Low-Cost High-Performance MRI (original) (raw)
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High resolution MRI of the brain at 4.7 Tesla using fast spin echo imaging
British Journal of Radiology, 2003
Over recent years, high field MR scanners (3 T and above) have become increasingly widespread due to potential advantages such as higher signal-to-noise ratio. However, few examples of high resolution images covering the whole brain in reasonable acquisition times have been published to date and none have used fast spin echo (FSE), a sequence commonly employed for the acquisition of T 2 weighted images at 1.5 T. This is mostly due to the increased technical challenges associated with uniform signal generation and the increasingly restrictive constraints of current safety guidelines at high field. We investigated 10 volunteers using an FSE sequence optimized to the 4.7 T environment. This sequence allows the acquisition of 17-and 34-slice data sets with an in-plane resolution of approximately 500 mm6500 mm and a slice thickness of 2 mm, in 5 min 40 s and 11 min 20 s, respectively. The images appear T 2 weighted, although the contrast is due to the combined effects of chosen echo time, magnetization transfer, direct radio frequency saturation and diffusion as well as the T 1 and T 2 relaxation times of the tissue. The result is an excellent detailed visualization of anatomical structures, demonstrating the great potential of 4.7 T MRI for clinical applications. This paper shows that, with careful optimization of sequence parameters, FSE imaging can be used at high field to generate images with high spatial resolution and uniform contrast across the whole brain within the prescribed power deposition limits.
Superconducting magnets for magnetic resonance imaging
Applied Superconductivity, 1993
Clinical magnetic resonance imaging (MRI) is characterised by the use of large, expensive whole-body magnets. In recent years the need for these large magnets has been challenged by the evolution of compact and targetted magnet systems.
Magnetic Resonance in Medicine, 2013
Ultra-low-field MRI uses microtesla fields for signal encoding and sensitive superconducting quantum interference devices for signal detection. Similarly, modern magnetoencephalography (MEG) systems use arrays comprising hundreds of superconducting quantum interference device channels to measure the magnetic field generated by neuronal activity. In this article, hybrid MEG-MRI instrumentation based on a commercial wholehead MEG device is described. The combination of ultra-low-field MRI and MEG in a single device is expected to significantly reduce coregistration errors between the two modalities, to simplify MEG analysis, and to improve MEG localization accuracy. The sensor solutions, MRI coils (including a superconducting polarizing coil), an optimized pulse sequence, and a reconstruction method suitable for hybrid MEG-MRI measurements are described. The performance of the device is demonstrated by presenting ultra-low-field-MR images and MEG recordings that are compared with data obtained with a 3T scanner and a commercial MEG device.
A readout magnet for prepolarized MRI
Magnetic Resonance in Medicine, 1996
Conventional MRI systems rely on large magnets to generate a field that is both strong and extremely uniform. This field is usually produced by a heavy permanent magnet or a cryogenically cooled superconductor. An alternative approach, called prepolarized MRI (PMRI), employs two separate fields produced by two different magnets. A strong and inhomogeneous magnetic field is used to polarize the sample. After polarization, a weak magnetic field is used for readout. These fields can be produced by two separate resistive electromagnets that cost significantly less than a single permanent or superconducting magnet. At Stanford, the authors are constructing a PMRI prototype scanner suitable for imaging human extremities roughly 20 cm in diameter. With this system the authors hope to demonstrate comparable image quality to MRI with reduced system cost. The authors' initial work on low-frequency reception indicates that it will be possible to obtain comparable image signal-to-noise ratio to an MRI scanner operating at the same polarizing field strength. To reduce the capital cost of the system, the authors use resistive electromagnets. Here the authors discuss the full development of the readout magnet including important design considerations, shimming, and field plots. These encouraging results are an important step toward evaluating the cost effectiveness of PMRI.
Magnetic spin imaging under ambient conditions with sub-cellular resolution
Nature Communications, 2013
Measuring spins is the corner stone of a variety of analytical techniques including modern magnetic resonance imaging (MRI). The full potential of spin imaging and sensing across length scales is hindered by the achievable signal-to-noise in inductive detection schemes. Here we show that a proximal Nitrogen-Vacancy (NV) ensemble serves as a precision sensing array. Monitoring its
Ultra-High Field NMR and MRI—The Role of Magnet Technology to Increase Sensitivity and Specificity
Frontiers in Physics, 2017
Starting with postwar developments in nuclear magnetic resonance (NMR) a race for stronger and stronger magnetic fields has begun in the 1950s to overcome the inherently low sensitivity of this promising method. Further challenges were larger magnet bores to accommodate small animals and eventually humans. Initially, resistive electromagnets with small pole distances, or sample volumes, and field strengths up to 2.35 T (or 100 MHz 1 H frequency) were used in applications in physics, chemistry, and material science. This was followed by stronger and more stable (Nb-Ti based) superconducting magnet technology typically implemented first for small-bore systems in analytical chemistry, biochemistry and structural biology, and eventually allowing larger horizontal-bore magnets with diameters large enough to fit small laboratory animals. By the end of the 1970s, first low-field resistive magnets big enough to accommodate humans were developed and superconducting whole-body systems followed. Currently, cutting-edge analytical NMR systems are available at proton frequencies up to 1 GHz (23.5 T) based on Nb 3 Sn at 1.9 K. A new 1.2 GHz system (28 T) at 1.9 K, operating in persistent mode but using a combination of low and high temperature multi-filament superconductors is to be released. Preclinical instruments range from small-bore animal systems with typically 600-800 MHz (14.1-18.8 T) up to 900 MHz (21 T) at 1.9 K. Human whole-body MRI systems currently operate up to 10.5 T. Hybrid combined superconducting and resistive electromagnets with even higher field strength of 45 T dc and 100 T pulsed, are available for material research, of course with smaller free bore diameters. This rather costly development toward higher and higher field strength is a consequence of the inherently low and, thus, urgently needed sensitivity in all NMR experiments. This review particularly describes and compares the developments in superconducting magnet technology and, thus, sensitivity in three Moser et al. UHF MR-Magnet Technology fields of research: analytical NMR, biomedical and preclinical research, and human MRI and MRS, highlighting important steps and innovations. In addition, we summarize our knowledge on safety issues. An outlook into even stronger magnetic fields using different superconducting materials and/or hybrid magnet designs is presented.
IEEE Transactions on Applied Superconductivity, 2010
High-Field MRI provides high resolutions, welldefined chemical shift spectra and large data acquisition rates, and may bring about a paradigm shift in medicine through the in-vivo observation of metabolism. An 11.7 T whole body MRI magnet, for example, should be able to observe metabolic reactions occurring in a human body in addition to producing very precise images of body structures. At this field 13 C-NMR and biochemical reactions of organic molecules can be detected and analyzed in-situ. Then, organs, tissues, vessels and biochemical processes responsible for irregularities in question will be identified. However, an 11.7 T MRI magnet with a bore diameter of 900 mm is a big challenge to the present magnet technology. Field strengths, magnet sizes and superconducting materials to be needed for future high-field MRI are described.
Physics in Medicine and Biology, 2006
It is well known that magnetic susceptibility variations lead to signal voids in MRI. However, recent work has shown that positive-contrast imaging of susceptibility-induced field variations can provide signal enhancements rather than signal losses. In this paper, we propose a new method for generating positive contrast from off-resonant spins with steady-state free precession (SSFP) magnetic resonance imaging. Based on theory and experiments, we demonstrate that positive-contrast images can be acquired in the presence of susceptibility-shift media with low flip angle excitations that are determined by the spin relaxation time constants of the imaging medium. Compared to other techniques, this technique is substantially faster and has low specific absorption rates, permitting high-field imaging. In addition to acquiring positive-contrast images, we also show that it is possible to suppress the imaging medium to desired levels; thereby allowing for simultaneous registration of the background details surrounding the susceptibility-shift media. Among practical applications, we anticipate that the proposed technique can potentially facilitate high field magnetic-resonance-based molecular imaging.
Ultra-low-field magnetic resonance imaging combined with magnetoencephalography
2011
Human brain activity can be monitored with magnetoencephalography (MEG) by measuring the femtoteslalevel extracerebral magnetic fields with SQUID magnetometers. On the other hand, the structure of the brain can be determined with magnetic resonance imaging (MRI), where the applied fields may be 15 orders of magnitude higher than the smallest neuromagnetic signals, ruling out simultaneous MEG. It has been demonstrated recently that simultaneous MRI and MEG is possible: the trick is prepolarization at about 0.1 tesla and MRI at about 0.1 mT. We have designed and are building a hybrid multichannel helmet-shaped MEG-MRI device, which will be capable of simultaneous ultra-low-field MRI and MEG.