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Yin Y, Song Y, Jia Y, Xia J, Bai R, Kong X. Sodium Dynamics in the Cellular Environment. J Am Chem Soc 2023; 145:10522-10532. [PMID: 37104830 DOI: 10.1021/jacs.2c13271] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Abstract
Sodium ions are essential for the functions of biological cells, and they are maintained at the balance between intra- and extracellular environments. The quantitative assessment of intra- and extracellular sodium as well as its dynamics can provide crucial physiological information on a living system. 23Na nuclear magnetic resonance (NMR) is a powerful and noninvasive technique to probe the local environment and dynamics of sodium ions. However, due to the complex relaxation behavior of the quadrupolar nucleus in the intermediate-motion regime and because of the heterogeneous compartments and diverse molecular interactions in the cellular environment, the understanding of the 23Na NMR signal in biological systems is still at the early stage. In this work, we characterize the relaxation and diffusion of sodium ions in the solutions of proteins and polysaccharides, as well as in the in vitro samples of living cells. The multi-exponential behavior of 23Na transverse relaxation has been analyzed according to the relaxation theory to derive the crucial information related to the ionic dynamics and molecular binding in the solutions. The bi-compartment model of transverse relaxation and diffusion measurements can corroborate each other to quantify the fractions of intra- and extracellular sodium. We show that 23Na relaxation and diffusion can be used to monitor the viability of human cells, which offers versatile NMR metrics for in vivo studies.
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Affiliation(s)
- Yu Yin
- Department of Chemistry, Zhejiang University, 310027 Hangzhou, P. R. China
| | - Yifan Song
- Department of Chemistry, Zhejiang University, 310027 Hangzhou, P. R. China
| | - Yinhang Jia
- Key Laboratory of Biomedical Engineering of Education Ministry, College of Biomedical Engineering and Instrument Science, Zhejiang University, 310027 Hangzhou, Zhejiang, P. R. China
| | - Juntao Xia
- Department of Chemistry, Zhejiang University, 310027 Hangzhou, P. R. China
| | - Ruiliang Bai
- Key Laboratory of Biomedical Engineering of Education Ministry, College of Biomedical Engineering and Instrument Science, Zhejiang University, 310027 Hangzhou, Zhejiang, P. R. China
- Interdisciplinary Institute of Neuroscience and Technology, School of Medicine, Zhejiang University, 310029 Hangzhou, China
- Department of Physical Medicine and Rehabilitation, Sir Run Run Shaw Hospital, Zhejiang University, 310016 Hangzhou, China
| | - Xueqian Kong
- Department of Chemistry, Zhejiang University, 310027 Hangzhou, P. R. China
- Department of Physical Medicine and Rehabilitation, Sir Run Run Shaw Hospital, Zhejiang University, 310016 Hangzhou, China
- Institute of Translational Medicine, Shanghai Jiao Tong University, 200240 Shanghai, P. R. China
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2
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Vaeggemose M, Schulte RF, Laustsen C. Clinically feasible B 1 field correction for multi-organ sodium imaging at 3 T. NMR IN BIOMEDICINE 2023; 36:e4835. [PMID: 36115017 PMCID: PMC10078323 DOI: 10.1002/nbm.4835] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 09/12/2022] [Accepted: 09/12/2022] [Indexed: 06/15/2023]
Abstract
Sodium MRI allows the non-invasive quantification of intra-organ sodium concentration. RF inhomogeneity introduces uncertainty in this estimated concentration. B1 field corrections can be used to overcome some of these limitations. However, the low signal-to-noise ratio in sodium MRI makes accurate B1 mapping in reasonable scan times challenging. The study aims to evaluate Bloch-Siegert off-resonance (BLOSI) B1 field correction for sodium MRI using a 3D Fermat looped, orthogonally encoded trajectories (FLORET) read-out trajectory. We propose a clinically feasible B1 field map correction method for sodium imaging at 3 T, evaluating five healthy subjects' brain, heart blood, kidneys, and thigh muscle. We scanned the subjects twice for repeatability measures and used sodium phantoms to determine organ total sodium concentration. Conventional proton scans were compared with sodium images for organ structural integrity. The BLOSI approach based on the 3D FLORET read-out trajectory was used in B1 field correction and 3D density-adapted radial acquisition for sodium imaging. Results indicate improvements in sodium imaging based on B1 field correction in a clinically feasible protocol. Improvements are determined in all organs by enhanced anatomical representation, organ homogeneity, and an increase in the total sodium concentration after applying a B1 field correction. The proposed BLOSI-based B1 field correction using a 3D FLORET read-out trajectory is clinically feasible for sodium imaging, which is shown in the brain, heart, kidney, and thigh muscle. This supports using fast B1 field mapping in the clinical setting.
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Affiliation(s)
- Michael Vaeggemose
- GE HealthcareBrondbyDenmark
- MR Research Centre, Department of Clinical MedicineAarhus UniversityAarhusDenmark
| | | | - Christoffer Laustsen
- MR Research Centre, Department of Clinical MedicineAarhus UniversityAarhusDenmark
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3
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Yurista SR, Eder RA, Kwon DH, Farrar CT, Yen YF, Tang WHW, Nguyen CT. Magnetic resonance imaging of cardiac metabolism in heart failure: how far have we come? Eur Heart J Cardiovasc Imaging 2022; 23:1277-1289. [PMID: 35788836 PMCID: PMC10202438 DOI: 10.1093/ehjci/jeac121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Revised: 06/06/2022] [Accepted: 06/10/2022] [Indexed: 11/12/2022] Open
Abstract
As one of the highest energy consumer organs in the body, the heart requires tremendous amount of adenosine triphosphate (ATP) to maintain its continuous mechanical work. Fatty acids, glucose, and ketone bodies are the primary fuel source of the heart to generate ATP with perturbations in ATP generation possibly leading to contractile dysfunction. Cardiac metabolic imaging with magnetic resonance imaging (MRI) plays a crucial role in understanding the dynamic metabolic changes occurring in the failing heart, where the cardiac metabolism is deranged. Also, targeting and quantifying metabolic changes in vivo noninvasively is a promising approach to facilitate diagnosis, determine prognosis, and evaluate therapeutic response. Here, we summarize novel MRI techniques used for detailed investigation of cardiac metabolism in heart failure including magnetic resonance spectroscopy (MRS), hyperpolarized MRS, and chemical exchange saturation transfer based on evidence from preclinical and clinical studies and to discuss the potential clinical application in heart failure.
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Affiliation(s)
- Salva R Yurista
- Cardiovascular Research Center, Corrigan Minehan Heart Center, Massachusetts General Hospital, Harvard Medical School, 149 13th St, Charlestown, MA 02129, USA
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, 149 13th St, Charlestown, MA 02129, USA
| | - Robert A Eder
- Cardiovascular Research Center, Corrigan Minehan Heart Center, Massachusetts General Hospital, Harvard Medical School, 149 13th St, Charlestown, MA 02129, USA
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, 149 13th St, Charlestown, MA 02129, USA
| | - Deborah H Kwon
- Department of Cardiovascular Medicine, Heart, Vascular, and Thoracic Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195, USA
| | - Christian T Farrar
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, 149 13th St, Charlestown, MA 02129, USA
| | - Yi Fen Yen
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, 149 13th St, Charlestown, MA 02129, USA
| | - W H Wilson Tang
- Department of Cardiovascular Medicine, Heart, Vascular, and Thoracic Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195, USA
| | - Christopher T Nguyen
- Cardiovascular Research Center, Corrigan Minehan Heart Center, Massachusetts General Hospital, Harvard Medical School, 149 13th St, Charlestown, MA 02129, USA
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, 149 13th St, Charlestown, MA 02129, USA
- Division of Health Science Technology, Harvard-Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA
- Cardiovascular Innovation Research Center, Heart, Vascular, and Thoracic Institute, Cleveland Clinic, Cleveland, 9500 Euclid Avenue, Cleveland, OH 44195, USA
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4
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Giovannetti G, Flori A, Martini N, Francischello R, Aquaro GD, Pingitore A, Frijia F. Sodium Radiofrequency Coils for Magnetic Resonance: From Design to Applications. ELECTRONICS 2021; 10:1788. [DOI: 10.3390/electronics10151788] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/30/2023]
Abstract
Sodium (23Na) is the most abundant cation present in the human body and is involved in a large number of vital body functions. In the last few years, the interest in Sodium Magnetic Resonance Imaging (23Na MRI) has considerably increased for its relevance in physiological and physiopathological aspects. Indeed, sodium MRI offers the possibility to extend the anatomical imaging information by providing additional and complementary information on physiology and cellular metabolism with the heteronuclear Magnetic Resonance Spectroscopy (MRS). Constraints are the rapidly decaying of sodium signal, the sensitivity lack due to the low sodium concentration versus 1H-MRI induce scan times not clinically acceptable and it also constitutes a challenge for sodium MRI. With the available magnetic fields for clinical MRI scanners (1.5 T, 3 T, 7 T), and the hardware capabilities such as strong gradient strengths with high slew rates and new dedicated radiofrequency (RF) sodium coils, it is possible to reach reasonable measurement times (~10–15 min) with a resolution of a few millimeters, where it has already been applied in vivo in many human organs such as the brain, cartilage, kidneys, heart, as well as in muscle and the breast. In this work, we review the different geometries and setup of sodium coils described in the available literature for different in vivo applications in human organs with clinical MR scanners, by providing details of the design, modeling and construction of the coils.
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Zaric O, Juras V, Szomolanyi P, Schreiner M, Raudner M, Giraudo C, Trattnig S. Frontiers of Sodium MRI Revisited: From Cartilage to Brain Imaging. J Magn Reson Imaging 2020; 54:58-75. [PMID: 32851736 PMCID: PMC8246730 DOI: 10.1002/jmri.27326] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Revised: 05/20/2020] [Accepted: 05/20/2020] [Indexed: 12/19/2022] Open
Abstract
Sodium magnetic resonance imaging (23 Na-MRI) is a highly promising imaging modality that offers the possibility to noninvasively quantify sodium content in the tissue, one of the most relevant parameters for biochemical investigations. Despite its great potential, due to the intrinsically low signal-to-noise ratio (SNR) of sodium imaging generated by low in vivo sodium concentrations, low gyromagnetic ratio, and substantially shorter relaxation times than for proton (1 H) imaging, 23 Na-MRI is extremely challenging. In this article, we aim to provide a comprehensive overview of the literature that has been published in the last 10-15 years and which has demonstrated different technical designs for a range of 23 Na-MRI methods applicable for disease diagnoses and treatment efficacy evaluations. Currently, a wider use of 3.0T and 7.0T systems provide imaging with the expected increase in SNR and, consequently, an increased image resolution and a reduced scanning time. A great interest in translational research has enlarged the field of sodium MRI applications to almost all parts of the body: articular cartilage tendons, spine, heart, breast, muscle, kidney, and brain, etc., and several pathological conditions, such as tumors, neurological and degenerative diseases, and others. The quantitative parameter, tissue sodium concentration, which reflects changes in intracellular sodium concentration, extracellular sodium concentration, and intra-/extracellular volume fractions is becoming acknowledged as a reliable biomarker. Although the great potential of this technique is evident, there must be steady technical development for 23 Na-MRI to become a standard imaging tool. The future role of sodium imaging is not to be considered as an alternative to 1 H MRI, but to provide early, diagnostically valuable information about altered metabolism or tissue function associated with disease genesis and progression. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 1.
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Affiliation(s)
- Olgica Zaric
- Institute for Clinical Molecular MRI in the Musculoskeletal System, Karl Landsteiner Society, Vienna, Austria
| | - Vladimir Juras
- High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.,Department of Imaging Methods, Institute of Measurement Science, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Pavol Szomolanyi
- High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria
| | - Markus Schreiner
- Deartment of Orthopaedics and Trauma Surgery, Medical University of Vienna, Vienna, Austria
| | - Marcus Raudner
- High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria
| | - Chiara Giraudo
- Radiology Institute, Department of Medicine, DIMED Padova University Via Giustiniani 2, Padova, Italy
| | - Siegfried Trattnig
- Institute for Clinical Molecular MRI in the Musculoskeletal System, Karl Landsteiner Society, Vienna, Austria.,High-Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.,Christian Doppler Laboratory for Clinical Molecular MRI, Christian Doppler Forschungsgesellschaft, Vienna, Austria
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6
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Cardiorenal sodium MRI in small rodents using a quadrature birdcage volume resonator at 9.4 T. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2019; 33:121-130. [PMID: 31797228 DOI: 10.1007/s10334-019-00810-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Accepted: 11/22/2019] [Indexed: 12/30/2022]
Abstract
OBJECTIVE Design, implementation, evaluation and application of a quadrature birdcage radiofrequency (RF) resonator tailored for renal and cardiac sodium (23Na) magnetic resonance imaging (MRI) in rats at 9.4 T. MATERIALS AND METHODS A low pass birdcage resonator (16 rungs, din = 62 mm) was developed. The transmission field (B1+) was examined with EMF simulations. The scattering parameter (S-parameter) and the quality factor (Q-factor) were measured. For experimental validation B1+-field maps were acquired with the double-angle method. In vivo sodium imaging of the heart (spatial resolution: (1 × 1 × 5) mm3) and kidney (spatial resolution: (1 × 1 × 10) mm3) was performed with a FLASH technique. RESULTS The RF resonator exhibits RF characteristics, transmission field homogeneity and penetration that afford 23Na MR in vivo imaging of the kidney and heart at 9.4 T. For the renal cortex and medulla a SNRs of 8 and 13 were obtained and a SNRs of 14 and 15 were observed for the left and right ventricle. DISCUSSION These initial results obtained in vivo in rats using the quadrature birdcage volume RF resonator for 23Na MRI permit dedicated studies on experimental models of cardiac and renal diseases, which would contribute to translational research of the cardiorenal syndrome.
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Milani B, Delacoste J, Burnier M, Pruijm M. Exploring a new method for quantitative sodium MRI in the human upper leg with a surface coil and symmetrically arranged reference phantoms. Quant Imaging Med Surg 2019; 9:985-999. [PMID: 31367553 DOI: 10.21037/qims.2019.06.08] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Background The aim of this study is to validate and evaluate the reproducibility of a new setup for the quantification of the tissue sodium concentration (TSC) in the human upper leg muscles with sodium MRI at 3 Tesla. This setup is making use of an emit and receive single loop surface coil together with a set of square, symmetrically arranged reference phantoms. As a second aim, the performances of two MRI protocols for the TSC quantification in the upper leg muscles are compared: one using an ultra-short echo time (UTE) 3-dimensional radial sequence (UTE-protocol), and the other one using standard gradient echo sequence (GRE-protocol). Methods A validation test of the quantification of sodium concentration is performed in phantoms. The bias of the method is estimated and compared between both protocols. The reproducibility of TSC quantification is assessed in phantoms by the coefficient of variation (CV) and compared between both protocols. The reproducibility is also assessed in 11 health volunteers. Signal to noise ratio (SNR) maps are acquired in phantoms with both protocols in order to compare the resulting SNR. Results The apparatus and post processing were successfully implemented. The bias of the method was smaller than 10% in phantoms (excepted for Na concentration of 10 mmol/L when using the GRE protocol). The reproducibility of the method using symmetrically arranged phantoms was high in phantoms and humans (CV <5%). The GRE-protocol leads to a better SNR than the UTE-protocol in 2D images. Conclusions The use of symmetrically arranged reference phantoms lead to reproducible results in phantoms and humans. Sodium imaging in the human upper leg with a single loop surface coil should be performed with a standard 2-dimensional GRE protocol if an optimal SNR is needed. However, the quantification of the fast and slow decay time constants of the sodium signal, which plays a role in the TSC quantification, still has to be done with a UTE sequence. Moreover, the quantification of sodium concentration is more accurate with the UTE protocol for small sodium concentrations (<20 mmol).
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Affiliation(s)
- Bastien Milani
- Division of Nephrology and Hypertension, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland.,Departement de Radiologie, Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland.,Center for Biomedical Imaging (CIBM), Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland
| | - Jean Delacoste
- Departement de Radiologie, Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland.,Center for Biomedical Imaging (CIBM), Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland
| | - Michel Burnier
- Division of Nephrology and Hypertension, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland
| | - Menno Pruijm
- Division of Nephrology and Hypertension, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland
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Christa M, Weng AM, Geier B, Wörmann C, Scheffler A, Lehmann L, Oberberger J, Kraus BJ, Hahner S, Störk S, Klink T, Bauer WR, Hammer F, Köstler H. Increased myocardial sodium signal intensity in Conn's syndrome detected by 23Na magnetic resonance imaging. Eur Heart J Cardiovasc Imaging 2019; 20:263-270. [PMID: 30307545 PMCID: PMC6383057 DOI: 10.1093/ehjci/jey134] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2018] [Revised: 05/11/2018] [Accepted: 08/29/2018] [Indexed: 11/12/2022] Open
Abstract
AIMS Sodium intake has been linked to left ventricular hypertrophy independently of blood pressure, but the underlying mechanisms remain unclear. Primary hyperaldosteronism (PHA), a condition characterized by tissue sodium overload due to aldosterone excess, causes accelerated left ventricular hypertrophy compared to blood pressure matched patients with essential hypertension. We therefore hypothesized that the myocardium constitutes a novel site capable of sodium storage explaining the missing link between sodium and left ventricular hypertrophy. METHODS AND RESULTS Using 23Na magnetic resonance imaging, we investigated relative sodium signal intensities (rSSI) in the heart, calf muscle, and skin in 8 PHA patients (6 male, median age 55 years) and 12 normotensive healthy controls (HC) (8 male, median age 61 years). PHA patients had a higher mean systolic 24 h ambulatory blood pressure [152 (140; 163) vs. 125 (122; 130) mmHg, P < 0.001] and higher left ventricular mass index [71.0 (63.5; 106.8) vs. 55.0 (50.3; 66.8) g/m2, P = 0.037] than HC. Compared to HC, PHA patients exhibited significantly higher rSSI in the myocardium [0.31 (0.26; 0.34) vs. 0.24 (0.20; 0.27); P = 0.007], calf muscle [0.19 (0.16; 0.22) vs. 0.14 (0.13; 0.15); P = 0.001] and skin [0.28 (0.25; 0.33) vs. 0.19 (0.17; 0.26); P = 0.014], reflecting a difference of +27%, +38%, and +39%, respectively. Treatment of PHA resulted in significant reductions of the rSSI in the myocardium, calf muscle and skin by -13%, -27%, and -29%, respectively. CONCLUSION Myocardial tissue rSSI is increased in PHA patients and treatment of aldosterone excess effectively reduces rSSI, thus establishing the myocardium as a novel site of sodium storage in addition to skeletal muscle and skin.
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Affiliation(s)
- Martin Christa
- Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany.,Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
| | - Andreas M Weng
- Department of Diagnostic and Interventional Radiology, University of Würzburg, Würzburg, Germany
| | - Bettina Geier
- Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany
| | - Caroline Wörmann
- Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany
| | - Anne Scheffler
- Institute of Pharmacy and Food Chemistry, Chair of Food Chemistry, University of Würzburg, Würzburg, Germany
| | - Leane Lehmann
- Institute of Pharmacy and Food Chemistry, Chair of Food Chemistry, University of Würzburg, Würzburg, Germany
| | - Johannes Oberberger
- Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany.,Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
| | - Bettina J Kraus
- Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany.,Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
| | - Stefanie Hahner
- Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
| | - Stefan Störk
- Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany.,Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
| | - Thorsten Klink
- Department of Diagnostic and Interventional Radiology, University of Würzburg, Würzburg, Germany
| | - Wolfgang R Bauer
- Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany.,Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
| | - Fabian Hammer
- Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany.,Department of Internal Medicine, University Greifswald, Greifswald, Germany
| | - Herbert Köstler
- Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany.,Department of Diagnostic and Interventional Radiology, University of Würzburg, Würzburg, Germany
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Abstract
In this article, an overview of the current developments and research applications for non-proton magnetic resonance imaging (MRI) at ultrahigh magnetic fields (UHFs) is given. Due to technical and methodical advances, efficient MRI of physiologically relevant nuclei, such as Na, Cl, Cl, K, O, or P has become feasible and is of interest to obtain spatially and temporally resolved information that can be used for biomedical and diagnostic applications. Sodium (Na) MRI is the most widespread multinuclear imaging method with applications ranging over all regions of the human body. Na MRI yields the second largest in vivo NMR signal after the clinically used proton signal (H). However, other nuclei such as O and P (energy metabolism) or Cl and K (cell viability) are used in an increasing number of MRI studies at UHF. One major advancement has been the increased availability of whole-body MR scanners with UHFs (B0 ≥7T) expanding the range of detectable nuclei. Nevertheless, efforts in terms of pulse sequence and post-processing developments as well as hardware designs must be made to obtain valuable information in clinically feasible measurement times. This review summarizes the available methods in the field of non-proton UHF MRI, especially for Na MRI, as well as introduces potential applications in clinical research.
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Affiliation(s)
- Sebastian C Niesporek
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Armin M Nagel
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
- Institute of Medical Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Tanja Platt
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
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10
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Hu R, Kleimaier D, Malzacher M, Hoesl MA, Paschke NK, Schad LR. X‐nuclei imaging: Current state, technical challenges, and future directions. J Magn Reson Imaging 2019; 51:355-376. [DOI: 10.1002/jmri.26780] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2019] [Revised: 04/23/2019] [Accepted: 04/24/2019] [Indexed: 12/16/2022] Open
Affiliation(s)
- Ruomin Hu
- Computer Assisted Clinical MedicineHeidelberg University Mannheim Germany
| | - Dennis Kleimaier
- Computer Assisted Clinical MedicineHeidelberg University Mannheim Germany
| | - Matthias Malzacher
- Computer Assisted Clinical MedicineHeidelberg University Mannheim Germany
| | | | - Nadia K. Paschke
- Computer Assisted Clinical MedicineHeidelberg University Mannheim Germany
| | - Lothar R. Schad
- Computer Assisted Clinical MedicineHeidelberg University Mannheim Germany
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11
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Lott J, Platt T, Niesporek SC, Paech D, G. R. Behl N, Niendorf T, Bachert P, Ladd ME, Nagel AM. Corrections of myocardial tissue sodium concentration measurements in human cardiac
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Na MRI at 7 Tesla. Magn Reson Med 2019; 82:159-173. [DOI: 10.1002/mrm.27703] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Revised: 01/25/2019] [Accepted: 01/31/2019] [Indexed: 12/24/2022]
Affiliation(s)
- Johanna Lott
- German Cancer Research Center (DKFZ), Medical Physics in Radiology Heidelberg Germany
- University of Heidelberg, Faculty of Physics and Astronomy Heidelberg Germany
| | - Tanja Platt
- German Cancer Research Center (DKFZ), Medical Physics in Radiology Heidelberg Germany
| | | | - Daniel Paech
- German Cancer Research Center (DKFZ) Radiology, Heidelberg Germany
| | - Nicolas G. R. Behl
- German Cancer Research Center (DKFZ), Medical Physics in Radiology Heidelberg Germany
| | - Thoralf Niendorf
- Max Delbrueck Center for Molecular Medicine in the Helmholtz Association Berlin Germany
- MRI. TOOLS GmbH Berlin Germany
| | - Peter Bachert
- German Cancer Research Center (DKFZ), Medical Physics in Radiology Heidelberg Germany
- University of Heidelberg, Faculty of Physics and Astronomy Heidelberg Germany
| | - Mark E. Ladd
- German Cancer Research Center (DKFZ), Medical Physics in Radiology Heidelberg Germany
- University of Heidelberg, Faculty of Physics and Astronomy Heidelberg Germany
- University of Heidelberg Faculty of Medicine Heidelberg Germany
| | - Armin M. Nagel
- German Cancer Research Center (DKFZ), Medical Physics in Radiology Heidelberg Germany
- Friedrich‐Alexander‐Universität Erlangen‐Nürnberg (FAU), University Hospital Erlangen Institute of Radiology Erlangen Germany
- Friedrich‐Alexander‐Universität Erlangen‐Nürnberg (FAU) Institute of Medical Physics Erlangen Germany
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12
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Syeda W, Blunck Y, Kolbe S, Cleary JO, Johnston LA. A continuum of T 2 * components: Flexible fast fraction mapping in sodium MRI. Magn Reson Med 2019; 81:3854-3864. [PMID: 30652360 DOI: 10.1002/mrm.27659] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Revised: 11/28/2018] [Accepted: 12/20/2018] [Indexed: 12/31/2022]
Abstract
PURPOSE Parameter mapping in sodium MRI data is challenging due to inherently low SNR and spatial resolution, prompting the need to employ robust models and estimation techniques. This work aims to develop a continuum model of sodium T 2 * -decay to overcome the limitations of the commonly employed bi-exponential models. Estimates of mean T 2 * -decay and fast component fraction in tissue are emergent from the inferred continuum model. METHODS A closed-form continuum model was derived assuming a gamma distribution of T 2 * components. Sodium MRI was performed on four healthy human subjects and a phantom consisting of closely packed vials filled with an aqueous solution of varying sodium and agarose concentrations. The continuum model was applied to the phantom and in vivo human multi-echo 7T data. Parameter maps by voxelwise model-fitting were obtained. RESULTS The continuum model demonstrated comparable estimation performance to the bi-exponential model. The parameter maps provided improved contrast between tissue structures. The fast component fraction, an indicator of the heterogeneity of localised sodium motion regimes in tissue, was zero in CSF and high in WM structures. CONCLUSIONS The continuum distribution model provides high quality, high contrast parameter maps, and informative voxelwise estimates of the relative weighting between fast and slow decay components.
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Affiliation(s)
- Warda Syeda
- Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, Australia
| | - Yasmin Blunck
- Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, Australia.,Department of Biomedical Engineering, The University of Melbourne, Melbourne, Australia
| | - Scott Kolbe
- Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, Australia
| | - Jon O Cleary
- Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, Australia
| | - Leigh A Johnston
- Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, Australia.,Department of Biomedical Engineering, The University of Melbourne, Melbourne, Australia
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23-Sodium magnetic resonance imaging of the human heart revisited: new insights in patients with Conn’s syndrome. Eur Heart J Cardiovasc Imaging 2018; 20:255-256. [DOI: 10.1093/ehjci/jey151] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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14
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Platt T, Umathum R, Fiedler TM, Nagel AM, Bitz AK, Maier F, Bachert P, Ladd ME, Wielpütz MO, Kauczor HU, Behl NG. In vivo self-gated 23
Na MRI at 7 T using an oval-shaped body resonator. Magn Reson Med 2018; 80:1005-1019. [DOI: 10.1002/mrm.27103] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 12/08/2017] [Accepted: 01/02/2018] [Indexed: 12/24/2022]
Affiliation(s)
- Tanja Platt
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280; 69120 Heidelberg Germany
| | - Reiner Umathum
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280; 69120 Heidelberg Germany
| | - Thomas M. Fiedler
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280; 69120 Heidelberg Germany
| | - Armin M. Nagel
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280; 69120 Heidelberg Germany
- Institute of Radiology; University Hospital Erlangen, Maximiliansplatz 3; 91054 Erlangen Germany
| | - Andreas K. Bitz
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280; 69120 Heidelberg Germany
- Faculty of Electrical Engineering and Information Technology; University of Applied Sciences Aachen, Eupener Str. 70; 52066 Aachen Germany
| | - Florian Maier
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280; 69120 Heidelberg Germany
| | - Peter Bachert
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280; 69120 Heidelberg Germany
- Faculty of Physics and Astronomy; University of Heidelberg, Im Neuenheimer Feld 226; 69120 Heidelberg Germany
| | - Mark E. Ladd
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280; 69120 Heidelberg Germany
- Faculty of Physics and Astronomy; University of Heidelberg, Im Neuenheimer Feld 226; 69120 Heidelberg Germany
- Faculty of Medicine; University of Heidelberg, Im Neuenheimer Feld 672; 69120 Heidelberg Germany
| | - Mark O. Wielpütz
- Translational Lung Research Center (TLRC); University of Heidelberg, German Center for Lung Research (DZL), Im Neuenheimer Feld 430; 69120 Heidelberg Germany
- Department of Diagnostic and Interventional Radiology; University Hospital of Heidelberg, Im Neuenheimer Feld 110; 69120 Heidelberg Germany
- Department of Diagnostic and Interventional Radiology with Nuclear Medicine; Thoraxklinik at University of Heidelberg, Röntgenstr. 1; 69126 Heidelberg Germany
| | - Hans-Ulrich Kauczor
- Translational Lung Research Center (TLRC); University of Heidelberg, German Center for Lung Research (DZL), Im Neuenheimer Feld 430; 69120 Heidelberg Germany
- Department of Diagnostic and Interventional Radiology; University Hospital of Heidelberg, Im Neuenheimer Feld 110; 69120 Heidelberg Germany
- Department of Diagnostic and Interventional Radiology with Nuclear Medicine; Thoraxklinik at University of Heidelberg, Röntgenstr. 1; 69126 Heidelberg Germany
| | - Nicolas G.R. Behl
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280; 69120 Heidelberg Germany
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Lommen JM, Flassbeck S, Behl NG, Niesporek S, Bachert P, Ladd ME, Nagel AM. Probing the microscopic environment of 23
Na ions in brain tissue by MRI: On the accuracy of different sampling schemes for the determination of rapid, biexponential T2* decay at low signal-to-noise ratio. Magn Reson Med 2018; 80:571-584. [DOI: 10.1002/mrm.27059] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Revised: 11/21/2017] [Accepted: 12/05/2017] [Indexed: 01/28/2023]
Affiliation(s)
- Jonathan M. Lommen
- Medical Physics in Radiology, German Cancer Research Center (DKFZ); Heidelberg Germany
| | - Sebastian Flassbeck
- Medical Physics in Radiology, German Cancer Research Center (DKFZ); Heidelberg Germany
| | - Nicolas G.R. Behl
- Medical Physics in Radiology, German Cancer Research Center (DKFZ); Heidelberg Germany
| | - Sebastian Niesporek
- Medical Physics in Radiology, German Cancer Research Center (DKFZ); Heidelberg Germany
| | - Peter Bachert
- Medical Physics in Radiology, German Cancer Research Center (DKFZ); Heidelberg Germany
- University of Heidelberg, Faculty of Physics and Astronomy; Heidelberg Germany
| | - Mark E. Ladd
- Medical Physics in Radiology, German Cancer Research Center (DKFZ); Heidelberg Germany
- University of Heidelberg, Faculty of Physics and Astronomy; Heidelberg Germany
- University of Heidelberg, Faculty of Medicine; Heidelberg Germany
| | - Armin M. Nagel
- Medical Physics in Radiology, German Cancer Research Center (DKFZ); Heidelberg Germany
- Institute of Radiology; University Hospital Erlangen; Erlangen Germany
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Wang P, Deger MS, Kang H, Ikizler TA, Titze J, Gore JC. Sex differences in sodium deposition in human muscle and skin. Magn Reson Imaging 2017; 36:93-97. [PMID: 27989912 PMCID: PMC5222810 DOI: 10.1016/j.mri.2016.10.023] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Revised: 10/08/2016] [Accepted: 10/26/2016] [Indexed: 12/14/2022]
Abstract
The aim of this work was to investigate possible sex differences in the patterns of sodium deposition between muscle and skin using sodium MRI. A total of 38 subjects were examined for comparisons: 20 males, aged 25-79years with a median age of 51; 18 females, aged 38-66years, median age 53. All subjects underwent sodium MRI scans of the calf muscles together with cross sections through four calibration standards containing known sodium contents (10mM, 20mM, 30mM, and 40mM). Tissue sodium concentrations (TSC) in muscle and skin were then calculated by comparing signal intensities between tissues and reference standards using a linear analysis. A Wilcoxon rank sum test was applied to the ΔTSC (=TSCmuscle-TSCskin) series of males and females to examine if they were significantly different. Finally, a multiple linear regression was utilized to account for the effects from two potential confounders, age and body mass index (BMI). We found that sodium content appears to be higher in skin than in muscle for men, however women tend to have higher muscle sodium than skin sodium. This sex-relevant sodium deposition is statistically significant (P=3.10×10-5) by the Wilcoxon rank sum test, and this difference in distribution seems to be more reliable with increasing age. In the multiple linear regression, gender still has a statistically significant effect (P<1.0×10-4) on the difference between sodium deposition in muscle and skin, while taking the effects of age and BMI into account.
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Affiliation(s)
- Ping Wang
- Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA.
| | - Muge Serpil Deger
- Division of Nephrology and Hypertension, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Hakmook Kang
- Department of Biostatistics, Vanderbilt University Medical Center, Nashville, TN, USA
| | - T Alp Ikizler
- Division of Nephrology and Hypertension, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Jens Titze
- Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA
| | - John C Gore
- Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
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Zöllner FG, Konstandin S, Lommen J, Budjan J, Schoenberg SO, Schad LR, Haneder S. Quantitative sodium MRI of kidney. NMR IN BIOMEDICINE 2016; 29:197-205. [PMID: 25728879 DOI: 10.1002/nbm.3274] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Revised: 01/13/2015] [Accepted: 01/25/2015] [Indexed: 05/25/2023]
Abstract
One of the main tasks of the human kidneys is to maintain the homeostasis of the body's fluid and electrolyte balance by filtration of the plasma and excretion of the end products. Herein, the regulation of extracellular sodium in the kidney is of particular importance. Sodium MRI ((23)Na MRI) allows for the absolute quantification of the tissue sodium concentration (TSC) and thereby provides a direct link between TSC and tissue viability. Renal (23)Na MRI can provide new insights into physiological tissue function and viability thought to differ from the information obtained by standard (1)H MRI. Sodium imaging has the potential to become an independent surrogate biomarker not only for renal imaging, but also for oncology indications. However, this technique is now on the threshold of clinical implementation. Numerous, initial pre-clinical and clinical studies have already outlined the potential of this technique; however, future studies need to be extended to larger patient groups to show the diagnostic outcome. In conclusion, (23)Na MRI is seen as a powerful technique with the option to establish a non-invasive renal biomarker for tissue viability, but is still a long way from real clinical implementation.
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Affiliation(s)
- Frank G Zöllner
- Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Simon Konstandin
- Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
- MR-Imaging and Spectroscopy, Faculty 01 (Physics/Electrical Engineering), University of Bremen, Bremen, Germany
| | - Jonathan Lommen
- Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Johannes Budjan
- Institute of Clinical Radiology and Nuclear Medicine, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Stefan O Schoenberg
- Institute of Clinical Radiology and Nuclear Medicine, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Lothar R Schad
- Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Stefan Haneder
- Institute of Clinical Radiology and Nuclear Medicine, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
- Department of Radiology, University Hospital of Cologne, Cologne, Germany
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Bottomley PA. Sodium MRI in human heart: a review. NMR IN BIOMEDICINE 2016; 29:187-96. [PMID: 25683054 PMCID: PMC4868405 DOI: 10.1002/nbm.3265] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Revised: 12/30/2014] [Accepted: 01/05/2015] [Indexed: 05/13/2023]
Abstract
This paper offers a critical review of the properties, methods and potential clinical application of sodium ((23)Na) MRI in human heart. Because the tissue sodium concentration (TSC) in heart is about ~40 µmol/g wet weight, and the (23)Na gyromagnetic ratio and sensitivity are respectively about one-quarter and one-11th of that of hydrogen ((1)H), the signal-to-noise ratio of (23)Na MRI in the heart is about one-6000th of that of conventional cardiac (1)H MRI. In addition, as a quadrupolar nucleus, (23)Na exhibits ultra-short and multi-component relaxation behavior (T1 ~ 30 ms; T2 ~ 0.5-4 ms and 12-20 ms), which requires fast, specialized, ultra-short echo-time MRI sequences, especially for quantifying TSC. Cardiac (23)Na MRI studies from 1.5 to 7 T measure a volume-weighted sum of intra- and extra-cellular components present at cytosolic concentrations of 10-15 mM and 135-150 mM in healthy tissue, respectively, at a spatial resolution of about 0.1-1 ml in 10 min or so. Currently, intra- and extra-cellular sodium cannot be unambiguously resolved without the use of potentially toxic shift reagents. Nevertheless, increases in TSC attributable to an influx of intra-cellular sodium and/or increased extra-cellular volume have been demonstrated in human myocardial infarction consistent with prior animal studies, and arguably might also be seen in future studies of ischemia and cardiomyopathies--especially those involving defects in sodium transport. While technical implementation remains a hurdle, a central question for clinical use is whether cardiac (23)Na MRI can deliver useful information unobtainable by other more convenient methods, including (1)H MRI.
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Affiliation(s)
- Paul A Bottomley
- Division of MR Research, Department of Radiology, Park Bldg 310, Johns Hopkins University, 601 600 N, Caroline Wolfe Street, Baltimore MD, USA 21287-0843, PH: (USA) 410 955 0366, FAX: (USA) 410 614 1977,
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Retrospectively-gated CINE 23Na imaging of the heart at 7.0 Tesla using density-adapted 3D projection reconstruction. Magn Reson Imaging 2015; 33:1091-1097. [DOI: 10.1016/j.mri.2015.06.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2015] [Revised: 05/28/2015] [Accepted: 06/20/2015] [Indexed: 11/21/2022]
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Graessl A, Ruehle A, Waiczies H, Resetar A, Hoffmann SH, Rieger J, Wetterling F, Winter L, Nagel AM, Niendorf T. Sodium MRI of the human heart at 7.0 T: preliminary results. NMR IN BIOMEDICINE 2015; 28:967-975. [PMID: 26082025 DOI: 10.1002/nbm.3338] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2015] [Revised: 05/10/2015] [Accepted: 05/12/2015] [Indexed: 06/04/2023]
Abstract
The objective of this work was to examine the feasibility of three-dimensional (3D) and whole heart coverage (23)Na cardiac MRI at 7.0 T including single-cardiac-phase and cinematic (cine) regimes. A four-channel transceiver RF coil array tailored for (23)Na MRI of the heart at 7.0 T (f = 78.5 MHz) is proposed. An integrated bow-tie antenna building block is used for (1)H MR to support shimming, localization and planning in a clinical workflow. Signal absorption rate simulations and assessment of RF power deposition were performed to meet the RF safety requirements. (23) Na cardiac MR was conducted in an in vivo feasibility study. 3D gradient echo (GRE) imaging in conjunction with Cartesian phase encoding (total acquisition time T(AQ) = 6 min 16 s) and whole heart coverage imaging employing a density-adapted 3D radial acquisition technique (T(AQ) = 18 min 20 s) were used. For 3D GRE-based (23)Na MRI, acquisition of standard views of the heart using a nominal in-plane resolution of (5.0 × 5.0) mm(2) and a slice thickness of 15 mm were feasible. For whole heart coverage 3D density-adapted radial (23)Na acquisitions a nominal isotropic spatial resolution of 6 mm was accomplished. This improvement versus 3D conventional GRE acquisitions reduced partial volume effects along the slice direction and enabled retrospective image reconstruction of standard or arbitrary views of the heart. Sodium cine imaging capabilities were achieved with the proposed RF coil configuration in conjunction with 3D radial acquisitions and cardiac gating. Cardiac-gated reconstruction provided an enhancement in blood-myocardium contrast of 20% versus the same data reconstructed without cardiac gating. The proposed transceiver array enables (23)Na MR of the human heart at 7.0 T within clinical acceptable scan times. This capability is in positive alignment with the needs of explorations that are designed to examine the potential of (23)Na MRI for the assessment of cardiovascular and metabolic diseases.
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Affiliation(s)
- Andreas Graessl
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Anjuli Ruehle
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | | | - Ana Resetar
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Stefan H Hoffmann
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | | | | | - Lukas Winter
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Armin M Nagel
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
- Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max-Delbrück Center for Molecular Medicine, Berlin, Germany
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Maguire ML, Geethanath S, Lygate CA, Kodibagkar VD, Schneider JE. Compressed sensing to accelerate magnetic resonance spectroscopic imaging: evaluation and application to 23Na-imaging of mouse hearts. J Cardiovasc Magn Reson 2015; 17:45. [PMID: 26073300 PMCID: PMC4466859 DOI: 10.1186/s12968-015-0149-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Accepted: 05/15/2015] [Indexed: 11/23/2022] Open
Abstract
BACKGROUND Magnetic Resonance Spectroscopic Imaging (MRSI) has wide applicability for non-invasive biochemical assessment in clinical and pre-clinical applications but suffers from long scan times. Compressed sensing (CS) has been successfully applied to clinical 1H MRSI, however a detailed evaluation of CS for conventional chemical shift imaging is lacking. Here we evaluate the performance of CS accelerated MRSI, and specifically apply it to accelerate 23Na-MRSI on mouse hearts in vivo at 9.4 T. METHODS Synthetic phantom data representing a simplified section across a mouse thorax were used to evaluate the fidelity of the CS reconstruction for varying levels of under-sampling, resolution and signal-to-noise ratios (SNR). The amplitude of signals arising from within a compartment, and signal contamination arising from outside the compartment relative to noise-free Fourier-transformed (FT) data were determined. Simulation results were subsequently verified experimentally in phantoms and in three mouse hearts in vivo. RESULTS CS reconstructed MRSI data are scaled linearly relative to absolute signal intensities from the fully-sampled FT reconstructed case (R(2) > 0.8, p-value < 0.001). Higher acceleration factors resulted in a denoising of the reconstructed spectra, but also in an increased blurring of compartment boundaries, particularly at lower spatial resolutions. Increasing resolution and SNR decreased cross-compartment contamination and yielded signal amplitudes closer to the FT data. Proof-of-concept high-resolution, 3-fold accelerated 23Na-amplitude maps of murine myocardium could be obtained within ~23 mins. CONCLUSIONS Relative signal amplitudes (i.e. metabolite ratios) and absolute quantification of metabolite concentrations can be accurately determined with up to 5-fold under-sampled, CS-reconstructed MRSI. Although this work focused on murine cardiac 23Na-MRSI, the results are equally applicable to other nuclei and tissues (e.g., 1H MRSI in brain). Significant reduction in MRSI scan time will reduce the burden on the subject, increase scanner throughput, and may open new avenues for (pre-) clinical metabolic studies.
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Affiliation(s)
- Mahon L Maguire
- British Heart Foundation Experimental Magnetic Resonance Unit, Radcliffe Department of Medicine - Division of Cardiovascular Medicine, University of Oxford, Roosevelt Drive, Oxford, OX3 7BN, UK
| | - Sairam Geethanath
- Medical Imaging Research Centre, Dayananda Sagar College of Engineering, Bangalore, 560078, India
| | - Craig A Lygate
- British Heart Foundation Experimental Magnetic Resonance Unit, Radcliffe Department of Medicine - Division of Cardiovascular Medicine, University of Oxford, Roosevelt Drive, Oxford, OX3 7BN, UK
| | - Vikram D Kodibagkar
- School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ, 85287-9709, USA
| | - Jürgen E Schneider
- British Heart Foundation Experimental Magnetic Resonance Unit, Radcliffe Department of Medicine - Division of Cardiovascular Medicine, University of Oxford, Roosevelt Drive, Oxford, OX3 7BN, UK.
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Meßner NM, Zöllner FG, Kalayciyan R, Schad LR. Pre-clinical functional Magnetic Resonance Imaging Part II: The heart. Z Med Phys 2014; 24:307-22. [PMID: 25023418 DOI: 10.1016/j.zemedi.2014.06.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 05/09/2014] [Accepted: 06/17/2014] [Indexed: 12/21/2022]
Abstract
One third of all deaths worldwide in 2008 were caused by cardiovascular diseases (CVD), and the incidence of CVD related deaths rises ever more. Thus, improved imaging techniques and modalities are needed for the evaluation of cardiac morphology and function. Cardiac magnetic resonance imaging (CMRI) is a minimally invasive technique that is increasingly important due to its high spatial and temporal resolution, its high soft tissue contrast and its ability of functional and quantitative imaging. It is widely accepted as the gold standard of cardiac functional analysis. In the short period of small animal MRI, remarkable progress has been achieved concerning new, fast imaging schemes as well as purpose-built equipment. Dedicated small animal scanners allow for tapping the full potential of recently developed animal models of cardiac disease. In this paper, we review state-of-the-art cardiac magnetic resonance imaging techniques and applications in small animals at ultra-high fields (UHF).
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Affiliation(s)
- Nadja M Meßner
- Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Frank G Zöllner
- Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
| | - Raffi Kalayciyan
- Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Lothar R Schad
- Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
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Madelin G, Lee JS, Regatte RR, Jerschow A. Sodium MRI: methods and applications. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2014; 79:14-47. [PMID: 24815363 PMCID: PMC4126172 DOI: 10.1016/j.pnmrs.2014.02.001] [Citation(s) in RCA: 148] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Accepted: 02/12/2014] [Indexed: 05/11/2023]
Abstract
Sodium NMR spectroscopy and MRI have become popular in recent years through the increased availability of high-field MRI scanners, advanced scanner hardware and improved methodology. Sodium MRI is being evaluated for stroke and tumor detection, for breast cancer studies, and for the assessment of osteoarthritis and muscle and kidney functions, to name just a few. In this article, we aim to present an up-to-date review of the theoretical background, the methodology, the challenges, limitations, and current and potential new applications of sodium MRI.
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Affiliation(s)
- Guillaume Madelin
- New York University Langone Medical Center, Department of Radiology, Center for Biomedical Imaging, New York, NY 10016, USA
| | - Jae-Seung Lee
- New York University Langone Medical Center, Department of Radiology, Center for Biomedical Imaging, New York, NY 10016, USA; Chemistry Department, New York University, 100 Washington Square East, New York, NY 10003, USA
| | - Ravinder R Regatte
- New York University Langone Medical Center, Department of Radiology, Center for Biomedical Imaging, New York, NY 10016, USA
| | - Alexej Jerschow
- Chemistry Department, New York University, 100 Washington Square East, New York, NY 10003, USA.
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Gai ND, Rochitte C, Nacif MS, Bluemke DA. Optimized three-dimensional sodium imaging of the human heart on a clinical 3T scanner. Magn Reson Med 2014; 73:623-32. [PMID: 24639022 DOI: 10.1002/mrm.25175] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Revised: 01/14/2014] [Accepted: 01/20/2014] [Indexed: 12/24/2022]
Abstract
PURPOSE Optimization of sequence and sequence parameters to allow three-dimensional (3D) sodium imaging of the entire human heart in vivo in a clinically reasonable time. THEORY AND METHODS A stack of spirals pulse sequence was optimized for cardiac imaging by considering factors such as spoiling, nutation angles, repetition time, echo time, T1/T2 relaxation, off-resonance, data acquisition window, motion, and segmented k-space acquisition. Simulations based on Bloch equations as well as the exact trajectory used for data acquisition provided the basis for choice of parameter combinations for sodium imaging. Sodium phantom scanning was used to validate the choice of parameters and for corroboration with simulations. In vivo cardiac imaging in six volunteers was also performed with an optimized sequence. RESULTS Phantom studies showed good correlation with simulation results. Images obtained from human volunteers showed that the heart can be imaged with a nominal resolution of 5 × 5 × 10 mm(3) and with a signal-to-noise ratio >15 (in the septum) in about 6-10 minutes. Long axis views of the reformatted human heart show true 3D imaging capability. CONCLUSION Optimization of the sequence and its parameters allowed in vivo 3D sodium imaging of the entire human heart in a clinically reasonable time.
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Affiliation(s)
- Neville D Gai
- Radiology & Imaging Sciences, National Institutes of Health, Bethesda, MD, USA
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25
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Erturk MA, El-Sharkawy AMM, Moore J, Bottomley PA. 7 Tesla MRI with a transmit/receive loopless antenna and B1-insensitive selective excitation. Magn Reson Med 2013; 72:220-6. [PMID: 23963978 DOI: 10.1002/mrm.24910] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Revised: 06/25/2013] [Accepted: 07/15/2013] [Indexed: 11/10/2022]
Abstract
PURPOSE Use of external coils with internal detectors or conductors is challenging at 7 Tesla (T) due to radiofrequency (RF) field (B1 ) penetration, B1 -inhomogeneity, mutual coupling, and potential local RF heating. The present study tests whether the near-quadratic gains in signal-to-noise ratio and field-of-view with field-strength previously reported for internal loopless antennae at 7T can suffice to perform MRI with an interventional transmit/receive antenna without using any external coils. METHODS External coils were replaced by semi-rigid or biocompatible transmit/receive loopless antennae requiring only a few Watts of peak RF power. Slice selection was provided by spatially selective B1 -insensitive composite RF pulses that compensate for the antenna's intrinsically nonuniform B1 -field. Power was adjusted to maintain local temperature rise ≤1°C. Fruit, intravascular MRI of diseased human vessels in vitro, and MRI of rabbit aorta in vivo are demonstrated. RESULTS Scout MRI with the transmit/receive antennae yielded a ≤10 cm cylindrical field-of-view, enabling subsequent targeted localization at ∼100 μm resolution in 10-50 s and/or 50 μm MRI in ∼2 min in vitro, and 100-300 μm MRI of the rabbit aorta in vivo. CONCLUSION A simple, low-power, one-device approach to interventional MRI at 7T offers the potential of truly high-resolution MRI, while avoiding issues with external coil excitation and interactions at 7T.
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Affiliation(s)
- M Arcan Erturk
- Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland, USA; Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University, Baltimore, Maryland, USA
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Madelin G, Regatte RR. Biomedical applications of sodium MRI in vivo. J Magn Reson Imaging 2013; 38:511-29. [PMID: 23722972 DOI: 10.1002/jmri.24168] [Citation(s) in RCA: 166] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Accepted: 03/12/2013] [Indexed: 12/13/2022] Open
Abstract
In this article we present an up-to-date overview of the potential biomedical applications of sodium magnetic resonance imaging (MRI) in vivo. Sodium MRI is a subject of increasing interest in translational imaging research as it can give some direct and quantitative biochemical information on the tissue viability, cell integrity and function, and therefore not only help the diagnosis but also the prognosis of diseases and treatment outcomes. It has already been applied in vivo in most human tissues, such as brain for stroke or tumor detection and therapeutic response, in breast cancer, in articular cartilage, in muscle, and in kidney, and it was shown in some studies that it could provide very useful new information not available through standard proton MRI. However, this technique is still very challenging due to the low detectable sodium signal in biological tissue with MRI and hardware/software limitations of the clinical scanners. The article is divided in three parts: 1) the role of sodium in biological tissues, 2) a short review on sodium magnetic resonance, and 3) a review of some studies on sodium MRI on different organs/diseases to date.
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Affiliation(s)
- Guillaume Madelin
- New York University Langone Medical Center, Department of Radiology, Center for Biomedical Imaging, New York, NY 10016, USA.
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Inglese M, Oesingmann N, Zaaraoui W, Ranjeva JP, Fleysher L. Sodium imaging as a marker of tissue injury in patients with multiple sclerosis. Mult Scler Relat Disord 2013; 2:263-9. [PMID: 25877838 DOI: 10.1016/j.msard.2013.03.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Revised: 03/15/2013] [Accepted: 03/20/2013] [Indexed: 12/30/2022]
Abstract
Recent studies have suggested that intra-axonal sodium accumulation contribute to axonal degeneration in patients with MS. Advances in MRI hardware and software allow acquisition of brain sodium signal in vivo. This review begins with a summary of the experimental evidence for impairment of sodium homeostasis in MS. Then, MRI methods for sodium acquisition are reviewed and the application of the techniques in patients with MS is discussed. Sodium imaging and ultra-high field MRI have the potential to provide tissue-specific markers of neurodegeneration in MS.
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Affiliation(s)
- M Inglese
- Department of Neurology, Mount Sinai School of Medicine, NY, USA; Department of Radiology, Mount Sinai School of Medicine, NY, USA; Department of Neuroscience, Mount Sinai School of Medicine, NY, USA.
| | - N Oesingmann
- Siemens Medical Solutions USA, Inc., New York University, NY, USA
| | - W Zaaraoui
- CRMBM-CEMEREM, UMR 7339, CNRS, Aix-Marseille université, France; Siemens Medical Solutions USA, Inc., New York University, NY, USA
| | - J P Ranjeva
- CRMBM-CEMEREM, UMR 7339, CNRS, Aix-Marseille université, France; Siemens Medical Solutions USA, Inc., New York University, NY, USA
| | - L Fleysher
- Department of Radiology, Mount Sinai School of Medicine, NY, USA
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Konstandin S, Schad LR. Two-dimensional radial sodium heart MRI using variable-rate selective excitation and retrospective electrocardiogram gating with golden angle increments. Magn Reson Med 2012; 70:791-9. [PMID: 23081799 DOI: 10.1002/mrm.24523] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Revised: 09/04/2012] [Accepted: 09/18/2012] [Indexed: 12/31/2022]
Abstract
PURPOSE Two-dimensional projection reconstruction methods provide advantages over three-dimensional techniques because of higher flexibility regarding the resolution and shorter scan time needed. To optimize a two-dimensional radial sequence with respect to signal-to-noise ratio, variable-rate selective excitation and retrospective electrocardiogram gating is investigated. METHODS The minimal radiofrequency pulse duration is simulated in dependence of the flip angle and coil parameters using sinc waveforms with two different variable-rate selective excitation approaches and a Fermi pulse. Retrospectively electrocardiogram-gated imaging with Golden Angle incremented projections was implemented to allow for continuous data acquisition enabling the possibility of dynamic electrocardiogram-gated heart imaging. RESULTS Especially for abdominal coils with high transmitter voltages required, variable-rate selective excitation strongly reduces the radiofrequency pulse duration and echo time resulting in a signal-to-noise ratio gain up to 15.5% (if the fast relaxation component of sodium is in the order of the radiofrequency pulse duration) compared with standard sinc-shaped radiofrequency pulses. Retrospective electrocardiogram gating shows higher flexibility with regard to the trigger delay enabling the trade-off between heart motion artifacts and signal-to-noise ratio. CONCLUSION A two-dimensional radial sequence is optimized for sodium heart imaging regarding signal-to-noise ratio. Different sodium contrasts of the human heart are shown, which can give additional information on heart diseases.
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Affiliation(s)
- Simon Konstandin
- Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Germany
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Decker CM, Zöllner FG, Konstandin S, Schad LR. Comparing anisotropic diffusion filters for the enhancement of sodium magnetic resonance images. Magn Reson Imaging 2012; 30:1192-200. [PMID: 22819174 DOI: 10.1016/j.mri.2012.04.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Revised: 03/07/2012] [Accepted: 04/02/2012] [Indexed: 11/19/2022]
Abstract
The anisotropic diffusion (AND) filter, an image processing technique derived from physics, was applied to low-resolution sodium magnetic resonance imaging (MRI) to examine the possibilities of image enhancement by postprocessing. We compared six different variants of AND filters. Besides the qualitative good results on phantom measurements, quantitative analyses on MRI of human kidney yielded major improvements in noise reduction and other quality measures: the noise (i.e., the standard deviation in the image background) could be reduced to 1%-2% of its original value, while linear filters (Gaussian, Fermi, Hamming) achieved a reduction to 42%-64%. Besides that, less than 5% of structures and intensities are lost when using AND filters. Comparing the different variants, the two-dimensional and the three-dimensional AND filter outperformed the histogram-of-gradient and tensor-based AND filter. We envision that by using these AND filters, quantitative analysis of sodium MRI of kidney could be improved.
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Affiliation(s)
- Christoph M Decker
- Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
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Qian Y, Zhao T, Zheng H, Weimer J, Boada FE. High-resolution sodium imaging of human brain at 7 T. Magn Reson Med 2011; 68:227-33. [PMID: 22144258 DOI: 10.1002/mrm.23225] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2011] [Revised: 08/29/2011] [Accepted: 08/30/2011] [Indexed: 01/17/2023]
Abstract
The feasibility of high-resolution sodium magnetic resonance imaging on human brain at 7 T was demonstrated in this study. A three-dimensional anisotropic resolution data acquisition was used to address the challenge of low signal-to-noise ratio associated with high resolution. Ultrashort echo-time sequence was used for the anisotropic data acquisition. Phantoms and healthy human brains were studied on a whole-body 7-T magnetic resonance imaging scanner. Sodium images were obtained at two high nominal in-plane resolutions (1.72 and 0.86 mm) at a slice thickness of 4 mm. Signal-to-noise ratio in the brain image (cerebrospinal fluid) was measured as 14.4 and 6.8 at the two high resolutions, respectively. The actual in-plane resolution was measured as 2.9 and 1.6 mm, 69-86% larger than their nominal values. The quantification of sodium concentration on the phantom and brain images enabled better accuracy at the high nominal resolutions than at the low nominal resolution of 3.44 mm (measured resolution 5.5 mm) due to the improvement of in-plane resolution.
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Affiliation(s)
- Yongxian Qian
- MR Research Center, Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
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Lu A, Atkinson IC, Vaughn JT, Thulborn KR. Impact of gradient timing error on the tissue sodium concentration bioscale measured using flexible twisted projection imaging. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 213:176-181. [PMID: 21944734 PMCID: PMC3217314 DOI: 10.1016/j.jmr.2011.08.036] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Revised: 08/12/2011] [Accepted: 08/29/2011] [Indexed: 05/31/2023]
Abstract
The rapid biexponential transverse relaxation of the sodium MR signal from brain tissue requires efficient k-space sampling for quantitative imaging in a time that is acceptable for human subjects. The flexible twisted projection imaging (flexTPI) sequence has been shown to be suitable for quantitative sodium imaging with an ultra-short echo time to minimize signal loss. The fidelity of the k-space center location is affected by the readout gradient timing errors on the three physical axes, which is known to cause image distortion for projection-based acquisitions. This study investigated the impact of these timing errors on the voxel-wise accuracy of the tissue sodium concentration (TSC) bioscale measured with the flexTPI sequence. Our simulations show greater than 20% spatially varying quantification errors when the gradient timing errors are larger than 10 μs on all three axes. The quantification is more tolerant of gradient timing errors on the Z-axis. An existing method was used to measure the gradient timing errors with <1 μs error. The gradient timing error measurement is shown to be RF coil dependent, and timing error differences of up to ∼16 μs have been observed between different RF coils used on the same scanner. The measured timing errors can be corrected prospectively or retrospectively to obtain accurate TSC values.
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Affiliation(s)
- Aiming Lu
- Center for Magnetic Resonance Research, University of Illinois at Chicago, Chicago, IL 60612, United States.
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Stobbe RW, Beaulieu C. Assessment of averaging spatially correlated noise for 3-D radial imaging. IEEE TRANSACTIONS ON MEDICAL IMAGING 2011; 30:1381-1390. [PMID: 21335306 DOI: 10.1109/tmi.2011.2116799] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Any measurement of signal intensity obtained from an image will be corrupted by noise. If the measurement is from one voxel, an error bound associated with noise can be assigned if the standard deviation of noise in the image is known. If voxels are averaged together within a region of interest (ROI) and the image noise is uncorrelated, the error bound associated with noise will be reduced in proportion to the square root of the number of voxels in the ROI. However, when 3-D-radial images are created the image noise will be spatially correlated. In this paper, an equation is derived and verified with simulated noise for the computation of noise averaging when image noise is correlated, facilitating the assessment of noise characteristics for different 3-D-radial imaging methodologies. It is already known that if the radial evolution of projections are altered such that constant sampling density is produced in k-space, the signal-to-noise ratio (SNR) inefficiency of standard radial imaging (SR) can effectively be eliminated (assuming a uniform transfer function is desired). However, it is shown in this paper that the low-frequency noise power reduction of SR will produce beneficial (anti-) correlation of noise and enhanced noise averaging characteristics. If an ROI contains only one voxel a radial evolution altered uniform k-space sampling technique such as twisted projection imaging (TPI) will produce an error bound ~35% less with respect to noise than SR, however, for an ROI containing 16 voxels the SR methodology will facilitate an error bound ~20% less than TPI. If a filtering transfer function is desired, it is shown that designing sampling density to create the filter shape has both SNR and noise correlation advantages over sampling k-space uniformly. In this context SR is also beneficial. Two sets of 48 images produced from a saline phantom with sodium MRI at 4.7T are used to experimentally measure noise averaging characteristics of radial imaging and good agreement with theory is obtained.
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Affiliation(s)
- Robert W Stobbe
- Department of Biomedical Engineering, University of Alberta, Alberta, AB, Canada.
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Montet-Abou K, Viallon M, Hyacinthe JN, Delattre B, Vallee JP, Didier D, Croisille P, Montet X. The role of imaging and molecular imaging in the early detection of metabolic and cardiovascular dysfunctions. Int J Obes (Lond) 2011; 34 Suppl 2:S67-81. [PMID: 21151150 DOI: 10.1038/ijo.2010.242] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Despite intense effort, obesity is still rising throughout the world. Links between obesity and cardiovascular diseases are now well established. Most of the cardiovascular changes related to obesity can be followed by magnetic resonance imaging (MRI) or by magnetic resonance spectroscopy (MRS). In particular, we will see in this review that MRI/MRS is extremely well suited to depict (1) changes in cardiac mass and function, (2) changes in stroke volume, (3) accumulation of fat inside the mediastinum or even inside the cardiomyocytes, (4) cell viability and (5) molecular changes during early cardiovascular diseases.
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Affiliation(s)
- K Montet-Abou
- Department of Radiology, Geneva University Hospital, Geneva, Switzerland
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Balchandani P, Pauly J, Spielman D. Designing adiabatic radio frequency pulses using the Shinnar-Le Roux algorithm. Magn Reson Med 2011; 64:843-51. [PMID: 20806378 DOI: 10.1002/mrm.22473] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Adiabatic pulses are a special class of radio frequency (RF) pulses that may be used to achieve uniform flip angles in the presence of a nonuniform B(1) field. In this work, we present a new, systematic method for designing high-bandwidth (BW), low-peak-amplitude adiabatic RF pulses that utilizes the Shinnar-Le Roux (SLR) algorithm for pulse design. Currently, the SLR algorithm is extensively employed to design nonadiabatic pulses for use in magnetic resonance imaging and spectroscopy. We have adapted the SLR algorithm to create RF pulses that also satisfy the adiabatic condition. By overlaying sufficient quadratic phase across the spectral profile before the inverse SLR transform, we generate RF pulses that exhibit the required spectral characteristics and adiabatic behavior. Application of quadratic phase also distributes the RF energy more uniformly, making it possible to obtain the same spectral BW with lower RF peak amplitude. The method enables the pulse designer to specify spectral profile parameters and the degree of quadratic phase before pulse generation. Simulations and phantom experiments demonstrate that RF pulses designed using this new method behave adiabatically.
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Affiliation(s)
- Priti Balchandani
- Department of Radiology, Stanford University, Stanford, California, USA.
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Abstract
Sodium ((23)Na) imaging has a place somewhere between (1)H-MRI and MR spectroscopy (MRS). Like MRS it potentially provides information on metabolic processes, but only one single resonance of ionic (23)Na is observed. Therefore pulse sequences do not need to code for a chemical shift dimension, allowing (23)Na images to be obtained at high resolutions as compared to MRS. In this chapter the biological significance of sodium in the brain will be discussed, as well as methods for observing it with (23)Na-MRI. Many vital cellular processes and interactions in excitable tissues depend on the maintenance of a low intracellular and high extracellular sodium concentration. Healthy cells maintain this concentration gradient at the cost of energy. Leaky cell membranes or an impaired energy metabolism immediately leads to an increase in cytosolic total tissue sodium. This makes sodium a biomarker for ischemia, cancer, excessive tissue activation, or tissue damage as might be caused by ablation therapy. Special techniques allow quantification of tissue sodium for the monitoring of disease or therapy in longitudinal studies or preferential observation of the intracellular component of the tissue sodium. New methods and high-field magnet technology provide new opportunities for (23)Na-MRI in clinical and biomedical research.
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Affiliation(s)
- Ronald Ouwerkerk
- Cardiovascular Imaging, National Institute of Diabetes and Digestive and Kidney Disease, National Institute of Health, Bethesda, MD, USA.
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Jacobs MA, Stearns V, Wolff AC, Macura K, Argani P, Khouri N, Tsangaris T, Barker PB, Davidson NE, Bhujwalla ZM, Bluemke DA, Ouwerkerk R. Multiparametric magnetic resonance imaging, spectroscopy and multinuclear (²³Na) imaging monitoring of preoperative chemotherapy for locally advanced breast cancer. Acad Radiol 2010; 17:1477-85. [PMID: 20863721 DOI: 10.1016/j.acra.2010.07.009] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2010] [Revised: 07/09/2010] [Accepted: 07/10/2010] [Indexed: 12/12/2022]
Abstract
RATIONALE AND OBJECTIVES The aim of this prospective study was to investigate using multiparametric and multinuclear magnetic resonance imaging during preoperative systemic therapy for locally advanced breast cancer. MATERIALS AND METHODS Women with operable stage 2 or 3 breast cancer who received preoperative systemic therapy were studied using dynamic contrast-enhanced magnetic resonance imaging, magnetic resonance spectroscopy, and ²³Na magnetic resonance. Quantitative metrics of choline peak signal-to-noise ratio, total tissue sodium concentration, tumor volumes, and Response Evaluation Criteria in Solid Tumors were determined and compared to final pathologic results using receiver-operating characteristic analysis. Hormonal markers were investigated. Statistical significance was set at P < .05. RESULTS Eighteen eligible women were studied. Fifteen responded to therapy, four (22%) with pathologic complete response and 11 (61%) with pathologic partial response. Three patients (17%) had no response. Among estrogen receptor-positive, HER2-positive, and triple-negative phenotypes, observed frequencies of pathologic complete response, pathologic partial response, and no response were 2, 5, and 0; 1, 4, and 0; and 1, 1, and 3, respectively. Responders (pathologic complete response and pathologic partial response) had the largest reductions in choline signal-to-noise ratio (35%, from 7.2 ± 2.3 to 4.6 ± 2; P < .01) compared to nonresponders (11%, from 8.4 ± 2.7 to 7.5 ± 3.6; P = .13) after the first cycle. Total tissue sodium concentration significantly decreased in responders (27%, from 66 ± 18 to 48.4 ± 8 mmol/L; P = .01), while there was little change in nonresponders (51.7 ± 7.6 to 56.5 ± 1.6 mmol/L; P = .50). Lesion volume decreased in responders (40%, from 78 ± 78 to 46 ± 51 mm³; P = .01) and nonresponders (21%, from 100 ± 104 to 79.2 ± 87 mm³; P = .23) after the first cycle. The largest reduction in Response Evaluation Criteria in Solid Tumors occurred after the first treatment in responders (18%, from 24.5 ± 20 to 20.2 ± 18 mm; P = .01), with a slight decrease in tumor diameter noted in nonresponders (17%, from 23 ± 19 to 19.2 ± 19.1 mm; P = .80). CONCLUSIONS Multiparametric and multinuclear imaging parameters were significantly reduced after the first cycle of preoperative systemic therapy in responders, specifically, choline signal-to-noise ratio and sodium. These new surrogate radiologic biomarkers maybe able to predict and provide a platform for potential adaptive therapy in patients.
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Affiliation(s)
- Michael A Jacobs
- The Russell H. Morgan Department of Radiology and Radiological Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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El-Sharkawy AM, Schär M, Ouwerkerk R, Weiss RG, Bottomley PA. Quantitative cardiac 31P spectroscopy at 3 Tesla using adiabatic pulses. Magn Reson Med 2009; 61:785-95. [PMID: 19195018 DOI: 10.1002/mrm.21867] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Cardiac phosphorus magnetic resonance spectroscopy (MRS) with surface coils promises better quantification at 3 Tesla (T) from improved signal-to-noise ratios and spectral resolution compared with 1.5 T. However, Bloch equation and field analyses at 3T show that for efficient quantitative MRS protocols using small-angle adiabatic (BIR4/BIRP) pulses the excitation-field is limited by radiofrequency (RF) power requirements and power deposition. When BIR4/BIRP pulse duration is increased to reduce power levels, T2-decay can introduce flip-angle dependent errors in the steady-state magnetization, causing errors in saturation corrections for metabolite quantification and in T1s measured by varying the flip-angle. A new dual-repetition-time (2TR) T1 method using frequency-sign-cycled adiabatic-half-passage pulses is introduced to alleviate power requirements, and avoid the problem related to T2 relaxation during the RF pulse. The 2TR method is validated against inversion-recovery in phantoms using a practical transmit/receive coil set designed for phosphorus MRS of the heart at depths of 9-10 cm with 4 kW of pulse power. The T1s of phosphocreatine (PCr) and adenosine triphosphate (gamma-ATP) in the calf-muscle (n=9) at 3 T are 6.8+/-0.3 s and 5.4+/-0.6 s, respectively. For heart (n=10) the values are 5.8+/-0.5 s (PCr) and 3.1+/-0.6 s (gamma-ATP). The 2TR protocol measurements agreed with those obtained by conventional methods to within 10%.
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Affiliation(s)
- AbdEl-Monem El-Sharkawy
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA
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Jacobs MA, Ouwerkerk R, Kamel I, Bottomley PA, Bluemke DA, Kim HS. Proton, diffusion-weighted imaging, and sodium (23Na) MRI of uterine leiomyomata after MR-guided high-intensity focused ultrasound: a preliminary study. J Magn Reson Imaging 2009; 29:649-56. [PMID: 19243047 PMCID: PMC4151255 DOI: 10.1002/jmri.21677] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
PURPOSE To determine the feasibility of using combined proton (1H), diffusion-weighted imaging (DWI), and sodium (23Na) magnetic resonance imaging (MRI) to monitor the treatment of uterine leiomyomata (fibroids). MATERIALS AND METHODS Eight patients with uterine leiomyomata were enrolled and treated using MRI-guided high-intensity frequency ultrasound surgery (MRg-HIFUS). MRI scans collected at baseline and posttreatment consisted of T2-, T1-, and 1H DWI, as well as posttreatment 23Na MRI. The 23Na and 1H MRi were coregistered using a replacement phantom method. Regions of interest in treated and untreated uterine leiomyoma tissue were drawn on 1H MRI and DWI, wherein the tissue apparent diffusion coefficient of water (ADC) and absolute sodium concentrations were measured. RESULTS Regions of treated uterine tissue were clearly identified on both DWI and 23Na images. The sodium concentrations in normal myometrium tissue were 35.8+/-2.1 mmol (mM), in the fundus; 43.4+/-3.8 mM, and in the bladder; 65.3+/-0.8 mM with ADC in normal myometrium of 2.2+/-0.3x10(-3) mm2/sec. Sodium concentration in untreated leiomyomata were 28+/-5 mM, and were significantly elevated (41.6+/-7.6 mM, P<0.05) after treatment. Apparent diffusion coefficient values in the treated leiomyomata (1.30+/-0.38x10(-3) mm2/sec) were decreased compared to areas of untreated leiomyomata (1.75+/--4048micro-4050micro36x10(-3) mm2/sec; P=0.04). CONCLUSION Multiparametric imaging permits identification of uterine leiomyomata, revealing altered 23Na MRI and DWI levels following noninvasive treatment that provides a mechanism to explore the molecular and metabolic pathways after treatment.
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Affiliation(s)
- Michael A Jacobs
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205, USA.
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Parallel imaging with 3D TPI trajectory: SNR and acceleration benefits. Magn Reson Imaging 2008; 27:656-63. [PMID: 19110392 DOI: 10.1016/j.mri.2008.10.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2008] [Revised: 09/05/2008] [Accepted: 10/14/2008] [Indexed: 11/20/2022]
Abstract
Three-dimensional (3D) twisted projection imaging (TPI) trajectory has a unique advantage in sodium ((23)Na) imaging on clinical MRI scanners at 1.5 or 3 T, generating a high signal-to-noise ratio (SNR) with a short acquisition time (approximately 10 min). Parallel imaging with an array of coil elements transits SNR benefits from small coil elements to acquisition efficiency by sampling partial k-space. This study investigates the feasibility of parallel sodium imaging with emphases on SNR and acceleration benefits provided by the 3D TPI trajectory. Computer simulations were used to find available acceleration factors and noise amplification. Human head studies were performed on clinical 1.5/3-T scanners with four-element coil arrays to verify simulation outcomes. In in vivo studies, proton ((1)H) data, however, were acquired for concept-proof purpose. The sensitivity encoding (SENSE) method with the conjugate gradient algorithm was used to reconstruct images from accelerated TPI-SENSE data sets. Self-calibration was employed to estimate coil sensitivities. Noise amplification in TPI-SENSE was evaluated using multiple noise trials. It was found that the acceleration factor was as high as 5.53 (corresponding to acceleration number 2 x 3, ring-by-rotation), with a small image error of 6.9% when TPI projections were reduced in both polar (ring) and azimuthal (rotation) directions. The average noise amplification was as low as 98.7%, or 27% lower than Cartesian SENSE at that acceleration factor. The 3D nature of both TPI trajectory and coil sensitivities might be responsible for the high acceleration and low noise amplification. Consequently, TPI-SENSE may have potential advantages for parallel sodium imaging.
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Ouwerkerk R, Bottomley PA, Solaiyappan M, Spooner AE, Tomaselli GF, Wu KC, Weiss RG. Tissue sodium concentration in myocardial infarction in humans: a quantitative 23Na MR imaging study. Radiology 2008; 248:88-96. [PMID: 18566171 DOI: 10.1148/radiol.2481071027] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To prospectively determine whether the absolute tissue sodium concentration (TSC) increases in myocardial infarctions (MIs) in humans and whether TSC is related to infarct size, infarct age, ventricular dysfunction, and/or electrophysiologic inducibility of ventricular arrhythmias. MATERIALS AND METHODS Delayed contrast material-enhanced 1.5-T hydrogen 1 ((1)H) magnetic resonance (MR) imaging was used to measure the size and location of nonacute MIs in 20 patients (18 men, two women; mean age, 63 years +/- 9 [standard deviation]; age range, 48-82 years) examined at least 90 days after MI. End-systolic and end-diastolic volumes, ejection fraction, and left ventricle (LV) mass were measured with cine MR imaging. The TSC in normal, infarcted, and adjacent myocardial tissue was measured on sodium 23 ((23)Na) MR images coregistered with delayed contrast-enhanced (1)H MR images. Programmed electric stimulation to induce monomorphic ventricular tachycardia (MVT) was used to assess arrhythmic potential, and myocardial TSC was compared between the inducible MVT and noninducible MVT patient groups. RESULTS The mean TSC for MIs (59 micromol/g wet weight +/- 10) was 30% higher than that for noninfarcted (remote) LV regions (45 micromol/g wet weight +/- 5, P < .001) and that for healthy control subjects, and TSC did not correlate with infarct age or functional and morphologic indices. The mean TSC for tissue adjacent to the MI (50 micromol/g wet weight +/- 6) was intermediate between that for the MI and that for remote regions. The elevated TSC measured in the MI at (23)Na MR imaging lacked sufficient contrast and spatial resolution for routine visualization of MI. Cardiac TSC did not enable differentiation between patients in whom MVT was inducible and those in whom it was not. CONCLUSION Absolute TSC is measurable with (23)Na MR imaging and is significantly elevated in human MI; however, TSC increase is not related to infarct age, infarct size, or global ventricular function. In regions adjacent to the MI, TSC is slightly increased but not to levels in the MI.
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Affiliation(s)
- Ronald Ouwerkerk
- Division of Magnetic Resonance Research, Department of Radiology, Johns Hopkins University, School of Medicine, 601 N Caroline St, JHOC 4241, Baltimore, MD 21287-0845, USA.
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Abstract
Introduction Cardiovascular molecular imaging is a rapidly evolving field of research, aiming to image and quantify molecular and cellular targets in vivo. MR imaging has some inherent properties that make it very suitable for cardiovascular molecular imaging. Until now, only a limited number of studies have been published on cardiovascular molecular imaging using MR imaging. Review In the current review, MR techniques that have already shown potential are discussed. Metabolic MR imaging can be performed by 31P-MR spectroscopy, 23Na MR spectroscopy and 1H-MR spectroscopy; some examples are shown. Furthermore, a concise overview is given of several aspecific and specific contrast agents for cardiovascular molecular MR imaging, such as gadolinium-based contrast agents, iron oxide MR contrast agents and fibrin-targeted MR contrast agents. Conclusion We expect that in the next decade currently promising MR molecular imaging agents will be introduced into the clinical arena to guide diagnosis and therapy of cardiovascular disease.
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Affiliation(s)
- H J Lamb
- Department of Radiology, C2S, Leiden University Medical Center, P.O. Box 9600, 2300 RC Leiden, The Netherlands.
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Abstract
Magnetic resonance (MR) imaging has become established as a diagnostic and research tool in many areas of medicine because of its ability to provide excellent soft-tissue delineation in different areas of interest. In addition to T1- and T2-weighted imaging, many specialized MR techniques have been designed to extract metabolic or biophysical information. Diffusion-weighted imaging gives insight into the movement of water molecules in tissue, and diffusion-tensor imaging can reveal fiber orientation in the white matter tracts. Metabolic information about the object of interest can be obtained with spectroscopy of protons, in addition to imaging of other nuclei, such as sodium. Dynamic contrast material-enhanced imaging and recently proton spectroscopy play an important role in oncologic imaging. When these techniques are combined, they can assist the physician in making a diagnosis or monitoring a treatment regimen. One of the major advantages of the different types of MR imaging is the ability of the operator to manipulate image contrast with a variety of selectable parameters that affect the kind and quality of the information provided. The elements used to obtain MR images and the factors that affect formation of an MR image include MR instrumentation, localization of the MR signal, gradients, k-space, and pulse sequences.
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Affiliation(s)
- Michael A Jacobs
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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Ouwerkerk R, Jacobs MA, Macura KJ, Wolff AC, Stearns V, Mezban SD, Khouri NF, Bluemke DA, Bottomley PA. Elevated tissue sodium concentration in malignant breast lesions detected with non-invasive 23Na MRI. Breast Cancer Res Treat 2007; 106:151-60. [PMID: 17260093 DOI: 10.1007/s10549-006-9485-4] [Citation(s) in RCA: 142] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2006] [Accepted: 12/07/2006] [Indexed: 10/23/2022]
Abstract
BACKGROUND The hypothesis that physiological and biochemical changes associated with proliferating malignant tumors may cause an increase in total tissue sodium concentration (TSC) was tested with non-invasive, quantitative sodium ((23)Na) magnetic resonance imaging (MRI) in patients with benign and malignant breast tumors. METHODS (23)Na and (1)H MRI of the breast was performed on 22 women with suspicious breast lesions (> or =1 cm) at 1.5 Tesla. A commercial proton ((1)H) phased array breast coil and custom solenoidal (23)Na coil were used to acquire (1)H and (23)Na images during the same MRI examination. Quantitative 3-dimensional (23)Na projection imaging was implemented with negligible signal loss from MRI relaxation, or from radio-frequency field inhomogeneity, in less than 15 min. Co-registered (1)H and (23)Na images permitted quantification of TSC in normal and suspicious tissues on the basis of (1)H MRI contrast enhancement and anatomy, with histology confirmed by biopsy. RESULTS Sodium concentrations were consistently elevated in (N = 19) histologically proven malignant breast lesions by an average of 63% compared to glandular tissue. The increase in sodium concentration in malignant tissue was highly significant compared to unaffected glandular tissue (P < 0.0001, paired t-test), adipose tissue, and TSC in three patients with benign lesions. CONCLUSION Elevated TSC in breast lesions measured by non-invasive (23)Na MRI appears to be a cellular-level indicator associated with malignancy. This method may have potential to improve the specificity of breast MRI with only a modest increase in scan time per patient.
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Affiliation(s)
- Ronald Ouwerkerk
- Division of MR Research, Russel H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, School of Medicine, Baltimore, MD 21287-0845, USA.
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Idiyatullin D, Corum C, Park JY, Garwood M. Fast and quiet MRI using a swept radiofrequency. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2006; 181:342-9. [PMID: 16782371 DOI: 10.1016/j.jmr.2006.05.014] [Citation(s) in RCA: 250] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2006] [Revised: 04/25/2006] [Accepted: 05/27/2006] [Indexed: 05/10/2023]
Abstract
A novel fast and quiet method of magnetic resonance imaging (MRI) is introduced which creates new opportunities for imaging in medicine and materials science. The method is called SWIFT, sweep imaging with Fourier transformation. In SWIFT, time-domain signals are acquired in a time-shared manner during a swept radiofrequency excitation of the nuclear spins. With negligible time between excitation and signal acquisition, new possibilities exist for imaging objects consisting of spins with extremely fast transverse relaxation rates, such as macromolecules, semi-solids, and quadrupolar nuclei. The field gradient used for spatial-encoding is not pulsed on and off, but rather is stepped in orientation in an incremental manner, which results in low acoustic noise. This unique acquisition method is expected to be relatively insensitive to sample motion, which is important for imaging live objects. Additionally, the frequency-swept excitation distributes the signal energy in time and thus dynamic range requirements for proper signal digitization are reduced compared with conventional MRI. For demonstration, images of a plastic object and cortical bone are shown.
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Affiliation(s)
- Djaudat Idiyatullin
- Center for Magnetic Resonance Research, Cancer Center and Department of Radiology, University of Minnesota Medical School, 2021 6th Street SE, Minneapolis, MN 55455, USA
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