Magnetic Resonance, Medical University Berlin, Charité Campus Buch, HELIOS-Klinikum Berlin-Buch, Dept. of Cardiology and Nephrology, Berlin, Germany
- Experimental and Clinical Research Center, Charité - Campus Buch, Humboldt-University, Berlin, Germany
| | - Florian von Knobelsdorff-Brenkenhoff
- Working Group on Cardiovascular Magnetic Resonance, Medical University Berlin, Charité Campus Buch, HELIOS-Klinikum Berlin-Buch, Dept. of Cardiology and Nephrology, Berlin, Germany
- Experimental and Clinical Research Center, Charité - Campus Buch, Humboldt-University, Berlin, Germany
| | - Marcel Prothmann
- Working Group on Cardiovascular Magnetic Resonance, Medical University Berlin, Charité Campus Buch, HELIOS-Klinikum Berlin-Buch, Dept. of Cardiology and Nephrology, Berlin, Germany
| | - Jeanette Schulz Menger
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- Working Group on Cardiovascular Magnetic Resonance, Medical University Berlin, Charité Campus Buch, HELIOS-Klinikum Berlin-Buch, Dept. of Cardiology and Nephrology, Berlin, Germany
- Experimental and Clinical Research Center, Charité - Campus Buch, Humboldt-University, Berlin, Germany
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- Experimental and Clinical Research Center, Charité - Campus Buch, Humboldt-University, Berlin, Germany
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95
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van Elderen SGC, Versluis MJ, Westenberg JJM, Agarwal H, Smith NB, Stuber M, de Roos A, Webb AG. Right coronary MR angiography at 7 T: a direct quantitative and qualitative comparison with 3 T in young healthy volunteers. Radiology 2010; 257:254-9. [PMID: 20851943 DOI: 10.1148/radiol.100615] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
PURPOSE To objectively compare quantitative parameters related to image quality attained at coronary magnetic resonance (MR) angiography of the right coronary artery (RCA) performed at 7 T and 3 T. MATERIALS AND METHODS Institutional review board approval was obtained, and volunteers provided signed informed consent. Ten healthy adult volunteers (mean age ± standard deviation, 25 years ± 4; seven men, three women) underwent navigator-gated three-dimensional MR angiography of the RCA at 7 T and 3 T. For 7 T, a custom-built quadrature radiofrequency transmit-receive surface coil was used. At 3 T, a commercial body radiofrequency transmit coil and a cardiac coil array for signal reception were used. Segmented k-space gradient-echo imaging with spectrally selective adiabatic fat suppression was performed, and imaging parameters were similar at both field strengths. Contrast-to-noise ratio between blood and epicardial fat; signal-to-noise ratio of the blood pool; RCA vessel sharpness, diameter, and length; and navigator efficiency were quantified at both field strengths and compared by using a Mann-Whitney U test. RESULTS The contrast-to-noise ratio between blood and epicardial fat was significantly improved at 7 T when compared with that at 3 T (87 ± 34 versus 52 ± 13; P = .01). Signal-to-noise ratio of the blood pool was increased at 7 T (109 ± 47 versus 67 ± 19; P = .02). Vessel sharpness obtained at 7 T was also higher (58% ± 9 versus 50% ± 5; P = .04). At the same time, RCA vessel diameter and length and navigator efficiency showed no significant field strength-dependent difference. CONCLUSION In our quantitative and qualitative study comparing in vivo human imaging of the RCA at 7 T and 3 T in young healthy volunteers, parameters related to image quality attained at 7 T equal or surpass those from 3 T.
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Affiliation(s)
- Saskia G C van Elderen
- Department of Radiology, Leiden University Medical Center, Albinusdreef 2, Leiden, the Netherlands
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96
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The Year in Coronary Artery Disease. JACC Cardiovasc Imaging 2010; 3:1065-77. [DOI: 10.1016/j.jcmg.2010.08.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2010] [Revised: 07/27/2010] [Accepted: 08/30/2010] [Indexed: 01/29/2023]
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97
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Umutlu L, Orzada S, Kinner S, Maderwald S, Brote I, Bitz AK, Kraff O, Ladd SC, Antoch G, Ladd ME, Quick HH, Lauenstein TC. Renal imaging at 7 Tesla: preliminary results. Eur Radiol 2010; 21:841-9. [PMID: 20872006 DOI: 10.1007/s00330-010-1962-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2010] [Revised: 08/02/2010] [Accepted: 08/03/2010] [Indexed: 12/23/2022]
Abstract
OBJECTIVE To investigate the feasibility of 7T MR imaging of the kidneys utilising a custom-built 8-channel transmit/receive radiofrequency body coil. METHODS In vivo unenhanced MR was performed in 8 healthy volunteers on a 7T whole-body MR system. After B(0) shimming the following sequences were obtained: 1) 2D and 3D spoiled gradient-echo sequences (FLASH, VIBE), 2) T1-weighted 2D in and opposed phase 3) True-FISP imaging and 4) a T2-weighted turbo spin echo (TSE) sequence. Visual evaluation of the overall image quality was performed by two radiologists. RESULTS Renal MRI at 7T was feasible in all eight subjects. Best image quality was found using T1-weighted gradient echo MRI, providing high anatomical details and excellent conspicuity of the non-enhanced vasculature. With successful shimming, B(1) signal voids could be effectively reduced and/or shifted out of the region of interest in most sequence types. However, T2-weighted TSE imaging remained challenging and strongly impaired because of signal heterogeneities in three volunteers. CONCLUSION The results demonstrate the feasibility and diagnostic potential of dedicated 7T renal imaging. Further optimisation of imaging sequences and dedicated RF coil concepts are expected to improve the acquisition quality and ultimately provide high clinical diagnostic value.
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Affiliation(s)
- Lale Umutlu
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Hufelandstr. 55, Essen, Germany.
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98
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Metzger GJ, van de Moortele PF, Akgun C, Snyder CJ, Moeller S, Strupp J, Andersen P, Shrivastava D, Vaughan T, Ugurbil K, Adriany G. Performance of external and internal coil configurations for prostate investigations at 7 T. Magn Reson Med 2010; 64:1625-39. [PMID: 20740657 DOI: 10.1002/mrm.22552] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Revised: 05/23/2010] [Accepted: 06/03/2010] [Indexed: 11/05/2022]
Abstract
Three different coil configurations were evaluated through simulation and experimentally to determine safe operating limits and evaluate subject size-dependent performance for prostate imaging at 7 T. The coils included a transceiver endorectal coil (trERC), a 16-channel transceiver external surface array (trESA) and a trESA combined with a receive-only ERC (trESA+roERC). Although the transmit B(1) (B 1+) homogeneity was far superior for the trESA, the maximum achievable B 1+ is subject size dependent and limited by transmit chain losses and amplifier performance. For the trERC, limitations in transmit homogeneity greatly compromised image quality and limited coverage of the prostate. Despite these challenges, the high peak B 1+ close to the trERC and subject size-independent performance provides potential advantages especially for spectroscopic localization where high-bandwidth radiofrequency pulses are required. On the receive side, the combined trESA+roERC provided the highest signal-to-noise ratio and improved homogeneity over the trERC resulting in better visualization of the prostate and surrounding anatomy. In addition, the parallel imaging performance of the trESA+roERC holds strong promise for diffusion-weighted imaging and dynamic contrast-enhanced MRI.
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Affiliation(s)
- Gregory J Metzger
- Department of Radiology, Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA.
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99
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Umutlu L, Maderwald S, Kraff O, Theysohn JM, Kuemmel S, Hauth EA, Forsting M, Antoch G, Ladd ME, Quick HH, Lauenstein TC. Dynamic contrast-enhanced breast MRI at 7 Tesla utilizing a single-loop coil: a feasibility trial. Acad Radiol 2010; 17:1050-6. [PMID: 20599158 DOI: 10.1016/j.acra.2010.03.017] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Revised: 03/26/2010] [Accepted: 03/29/2010] [Indexed: 10/19/2022]
Abstract
RATIONALE AND OBJECTIVES The aim of this study was to assess the feasibility of dynamic contrast-enhanced ultra-high-field breast imaging at 7 Tesla. MATERIAL AND METHODS A total of 15 subjects, including 5 patients with histologically proven breast cancer, were examined on a 7 Tesla whole-body magnetic resonance imaging system using a unilateral linearly polarized single-loop coil. Subjects were placed in prone position on a biopsy support system, with the coil placed directly below the region of interest. The examination protocol included the following sequences: 1) T2-weighted turbo spin echo sequence; 2) six dynamic T1-weighted spoiled gradient-echo sequences; and 3) subtraction imaging. RESULTS Contrast-enhanced T1-weighted imaging at 7 Tesla could be obtained at high spatial resolution with short acquisition times, providing good image accuracy and a conclusively good delineation of small anatomical and pathological structures. T2-weighted imaging could be obtained with high spatial resolution at adequate acquisition times. Because of coil limitations, four high-field magnetic resonance examinations showed decreased diagnostic value. CONCLUSIONS This first scientific approach of dynamic contrast-enhanced breast magnetic resonance imaging at 7 Tesla demonstrates the complexity of ultra-high-field breast magnetic resonance imaging and countenances the implementation of further advanced bilateral coil concepts to circumvent current limitations from the coil and ultra-high-field magnetic strength.
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100
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Niendorf T, Sodickson DK, Krombach GA, Schulz-Menger J. Toward cardiovascular MRI at 7 T: clinical needs, technical solutions and research promises. Eur Radiol 2010; 20:2806-16. [PMID: 20676653 DOI: 10.1007/s00330-010-1902-8] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2010] [Revised: 07/09/2010] [Accepted: 07/14/2010] [Indexed: 12/18/2022]
Abstract
OBJECTIVE To consider potential clinical needs, technical solutions and research promises of ultrahigh-field strength cardiovascular MR (CMR). METHODS A literature review is given, surveying advantages and disadvantages of CMR at ultrahigh fields (UHF). Key concepts, emerging technologies, practical considerations and applications of UHF CMR are provided. Examples of UHF CMR imaging strategies and their added value are demonstrated, including the numerous unsolved problems. A concluding section explores future directions in UHF CMR. RESULTS UHF CMR can be regarded as one of the most challenging MRI applications. Image quality achievable at UHF is not always exclusively defined by signal-to-noise considerations. Some of the inherent advantages of UHF MRI are offset by practical challenges. But UHF CMR can boast advantages over its kindred lower field counterparts by trading the traits of high magnetic fields for increased temporal and/or spatial resolution. CONCLUSIONS CMR at ultrahigh-field strengths is a powerful motivator, since speed and signal may be invested to overcome the fundamental constraints that continue to hamper traditional CMR. If practical challenges can be overcome, UHF CMR will help to open the door to new approaches for basic science and clinical research.
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Affiliation(s)
- Thoralf Niendorf
- Berlin Ultrahigh Field Facility, Max Delbrueck Center for Molecular Medicine, Robert-Roessle-Strasse 10, 13125 Berlin, Germany.
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