Optimized radiofrequency coil setup for MR examination of living isolated rat hearts in a horizontal 9.4T magnet (original) (raw)
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Reviews in Cardiovascular Medicine
Cardiac magnetic resonance (CMR) is a relevant diagnostic tool for the evaluation of cardiac morphology, function, and mass. The assessment of myocardial tissue content through the measurement of longitudinal (T1) and transversal (T2) relaxation properties and the development of different technical advances are important clinical novelties of CMR. Recently, magnetic resonance spectroscopy has been explored for the assessment of the metabolic state of tissue for cardiac function evaluation by using nuclei other than protons, such as 13 C and 23 Na, expanding our knowledge of the kinetics of metabolic processes. The design and development of dedicated radiofrequency coils and pulse sequences are fundamental to maximizing signal-to-noise ratio data while achieving faster cardiac examination. This review highlights the new technical developments in CMR sequences and coils.
Electronics, 2021
Hyperpolarized 13C magnetic resonance (MR) is a promising technique for the noninvasive assessment of the regional cardiac metabolism since it permits heart physiology studies in pig and mouse models. The main objective of the present study is to resume the work carried out at our electromagnetic laboratory in the field of radio frequency (RF) coil design, building, and testing. In this paper, first, we review the principles of RF coils, coil performance parameters, and estimation methods by using simulations, workbench, and MR imaging experiments. Then, we describe the simulation, design, and testing of different 13C coil configurations and acquisition settings for hyperpolarized studies on pig and mouse heart with a clinical 3T MRI scanner. The coil simulation is performed by developing a signal-to-noise ratio (SNR) model in terms of coil resistance, sample-induced resistance, and magnetic field pattern. Coil resistance was calculated from Ohm’s law and sample-induced resistances ...
Journal of Medical and Biological Engineering, 2016
Purpose: Magnetic resonance spectroscopy of hyperpolarized 13C pyruvate and its metabolites in large animal models is a powerful tool for assessing cardiac metabolism in patho-physiological conditions. In 13C studies the Signal-to-Noise Ratio (SNR) could be crucial, to overcome intrinsic data quality limitation due to the low molar concentration of certain metabolites as well as the low flux of conversion. On the other hand, since 13C-MRS is essentially a semi-quantitative technique, the SNR among the spectra acquired in different myocardial segments should be homogeneous. MR coil design plays an important role in achieving both targets. Materials and Methods: In this study, a receive 16-channels surface coil was designed for 13C hyperpolarized studies of pig heart with a clinical 3T scanner. The coil performances were characterized by phantom experiments, and compared with a birdcage coil used in transmit/receive mode. Segmental signal distribution in the left ventricle (LV) was assessed by experiments on six healthy mini pigs. Results: The proposed coil showed a significant increase in SNR in the LV wall close to the coil surface with respect to the birdcage but also a significant segmental inhomogeneity. Conclusion: The use of the 16-channel coil would be recommended in studies of septal and anterior LV walls.
Magnetic Resonance in Medicine, 1993
Measurement of regional myocardial perfusion is important for the diagnosis and treatment of coronary artery disease. Currently used methods for the measurement of myocardial tissue perfusion are either invasive or not quantitative. Here, we demonstrate a technique for the measurement of myocardial perfusion using magnetic resonance imaging (MRI) with spin tagging of arterial water. In addition, it is shown that changes in perfusion can be quantitated by measuring changes in tissue T1. Perfusion images are obtained in Langondorff-perfused, isolated rat hearts for perfusion rates ranging from 5 to 22 ml/g/rnin. The MRI-determined perfusion rates are in excellent agreement with perfusion rates determined from measurement of bulk perfusate flow (r = 0.98). The predicted linear dependence of the measured Tl (TIBpp) on perfusion is also demonstrated. The ability of perfusion imaging to measure regional variations in flow is demonstrated with hearts in which perfusion defects were created by ligation of a (coronary artery. These results indicate that MRI of perfusion using spin inversion of arterial water gives quantitative maps of cardiac perfusion. Key words: cardiac l H MRI; blood flow; ischemia. INITRODUCTION There are currently several methods available for measuring blood flow to the heart. Transit-time analysis or indicator-dilution analysis are invasive, requiring cardiac catheterization, and often inaccurate (1, 2). ZolTl or Technetium 99m imaging detects segmental perfusion differences but is not suitable for absolute quantification of myocardial blood flow (3). Recently, contrast-enhanced MRI, fast CT, and PET have been used to measure and image perfusion of the myocardium (4-6). These methods are invasive in that they involve the external administration of a tracer, and are often limited to a few measurements due to the finite washout time andlor the toxicity of the tracer (4-6). In some cases, quantitation is limited by knowledge of the b1ood:tissue partition coefficient of the tracer. An MRI technique to image regional perfusion has recently been developed that uses magnetic labeling of ar
MRI evaluation of myocardial perfusion without a contrast agent using magnetization transfer
Magnetic Resonance in Medicine, 1993
We ipropose a new magnetic msonance imaging (MRI) technique that is sensitive to myocardial tissue perfusion that obviates the use of an extrinsic contrast agent. Significant advantages of such a technique are that It avoids accumulation of contrasr agent when repeated studles are pertormed on the same subject and that it is completely noninvasive. The method makes use of a combination of magnetization transfer (?AT) and TI ut (measured spin-lattice retaxation time in the presence of MT) weighting. in this Communication, we present observations from experiments with an isolated rat heart model that demonstrate Increase of MT-weighted signal Intensity iind T1" wlth flow. Also included are data showing that theso effects can be made synergistic for enhancing the sensitivity to perfusion. We have observed about a 3% change in MT-weighted int6nsity end up to 10% change in MTTIUtweighted intensity for a change of 1 mVmin in global flow rate.
Intercomparison of performance of RF coil geometries for high field mouse cardiac MRI
Concepts in Magnetic Resonance Part A, 2011
Multi-turn spiral surface coils are constructed in flat and cylindrical arrangements and used for high field (7.1 T) mouse cardiac MRI. Their electrical and imaging performances, based on experimental measurements, simulations, and MRI experiments in free space, and under phantom, and animal loading conditions, are compared with a commercially available birdcage coil. Results show that the four-turn cylindrical spiral coil exhibits improved relative SNR (rSNR) performance to the flat coil counterpart, and compares fairly well with a commercially available birdcage coil. Phantom experiments indicate a 50% improvement in the SNR for penetration depths ≤ 6.1 mm from the coil surface compared to the birdcage coil, and an increased penetration depth at the halfmaximum field response of 8 mm in the 4-spiral cylindrical coil case, in contrast to 2.9 mm in the flat 4-turn spiral case. Quantitative comparison of the performance of the two spiral coil geometries in anterior, lateral, inferior, and septal regions of the murine heart yield maximum mean percentage rSNR increases of the order of 27-167% in vivo post-mortem (cylindrical compared to flat coil). The commercially available birdcage outperforms the cylindrical spiral coil in rSNR by a factor of 3-5 times. The comprehensive approach and methodology adopted to accurately design, simulate, implement, and test radiofrequency coils of any geometry and type, under any loading conditions, can be generalized for any application of high field mouse cardiac MRI.
Journal of Magnetic Resonance Imaging, 2010
Purpose: To test whether image normalization using either a separate 3D proton-density (PD)-weighted prescan, or 2D PD-weighted images prior to the perfusion series, improves correction of differences in spatial sensitivity induced by radiofrequency (RF) surface receiver coils. Originally, this correction was applied using the baseline signal in the myocardium before arrival of the contrast agent. This is of importance, as quantitative analysis of magnetic resonance (MR) myocardial perfusion using deconvolution with the arterial input assumes equal signal sensitivity over the heart.
Review of Scientific Instruments, 2021
Hyperpolarized 13 C Magnetic Resonance (MR) is a promising technique for in vivo non-invasive assessment of metabolism in humans. Despite the considerable signal increase provided by hyperpolarization techniques, the low molar concentration of derivate 13 C metabolites gives rise to technological limits in terms of data quality. The development of dedicated radio frequency coils, capable of providing a large field of view with high signal-to-noise ratio data, is thus a fundamental task. This work describes the design, simulation, and test of a surface and a volume coil, both designed to be integrated with a clinical scanner for hyperpolarized 13 C studies in small animal models, with the purpose to provide a detailed characterization and comparison of their performance. In particular, coil inductance was evaluated with analytical calculation, while the magnetostatic theory was employed for coils magnetic field pattern estimation. Workbench tests permitted us to characterize coil performance in terms of quality factor and efficiency. Additionally, this Tutorial summarizes the acquisition experience for the reconstruction of 13 C spectroscopic maps in phantom using the two designed coils and a 3 T MR clinical scanner. We believe that this Tutorial could be interesting for graduate students and researchers in the field of magnetic resonance coil design and development, especially for 13 C studies.
Review of Scientific Instruments
Hyperpolarized 13 C Magnetic Resonance (MR) is a promising technique for in vivo non-invasive assessment of metabolism in humans. Despite the considerable signal increase provided by hyperpolarization techniques, the low molar concentration of derivate 13 C metabolites gives rise to technological limits in terms of data quality. The development of dedicated radio frequency coils, capable of providing a large field of view with high signal-to-noise ratio data, is thus a fundamental task. This work describes the design, simulation, and test of a surface and a volume coil, both designed to be integrated with a clinical scanner for hyperpolarized 13 C studies in small animal models, with the purpose to provide a detailed characterization and comparison of their performance. In particular, coil inductance was evaluated with analytical calculation, while the magnetostatic theory was employed for coils magnetic field pattern estimation. Workbench tests permitted us to characterize coil performance in terms of quality factor and efficiency. Additionally, this Tutorial summarizes the acquisition experience for the reconstruction of 13 C spectroscopic maps in phantom using the two designed coils and a 3 T MR clinical scanner. We believe that this Tutorial could be interesting for graduate students and researchers in the field of magnetic resonance coil design and development, especially for 13 C studies.