Ultra-low Field Magnetic Resonance Imaging Research Articles

SQUIDs vs. Induction Coils for Ultra-Low Field Nuclear Magnetic Resonance: Experimental and Simulation Comparison

Nuclear magnetic resonance (NMR) is widely used in medicine, chemistry and industry. One application area is magnetic resonance imaging (MRI). Recently it has become possible to perform NMR and MRI in the ultra-low field (ULF) regime requiring measurement field strengths of the order of only 1 Gauss. This technique exploits the advantages offered by superconducting quantum interference devices or SQUIDs. Our group has built SQUID based MRI systems for brain imaging and for liquid explosives detection at airport security checkpoints. The requirement for liquid helium cooling limits potential applications of ULF MRI for liquid identification and security purposes. Our experimental comparative investigation shows that room temperature inductive magnetometers may provide enough sensitivity in the 3-10 kHz range and can be used for fast liquid explosives detection based on ULF NMR technique. We describe experimental and computer-simulation results comparing multichannel SQUID based and induction coils based instruments that are capable of performing ULF MRI for liquid identification.

Development of Ultra Low Field Nuclear Magnetic Resonance Imaging System Using HTS rf SQUID

We constructed and studied an ultra low-field nuclear magnetic resonance imaging system using a HTS rf SQUID and room-temperature coils. We recorded the free induction decay signals of 1H by employing a measuring field, Bm, of 44.8 μT and a polarizing field, Bp, of 36.8 mT; in the presence of ∂BZ/∂z and ∂BZ/∂y gradients of the order of 0.8 μT/m, we were able to obtain a quasi two-dimensional 4-pixels image of a simple water phantom.

Introduction to Ultra-Low Field (ULF) Magnetic Resonance Imaging (MRI) Applications

Event Abstract Back to Event Introduction to Ultra-Low Field (ULF) Magnetic Resonance Imaging (MRI) Applications Robert Kraus, Jr.1* 1 Los Alamos National Laboratory, United States Nuclear Magnetic Resonance (NMR) was initially and independently described by Purcell and Bloch in 1946. In 1973, Lauterbur is credited with describing how a NMR image could be generated by adding magnetic field gradients to spatially encode the NMR signal. This led to the now ubiquitous medical MRI used throughout the world. Typical MRI requires extremely high magnetic fields, typically near 1 Tesla (10,000 Gauss) or more. MRI at extremely high fields (3T or more) provide exquisite spatial resolution. NMR at extremely low magnetic fields was speculated to have promise by Borodin in 1967 and later by Bene in 1980 and Bergmann in 1981. Seton reported the first SQUID-based NMR at low field in 1992 for room temperature samples at 10mT. Seton subsequently demonstrated low-field (LF) MRI at 10mT in 1997. McDermott, et al. reported the first "ultra-low" field NMR at measurement fields of a few microtesla in 2002 and MRI at measurement fields of ~100 microtesla. This early work led to several groups around the world to pursue both NMR and MRI applications at ULF. Not only does ULF avoid many problems encountered at high field (RF heating, field distortions, forces on ferromagnetic materials to name only a few), but it provides new information such as field-dependent relaxation times, extraordinary sensitivity to spin-spin coupling, among others. These differences are being exploited into a variety of applications from medicine to material detection to basic physics. This talk will review some of the applications being currently pursued in ULF-MRI and speculate about other possible applications this new technique may provide in the future. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Oral Presentation Topic: Instrumentation and Multi-modal Integrations: MEG, Low-field MRI,EEG, fMRI,TMS,NIRS Citation: Kraus, Jr. R (2010). Introduction to Ultra-Low Field (ULF) Magnetic Resonance Imaging (MRI) Applications. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00006 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 18 Mar 2010; Published Online: 18 Mar 2010. * Correspondence: Robert Kraus, Jr., Los Alamos National Laboratory, Los Alamos, United States, rkraus@lanl.gov Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Robert Kraus, Jr. Google Robert Kraus, Jr. Google Scholar Robert Kraus, Jr. PubMed Robert Kraus, Jr. Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Ultra-Low Field Magnetic Resonance Imaging of the Human Brain

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Surgical treatment of cerebral abscess with the use of a mobile ultralow-field MRI

Surgical intervention in cerebral abscess is indicated to confirm diagnosis, to identify pathogens for specific antibiotic therapy, or to reduce mass effect. Regarding long-term outcome, freehand or stereotactic aspiration are equally efficient compared to surgical resection. However, direct observation of relief of mass effect is not possible by either method. Six patients presenting with neurological symptoms and laboratory signs of infection and diagnosed with an intra-axial cystic lesion underwent frameless stereotactic aspiration of a cerebral abscess in our institution with the use of a mobile intraoperative magnetic resonance imaging (MRI) with a field strength of 0.15 T. Images were acquired before and during the procedure and used for neuronavigation. In all six cases, complete evacuation of the abscess with collapse of the cyst could be achieved and documented intraoperatively. No complications were observed. All patients showed clinical improvement postoperatively. We highlight the advantages of using a mobile intraoperative MRI unit with an illustrative case of a patient who had already undergone abscess evacuation without alleviation of symptoms before using intraoperative MRI. Finally, we discuss surgical treatment options of cerebral abscesses.

INTRAOPERATIVE NEUROPHYSIOLOGICAL MONITORING IN AN OPEN LOW-FIELD MAGNETIC RESONANCE IMAGING SYSTEM

The intraoperative combination of an open magnetic resonance imaging (MRI) system with neurophysiological localization and continuous monitoring techniques allows for the best available anatomic and physiological orientation as well as real-time functional monitoring. Methodological aspects and technical adaptations for this combination of methods and the experience in 29 patients with tumors in the central region are reported. MRI-compatible platinum/iridium electrodes for intraoperative neuromonitoring were attached to the patient's head. All other electrodes located outside the magnet were stainless steel needle-electrodes for recording of motor evoked potentials and for stimulating somatosensory evoked potentials. Intraoperative MRI was performed using a 0.15-T intraoperative magnetic resonance scanner (PoleStar N20; Medtronic Surgical Navigation Technologies, Louisville, KY). The calculated and measured values of the maximum induced magnetic field (2 x 10(-6) T), induced voltage (0.1 V), and force (0.01 N) by the static or changing magnetic field within all attached electrodes were negligible and proved the method's safety. In 29 patients, platinum/iridium electrodes with low susceptibility showed no interference with the imaging quality. Furthermore, neurophysiological monitoring could be performed with unaffected recording quality. Side effects (e.g., thermal induction) were not observed. Neurophysiological monitoring for evoked potentials and direct cortical stimulation can be performed with standard quality within a low-field intraoperative MRI system. Electrodes fixed to the head should be of low magnetic susceptibility to guarantee optimal imaging quality. The combined use of an open ultra low-field MRI system and intraoperative monitoring allows for resection control and continuous functional monitoring.

USEFULNESS OF INTRAOPERATIVE ULTRA LOW-FIELD MAGNETIC RESONANCE IMAGING IN GLIOMA SURGERY

The aim of this study was to demonstrate the usefulness of a mobile, intraoperative 0.15-T magnetic resonance imaging (MRI) scanner in glioma surgery. We analyzed our prospectively collected database of patients with glial tumors who underwent tumor resection with the use of an intraoperative ultra low-field MRI scanner (PoleStar N-20; Odin Medical Technologies, Yokneam, Israel/Medtronic, Louisville, CO). Sixty-three patients with World Health Organization Grade II to IV tumors were included in the study. All patients were subjected to postoperative 1.5-T imaging to confirm the extent of resection. Intraoperative image quality was sufficient for navigation and resection control in both high- and low-grade tumors. Primarily enhancing tumors were best detected on T1-weighted imaging, whereas fluid-attenuated inversion recovery sequences proved best for nonenhancing tumors. Intraoperative resection control led to further tumor resection in 12 (28.6%) of 42 patients with contrast-enhancing tumors and in 10 (47.6%) of 21 patients with noncontrast-enhancing tumors. In contrast-enhancing tumors, further resection led to an increased rate of complete tumor resection (71.2 versus 52.4%), and the surgical goal of gross total removal or subtotal resection was achieved in all cases (100.0%). In patients with noncontrast-enhancing tumors, the surgical goal was achieved in 19 (90.5%) of 21 cases, as intraoperative MRI findings were inconsistent with postoperative high-field imaging in 2 cases. The use of the PoleStar N-20 intraoperative ultra low-field MRI scanner helps to evaluate the extent of resection in glioma surgery. Further tumor resection after intraoperative scanning leads to an increased rate of complete tumor resection, especially in patients with contrast-enhancing tumors. However, in noncontrast- enhancing tumors, the intraoperative visualization of a complete resection seems less specific, when compared with postoperative 1.5-T MRI.

Overhauser–enhanced MRI

The low signal-to-noise ratio (SNR) found in ultralow field magnetic resonance imaging (MRI) may be increased using the Overhauser effect ( 1 Leunbach I. European Patent 0409292 A2 1994 Google Scholar , 2 Overhauser AW Polarization of nuclei in metals. Phys Rev. 1953; 92: 411-412 Crossref Scopus (1120) Google Scholar ) or other dynamic nuclear polarization (DNP) techniques ( 3 Planinšic G Grucker D Stepišnik J New method for contrast manipulation in DNP-enhanced MRI. Magn Reson Med. 1996; 35: 379-383 Crossref PubMed Scopus (1) Google Scholar ). The spin polarization, from an unpaired electron present in a contrast medium molecule, can be transferred to the protons of water and result in an enhanced nuclear magnetic resonance (NMR) water signal. The theoretical maximum available enhancement, if the electron spin transition in the contrast medium molecule is fully saturated, may be as high as 329. The theory for signal enhancement using this technique is described elsewhere ( 4 Ardenkjær-Larsen J-H EPR and DNP properties of certain novel single electron contrast agents intended for oximetrical imaging. J Magn Reson. 1998; 133: 1-12 Crossref PubMed Scopus (290) Google Scholar ).

Magnetic resonance imaging for the evaluation of patients with occult cervical spine injury.

Because it is often difficult to diagnose accurately the structurally intact cervical spine after acute trauma, a series of patients was evaluated with magnetic resonance (MR) imaging to assess its efficacy for the evaluation and clearance of the cervical spine in a trauma victim in the early posttrauma period. Ultralow-field MR imaging was used to evaluate 174 posttraumatic patients in whom physical findings indicated the potential for spine injury or minor radiographic findings indicated injury. This series includes only those patients who did not appear to harbor disruption of spinal integrity on the basis of a routine x-ray film. None had clinically obvious injury. Of the 174 patients, 62 (36%) had soft-tissue abnormalities identified by MR imaging, including disc interspace disruption in 27 patients (four with ventral and dorsal ligamentous injury, three with ventral ligamentous injury alone, 18 with dorsal ligamentous injury alone, and two without ventral or dorsal ligamentous injury). Isolated ligamentous injury was observed in 35 patients (eight with ventral and dorsal ligamentous injury, five with ventral ligamentous injury alone, and 22 with dorsal ligamentous injury alone). One patient underwent a surgical fusion procedure, 35 patients (including the one treated surgically) were placed in a cervical collar for at least 1 month, and 27 patients were placed in a thermoplastic Minerva jacket for at least 2 months. All had a satisfactory outcome without evidence of instability. The T2-weighted sagittal images were most useful in defining acute soft-tissue injury; axial images were of minimal assistance. Posttraumatic soft-tissue cervical spine injuries and disc herniations (most likely proexisting the trauma) are more common than expected. A negative MR image should be considered as confirmation of a negative or "cleared" subaxial cervical spine. Diagnostic and patient management algorithms may be appropriately tailored by this information. Thus, MR imaging is useful for early acute posttrauma assessment in a very select group of patients.

Skeletal muscle of patients with gyrate atrophy of the choroid and retina and hyperornithinaemia in ultralow-field magnetic resonance imaging and computed tomography.

Gyrate atrophy of the choroid and retina with hyperornithinaemia (GA), an autosomal recessive disease, affects skeletal muscle in addition to the eye. Muscle biopsy samples show prominent type 2 muscle fibre atrophy. Atrophic fibres also contain accumulations of tubular aggregates in electron microscopy. To evaluate skeletal muscle involvement in detail, the thigh muscles of 7 patients with GA were examined using semi-open conchotome muscle biopsies, computed tomography (CT) and ultralow-field magnetic resonance imaging (MRI) at 0.02 T. In MRI, the T1 and T2 proton relaxation times were measured. Type 2 muscle fibre atrophy was found in all biopsy samples (100%) and tubular aggregates in 6 of the 7 samples studied (87%). The CT density of the muscle tissue was increased in the only child of the study, decreased in 3 elderly subjects, and normal in the remaining 3 patients. Mean T1 relaxation times of the patients were decreased (135 +/- 5 ms) as compared to those of 6 healthy controls (157 +/- 12 ms) (p = 0.002). The T2 relaxation time was slightly increased (40 +/- 3 ms) as compared to the controls (35 +/- 7 ms; not significant, p = 0.3). Our findings suggest that the thigh muscles of the patients with GA universally show changes in CT and MRI studies, but relaxation time measurements gave little additional information on the muscle metabolism.

Ultra-low field MR imaging of hepatic hemangiomas (at 0.02 and 0.04 T)

Twelve patients with cavernous hemangiomas of the liver were studied with computed tomography (CT) and ultra-low field magnetic resonance imaging (MRI). Seven patients were examined at a field strength of 0.02 T and 5 patients at 0.04 T, while 3 patients were studied at both field strengths. On T2-weighted images all hemangiomas had the same characteristic appearance of a homogeneous high signal intensity that has been described at higher field strengths. Signal characteristics of the hemangiomas were the same at 0.02 and 0.04 T, but the higher field strength provided better signal-to-noise ( S N ) ratio and hence improved image quality. Homogeneous contrast enhancement was seen in three hemangiomas examined after intravenous administration of gadopentetate dimeglumine. Our results indicate that ultra-low field MRI can be useful in the differential diagnosis of hepatic hemangiomas.

Evaluation of syringomyelia and Chiari malformations using ultra-low magnetic resonance imaging

The accuracy of ultra-low field magnetic resonance imaging (MRI) compared to medium-field MRI in detecting syringomyelia and associated Chiari malformations is examined. In all cases the size of the syrinxes and the type and extent of the Chiari malformations was clearly shown at low-field MRI. The present spatial solution and high sensitivity allows for low-field imagers to localize even minor morphological changes of the spinal cord, brainstem, and cerebellum.

Detection of Soft-Tissue and Skeletal Infections with Ultra Low-Field (0.02 T) Mr Imaging

To evaluate the use of ultra low-field (0.02 T) magnetic resonance (MR) imaging in the diagnosis of musculoskeletal infection, MR examinations with T2 weighted sequences were performed in 61 patients thought to be suffering from one of four major diagnostic categories: Soft-tissue abscesses (n = 22), osteomyelitis (n = 21), septic arthritis (n = 9) and spondylitis (n = 9). Infection was confirmed for 37 of these 61 patients. The verified abscesses, arthritis, spondylitis and acute osteomyelitis could be detected by 0.02 T MR. The sensitivity was poor in cases of chronic osteomyelitis. There was one false positive finding in a patient with a possible soft tissue infection. The 0.02 T MR examination failed four times. Two patients were too heavy and another 2 patients had magnetic material in or near the scanning field. Compared with computed tomography and isotope scanning, 0.02 T MR proved a little more informative, but without any statistical significance.

Evaluation of cervical disc degeneration with ultralow field MRI and discography. An experimental study on cadavers.

The purpose of this study was to test the value of low-field magnetic resonance imaging (MRI) and discography in visualizing disc degeneration of the cervical spine. Plain roentgenograms, MR images, discograms, and macroanatomic appearance of the cervical spines of ten cadavers were compared. At levels C4-5-C7-T1, general disc degeneration seen in discography correlated well with macroanatomy (weighted kappa (Kw) = 0.77). The nuclear shape in MRI showed a weak correlation with macroanatomy (Kw = 0.31) and general disc degeneration in discography (Kw = 0.32), whereas nuclear intensity in MRI underestimated such changes. Magnetic resonance imaging showed posterior extension of the nucleus in most cases where moderate or severe leaking was seen in discography. The latter phenomenon represents an increase to our information on structural changes not available by any other noninvasive and nonirradiative method of examination.

Otoneurological and ultra low field MRI findings in multiple sclerosis patients.

Otoneurological and ultra low field MRI findings in multiple sclerosis patients: 22 patients suffering from multiple sclerosis (MS) underwent thorough neurological and otological examination, extensive ENG testing and Magnetic Resonance Imaging (MRI) examination of the central nervous system. All patients fulfilled the Schumacher criteria for a diagnosis of definitive MS. 20 of the patients had been included in previous otoneurological studies three to five years ago. The general disability assessed according to Hyllested's scale was: Class 1-7, Class 2-4, Class 3-6, Class 4-3, Class 5-2 patients. Thus 11 patients had none or only slight disability. Nevertheless, all patients showed abnormal findings when classified according to the Kurtzke disability scale, which reflects the involvement of separate neuronal entities. The ENG examination revealed abnormal findings in all patients. The most common abnormalities found were as follows: abnormal pendular test 19, ocular fixation index 18, optokinetic nystagmus 14, saccadic eye movements 14 and spontaneous nystagmus 12. 14 patients had uni- or bilateral abnormally slow adduction movements in the saccadic test consistent with internuclear ophthalmoplegia (INO), which is caused by a lesion of the brain stem. MRI examination of the 21 patients studied revealed abnormal findings consistent with MS in sixteen cases. The lesions were unilateral in 5 and bilateral in 11 patients. The most common location for these abnormal findings consistent with MS plaques were in the white matter around the lateral ventricles. Plaques in the brain stem and/or cerebellum were found in only two cases despite numerous clinical and otoneurological findings that indicated the presence of functional lesions in these areas.