Mitigating RF heating near medical devices in Magnetic Resonance Imaging

2012 ◽  
Author(s):  
James E. Brown ◽  
Choon S. Lee
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Medical Devices ◽  
Rf Heating ◽  
Resonance Imaging

Open Source Medical Devices for Innovation, Education and Global Health: Case Study of Open Source Magnetic Resonance Imaging

2018 ◽  
pp. 147-163
Author(s):  
Lukas Winter ◽  
Ruben Pellicer-Guridi ◽  
Lionel Broche ◽  
Simone A. Winkler ◽  
Henning M. Reimann ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Global Health ◽  
Open Source ◽  
Medical Devices ◽  
Resonance Imaging

Magnetic Resonance Imaging Conditionally Safe Neurostimulation Leads

Neurosurgery ◽  
2013 ◽  
Vol 74 (2) ◽  
pp. 215-225 ◽  
Author(s):  
Robert J. Coffey ◽  
Ron Kalin ◽  
James M. Olsen
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Animal Studies ◽  
Thermal Damage ◽  
Neurological Injury ◽  
Cns Injury ◽  
Thermal Dose ◽  
Rf Heating ◽  
Resonance Imaging ◽  
Increased Risk

Abstract BACKGROUND: Magnetic resonance imaging (MRI) is preferred for imaging the central nervous system (CNS). An important hazard for neurostimulation patients is heating at the electrode interface induced, for example, by 64-MHz radiofrequency (RF) magnetic fields of a 1.5T scanner. OBJECTIVE: We performed studies to define the thermal dose (time and temperature) that would not cause symptomatic neurological injury. METHODS: Approaches included animal studies where leads with temperature probes were implanted in the brain or spine of sheep and exposed to RF-induced temperatures of 37°C to 49°C for 30 minutes. Histopathological examinations were performed 7 days after recovery. We also reviewed the threshold for RF lesions in the CNS, and for CNS injury from cancer hyperthermia. Cumulative equivalent minutes at 43°C was used to normalize the data to exposure times and temperatures expected during MRI. RESULTS: Deep brain and spinal RF heating up to 43°C for 30 minutes produced indistinguishable effects compared with 37°C controls. Exposures greater than 43°C for 30 minutes produced temperature-dependent, localized thermal damage. These results are consistent with limits on hyperthermia exposure to 41.8°C for 60 minutes in patients who have cancer and with the reversibility of low-temperature and short-duration trial heating during RF lesion procedures. CONCLUSION: A safe temperature for induced lead heating is 43°C for 30 minutes. MRI-related RF heating above 43°C or longer than 30 minutes may be associated with increased risk of clinically evident thermal damage to neural structures immediately surrounding implanted leads. The establishment of a thermal dose limit is a first step toward making specific neurostimulation systems conditionally safe during MRI procedures.

scholarly journals Design of a Dual-Purpose Patch Antenna for Magnetic Resonance Imaging and Induced RF Heating for Small Animal Hyperthermia

2021 ◽  
Vol 11 (16) ◽  
pp. 7290
Author(s):  
Donghyuk Kim ◽  
Daniel Hernandez ◽  
Kyoung-Nam Kim
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Patch Antenna ◽  
Larmor Frequency ◽  
Magnetic Flux Density ◽  
Cancer Tissue ◽  
Patch Antennas ◽  
Rf Heating ◽  
Resonance Imaging ◽  
B1 Field

The popularity of patch antennas in magnetic resonance imaging (MRI) has reduced because of the large size required for patch antennae to resonate. Since the size of the patch antenna is associated with the wavelength and the wavelengths that are used in MRI are substantially large, large antennas are used. Methods of reducing patch antenna sizes have been proposed; however, these methods reduce the penetration depth and uniformity. In this study, we reduced the area of the patch antenna by 30% by folding the ground and patch planes in a zigzag pattern. The patch antenna produced two main resonant modes. The first mode produced a uniform magnetic field that was used for MRI. The second mode produced a strong and focused electric (|E|)-field, which was used for radiofrequency (RF) heating. Furthermore, we explored the use of a combination of two patch antennas aligned along the z-axis to provide a circular uniform magnetic flux density (|B1|) field at 300 MHz, which corresponds to the Larmor frequency in the 7T MRI system. In addition, the patch antenna configuration will be used for RF heating hyperthermia operating at 1.06 GHz. The target object was a small rat with insertion of colon cancer. Using the proposed configuration, we achieved |B1|-field uniformity with a standard deviation of 3% and a temperature increment of 1 °C in the mimic cancer tissue.

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