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Baadsvik EL, Weiger M, Froidevaux R, Schildknecht CM, Ineichen BV, Pruessmann KP. Myelin bilayer mapping in the human brain in vivo. Magn Reson Med 2024; 91:2332-2344. [PMID: 38171541 DOI: 10.1002/mrm.29998] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Revised: 11/27/2023] [Accepted: 12/15/2023] [Indexed: 01/05/2024]
Abstract
PURPOSE To quantitatively map the myelin lipid-protein bilayer in the live human brain. METHODS This goal was pursued by integrating a multi-TE acquisition approach targeting ultrashort T2 signals with voxel-wise fitting to a three-component signal model. Imaging was performed at 3 T in two healthy volunteers using high-performance RF and gradient hardware and the HYFI sequence. The design of a suitable imaging protocol faced substantial constraints concerning SNR, imaging volume, scan time, and RF power deposition. Model fitting to data acquired using the proposed protocol was made feasible through simulation-based optimization, and filtering was used to condition noise presentation and overall depiction fidelity. RESULTS A multi-TE protocol (11 TEs of 20-780 μs) for in vivo brain imaging was developed in adherence with applicable safety regulations and practical scan time limits. Data acquired using this protocol produced accurate model fitting results, validating the suitability of the protocol for this purpose. Structured, grainy texture of myelin bilayer maps was observed and determined to be a manifestation of correlated image noise resulting from the employed acquisition strategy. Map quality was significantly improved by filtering to uniformize the k-space noise distribution and simultaneously extending the k-space support. The final myelin bilayer maps provided selective depiction of myelin, reconciling competitive resolution (1.4 mm) with adequate SNR and benign noise texture. CONCLUSION Using the proposed technique, quantitative maps of the myelin bilayer can be obtained in vivo. These maps offer unique information content with potential applications in basic research, diagnosis, disease monitoring, and drug development.
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Affiliation(s)
- Emily Louise Baadsvik
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Markus Weiger
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Romain Froidevaux
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | | | - Benjamin Victor Ineichen
- Department of Neuroradiology, Clinical Neuroscience Center, University Hospital Zurich, University of Zurich, Zurich, Switzerland
- Center for Reproducible Science, University of Zurich, Zurich, Switzerland
| | - Klaas Paul Pruessmann
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
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2
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Baadsvik EL, Weiger M, Froidevaux R, Faigle W, Ineichen BV, Pruessmann KP. Quantitative magnetic resonance mapping of the myelin bilayer reflects pathology in multiple sclerosis brain tissue. SCIENCE ADVANCES 2023; 9:eadi0611. [PMID: 37566661 PMCID: PMC10421026 DOI: 10.1126/sciadv.adi0611] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 07/07/2023] [Indexed: 08/13/2023]
Abstract
Multiple sclerosis (MS) is a neuroinflammatory disease characterized by loss of myelin (demyelination) and, to a certain extent, subsequent myelin repair (remyelination). To better understand the pathomechanisms underlying de- and remyelination and to monitor the efficacy of treatments aimed at regenerating myelin, techniques offering noninvasive visualizations of myelin are warranted. Magnetic resonance (MR) imaging has long been at the forefront of efforts to visualize myelin, but it has only recently become feasible to access the rapidly decaying resonance signals stemming from the myelin lipid-protein bilayer itself. Here, we show that direct MR mapping of the bilayer yields highly specific myelin maps in brain tissue from patients with MS. Furthermore, examination of the bilayer signal behavior is found to reveal pathological alterations in normal-appearing white and gray matter. These results indicate promise for in vivo implementations of the myelin bilayer mapping technique, with prospective applications in basic research, diagnostics, disease monitoring, and drug development.
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Affiliation(s)
- Emily Louise Baadsvik
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Markus Weiger
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Romain Froidevaux
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Wolfgang Faigle
- Neuroimmunology and MS Research Section, Neurology Clinic, University of Zurich, University Hospital Zurich, Zurich, Switzerland
- Institut Curie, Immunity and Cancer Unit 932, Paris, France
| | - Benjamin V. Ineichen
- Department of Neuroradiology, Clinical Neuroscience Center, University Hospital Zurich, University of Zurich, Zurich, Switzerland
- Center for Reproducible Science, University of Zurich, Zurich, Switzerland
| | - Klaas P. Pruessmann
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
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3
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Baadsvik EL, Weiger M, Froidevaux R, Faigle W, Ineichen BV, Pruessmann KP. Mapping the myelin bilayer with short-T 2 MRI: Methods validation and reference data for healthy human brain. Magn Reson Med 2023; 89:665-677. [PMID: 36253953 PMCID: PMC10091754 DOI: 10.1002/mrm.29481] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Revised: 08/24/2022] [Accepted: 09/20/2022] [Indexed: 12/13/2022]
Abstract
PURPOSE To explore the properties of short-T2 signals in human brain, investigate the impact of various experimental procedures on these properties and evaluate the performance of three-component analysis. METHODS Eight samples of non-pathological human brain tissue were subjected to different combinations of experimental procedures including D2 O exchange and frozen storage. Short-T2 imaging techniques were employed to acquire multi-TE (33-2067 μs) data, to which a three-component complex model was fitted in two steps to recover the properties of the underlying signal components and produce amplitude maps of each component. For validation of the component amplitude maps, the samples underwent immunohistochemical myelin staining. RESULTS The signal component representing the myelin bilayer exhibited super-exponential decay with T2,min of 5.48 μs and a chemical shift of 1.07 ppm, and its amplitude could be successfully mapped in both white and gray matter in all samples. These myelin maps corresponded well to myelin-stained tissue sections. Gray matter signals exhibited somewhat different components than white matter signals, but both tissue types were well represented by the signal model. Frozen tissue storage did not alter the signal components but influenced component amplitudes. D2 O exchange was necessary to characterize the non-aqueous signal components, but component amplitude mapping could be reliably performed also in the presence of H2 O signals. CONCLUSIONS The myelin mapping approach explored here produced reasonable and stable results for all samples. The extensive tissue and methodological investigations performed in this work form a basis for signal interpretation in future studies both ex vivo and in vivo.
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Affiliation(s)
- Emily Louise Baadsvik
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Markus Weiger
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Romain Froidevaux
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Wolfgang Faigle
- Neuroimmunology and MS Research Section, Neurology Clinic, University of Zurich, University Hospital Zurich, Zurich, Switzerland
| | - Benjamin Victor Ineichen
- Department of Neuroradiology, Clinical Neuroscience Center, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Klaas Paul Pruessmann
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
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4
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Lombardi AF, Ma YJ, Jang H, Jerban S, Du J, Chang EY, Chung CB. Synthetic CT in Musculoskeletal Disorders: A Systematic Review. Invest Radiol 2023; 58:43-59. [PMID: 36070535 PMCID: PMC9742139 DOI: 10.1097/rli.0000000000000916] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
ABSTRACT Repeated computed tomography (CT) examinations increase patients' ionizing radiation exposure and health costs, making an alternative method desirable. Cortical and trabecular bone, however, have short T2 relaxation times, causing low signal intensity on conventional magnetic resonance (MR) sequences. Different techniques are available to create a "CT-like" contrast of bone, such as ultrashort echo time, zero echo time, gradient-echo, and susceptibility-weighted image MR sequences, and artificial intelligence. This systematic review summarizes the essential technical background and developments of ultrashort echo time, zero echo time, gradient-echo, susceptibility-weighted image MR imaging sequences and artificial intelligence; presents studies on research and clinical applications of "CT-like" MR imaging; and describes their main advantages and limitations. We also discuss future opportunities in research, which patients would benefit the most, the most appropriate situations for using the technique, and the potential to replace CT in the clinical workflow.
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Affiliation(s)
- Alecio F Lombardi
- From the Department of Radiology, University of California San Diego, La Jolla, and the Research Service, Veterans Affairs San Diego Healthcare System, California
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5
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Giovannetti G, Guerrini A, Minozzi S, Panetta D, Salvadori PA. Computer tomography and magnetic resonance for multimodal imaging of fossils and mummies. Magn Reson Imaging 2022; 94:7-17. [PMID: 36084902 DOI: 10.1016/j.mri.2022.08.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Revised: 08/26/2022] [Accepted: 08/31/2022] [Indexed: 11/24/2022]
Abstract
The study of fossils and mummies has largely benefited from the use of modern noninvasive and nondestructive imaging technologies and represents a fast developing area. In this review, we describe the emerging role of imaging based on Magnetic Resonance (MR) and Computer Tomography (CT) employed for the study of ancient remains and mummies. For each methodology, the state of the art in paleoradiology applications is described, by emphasizing new technologies developed in the field of both CT, such as micro- and nano-CT, dual-energy and multi-energy CT, and MR, with the description of novel dedicated sequences, radiofrequency coils and gradients. The complementarity of CT and MR in paleoradiology is also discussed, by pointing out what MR provides in addition to CT, with an overview on the state of the art of emerging strategies in the use of CT/MR combination for the study of a sample following a multimodal integrated approach.
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Affiliation(s)
- Giulio Giovannetti
- Institute of Clinical Physiology, National Council of Research, via G. Moruzzi 1, 56124 Pisa, Italy.
| | - Andrea Guerrini
- Gruppo Archeologico e Paleontologico Livornese, Museo di Storia Naturale del Mediterraneo, via Roma, 234, 57127 Leghorn, Italy
| | - Simona Minozzi
- Division of Paleopathology, Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, Via Roma 57, 56100 Pisa, Italy
| | - Daniele Panetta
- Institute of Clinical Physiology, National Council of Research, via G. Moruzzi 1, 56124 Pisa, Italy
| | - Piero A Salvadori
- Institute of Clinical Physiology, National Council of Research, via G. Moruzzi 1, 56124 Pisa, Italy
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Borreguero Morata J, González JM, Pallás E, Rigla JP, Algarín JM, Bosch R, Galve F, Grau‐Ruiz D, Pellicer R, Ríos A, Benlloch JM, Alonso J. Prepolarized MRI of hard tissues and solid-state matter. NMR IN BIOMEDICINE 2022; 35:e4737. [PMID: 35384092 PMCID: PMC9540585 DOI: 10.1002/nbm.4737] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2021] [Revised: 03/25/2022] [Accepted: 03/31/2022] [Indexed: 05/25/2023]
Abstract
Prepolarized MRI (PMRI) is a long-established technique conceived to counteract the loss in signal-to-noise ratio (SNR) inherent to low-field MRI systems. When it comes to hard biological tissues and solid-state matter, PMRI is severely restricted by their ultra-short characteristic relaxation times. Here we demonstrate that efficient hard-tissue prepolarization is within reach with a special-purpose 0.26 T scanner designed for ex vivo dental MRI and equipped with suitable high-power electronics. We have characterized the performance of a 0.5 T prepolarizer module, which can be switched on and off in 200 μs. To this end, we have used resin, dental and bone samples, all with T1 times of the order of 20 ms at our field strength. The measured SNR enhancement is in good agreement with a simple theoretical model, and deviations in extreme regimes can be attributed to mechanical vibrations due to the magnetic interaction between the prepolarization and main magnets.
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Affiliation(s)
| | | | - Eduardo Pallás
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M)Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV)ValenciaSpain
- Instituto de Instrumentación para Imagen MolecularCentro Mixto CSIC–Universitat Politècnica de ValènciaValenciaSpain
| | | | - José M. Algarín
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M)Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV)ValenciaSpain
- Instituto de Instrumentación para Imagen MolecularCentro Mixto CSIC–Universitat Politècnica de ValènciaValenciaSpain
| | | | - Fernando Galve
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M)Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV)ValenciaSpain
- Instituto de Instrumentación para Imagen MolecularCentro Mixto CSIC–Universitat Politècnica de ValènciaValenciaSpain
| | | | - Rubén Pellicer
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M)Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV)ValenciaSpain
- Asociación de investigación MPCSan SebastiánSpain
| | | | - José M. Benlloch
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M)Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV)ValenciaSpain
- Instituto de Instrumentación para Imagen MolecularCentro Mixto CSIC–Universitat Politècnica de ValènciaValenciaSpain
| | - Joseba Alonso
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M)Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV)ValenciaSpain
- Instituto de Instrumentación para Imagen MolecularCentro Mixto CSIC–Universitat Politècnica de ValènciaValenciaSpain
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7
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Wiesinger F, Ho ML. Zero-TE MRI: principles and applications in the head and neck. Br J Radiol 2022; 95:20220059. [PMID: 35616709 PMCID: PMC10162052 DOI: 10.1259/bjr.20220059] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Zero echo-time (ZTE) MRI is a novel imaging technique that utilizes ultrafast readouts to capture signal from short-T2 tissues. Additional sequence advantages include rapid imaging times, silent scanning, and artifact resistance. A robust application of this technology is imaging of cortical bone without the use of ionizing radiation, thus representing a viable alternative to CT for both rapid screening and "one-stop-shop" MRI. Although ZTE is increasingly used in musculoskeletal and body imaging, neuroimaging applications have historically been limited by complex anatomy and pathology. In this article, we review the imaging physics of ZTE including pulse sequence options, practical limitations, and image reconstruction. We then discuss optimization of settings for ZTE bone neuroimaging including acquisition, processing, segmentation, synthetic CT generation, and artifacts. Finally, we examine clinical utility of ZTE in the head and neck with imaging examples including malformations, trauma, tumors, and interventional procedures.
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Affiliation(s)
- Florian Wiesinger
- Department for Neuroimaging, Institute of Psychiatry & Neuroscience, King's College London, London, UK.,Principal Scientist at GE Healthcare, Munich, Germany
| | - Mai-Lan Ho
- Nationwide Children's Hospital and The Ohio State University, Columbus, USA
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8
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Aydıngöz Ü, Yıldız AE, Ergen FB. Zero Echo Time Musculoskeletal MRI: Technique, Optimization, Applications, and Pitfalls. Radiographics 2022; 42:1398-1414. [PMID: 35904982 DOI: 10.1148/rg.220029] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Zero echo time (ZTE) imaging is an MRI technique that produces images similar to those obtained with radiography or CT. In ZTE MRI, the very short T2 signal from the mineralized trabecular bone matrix and especially cortical bone-both of which have a low proton density (PD)-is sampled in a unique sequence setup. Additionally, the PD weighting of the ZTE sequence results in less contrast between soft tissues. Therefore, along with gray-scale inversion from black to white and vice versa, ZTE imaging provides excellent contrast between cortical bone and soft tissues similar to that of radiography and CT. However, despite isotropic or near-isotropic three-dimensional (3D) imaging capabilities of the ZTE sequence, spatial resolution in this technique is still inferior to that of radiography and CT, and 3D volume renderings are currently time-consuming and require postprocessing software that features segmentation and manual contouring. Optimization of ZTE MRI mostly entails adjustments of bandwidth, flip angle, field of view, and image matrix. A wide range of structural abnormalities and disease or healing processes in the musculoskeletal system are well delineated with ZTE MRI, including conditions that involve bone-based morphometric analyses (which aid diagnosis, help prognostication, and guide surgery), impaction, avulsion and stress fractures, loose bodies or erosions in and around joints, soft-tissue calcifications and ossifications, and bone tumors (including treatment response). The pitfalls of ZTE imaging include mimics of foci of calcification or ossification such as intra-articular gas and susceptibility artifacts from surgical materials and hemosiderin deposition, which can be avoided in many instances by cross-referencing images obtained with other MRI sequences. Online supplemental material is available for this article. ©RSNA, 2022.
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Affiliation(s)
- Üstün Aydıngöz
- From the Department of Radiology, Hacettepe University School of Medicine, 06230 Ankara, Turkey
| | - Adalet Elçin Yıldız
- From the Department of Radiology, Hacettepe University School of Medicine, 06230 Ankara, Turkey
| | - F Bilge Ergen
- From the Department of Radiology, Hacettepe University School of Medicine, 06230 Ankara, Turkey
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Ljungberg E, Wood TC, Solana AB, Williams SCR, Barker GJ, Wiesinger F. Motion corrected silent ZTE neuroimaging. Magn Reson Med 2022; 88:195-210. [PMID: 35381110 PMCID: PMC9321117 DOI: 10.1002/mrm.29201] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Revised: 01/16/2022] [Accepted: 01/28/2022] [Indexed: 11/11/2022]
Abstract
Purpose To develop self‐navigated motion correction for 3D silent zero echo time (ZTE) based neuroimaging and characterize its performance for different types of head motion. Methods The proposed method termed MERLIN (Motion Estimation & Retrospective correction Leveraging Interleaved Navigators) achieves self‐navigation by using interleaved 3D phyllotaxis k‐space sampling. Low resolution navigator images are reconstructed continuously throughout the ZTE acquisition using a sliding window and co‐registered in image space relative to a fixed reference position. Rigid body motion corrections are then applied retrospectively to the k‐space trajectory and raw data and reconstructed into a final, high‐resolution ZTE image. Results MERLIN demonstrated successful and consistent motion correction for magnetization prepared ZTE images for a range of different instructed motion paradigms. The acoustic noise response of the self‐navigated phyllotaxis trajectory was found to be only slightly above ambient noise levels (<4 dBA). Conclusion Silent ZTE imaging combined with MERLIN addresses two major challenges intrinsic to MRI (i.e., subject motion and acoustic noise) in a synergistic and integrated manner without increase in scan time and thereby forms a versatile and powerful framework for clinical and research MR neuroimaging applications.
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Affiliation(s)
- Emil Ljungberg
- Department of Neuroimaging, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK.,Department of Medical Radiation Physics, Lund University, Lund, Sweden
| | - Tobias C Wood
- Department of Neuroimaging, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK
| | | | - Steven C R Williams
- Department of Neuroimaging, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK
| | - Gareth J Barker
- Department of Neuroimaging, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK
| | - Florian Wiesinger
- Department of Neuroimaging, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK.,GE Healthcare, Munich, Germany
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10
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Ilbey S, Jungmann PM, Fischer J, Jung M, Bock M, Özen AC. Single point imaging with radial acquisition and compressed sensing. Magn Reson Med 2022; 87:2685-2696. [PMID: 35037292 DOI: 10.1002/mrm.29156] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 11/26/2021] [Accepted: 12/23/2021] [Indexed: 12/22/2022]
Abstract
PURPOSE To accelerate the Pointwise Encoding Time Reduction with Radial Acquisition (PETRA) sequence using compressed sensing while preserving the image quality for high-resolution MRI of tissue with ultra-short T 2 ∗ values. METHODS Compressed sensing was introduced in the PETRA sequence (csPETRA) to accelerate the time-consuming single point acquisition of the k-space center data. Random undersampling was applied to achieve acceleration factors up to Acc = 32. Phantom and in vivo images of the knee joint of six volunteers were measured at 3T using csPETRA sequence with Acc = 4, 8, 12, 16, 24, and 32. Images were compared against fully sampled PETRA data (Acc = 1) for structural similarity and normalized-mean-square-error. Qualitative and semi-quantitative analyses were performed to assess the effect of the acceleration on image artifacts, image quality, and delineation of anatomical structures at the knee. RESULTS Even at high acceleration factors of Acc = 16 no aliasing artifacts were observed, and the anatomical details were preserved compared with the fully sampled data. The normalized-mean-square-error was less than 1% for Acc = 16, in which single point imaging acquisition time was reduced from 165 to 10 s, reducing the total scan time from 7.8 to 5.2 min. Semi-quantitative analyses suggest that Acc = 16 yields comparable diagnostic quality as the fully sampled data for knee imaging at a scan time of 5.2 min. CONCLUSION csPETRA allows for ultra-short T 2 ∗ imaging of the knee joint in clinically acceptable scan times while maintaining the image quality of original non-accelerated PETRA sequence.
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Affiliation(s)
- Serhat Ilbey
- Department of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Pia M Jungmann
- Department of Diagnostic and Interventional Radiology, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.,Department of Radiology, Cantonal Hospital Grisons, Chur, Switzerland
| | - Johannes Fischer
- Department of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Matthias Jung
- Department of Diagnostic and Interventional Radiology, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Michael Bock
- Department of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Ali Caglar Özen
- Department of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
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11
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Froidevaux R, Weiger M, Pruessmann KP. Pulse encoding for ZTE imaging: RF excitation without dead-time penalty. Magn Reson Med 2021; 87:1360-1374. [PMID: 34775617 PMCID: PMC9299067 DOI: 10.1002/mrm.29056] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Revised: 09/09/2021] [Accepted: 10/04/2021] [Indexed: 11/23/2022]
Abstract
Purpose To overcome limitations in the duration of RF excitation in zero‐TE (ZTE) MRI by exploiting intrinsic encoding properties of RF pulses to retrieve data missed during the dead time caused by the pulse. Methods An enhanced ZTE signal model was developed using multiple RF pulses, which enables accessing information hidden in the pulse‐induced dead time via encoding intrinsically applied by the RF pulses. Such ZTE with pulse encoding was implemented by acquisition of two ZTE data sets using excitation with similar frequency‐swept pulses differing only by a small off‐resonance in their center frequency. In this way, the minimum scan time is doubled but each acquisition contributes equally to the SNR, as with ordinary averaging. The method was demonstrated on long‐T2 and short‐T2 phantoms as well as in in vivo experiments. Results ZTE with pulse encoding provided good image quality at unprecedented dead‐time gaps, demonstrated here up to 6 Nyquist dwells. In head imaging, the ability to use longer excitation pulses led to approximately 2‐fold improvements in SNR efficiency as compared with conventional ZTE and allowed the creation of T1 contrast. Conclusion Exploiting intrinsic encoding properties of RF pulses in a new signal model enables algebraic reconstruction of ZTE data sets with large dead‐time gaps. This permits larger flip angles, which can be used to achieve enhanced T1 contrast and significant improvements in SNR efficiency in case the Ernst angle can be better approached, thus broadening the range of application of ZTE MRI.
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Affiliation(s)
- Romain Froidevaux
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Markus Weiger
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Klaas P Pruessmann
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
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12
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Fischer J, Özen AC, Ilbey S, Traser L, Echternach M, Richter B, Bock M. Sub-millisecond 2D MRI of the vocal fold oscillation using single-point imaging with rapid encoding. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2021; 35:301-310. [PMID: 34542771 PMCID: PMC8995286 DOI: 10.1007/s10334-021-00959-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Revised: 08/06/2021] [Accepted: 09/06/2021] [Indexed: 10/24/2022]
Abstract
OBJECTIVE The slow spatial encoding of MRI has precluded its application to rapid physiologic motion in the past. The purpose of this study is to introduce a new fast acquisition method and to demonstrate feasibility of encoding rapid two-dimensional motion of human vocal folds with sub-millisecond resolution. METHOD In our previous work, we achieved high temporal resolution by applying a rapidly switched phase encoding gradient along the direction of motion. In this work, we extend phase encoding to the second image direction by using single-point imaging with rapid encoding (SPIRE) to image the two-dimensional vocal fold oscillation in the coronal view. Image data were gated using electroglottography (EGG) and motion corrected. An iterative reconstruction with a total variation (TV) constraint was used and the sequence was also simulated using a motion phantom. RESULTS Dynamic images of the vocal folds during phonation at pitches of 150 and 165 Hz were acquired in two volunteers and the periodic motion of the vocal folds at a temporal resolution of about 600 µs was shown. The simulations emphasize the necessity of SPIRE for two-dimensional motion encoding. DISCUSSION SPIRE is a new MRI method to image rapidly oscillating structures and for the first time provides dynamic images of the vocal folds oscillations in the coronal plane.
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Affiliation(s)
- Johannes Fischer
- Department of Radiology, Medical Physics, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
| | - Ali Caglar Özen
- Department of Radiology, Medical Physics, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.,German Consortium for Translational Cancer Research Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Serhat Ilbey
- Department of Radiology, Medical Physics, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Louisa Traser
- Freiburg Institute for Musicians' Medicine, Freiburg University Medical Center, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Matthias Echternach
- Division of Phoniatrics and Pediatric Audiology, Department of Otorhinolaryngology, Head and Neck Surgery, Ludwig-Maximilians-University, Munich, Germany
| | - Bernhard Richter
- Freiburg Institute for Musicians' Medicine, Freiburg University Medical Center, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Michael Bock
- Department of Radiology, Medical Physics, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
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Froidevaux R, Weiger M, Rösler MB, Brunner DO, Pruessmann KP. HYFI: Hybrid filling of the dead-time gap for faster zero echo time imaging. NMR IN BIOMEDICINE 2021; 34:e4493. [PMID: 33624305 PMCID: PMC8244056 DOI: 10.1002/nbm.4493] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2020] [Revised: 01/25/2021] [Accepted: 01/29/2021] [Indexed: 05/31/2023]
Abstract
The aim of this work was to improve the SNR efficiency of zero echo time (ZTE) MRI pulse sequences for faster imaging of short-T2 components at large dead-time gaps. ZTE MRI with hybrid filling (HYFI) is a strategy for retrieving inner k-space data missed during the dead-time gaps arising from radio-frequency excitation and switching in ZTE imaging. It performs hybrid filling of the inner k-space with a small single-point-imaging core surrounded by a stack of shells acquired on radial readouts in an onion-like fashion. The exposition of this concept is followed by translation into guidelines for parameter choice and implementation details. The imaging properties and performance of HYFI are studied in simulations as well as phantom, in vitro and in vivo imaging, with an emphasis on comparison with the pointwise encoding time reduction with radial acquisition (PETRA) technique. Simulations predict higher SNR efficiency for HYFI compared with PETRA at preserved image quality, with the advantage increasing with the size of the k-space gap. These results are confirmed by imaging experiments with gap sizes of 25 to 50 Nyquist dwells, in which scan times for similar image quality could be reduced by 25% to 60%. The HYFI technique provides both high SNR efficiency and image quality, thus outperforming previously known ZTE-based pulse sequences, in particular for large k-space gaps. Promising applications include direct imaging of ultrashort-T2 components, such as the myelin bilayer or collagen, T2 mapping of ultrafast relaxing signals, and ZTE imaging with reduced chemical shift artifacts.
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Affiliation(s)
- Romain Froidevaux
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Markus Weiger
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Manuela B Rösler
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - David O Brunner
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Klaas P Pruessmann
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
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