RF heating of deep brain stimulation implants in open-bore vertical MRI systems: A simulation study with realistic device configurations.
Ontology highlight
ABSTRACT: Purpose
Patients with deep brain stimulation (DBS) implants benefit highly from MRI, however, access to MRI is restricted for these patients because of safety hazards associated with RF heating of the implant. To date, all MRI studies on RF heating of medical implants have been performed in horizontal closed-bore systems. Vertical MRI scanners have a fundamentally different distribution of electric and magnetic fields and are now available at 1.2T, capable of high-resolution structural and functional MRI. This work presents the first simulation study of RF heating of DBS implants in high-field vertical scanners.Methods
We performed finite element electromagnetic simulations to calculate specific absorption rate (SAR) at tips of DBS leads during MRI in a commercially available 1.2T vertical coil compared to a 1.5T horizontal scanner. Both isolated leads and fully implanted systems were included.Results
We found 10- to 30-fold reduction in SAR implication at tips of isolated DBS leads, and up to 19-fold SAR reduction at tips of leads in fully implanted systems in vertical coils compared to horizontal birdcage coils.Conclusions
If confirmed in larger patient cohorts and verified experimentally, this result can open the door to plethora of structural and functional MRI applications to guide, interpret, and advance DBS therapy.
SUBMITTER: Golestanirad L
PROVIDER: S-EPMC7047541 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:Patients who have implanted medical devices with long conductive leads are often restricted from receiving MRI scans due to the danger of RF-induced heating near the lead tips. Phantom studies have shown that this heating varies significantly on a case-by-case basis, indicating that many patients with implanted devices can receive clinically useful MRI scans without harm. However, the difficulty of predicting RF-induced lead tip heating prior to scanning prevents numerous implant recipients from being scanned. Here, we demonstrate that thermo-acoustic ultrasound (TAUS) has the potential to be utilized for a pre-scan procedure assessing the risk of RF-induced lead tip heating in MRI. A system was developed to detect TAUS signals by four different TAUS acquisition methods. We then integrated this system with an MRI scanner and detected a peak in RF power absorption near the tip of a model lead when transmitting from the scanner's body coil. We also developed and experimentally validated simulations to characterize the thermo-acoustic signal generated near lead tips. These results indicate that TAUS is a promising method for assessing RF implant safety, and with further development, a TAUS pre-scan could allow many more patients to have access to MRI scans of significant clinical value.
| S-EPMC5942199 | biostudies-literature
Project description:Access to MRI is limited for patients with deep brain stimulation (DBS) implants due to safety hazards, including radiofrequency (RF) heating of tissue surrounding the leads. Computational models provide an exquisite tool to explore the multi-variate problem of RF heating and help better understand the interaction of electromagnetic fields and biological tissues. This paper presents a computational approach to assess RF-induced heating, in terms of specific absorption rate (SAR) in the tissue, around the tip of bilateral DBS leads during MRI at 64MHz/1.5 T and 127 MHz/3T. Patient-specific realistic lead models were constructed from post-operative CT images of nine patients operated for sub-thalamic nucleus DBS. Finite element method was applied to calculate the SAR at the tip of left and right DBS contact electrodes. Both transmit head coils and transmit body coils were analyzed. We found a substantial difference between the SAR and temperature rise at the tip of right and left DBS leads, with the lead contralateral to the implanted pulse generator (IPG) exhibiting up to 7 times higher SAR in simulations, and up to 10 times higher temperature rise during measurements. The orientation of incident electric field with respect to lead trajectories was explored and a metric to predict local SAR amplification was introduced. Modification of the lead trajectory was shown to substantially reduce the heating in phantom experiments using both conductive wires and commercially available DBS leads. Finally, the surgical feasibility of implementing the modified trajectories was demonstrated in a patient operated for bilateral DBS.
| S-EPMC6475594 | biostudies-literature
Project description:This study describes the MRI-related radio frequency (RF) safety evaluation of breast tissue expander devices to establish safety criteria. Numerical simulations and experimental measurements were performed at 64 MHz with a gel phantom containing a breast expander. Additionally, computational modeling was performed (64 and 128 MHz) with an adult female model, containing a virtually implanted breast tissue expander device for four imaging landmark positions. The presence of the breast tissue expander device led to significant alterations in specific absorption rate (SAR) and|B1+|distributions. The main source of SAR alterations with the use of the breast expander device was the saline-filled pouch of the expander. Conversely, the variation of RF magnetic field (B1+) was mainly caused by the metallic port. The measured values of electric field magnitude did not increase significantly due to the introduction of the expander device. The maximum 1g- or 10g-averaged SAR values in tissues near the implant were lower than those expected in other regions of the patient body with normalization of both|B1+|equal to 2 μT at the coil isocenter and whole body averaged SAR equal to 4W/kg.
| S-EPMC5814144 | biostudies-other
Project description:BackgroundMRI induced heating on PM leads is a very complex issue. The widely varying results described in literature suggest that there are many factors that influence the degree of heating and that not always are adequately addressed by existing testing methods.MethodsWe present a wide database of experimental measurements of the heating of metallic wires and PM leads in a 1.5 T RF coil. The aim of these measurements is to systematically quantify the contribution of some potential factors involved in the MRI induced heating: the length and the geometric structure of the lead; the implant location within the body and the lead path; the shape of the phantom used to simulate the human trunk and its relative position inside the RF coil.ResultsWe found that the several factors are the primary influence on heating at the tip. Closer locations of the leads to the edge of the phantom and to the edge of the coil produce maximum heating. The lead length is the other crucial factor, whereas the implant area does not seem to have a major role in the induced temperature increase. Also the lead structure and the geometry of the phantom revealed to be elements that can significantly modify the amount of heating.ConclusionOur findings highlight the factors that have significant effects on MRI induced heating of implanted wires and leads. These factors must be taken into account by those who plan to study or model MRI heating of implants. Also our data should help those who wish to develop guidelines for defining safe medical implants for MRI patients. In addition, our database of the entire set of measurements can help those who wish to validate their numerical models of implants that may be exposed to MRI systems.
| S-EPMC2292730 | biostudies-literature
Project description:PurposeSimultaneous multi-slice techniques are reliant on multiband RF pulses, for which conventional design strategies result in long pulse durations, lengthening echo-times so lowering SNR for spin-echo imaging, and lengthening repetition times for gradient echo sequences. Pulse durations can be reduced with advanced RF pulse design methods that use time-variable selection gradients. However, the ability of gradient systems to reproduce fast switching pulses is often limited and can lead to image artifacts when ignored. We propose a time-efficient pulse design method that inherently produces gradient waveforms with lower temporal bandwidth.MethodsEfficient multiband RF pulses with time-variable gradients were designed using time-optimal VERSE. Using VERSE directly on multiband pulses leads to gradient waveforms with high temporal bandwidth, whereas VERSE applied first to singleband RF pulses and then modulated to make them multiband, significantly reduces this. The relative performance of these approaches was compared using simulation and experimental measurements.ResultsApplying VERSE before multiband modulation was successful at removing out-of-band slice distortion. This effectively removes the need for high frequency modulation in the gradient waveform while preserving the benefit of time-efficiency inherited from VERSE.ConclusionWe propose a time-efficient RF pulse design that produces gradient pulses with lower temporal bandwidth, reducing image artifacts associated with finite temporal bandwidth of gradient systems.
| S-EPMC6334175 | biostudies-literature
Project description:This paper presents Contextual Fibre Growth (ConFiG), an approach to generate white matter numerical phantoms by mimicking natural fibre genesis. ConFiG grows fibres one-by-one, following simple rules motivated by real axonal guidance mechanisms. These simple rules enable ConFiG to generate phantoms with tuneable microstructural features by growing fibres while attempting to meet morphological targets such as user-specified density and orientation distribution. We compare ConFiG to the state-of-the-art approach based on packing fibres together by generating phantoms in a range of fibre configurations including crossing fibre bundles and orientation dispersion. Results demonstrate that ConFiG produces phantoms with up to 20% higher densities than the state-of-the-art, particularly in complex configurations with crossing fibres. We additionally show that the microstructural morphology of ConFiG phantoms is comparable to real tissue, producing diameter and orientation distributions close to electron microscopy estimates from real tissue as well as capturing complex fibre cross sections. Signals simulated from ConFiG phantoms match real diffusion MRI data well, showing that ConFiG phantoms can be used to generate realistic diffusion MRI data. This demonstrates the feasibility of ConFiG to generate realistic synthetic diffusion MRI data for developing and validating microstructure modelling approaches.
| S-EPMC7903162 | biostudies-literature
Project description:PURPOSE:To facilitate assessment of RF power deposition and temperature rise within the breast, we present a method to seamlessly join heterogeneous breast models with standard whole-body models and demonstrate simulations at 7 T. METHODS:Finite-difference time-domain electromagnetic and bioheat simulations are performed to analyze the specific absorption rate (SAR) and temperature rise distributions in 36 Breast Imaging Reporting and Data System (BI-RADS) categorized breast models fused to 2 female whole-body models while transmitting from a 7T breast volume coil. The breast models are uncompressed in the prone position and feature heterogeneous tissue contents; fusion with human models uses affine transformation and the level-set method. RESULTS:The fusion method produces a continuous transient from the chest region to the posterior portion of breast models while preserving the original volume and shape of breast models. Simulation results of both Ella and Hanako models indicate that the maximum local SAR, partial body SAR, and local tissue temperature rise are positively correlated with both breast density and the highest BI-RADS density classification. Additionally, maximum local tissue temperature rise is positively correlated with maximum 10-g SAR values. CONCLUSION:Fibroglandular tissue content plays an important role in the distribution of SAR and temperature rise within breast tissue. The combined body-breast models preserve the integrity of breast models while concurrently exhibiting the loading of whole-body human models. The procedures presented in this simulation study facilitate safety assessments for breast MRI across the population at both clinical and ultrahigh field strengths.
| S-EPMC6380517 | biostudies-literature
Project description:PurposeAnalytical phantoms have closed form Fourier transform expressions and are used to simulate MRI acquisitions. Existing three-dimensional (3D) analytical phantoms are unable to accurately model shapes of biomedical interest. The goal of this study was to demonstrate that polyhedral analytical phantoms have closed form Fourier transform expressions and can accurately represent 3D biomedical shapes.MethodsThe Fourier transform of a polyhedron was implemented and its accuracy in representing faceted and smooth surfaces was characterized. Realistic anthropomorphic polyhedral brain and torso phantoms were constructed and their use in simulated 3D and two-dimensional (2D) MRI acquisitions was described.ResultsUsing polyhedra, the Fourier transform of faceted shapes can be computed to within machine precision. Smooth surfaces can be approximated with increasing accuracy by increasing the number of facets in the polyhedron; the additional accumulated numerical imprecision of the Fourier transform of polyhedra with many faces remained small. Simulations of 3D and 2D brain and 2D torso cine acquisitions produced realistic reconstructions free of high frequency edge aliasing compared with equivalent voxelized/rasterized phantoms.ConclusionAnalytical polyhedral phantoms are easy to construct and can accurately simulate shapes of biomedical interest. Magn Reson Med 76:663-678, 2016. © 2015 Wiley Periodicals, Inc.
| S-EPMC4837112 | biostudies-literature
Project description:Electron heating is a fundamental and multidisciplinary phenomenon in partially ionized gases, from the planet's ionosphere to laboratory-scale plasmas. Plasmas produced at ambient or reduced pressures have recently shown potential for scientific and industrial applications. However, electron heating, which is strongly coupled to the physicochemical properties of these plasmas, has been poorly understood. We experimentally found the rapid structural transition from non-local to local electron heating in collisional radio-frequency discharges at atmospheric-to-subatmospheric pressures. As the gas pressure decreased from 760 to 200 Torr, the time-averaged electron density increased from 1.3 × 1012 to 1.3 × 1013 cm-3, and the electron temperature decreased from 2.5 to 1.1 eV at the maximum allowable discharge current in the abnormal α-mode in the plasma bulk. The spatiotemporal evolution of the electron temperature clearly shows that the electron temperature increases uniformly throughout the bulk plasma region during sheath expansion and collapse at 760 Torr, but the electron heating weakens with sheath collapse as the gas pressure decreases.
| S-EPMC6033924 | biostudies-literature
Project description:BackgroundMicroarray technologies have become common tools in biological research. As a result, a need for effective computational methods for data analysis has emerged. Numerous different algorithms have been proposed for analyzing the data. However, an objective evaluation of the proposed algorithms is not possible due to the lack of biological ground truth information. To overcome this fundamental problem, the use of simulated microarray data for algorithm validation has been proposed.ResultsWe present a microarray simulation model which can be used to validate different kinds of data analysis algorithms. The proposed model is unique in the sense that it includes all the steps that affect the quality of real microarray data. These steps include the simulation of biological ground truth data, applying biological and measurement technology specific error models, and finally simulating the microarray slide manufacturing and hybridization. After all these steps are taken into account, the simulated data has realistic biological and statistical characteristics. The applicability of the proposed model is demonstrated by several examples.ConclusionThe proposed microarray simulation model is modular and can be used in different kinds of applications. It includes several error models that have been proposed earlier and it can be used with different types of input data. The model can be used to simulate both spotted two-channel and oligonucleotide based single-channel microarrays. All this makes the model a valuable tool for example in validation of data analysis algorithms.
| S-EPMC1574357 | biostudies-literature