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To propose and validate a variation of the classic techniques for the estimation of the transfer function (TF) of a real pacemaker (PM) lead. The TF of three commercially available PM leads was measured by combining data from experimental measurements and numerical simulations generated by three sources: a) the experimental local SAR at the tip of the PM lead (single measurement point) exposed to a 64 MHz birdcage body coil; b) the experimental current distribution along the PM lead, obtained by directly injecting a 64 MHz signal inside the lead; c) the electric field (E-field) simulated with a computational model of the 64 MHz birdcage body coil adopted in the experimental measurement performed in a). The effect of the lead trajectory on the estimation of the TF was also estimated. The proposed methodology was validated by comparing the SAR obtained from the PM lead TF with experimental measurements: a maximum difference of 2.2 dB was observed. It was also shown that the estimation of the TF cannot be considered independent with the lead trajectory: a variation of the SAR estimation up to 3.4 dB was observed. For the three PM lead tested, the error in the SAR estimation is within the uncertainty level of SAR measurements (± 2 dB). Additionally, the estimation of the TF using the reciprocity principle is influenced by the particular lead trajectory adopted, even if the consequent variability in the SAR estimation is still close to the uncertainty level of SAR measurements.

A fusion-fission hybrid (FFH) reactor is a complex machine, which includes a tokamak fusion neutron source and two blankets: the tritium regeneration and the actinide burner zones. These three systems need their own diagnostics and controls. Problems associated with the implementation and integration of control systems call for a simplified technology. In this paper, the criteria determining the diagnostics needs of FFH reactors are reviewed bearing in mind the requirement that the measurements systems should be simple and robust, and their number be limited, considering the space occupied by the blankets. The diagnostics for the tokamak neutron source, including the machine protection and burn control are among the basic equipment. As the fusion and fission blankets can be integrated in a single subsystem their diagnostics must be conceived as an integrated package that includes the means for measuring isotope content, neutron multiplication and effective reactivity of the fission blanket, as well as tritium regeneration in the breeding blanket. The most recent technological developments the field of neutron spectroscopy for fusion and fission blankets are presented, including the diamond and self-powered neutron detectors technology.

Heating induced by radio frequency (RF) energy may be generated in tissues near active or passive devices implanted in a patient undergoing magnetic resonance imaging (MRI) examination. Recent normative documents for the assessment of RF energy-induced heating state that the net temperature increase (Δ T ) depends on the physical characteristics of the surrounding tissues and on the squared incident tangential electric field ( E tan( l )). The documents do not address the possible effect of multiple scattering from surrounding reflective interfaces, such as, for example, a plastic enclosure of the container (“phantom”) used for implant testing. In our study, we investigated the effect of multiple scattering on Δ T / E tan( l )2 in relation to the implant location when tested in a phantom filled with a gel. The test implant was a titanium alloy rod of 100 mm in length, used as a reference implant in standard documents. The applied RF was in the 128 MHz band, corresponding to the RF generated in a 3 T MRI system. Both the numerical model and measurement provided substantial evidence that Δ T / E tan( l )2 depends on the distance between the rod and phantom box enclosure. In the numerical model, up to 38% variation of this quantity was observed, suggesting that location of the implant with respect to the phantom enclosure would need to be included as a parameter when evaluating RF-induced heating of implants.

Since the 2018 IAEA FEC Conference, FTU operations have been devoted to several experiments covering a large range of topics, from the investigation of the behaviour of a liquid tin limiter to the runaway electrons mitigation and control and to the stabilization of tearing modes by electron cyclotron heating and by pellet injection. Other experiments have involved the spectroscopy of heavy metal ions, the electron density peaking in helium doped plasmas, the electron cyclotron assisted start-up and the electron temperature measurements in high temperature plasmas. The effectiveness of the laser induced breakdown spectroscopy system has been demonstrated and the new capabilities of the runaway electron imaging spectrometry system for in-flight runaways studies have been explored. Finally, a high resolution saddle coil array for MHD analysis and UV and SXR diamond detectors have been successfully tested on different plasma scenarios.

This study investigated the radiofrequency-induced heating due to interventional catheters at 1,5 T magnetic resonance image (MRI) based on a combined modeling and experimental method. Two types of interventional catheters, a “single wire” and a “dual wire” catheter, were studied. They were modeled inside a high-resolution anatomical human model along four trajectories. In total, 4 insertion depths, from 17.5 to 70 cm, and 13 scanning landmarks were studied to cover various clinically relevant scenarios. The computational model for the catheters was based on a transfer function approach, measured using the reciprocity theorem. Results of the study showed that the upper limit of the temperature rises near the catheter tip may reach up to 100 °C when scaled to the 2 W/kg average whole-body specific absorption rate (SAR). The computational model was validated experimentally by measuring the induced heating near the catheter in a gel-filled phantom. The data showed a good agreement between the result obtained by the combined method and the direct measurement method with a difference of less than 1 °C. The results suggest that the proposed combined approach, based on the transfer function method, may accurately and efficiently predict the temperature rises near ablation catheters at 1,5 T MRI exposure.

Social distancing and face masks are considered the best tools to prevent COVID-19 spread despite an impact on communication, hearing perception and quality of life. An observational study was performed among a population of normal hearing subjects (NHS) referring to Department of Otorhinolaryngology. Data were collected with a self-administered online questionnaire which included the Italian SF-36 Health Survey Questionnaire referred to face masks use, the Hamilton Rating Scale for Anxiety (HAM-A) and four questions focussed on communication difficulties due to facial masks use and social distancing (COVID-19 restrictions questions, CRQs). 200 NHS answered the online survey. Mean age was 40.46 (SD 13.6). The cohort was distributed according to the job performed: 137 were workers in contact with the public (Job in contact with Public, JP), while 63 were people who don’t work with the public (Job Non in contact with Public, JNP). An overall decrease in quality of life, related to the use of face masks, was detected. In fact, significant differences in the SF-36 Health Survey among our sample and the Italian normative sample were observed in 4 over 8 multi-item scales: Physical Functioning (PF), Role Functioning Physical (RP), Social Functioning (SF) and Role Functioning Emotional (RE). Furthermore, a worst general mental health (GMH) score was observed in the JNP group (p = .0008). The CRQs analysis showed that facial masks were more frequently held responsible for communication difficulties compared to social distancing, particularly due to an attenuation of sound volume and difficulties in rendering facial expressions. Significantly higher anxiety scores were reported in the JNP group, according to the HAM-A, although not reaching pathological level. An impact on communication and general health perception due to COVID-19 restrictions was referred in a large part of the population with differences between the two groups (JP vs. JNP).

Introduction COVID-19 complications can include neurological, psychiatric, psychological, and psychosocial impairments. Little is known on the consequences of SARS-COV-2 on cognitive functions of patients in the sub-acute phase of the disease. We aimed to investigate the impact of COVID-19 on cognitive functions of patients admitted to the COVID-19 Rehabilitation Unit of the San Raffaele Hospital (Milan, Italy). Material and methods 87 patients admitted to the COVID-19 Rehabilitation Unit from March 27th to June 20th 2020 were included. Patients underwent Mini Mental State Evaluation (MMSE), Montreal Cognitive Assessment (MoCA), Hamilton Rating Scale for Depression, and Functional Independence Measure (FIM). Data were divided in 4 groups according to the respiratory assistance in the acute phase: Group1 (orotracheal intubation), Group2 (non-invasive ventilation using Biphasic Positive Airway Pressure), Group3 (Venturi Masks), Group4 (no oxygen therapy). Follow-ups were performed at one month after home-discharge. Results Out of the 87 patients (62 Male, mean age 67.23 ± 12.89 years), 80% had neuropsychological deficits (MoCA and MMSE) and 40% showed mild-to-moderate depression. Group1 had higher scores than Group3 for visuospatial/executive functions (p = 0.016), naming (p = 0.024), short- and long-term memory (p = 0.010, p = 0.005), abstraction (p = 0.024), and orientation (p = 0.034). Group1 was younger than Groups2 and 3. Cognitive impairments correlated with patients’ age. Only 18 patients presented with anosmia. Their data did not differ from the other patients. FIM ( Conclusion Patients with severe functional impairments had important cognitive and emotional deficits which might have been influenced by the choice of ventilatory therapy, but mostly appeared to be related to aging, independently of FIM scores. These findings should be integrated for correct neuropsychiatric assistance of COVID-19 patients in the subacute phase of the disease, and show the need for long-term psychological support and treatment of post-COVID-19 patients.

To propose and validate a variation of the classic techniques for the estimation of the transfer function (TF) of a real pacemaker (PM) lead.The TF of three commercially available PM leads was measured by combining data from experimental measurements and numerical simulations generated by three sources: a) the experimental local SAR at the tip of the PM lead (single measurement point) exposed to a 64 MHz birdcage body coil; b) the experimental current distribution along the PM lead, obtained by directly injecting a 64 MHz signal inside the lead; c) the electric field (E-field) simulated with a computational model of the 64 MHz birdcage body coil adopted in the experimental measurement performed in a). The effect of the lead trajectory on the estimation of the TF was also estimated.The proposed methodology was validated by comparing the SAR obtained from the PM lead TF with experimental measurements: a maximum difference of 2.2 dB was observed. It was also shown that the estimation of the TF cannot be considered independent with the lead trajectory: a variation of the SAR estimation up to 3.4 dB was observed.For the three PM lead tested, the error in the SAR estimation is within the uncertainty level of SAR measurements (± 2 dB). Additionally, the estimation of the TF using the reciprocity principle is influenced by the particular lead trajectory adopted, even if the consequent variability in the SAR estimation is still close to the uncertainty level of SAR measurements.

Currently, the safety assessment of radio-frequency (RF) heating using computational modeling is limited by the available numerical models which are not patient specific. However, RF-induced heating depends on the physical characteristics of the patient. The numerical model generation is difficult due to the highly time-consuming segmentation process. Therefore, having fewer types of segmented structures simplifies the generation of numerical models and reduces computational burden as a result. In this study, we used the k-means clustering method to reduce the number of dielectric properties of an existing numerical model and investigated the resulting difference in specific absorption rate (SAR) with respect to the number of clusters.

Purpose The test reports for the RF-induced heating of metallic devices of hundreds of medical implants have been provided to the U.S. Food and Drug Administration as a part of premarket submissions. The main purpose of this study is to perform a retrospective analysis of the RF-induced heating data provided in the reports to analyze the trends and correlate them with implant geometric characteristics. Methods The ASTM-based RF heating test reports from 86 premarket U.S. Food and Drug Administration submissions were reviewed by three U.S. Food and Drug Administration reviewers. From each test report, the dimensions and RF-induced heating values for a given whole-body (WB) specific absorption rate (SAR) and local background (LB) SAR were extracted and analyzed. The data from 56 stents were analyzed as a subset to further understand heating trends and length dependence. Results For a given WB SAR, the LB/WB SAR ratio varied significantly across the test labs, from 2.3 to 11.3. There was an increasing trend on the temperature change per LB SAR with device length. The maximum heating for stents occurred at lengths of approximately 100 mm at 3 T, and beyond 150 mm at 1.5 T. Conclusions Differences in the LB/WB SAR ratios across testing labs and various MRI scanners could lead to inconsistent WB SAR labeling. Magnetic resonance (MR) conditional labeling based on WB SAR should be derived from a conservative estimate of global LB/WB ratios.

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 μ T at the coil isocenter and whole body averaged SAR equal to 4 W/kg.

PURPOSE This study aims to investigate how the positions of the feeding sources of the transmit radiofrequency (RF) coil, field orientation direction with respect to the patient, and patient dimensions affect the global and local electromagnetic exposure in human body models. METHODS Three RF coil models were implemented, namely a specific two-source (S2) feed and two multisource feed configurations: generic 32-source (G32) and hybrid 16-source (H16). Thirty-two feeding conditions were studied for the S2, whereas two were studied for the G32 and H16. The study was performed using five human body models. Additionally, for two of the body models, the case of a partially implanted lead was evaluated. RESULTS The results showed an overall variation due to coil feeding conditions of the whole-body specific absorption rate (SAR) of less than 20%, but deviations up to 98% of the magnitude of the electric field tangential to a possible lead path. For the analysis with the partially implanted lead, a variation of local SAR at the tip of the lead of up to 60% was observed with respect to feed position and field orientation direction. CONCLUSION The results of this study suggest that specific information about feed position and field orientation direction must be considered for an accurate evaluation of patient exposure. Magn Reson Med 79:1135-1144, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Objective: To evaluate the clinical characteristics and rehabilitation management of patients who undergo amputation for COVID-19-associated coagulopathy. Methods: Clinical and laboratory data for 3 patients were analysed and their rehabilitative management discussed. Results: The medical records of 3 patients who had undergone amputation due to acute lower extremity ischaemia and who were provided with rehabilitation in the COVID-19 unit at San Raffaele Scientific Insitute, Milan Italy were reviewed. Conclusion: Coagulation changes related to SARSCoV- 2 may complicate recovery from this devastating disease. The rehabilitation management of amputated patients for COVID-19 acute lower extremity ischaemia is based on a multilevel approach for clinical, functional, nutritional and neuropsychological needs. Based on this limited experience, a dedicated programme for this specific group of patients seems advantageous to warrant the best functional outcome and quality of life.

Purpose MRI may cause brain tissue around deep brain stimulation (DBS) electrodes to become excessively hot, causing lesions. The presence of extracranial loops in the DBS lead trajectory has been shown to affect the specific absorption rate (SAR) of the radiofrequency energy at the electrode tip, but experimental studies have reported controversial results. The goal of this study was to perform a systematic numerical study to provide a better understanding of the effects of extracranial loops in DBS leads on the local SAR during MRI at 64 and 127 MHz. Methods A total of 160 numerical simulations were performed on patient-derived data, in which relevant factors including lead length and trajectory, loop location and topology, and frequency of MRI radiofrequency (RF) transmitter were assessed. Results Overall, the presence of extracranial loops reduced the local SAR in the tissue around the DBS tip compared with straight trajectories with the same length. SAR reduction was significantly larger at 127 MHz compared with 64 MHz. SAR reduction was significantly more sensitive to variable loop parameters (eg, topology and location) at 127 MHz compared with 64 MHz. Conclusion Lead management strategies could exist that significantly reduce the risks of 3 Tesla (T) MRI for DBS patients. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

An intricate network of a variety of nerves is embedded within the complex anatomy of the human body. Although nerves are shielded from unwanted excitation, they can still be stimulated by external electromagnetic sources that induce strongly non-uniform field distributions. Current exposure safety standards designed to limit unwanted nerve stimulation are based on a series of explicit and implicit assumptions and simplifications. This paper demonstrates the applicability of functionalized anatomical phantoms with integrated coupled electromagnetic and neuronal dynamics solvers for investigating the impact of magnetic resonance exposure on nerve excitation within the full complexity of the human anatomy. The impact of neuronal dynamics models, temperature and local hot-spots, nerve trajectory and potential smoothing, anatomical inhomogeneity, and pulse duration on nerve stimulation was evaluated. As a result, multiple assumptions underlying current safety standards are questioned. It is demonstrated that coupled EM-neuronal dynamics modeling involving realistic anatomies is valuable to establish conservative safety criteria.

Purpose MRI of patients with deep brain stimulation (DBS) implants is strictly limited due to safety concerns, including high levels of local specific absorption rate (SAR) of radiofrequency (RF) fields near the implant and related RF-induced heating. This study demonstrates the feasibility of using a rotating linearly polarized birdcage transmitter and a 32-channel close-fit receive array to significantly reduce local SAR in MRI of DBS patients. Methods Electromagnetic simulations and phantom experiments were performed with generic DBS lead geometries and implantation paths. The technique was based on mechanically rotating a linear birdcage transmitter to align its zero electric-field region with the implant while using a close-fit receive array to significantly increase signal to noise ratio of the images. Results It was found that the zero electric-field region of the transmitter is thick enough at 1.5 Tesla to encompass DBS lead trajectories with wire segments that were up to 30 degrees out of plane, as well as leads with looped segments. Moreover, SAR reduction was not sensitive to tissue properties, and insertion of a close-fit 32-channel receive array did not degrade the SAR reduction performance. Conclusion The ensemble of rotating linear birdcage and 32-channel close-fit receive array introduces a promising technology for future improvement of imaging in patients with DBS implants. Magn Reson Med 77:1701-1712, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

PURPOSE: To assess the mean and variance performance of parallel transmission (pTx) coils for reduction of the absorbed power around electrodes (APAE) in patients implanted with deep brain stimulation devices (DBS). METHODS: We simulated four pTx coils (8 and 16 channels, head and body coils) and a birdcage body coil. We characterized the radiofrequency safety risk using the absorbed power around the DBS electrodes (APAE), which is the integral of the deposited power (in Watts) in a small cylindrical volume of brain tissue surrounding the electrode tips. We assessed the APAE mean and variance by simulation of five realistic DBS patient models that include the full DBS implant length, extracranial loops and the implanted pulse generator. RESULTS: PTx coils with 8 (16) channels were able to reduce the APAE by >18X (>169X) compared to the birdcage coil in average for all patient models, at no cost in term of flip-angle uniformity nor global SAR. Moreover, local pTx coils performed significantly better than body arrays. CONCLUSIONS: PTx is a possible solution to the problem of radiofrequency heating of DBS patients when performing MRI, but the large inter-patient variability of the APAE indicates that patient-specific safety monitoring may be needed.

Patients with implanted medical devices such as deep brain stimulation or spinal cord stimulation are often unable to receive magnetic resonance imaging (MRI). This is because once the device is within the radiofrequency (RF) field of the MRI scanner, electrically conductive leads act as antenna, amplifying the RF energy deposition in the tissue and causing possible excessive tissue heating. Here we propose a novel concept in lead design in which 40cm lead wires are coated with a ~1.2mm layer of high dielectric constant material (155 < εr < 250) embedded in a weakly conductive insulation (σ = 20 S/m). The technique called High-Dielectric Capacitive Bleeding of Current, or CBLOC, works by forming a distributed capacitance along the lengths of the lead, efficiently dissipating RF energy before it reaches the exposed tip. Measurements during RF exposure at 64 MHz and 123 MHz demonstrated that CBLOC leads generated 20-fold less heating at 1.5 T, and 40-fold less heating at 3 T compared to control leads. Numerical simulations of RF exposure at 297 MHz (7T) predicted a 15-fold reduction in specific absorption rate (SAR) of RF energy around the tip of CBLOC leads compared to control leads.

Purpose: The purpose of this study was to investigate the need for high-resolution detailed anatomical modeling to correctly estimate radio-frequency (RF) safety during magnetic resonance imaging (MRI). RF-induced heating near metallic implanted devices depends on the electric field tangential to the device (Etan). Etan and specific absorption rate (SAR) were analyzed in blood vessels of an anatomical model to understand if a standard gel phantom accurately represents the potential heating in tissues due to passive vascular implants such as stents. Methods: A numerical model of an RF birdcage body coil and an anatomically realistic virtual patient with a native spatial resolution of 1 mm3 were used to simulate the in vivo electric field at 64 MHz (1.5 T MRI system). Maximum values of SAR inside the blood vessels were calculated and compared with peaks in a numerical model of the ASTM gel phantom to see if the results from the simplified and homogeneous gel phantom were comparable to the results from the anatomical model. Etan values were also calculated in selected stent trajectories inside blood vessels and compared with the ASTM result. Results: Peak SAR values in blood vessels were up to ten times higher than those found in the ASTM standard gel phantom. Peaks were found in clinically significant anatomical locations, where stents are implanted as per intended use. Furthermore, Etan results showed that volume-averaged SAR values might not be sufficient to assess RF safety. Conclusion: Computational modeling with a high-resolution anatomical model indicated higher values of the incident electric field compared to the standard testing approach. Further investigation will help develop a robust safety testing method which reflects clinically realistic conditions.

This study investigates radiofrequency (RF)-induced heating in a head model with a 256-channel electroencephalogram (EEG) cap during magnetic resonance imaging (MRI). Nine computational models were implemented each with different EEG lead electrical conductivity, ranging from 1 to 5.8 × 10 7 S/m. The peak values of specific absorption rate (SAR) averaged over different volumes were calculated for each lead conductivity. Experimental measurements were also performed at 3-T MRI with a Gracilaria Lichenoides (GL) phantom with and without a low-conductive EEG lead cap (“InkNet”). The simulation results showed that SAR was a nonlinear function of the EEG lead conductivity. The experimental results were in line with the numerical simulations. Specifically, there was a ΔT of 1.7 °C in the GL phantom without leads compared to ΔT of 1.8 °C calculated with the simulations. Additionally, there was a ΔT of 1.5 °C in the GL phantom with the InkNet compared to a ΔT of 1.7 °C in the simulations with a cap of similar conductivity. The results showed that SAR is affected by specific location, number of electrodes, and the volume of tissue considered. As such, SAR averaged over the whole head, or even SAR averaged over volumes of 1 or 0.1 g, may conceal significant heating effects and local analysis of RF heating (in terms of peak SAR and temperature) is needed.

RF-induced heating of ablation catheters under 1.5T magnetic resonance image (MRI) is studied using combined computational modeling and bench testing. The transfer function of ablation catheters are measured experimentally without simplification. A high-resolution anatomical human model was then used to simulate clinical MRI RF exposure environment. The upper limit of the temperature rise was calculated around two types of catheters, namely a single wire catheter and twin wire catheter. Four different insertion depths between 17.5 cm to 70 cm inside human body model were evaluated, simulating procedure for brain or cardiac ablation. A temperature hotspot was observed around the tip of the catheter with an estimated maximum temperature rise higher than 100oC for the single lead catheter and around 94oC for twin lead catheter, with patient landmark varying from −200 mm to 1000 mm with respect to human eye-center. Three experiments were conducted in a standard phantom to validate this coupled method and it showed a good agreement between direct measurements and predicted heating results.

The total product life cycle (TPLC) of medical devices has been defined by four stages: discovery and ideation, regulatory decision, product launch, and postmarket monitoring. Manufacturers of medical devices intended for use in the peripheral vasculature, such as stents, inferior vena cava (IVC) filters, and stent-grafts, mainly use computational modeling and simulation (CM&S) to aid device development and design optimization, supplement bench testing for regulatory decisions, and assess postmarket changes or failures. For example, computational solid mechanics and fluid dynamics enable the investigation of design limitations in the ideation stage. To supplement bench data in regulatory submissions, manufactures can evaluate the effects of anatomical characteristics and expected in vivo loading environment on device performance. Manufacturers might also harness CM&S to aid root-cause analyses that are necessary when failures occur postmarket, when the device is exposed to broad clinical use. Once identified, CM&S tools can then be used for redesign to address the failure mode and re-establish the performance profile with the appropriate models. The Center for Devices and Radiological Health (CDRH) wants to advance the use of CM&S for medical devices and supports the development of virtual physiological patients, clinical trial simulations, and personalized medicine. Thus, the purpose of this paper is to describe specific examples of how CM&S is currently used to support regulatory submissions at different phases of the TPLC and to present some of the stakeholder-led initiatives for advancing CM&S for regulatory decision-making.

We present results of real-time and sensitive MR Thermometry (MRT) using a paramagnetic lanthanide complex thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethyl-1,4,7,10-tetraa-cetate (Tm-DOTMA) to study radio frequency (RF) heating induced by a copper wire and a titanium bone screw in an agarose gel phantom. The temperature dependent chemical shift coefficient (TDCSC) of the methyl resonance was found to be 0.7 ± 0.03 ppm/°;C in agarose gel. The methyl protons of Tm-DOTMA were imaged using 2D chemical shift imaging (CSI) and 3D phase mapping methods (PMM), approximately 7 sec long, and compared with conventional water proton resonance frequency (PRF) method. Two RF-induced heating approaches were tested: 1) using a prescan before the MRT; or 2) using the heating caused by the imaging pulse during continuous imaging. Both approaches allowed detection of temperature changes which are less than 1°;C and continuously mapping temperature changes around the copper wire. Using a heating pre-scan, the Tm-DOTMA 2D-CSI allowed better qualitative visualization of the temperature changes around the titanium screw compared with water phase shift thermometry. Numerical electromagnetic field simulations were also conducted for the evaluation of orientation dependency using the copper wire in 4.7 T (200 MHz). Thermometry approach using Tm-DOTMA can detect smaller temperature changes with decreased scanning time resulting in real-time and sensitive temperature mapping.

The test reports for the RF-induced heating of metallic devices of hundreds of medical implants have been provided to the U.S. Food and Drug Administration as a part of premarket submissions. The main purpose of this study is to perform a retrospective analysis of the RF-induced heating data provided in the reports to analyze the trends and correlate them with implant geometric characteristics.The ASTM-based RF heating test reports from 86 premarket U.S. Food and Drug Administration submissions were reviewed by three U.S. Food and Drug Administration reviewers. From each test report, the dimensions and RF-induced heating values for a given whole-body (WB) specific absorption rate (SAR) and local background (LB) SAR were extracted and analyzed. The data from 56 stents were analyzed as a subset to further understand heating trends and length dependence.For a given WB SAR, the LB/WB SAR ratio varied significantly across the test labs, from 2.3 to 11.3. There was an increasing trend on the temperature change per LB SAR with device length. The maximum heating for stents occurred at lengths of approximately 100 mm at 3 T, and beyond 150 mm at 1.5 T.Differences in the LB/WB SAR ratios across testing labs and various MRI scanners could lead to inconsistent WB SAR labeling. Magnetic resonance (MR) conditional labeling based on WB SAR should be derived from a conservative estimate of global LB/WB ratios.

To evaluate the local specific absorption rate (SAR) and heating around retained cardiac leads during MRI at 64 MHz (1.5T) and 127 MHz (3T) as a function of RF coil type and imaging landmark.Numerical models of retained cardiac leads were built from CT and X-ray images of 6 patients with retained cardiac leads. Electromagnetic simulations and bio-heat modeling were performed with MRI RF body and head coils tuned to 64 MHz and 127 MHz and positioned at 9 different imaging landmarks covering an area from the head to the lower limbs.For all patients and at both 1.5T and 3T, local transmit head coils produced negligible temperature rise (mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:mrowmml:moΔ/mml:momml:miT/mml:mimml:mo/mml:momml:mn0.1/mml:mnmml:mo°/mml:momml:miC/mml:mi/mml:mrow/mml:math) formml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:mrowmml:mrowmml:mo‖/mml:momml:mo‖/mml:momml:mrowmml:msubsupmml:miB/mml:mimml:mn1/mml:mnmml:mo+/mml:mo/mml:msubsup/mml:mrowmml:mo‖/mml:momml:mo‖/mml:mo/mml:mrowmml:mo≤/mml:momml:mn3/mml:mnmml:mo /mml:momml:moμ/mml:momml:miT/mml:mi/mml:mrow/mml:math. For body imaging with quadrature-driven coils at 1.5T,mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:mrowmml:moΔ/mml:momml:miT/mml:mi/mml:mrow/mml:mathduring a 10-min scan remained 3°C at all imaging landmarks formml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:mrowmml:mrowmml:mo‖/mml:momml:mo‖/mml:momml:mrowmml:msubsupmml:miB/mml:mimml:mn1/mml:mnmml:mo+/mml:mo/mml:msubsup/mml:mrowmml:mo‖/mml:momml:mo‖/mml:mo/mml:mrowmml:mo≤/mml:momml:mn3/mml:mnmml:mo /mml:momml:moμ/mml:momml:miT/mml:mi/mml:mrow/mml:mathand6°C formml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:mrowmml:mrowmml:mo‖/mml:momml:mo‖/mml:momml:mrowmml:msubsupmml:miB/mml:mimml:mn1/mml:mnmml:mo+/mml:mo/mml:msubsup/mml:mrowmml:mo‖/mml:momml:mo‖/mml:mo/mml:mrowmml:mo≤/mml:momml:mn4/mml:mnmml:mo /mml:momml:moμ/mml:momml:miT/mml:mi/mml:mrow/mml:math. For body imaging at 3T,mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:mrowmml:moΔ/mml:momml:miT/mml:mi/mml:mrow/mml:mathduring a 10-min scan remained 6°C at all imaging landmarks formml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:mrowmml:mrowmml:mo‖/mml:momml:mo‖/mml:momml:mrowmml:msubsupmml:miB/mml:mimml:mn1/mml:mnmml:mo+/mml:mo/mml:msubsup/mml:mrowmml:mo‖/mml:momml:mo‖/mml:mo/mml:mrowmml:mo≤/mml:momml:mn2/mml:mnmml:mo /mml:momml:moμ/mml:momml:miT/mml:mi/mml:mrow/mml:math. For shorter pulse sequences up to 2 min,mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:mrowmml:moΔ/mml:momml:miT/mml:mi/mml:mrow/mml:mathremained 6°C formml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:mrowmml:mrowmml:mo‖/mml:momml:mo‖/mml:momml:mrowmml:msubsupmml:miB/mml:mimml:mn1/mml:mnmml:mo+/mml:mo/mml:msubsup/mml:mrowmml:mo‖/mml:momml:mo‖/mml:mo/mml:mrowmml:mo≤/mml:momml:mn3/mml:mnmml:mo /mml:momml:moμ/mml:momml:miT/mml:mi/mml:mrow/mml:math.For the models based on 6 patients studied, simulations suggest that MRI could be performed safely using a local head coil at both 1.5T and 3T, and with a body coil at 1.5T with pulses that producedmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:mrowmml:mrowmml:mo‖/mml:momml:mo‖/mml:momml:mrowmml:msubsupmml:miB/mml:mimml:mn1/mml:mnmml:mo+/mml:mo/mml:msubsup/mml:mrowmml:mo‖/mml:momml:mo‖/mml:mo/mml:mrowmml:mo≤/mml:momml:mn4/mml:mnmml:mo /mml:momml:moμ/mml:momml:miT/mml:mi/mml:mrow/mml:math. MRI at 3T could be performed safely in these patients using pulses withmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:mrowmml:mrowmml:mo‖/mml:momml:mo‖/mml:momml:mrowmml:msubsupmml:miB/mml:mimml:mn1/mml:mnmml:mo+/mml:mo/mml:msubsup/mml:mrowmml:mo‖/mml:momml:mo‖/mml:mo/mml:mrowmml:mo≤/mml:momml:mn2/mml:mnmml:mo /mml:momml:moμ/mml:momml:miT/mml:mi/mml:mrow/mml:math.

This study investigates the use of pads with high dielectric constant (HDC) materials to alter electromagnetic field distributions in patients during magnetic resonance imaging (MRI). The study was performed with numerical simulations and phantom measurements. An initial proof-of-concept and validation was performed using a phantom at 64 MHz, showing increases of up to 10% in electromagnetic field when using distilled water as the high dielectric material. Additionally, numerical simulations with computational models of human anatomy were performed at 128 MHz. Results of these simulations using barium titanate (BaTiO3) beads showed a 61% increase of $| {\boldsymbol{B}_1^ + } |$ with a quadrature driven RF coil and a 64% increase with a dual-transmit array. The presence of the HDC material also allowed for a decrease of SAR up to twofold (e.g., peak 10 g-averaged SAR from 54 to 22 W/kg with a quadrature driven RF coil and from 27 to 22 W/kg with a dual-transmit array using CaTiO3 powder at 128 MHz). The results of this study show that the use of HDC pads at 128 MHz for MRI spine applications could result in improved magnetic fields within the region of interest, while decreasing SAR outside the region.