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Journal of Magnetic Resonance (San... Jul 2012This work describes our first efforts to implement SWIFT (SWeep Imaging with Fourier Transformation) in continuous mode for imaging and spectroscopy. We connected a...
This work describes our first efforts to implement SWIFT (SWeep Imaging with Fourier Transformation) in continuous mode for imaging and spectroscopy. We connected a standard quadrature hybrid with a quad coil and acquired NMR signal during continuous radiofrequency excitation. We utilized a chirped radiofrequency pulse to minimize the instantaneous radiofrequency field during excitation of the spin system for the target flip angle and bandwidth. Due to the complete absence of "dead time", continuous SWIFT has the potential to extend applications of MRI and spectroscopy in studies of spin systems having extremely fast relaxation or broad chemical shift distributions beyond the range of existing MRI sequences.
Topics: Equipment Design; Equipment Failure Analysis; Magnetic Resonance Imaging; Magnetic Resonance Spectroscopy; Transducers
PubMed: 22683578
DOI: 10.1016/j.jmr.2012.04.016 -
Biosensors & Bioelectronics May 2023Micro-coil magnetic stimulation of brain tissue presents new challenges for MEMS micro-coil probe fabrication. The main challenges are threefold; (i) low coil resistance...
Micro-coil magnetic stimulation of brain tissue presents new challenges for MEMS micro-coil probe fabrication. The main challenges are threefold; (i) low coil resistance for high power efficiency, (ii) low leak current from the probe into the in vitro experimental set-up, (iii) adaptive MEMS process technology because of the dynamic research area, which requires agile design changes. Taking on these challenges, we present a MEMS fabrication process that has three main features; (i) multilayer resist lift-off process to pattern up to 1800-nm-thick metal films, and special care is taken to obtain high conductivity thin-films by physical vapor deposition, and (ii) all micro-coil Al wires are encapsulated in at least 200 nm of ALD alumina and 6-μm-thick parylene C such the leak resistance is high (>210 GΩ), (iii) combining a multi-step DRIE process and maskless photolithography for adaptive design and device fabrication. The entire process requires four lithography steps. Because we avoided SOI wafers and lithography mask fabrication, the design-to-device time is shortened significantly. The resulting probes are 4-mm-long, 60-μm-thick, and down to 150 μm-wide. Selected MEMS coil devices were validated in vivo using mice and compared to previous work.
Topics: Animals; Mice; Micro-Electrical-Mechanical Systems; Biosensing Techniques; Metals; Brain; Electric Conductivity
PubMed: 36805270
DOI: 10.1016/j.bios.2023.115143 -
JACC. Clinical Electrophysiology Jan 2017The purpose of this investigation was to conduct a meta-analysis of studies comparing defibrillation threshold (DFT) and outcomes with single-coil and dual-coil... (Comparative Study)
Comparative Study Meta-Analysis
OBJECTIVES
The purpose of this investigation was to conduct a meta-analysis of studies comparing defibrillation threshold (DFT) and outcomes with single-coil and dual-coil implantable cardioverter-defibrillator (ICD) systems.
BACKGROUND
Use of dual-coil rather than single-coil defibrillator leads may lower the DFT with a transvenous ICD system; however, dual-coil ICDs may have higher lead-related complications.
METHODS
Sixteen studies, each with more than 10 human subjects, that compared single-coil and dual-coil ICD systems were included for the final analysis after a comprehensive publication search using predefined search terms and additional search from cross-references. A test of heterogeneity, pooling, and meta-analysis of the data from the studies were performed using R statistical software. A random effects model was used for meta-analysis.
RESULTS
Data pooled from 14 studies analyzed for difference in DFT showed an estimated difference in mean DFTs between single-coil and dual-coil ICDs of 0.81 J (95% confidence interval [CI]: 0.31 to 1.30 J), thus favoring dual-coil ICDs. However, pooled data from 5 studies revealed no difference in first-shock efficacy for dual-coil ICDs compared with single-coil ICDs (estimated overall odds ratio: 0.94; 95% CI: 0.49 to 1.78; p = 0.85). The all-cause mortality rate analyzed from 4 studies was lower in patients with single-coil ICDs (estimated hazard ratio: 0.91; 95% CI: 0.83 to 0.99).
CONCLUSIONS
There was a marginal difference in the defibrillation threshold of transvenous ICDs between single-coil and dual-coil lead systems. However, first-shock efficacy was no different between the 2 groups, and patients with single-coil ICDs had favorable all-cause mortality rates on the basis of data from nonrandomized studies. Potential risks and benefits of single-coil and dual-coil ICD leads should be carefully weighed.
Topics: Death, Sudden, Cardiac; Defibrillators, Implantable; Electric Countershock; Equipment Design; Humans; Proportional Hazards Models; Risk Factors; Treatment Outcome
PubMed: 29759689
DOI: 10.1016/j.jacep.2016.06.007 -
Canadian Respiratory Journal 2016There has been a surge of interest in endoscopic lung volume reduction (ELVR) strategies for advanced COPD. Valve implants, coil implants, biological LVR (BioLVR),... (Review)
Review
There has been a surge of interest in endoscopic lung volume reduction (ELVR) strategies for advanced COPD. Valve implants, coil implants, biological LVR (BioLVR), bronchial thermal vapour ablation, and airway stents are used to induce lung deflation with the ultimate goal of improving respiratory mechanics and chronic dyspnea. Patients presenting with severe air trapping (e.g., inspiratory capacity/total lung capacity (TLC) < 25%, residual volume > 225% predicted) and thoracic hyperinflation (TLC > 150% predicted) have the greatest potential to derive benefit from ELVR procedures. Pre-LVRS or ELVR assessment should ideally include cardiological evaluation, high resolution CT scan, ventilation and perfusion scintigraphy, full pulmonary function tests, and cardiopulmonary exercise testing. ELVR procedures are currently available in selected Canadian research centers as part of ethically approved clinical trials. If a decision is made to offer an ELVR procedure, one-way valves are the first option in the presence of complete lobar exclusion and no significant collateral ventilation. When the fissure is not complete, when collateral ventilation is evident in heterogeneous emphysema or when emphysema is homogeneous, coil implants or BioLVR (in that order) are the next logical alternatives.
Topics: Endoscopy; Humans; Prostheses and Implants; Pulmonary Disease, Chronic Obstructive
PubMed: 27445557
DOI: 10.1155/2016/6462352 -
Canadian Medical Association Journal Feb 1966Intrauterine devices have been used for over 2000 years. The modern devices (loop, coil and bow) were developed in 1959. The data on 11,222 first insertions from 43...
Intrauterine devices have been used for over 2000 years. The modern devices (loop, coil and bow) were developed in 1959. The data on 11,222 first insertions from 43 contributing institutions were analyzed by the National Committee on Maternal Health. With the intrauterine loop, expulsions occurred in less than 10% of patients, removals for medical and personal reasons in a further 15%, and pelvic infections in 1.7% during the first year following insertion. Pregnancies occurred during the first year in 2.4% of patients fitted with a loop. Typical of the modern intrauterine devices, the loop is highly effective, readily accepted, and well tolerated by approximately 75% of patients.
Topics: Contraceptive Devices; Female; Humans
PubMed: 5902705
DOI: No ID Found -
Journal of Vascular Surgery Jan 2013Malposition, embolization, fracture, and migration of endovascular devices are unfortunate consequences of endovascular intervention and will be encountered at some... (Review)
Review
Malposition, embolization, fracture, and migration of endovascular devices are unfortunate consequences of endovascular intervention and will be encountered at some point by nearly every practitioner. The existing literature on foreign body retrieval consists of large single-institution series and case reports. We provide an overview of this recent literature, clarifying what devices are being lost, what symptoms occur as a result, and how retrieval is being performed. We have identified all case series and case reports since the year 2000, summarized the results, and made some general observations and recommendations that may be useful to the practitioner faced with the prospect of retrieving a fractured medical device, malpositioned coil, or migrated inferior vena cava filter.
Topics: Blood Vessel Prosthesis; Blood Vessel Prosthesis Implantation; Device Removal; Endovascular Procedures; Foreign Bodies; Foreign-Body Migration; Humans; Iatrogenic Disease; Prosthesis Failure; Reoperation; Stents
PubMed: 23140798
DOI: 10.1016/j.jvs.2012.09.002 -
Hellenic Journal of Cardiology : HJC =... 2017Although the risk of MRI scanning on patients with conventional devices is lower than initially thought, the patient's safety can only be guaranteed when using... (Review)
Review
Although the risk of MRI scanning on patients with conventional devices is lower than initially thought, the patient's safety can only be guaranteed when using MRI-conditional devices. The most important modifications in MRI-conditional devices include a) Reduction in ferromagnetic components to reduce magnetic attraction and susceptibility artifacts; b) Replacement of the reed switch by a Hall sensor in order to avoid unpredictable reed switch behavior; c) Lead coil design to minimize lead heating and electrical current induction; d) Filter circuitry to prevent damage to the internal power supply; and e) Dedicated pacemaker programming to prevent inappropriate pacemaker inhibition and competing rhythms. Although many companies claim to have MRI-conditional devices, adoption in clinical practice is limited because a) Not all companies have MRI-conditional devices approved for both 1.5 and 3T; b) Not all companies offer the option of unlimited MRI scanning (without an exclusion zone in the thorax); c) Certain companies allow only a 30-min MRI scanning and only in afebrile patients; and d) Despite having MRI-conditional pacemakers, certain companies do not have MRI-conditional defibrillators and CRT systems. It is clear that this new technology opens the door for MRI to a growing number of patients; however, the widespread adoption of MRI-conditional devices will depend on real-life issues, such as cost, clinical indications for such a device and the permanent education of health care professionals.
Topics: Equipment Design; Equipment Failure; Equipment Safety; Health Personnel; Humans; Magnetic Resonance Imaging; Pacemaker, Artificial; Patient Safety; Risk
PubMed: 28089649
DOI: 10.1016/j.hjc.2017.01.001 -
Physics in Medicine and Biology Sep 2020Over the last 30 years, there have been dramatic changes in phased array coil technology leading to increasing channel density and parallel imaging functionality....
Over the last 30 years, there have been dramatic changes in phased array coil technology leading to increasing channel density and parallel imaging functionality. Current receiver array coils are rigid and often mismatched to patient's size. Recently there has been a move towards flexible coil technology, which is more conformal to the human anatomy. Despite the advances of so-called flexible surface coil arrays, these coils are still relatively rigid and limited in terms of design conformability, compromising signal-to-noise ratio (SNR) for flexibility, and are not designed for optimum parallel imaging performance. The purpose of this study is to report on the development and characterization of a 15-channel flexible foot and ankle coil, rapidly designed and constructed using highly decoupled radio-frequency (RF) coil elements. Coil performance was evaluated by performing SNR and g-factor measurements. In vivo testing was performed in a healthy volunteer using both the 15-channel coil and a commercially available 8-channel foot coil. The highly decoupled elements used in this design allow for extremely rapid development and prototyping of application-specific coils for different patient sizes (adult vs child) with minimal additional design consideration in terms of coil overlap and geometry. Image quality was comparable to a commercially available RF coil.
Topics: Adult; Child; Equipment Design; Healthy Volunteers; Humans; Magnetic Resonance Imaging; Phantoms, Imaging; Signal-To-Noise Ratio
PubMed: 32975219
DOI: 10.1088/1361-6560/abaffb -
Physical and Engineering Sciences in... Jun 2022Magnetic resonance-guided radiotherapy technology is relatively new and commissioning publications, quality assurance (QA) protocols and commercial products are limited....
Magnetic resonance-guided radiotherapy technology is relatively new and commissioning publications, quality assurance (QA) protocols and commercial products are limited. This work provides guidance for implementation measurements that may be performed on the Elekta Unity MR-Linac (Elekta, Stockholm, Sweden). Adaptations of vendor supplied phantoms facilitated determination of gantry angle accuracy and linac isocentre, whereas in-house developed phantoms were used for end-to-end testing and anterior coil attenuation measurements. Third-party devices were used for measuring beam quality, reference dosimetry and during treatment plan commissioning; however, due to several challenges, variations on standard techniques were required. Gantry angle accuracy was within 0.1°, confirmed with pixel intensity profiles, and MV isocentre diameter was < 0.5 mm. Anterior coil attenuation was approximately 0.6%. Beam quality as determined by TPR was 0.705 ± 0.001, in agreement with treatment planning system (TPS) calculations, and gamma comparison against the TPS for a 22.0 × 22.0 cm field was above 95.0% (2.0%, 2.0 mm). Machine output was 1.000 ± 0.002 Gy per 100 MU, depth 5.0 cm. During treatment plan commissioning, sub-standard results indicated issues with machine behaviour. Once rectified, gamma comparisons were above 95.0% (2.0%, 2.0 mm). Centres which may not have access to specialized equipment can use in-house developed phantoms, or adapt those supplied by the vendor, to perform commissioning work and confirm operation of the MRL within published tolerances. The plan QA techniques used in this work can highlight issues with machine behaviour when appropriate gamma criteria are set.
Topics: Gamma Rays; Particle Accelerators; Phantoms, Imaging; Radiometry; Radiotherapy, Image-Guided
PubMed: 35235188
DOI: 10.1007/s13246-022-01113-7 -
Magma (New York, N.Y.) Jul 2023Low-field MRI systems are expected to cause less RF heating in conventional interventional devices due to lower Larmor frequency. We systematically evaluate RF-induced...
OBJECTIVE
Low-field MRI systems are expected to cause less RF heating in conventional interventional devices due to lower Larmor frequency. We systematically evaluate RF-induced heating of commonly used intravascular devices at the Larmor frequency of a 0.55 T system (23.66 MHz) with a focus on the effect of patient size, target organ, and device position on maximum temperature rise.
MATERIALS AND METHODS
To assess RF-induced heating, high-resolution measurements of the electric field, temperature, and transfer function were combined. Realistic device trajectories were derived from vascular models to evaluate the variation of the temperature increase as a function of the device trajectory. At a low-field RF test bench, the effects of patient size and positioning, target organ (liver and heart) and body coil type were measured for six commonly used interventional devices (two guidewires, two catheters, an applicator and a biopsy needle).
RESULTS
Electric field mapping shows that the hotspots are not necessarily localized at the device tip. Of all procedures, the liver catheterizations showed the lowest heating, and a modification of the transmit body coil could further reduce the temperature increase. For common commercial needles no significant heating was measured at the needle tip. Comparable local SAR values were found in the temperature measurements and the TF-based calculations.
CONCLUSION
At low fields, interventions with shorter insertion lengths such as hepatic catheterizations result in less RF-induced heating than coronary interventions. The maximum temperature increase depends on body coil design.
Topics: Humans; Heating; Radio Waves; Magnetic Resonance Imaging; Temperature; Phantoms, Imaging; Hot Temperature
PubMed: 37195365
DOI: 10.1007/s10334-023-01099-7