Radiofrequency heating of metallic dental devices during 3.0 T MRI.
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ABSTRACT:
SUBMITTER: Hasegawa M
PROVIDER: S-EPMC3635774 | biostudies-other | 2013
REPOSITORIES: biostudies-other
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Project description:Failure to achieve properly localized, permanent tissue destruction is a common cause of arrhythmia recurrence after cardiac ablation. Current methods of assessing lesion size and location during cardiac radiofrequency ablation are unreliable or not suited for repeated assessment during the procedure. MRI thermography could be used to delineate permanent ablation lesions because tissue heating above 50°C is the cause of permanent tissue destruction during radiofrequency ablation. However, image artifacts caused by cardiac motion, the ablation electrode, and radiofrequency ablation currently pose a challenge to MRI thermography in the heart. In the current study, we sought to demonstrate the feasibility of MRI thermography during cardiac ablation.An MRI-compatible electrophysiology catheter and filtered radiofrequency ablation system was used to perform ablation in the left ventricle of 6 mongrel dogs in a 1.5-T MRI system. Fast gradient-echo imaging was performed before and during radiofrequency ablation, and thermography images were derived from the preheating and postheating images. Lesion extent by thermography was within 20% of the gross pathology lesion.MR thermography appears to be a promising technique for monitoring lesion formation and may allow for more accurate placement and titration of ablation, possibly reducing arrhythmia recurrences.
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Project description: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 × 107 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 ?T of 1.7 °C in the GL phantom without leads compared to ?T of 1.8 °C calculated with the simulations. Additionally, there was a ?T of 1.5 °C in the GL phantom with the InkNet compared to a ?T 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.
| S-EPMC6579539 | biostudies-literature
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.
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Project description:OBJECTIVE: To compare the effects of metal artefacts and acquisition time among slice encoding for metal artefact correction (SEMAC), SEMAC with dual-source parallel radiofrequency (SEMAC-DSPRF) transmission and fast spin echo (FSE) images using 3.0-T MRI. METHODS: The signal-to-noise ratio (SNR) was calculated in a phantom study using a pedicle screw. A total of 16 patients who underwent spinal surgery using pedicle screws were included in the clinical study. T1 weighted FSE, SEMAC and SEMAC-DSPRF images were obtained. Four imaging findings (visibility of the dural sac, neural foramens, bone-implant interface and overall artefacts) were evaluated by using five-point scales independently by two observers. The mean scan time was recorded. RESULTS: The mean SNR was 71.2, 25.7 and 28.4 for FSE, SEMAC and SEMAC-DSPRF images, respectively. FSE images were ranked lower than SEMAC and SEMAC-DSPRF images, and ranking of SEMAC and SEMAC-DSPRF images did not differ statistically for all four imaging findings. The mean scan time was 9 min 51 s and 6 min 31 s for SEMAC and SEMAC-DSPRF images, respectively. CONCLUSION: SEMAC can reduce metallic artefacts and improve the visualisation of anatomical structures around metal implants. An additional DSPRF technique can reduce the acquisition time of SEMAC images without the loss of SNR and image quality. ADVANCES IN KNOWLEDGE: This study demonstrates that the use of the DSPRF transmission technique can reduce the acquisition time of SEMAC images without loss of image quality in patients with metal implants.
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Project description: Not available
| S-EPMC5992954 | biostudies-literature
Project description:PurposeTo theoretically investigate the feasibility of a novel procedure for testing the MRI gradient-induced heating of medical devices and translating the results into clinical practice.MethodsThe concept of index of stress is introduced by decoupling the time waveform characteristics of the gradient field signals from the field spatial distribution within an MRI scanner. This index is also extended to consider the anisotropy of complex bulky metallic implants. Merits and drawbacks of the proposed index of stress are investigated through virtual experiments. In particular, the values of the index of stress evaluated for realistic orthopedic implants placed within an ASTM phantom are compared with accurate heating simulations performed with 2 anatomic body models (a man and a woman) implanted through a virtual surgery procedure.ResultsThe manipulation of the proposed index of stress allows to identify regions within the MRI bore where the implant could affect the safety of the examinations. Furthermore, the conducted analysis shows that the power dissipated into the implant by the induced eddy currents is a dosimetric quantity that estimates well the maximum temperature increase in the tissues surrounding the implant.ConclusionThe results support the adoption of an anisotropic index of stress to regulate the gradient-induced heating of geometrically complex implants. They also pave the way for a laboratory characterization of the implants based on electrical measurements, rather than on thermal measurements. The next step will be to set up a standardized experimental procedure to evaluate the index of stress associated with an implant.
| S-EPMC9314691 | biostudies-literature
Project description:PurposeThe risks of RF-induced heating of active implantable medical device (AIMD) leads during MR examinations must be well understood and realistically assessed. In this study, we evaluate the potential additional risks of broken and abandoned (cut) leads.MethodsFirst, we defined a generic AIMD with a metallic implantable pulse generator (IPG) and a 100-cm long lead containing 1 or 2 wires. Next, we numerically estimated the deposited in vitro lead-tip power for an intact lead, as well as with wire breaks placed at 10 cm intervals. We studied the effect of the break size (wire gap width), as well as the presence of an intact wire parallel to the broken wire, and experimentally validated the numeric results for the configurations with maximum deposited in vitro lead-tip power. Finally, we performed a Tier 3 assessment of the deposited in vivo lead-tip power for the intact and broken lead in 4 high resolution virtual population anatomic models for over 54,000 MR examination scenarios.ResultsThe enhancement of the deposited lead-tip power for the broken leads, compared to the intact lead, reached 30-fold in isoelectric exposure, and 16-fold in realistic clinical exposures. The presence of a nearby intact wire, or even a nearby broken wire, reduced this enhancement factor to <7-fold over the intact lead.ConclusionBroken and abandoned leads can pose increased risk of RF-induced lead-tip heating to patients undergoing MR examinations. The potential enhancement of deposited in vivo lead-tip power depends on location and type of the wire break, lead design, and clinical routing of the lead, and should be carefully considered when performing risk assessment for MR examinations and MR conditional labeling.
| S-EPMC8362172 | biostudies-literature
Project description:The recent COVID-19 pandemic has underscored the necessity of protecting health care providers (HCPs) against the transmission of infectious agents during dental procedures. To this end, the effectiveness of several air cleaning devices (ACDs) in reducing HCPs exposure to aerosols generated during dental procedures was estimated, separately or in combination with each other. These ACDs were a chairside unit capturing aerosols at the source of generation, and four ambient ACDs: a portable ambient ACD; a negative pressure module; a custom made, fan-operated and wall-mounted air filter (WMAF); and a smaller and passive version of the latter. The last three ACDs were intended for mobile dental clinics (MDCs) only. This assessment was performed in two different environments: in a dental clinic operatory and in a MDC. Two dental personnel, acting in the roles of dentist and dental assistant, performed on simulated patient aerosol-generating and non-aerosol-generating procedures. For each 5-minute scenario, the cumulative exposure to airborne particulate matter 10 µm in size or smaller (PM10) was determined by calculating the sum of all 1 second readings obtained with personal and ambient air monitors. The effectiveness of the ACDs in capturing PM10 was estimated based on the capability of the ACDs to keep PM10 level at or below the initial background level. In all conditions assessed in the dental clinic operatory, when both the chairside and portable ambient ACDs were functioning, an estimated effectiveness of 100% in capturing PM10 was achieved. In the MDC, in all conditions where the chairside ACD was used without the negative pressure module, an estimated effectiveness of 100% was also achieved. The simultaneous operation of the negative pressure module in the MDC, which led to a room negative pressure of -0.25 inch wc, reduced the chairside ACD's effectiveness in capturing aerosols. Conversely, the use of the WMAF in the MDC in combination with the chairside ACD further reduced exposure to PM10 below the initial background level. Nonetheless, in all conditions assessed in both settings (dental clinic operatory and MDC), larger visible aerosols were produced, often landing on the surrounding environment. A fair portion of these aerosols landed on the inside of the chairside ACD flange. This assessment suggests that the use of the tested chairside ACD, by capturing aerosols at the source of generation, had the greatest impact on reducing exposure of dental personnel to PM10 produced during dental procedures. This study also indicates that such exposure is further reduced with the addition of an ambient ACD. However, creating a negative pressure room as high as -0.25 inch wc can lead to air turbulence reducing the effectiveness of ACDs in capturing aerosols at the source. Furthermore, the presence of uncaptured droplets and spatter on the surrounding environment supports the need to complement the use of engineering controls with proper administrative controls and personal protective equipment, as recommended by governmental agencies and the scientific community for preventing the transmission of infection in health care settings.
| S-EPMC8344839 | biostudies-literature
Project description:Background The risks associated with MRI in individuals who have implanted cardiac devices are thought to arise from the interaction between the implanted device and static, gradient, and radiofrequency magnetic fields. Purpose To determine the relationship between the peak whole-body averaged specific absorption rate (SAR) and change in magnetic field per unit time (dB/dt), maximum specific energy dose, imaging region, and implanted cardiac device characteristics and their function in patients undergoing MRI. Materials and Methods This prospective observational cohort study was conducted from October 16, 2003, to January 22, 2015 (https://ClinicalTrials.gov, NCT01130896). Any individual with an implanted cardiac device who was referred for MRI was included. Clinical MRI protocols without SAR restriction were used. Exclusion criteria were newly implanted leads, abandoned or epicardial leads, and dependence on a pacemaker with an implantable cardioverter defibrillator without asynchronous pacing capability. For each MRI pulse sequence, the calculated whole-body values for SAR, dB/dt, and scan duration were collected. Atrial and ventricular sensing, lead impedance, and capture threshold were evaluated before and immediately after (within 10 minutes) completion of each MRI examination. Generalized estimating equations with Gaussian family, identity link, and an exchangeable working correlation matrix were used for statistical analysis. Results A total of 2028 MRI examinations were performed in 1464 study participants with 2755 device leads (mean age, 67 years ± 15 [standard deviation]; 930 men [64%]). There was no evidence of an association between radiofrequency energy deposition, dB/dt, or scan duration and changes in device parameters. Thoracic MRI was associated with decreased battery voltage immediately after MRI (β = -0.008 V, P < .001). Additionally, right ventricular (RV) lead length was associated with decreased RV sensing (β = -0.012 mV, P = .05) and reduced RV capture threshold (β = -0.002 V, P < .01) immediately after MRI. Conclusion There was no evidence of an association between MRI parameters that characterize patient exposure to radiofrequency energy and changes in device and lead parameters immediately after MRI. Nevertheless, device interrogation before and after MRI remains mandatory due to the potential for device reset and changes in lead or generator parameters. © RSNA, 2020 See also the editorial by Shellock in this issue.
| S-EPMC7193917 | biostudies-literature
Project description:IntroductionVisualization of passive devices during MRI-guided catheterizations often relies on a susceptibility artifact from the device itself or added susceptibility markers that impart a unique imaging signature. High-performance low field MRI systems offer reduced RF-induced heating of metallic devices during MRI-guided invasive procedures, but susceptibility artifacts are expected to diminish with field strength, reducing device visualization. In this study, field strength and orientation dependence of artifacts from susceptibility markers and metallic guidewires were evaluated using a prototype high-performance 0.55 T MRI system.Materials and methodsArtifact volume from nitinol and stainless steel passive susceptibility markers was quantified using histogram analysis of pixel intensities from three-dimensional gradient echo images at 0.55 T, 1.5 T and 3 T. In addition, visibility of commercially available clinical catheterization devices was compared between 0.55 T and 1.5 T using real-time bSSFP in phantoms and in vivo.ResultsA low-tensile strength stainless-steel marker produced field strength- and orientation-dependent artifact size (1.7 cm3, 1.95 cm3, 2.21 cm3 at 0.55 T, 1.5 T, 3 T, respectively). Whereas, a high-tensile strength steel marker, of the same alloy, produced field strength- and orientation-independent artifact size (3.35 cm3, 3.41 cm3, 3.42 cm3 at 0.55 T, 1.5 T, 3 T, respectively). Visibility of commercially available nitinol guidewires was reduced at 0.55 T, but imaging signature could be maintained using high-susceptibility stainless steel markers.Discussion and conclusionHigh-susceptibility stainless-steel markers generate field-independent artifacts between 0.55 T, 1.5 T and 3 T, indicating magnetic saturation at fields <0.55 T. Thus, artifact size can be tailored such that interventional devices produce identical imaging signatures across field strengths.
| S-EPMC8132593 | biostudies-literature