Ehsan Kazemivalipour1,2,3, Bhumi Bhusal1, Jasmine Vu1,4, Stella Lin1, Bach Thanh Nguyen1, John Kirsch5, Elizabeth Nowac6, Julie Pilitsis7, Joshua Rosenow8, Ergin Atalar2,3, Laleh Golestanirad1,4. 1. Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA. 2. Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey. 3. National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey. 4. Department of Biomedical Engineering, McCormick School of Engineering, Northwestern University, Evanston, Illinois, USA. 5. A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, Massachusetts, USA. 6. Department of Neurosurgery, Albany Medical Center, Albany, New York, USA. 7. Illinois Bone and Joint Institute (IBJI), Wilmette, Illinois, USA. 8. Department of Neurological Surgery, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Abstract
PURPOSE: Patients with active implants such as deep brain stimulation (DBS) devices are often denied access to MRI due to safety concerns associated with the radiofrequency (RF) heating of their electrodes. The majority of studies on RF heating of conductive implants have been performed in horizontal close-bore MRI scanners. Vertical MRI scanners which have a 90° rotated transmit coil generate fundamentally different electric and magnetic field distributions, yet very little is known about RF heating of implants in this class of scanners. We performed numerical simulations as well as phantom experiments to compare RF heating of DBS implants in a 1.2T vertical scanner (OASIS, Hitachi) compared to a 1.5T horizontal scanner (Aera, Siemens). METHODS: Simulations were performed on 90 lead models created from post-operative CT images of patients with DBS implants. Experiments were performed with wires and commercial DBS devices implanted in an anthropomorphic phantom. RESULTS: We found significant reduction of 0.1 g-averaged specific absorption rate (30-fold, P < 1 × 10-5 ) and RF heating (9-fold, P < .026) in the 1.2T vertical scanner compared to the 1.5T conventional scanner. CONCLUSION: Vertical MRI scanners appear to generate lower RF heating around DBS leads, providing potentially heightened safety or the flexibility to use sequences with higher power levels than on conventional systems.
PURPOSE: Patients with active implants such as deep brain stimulation (DBS) devices are often denied access to MRI due to safety concerns associated with the radiofrequency (RF) heating of their electrodes. The majority of studies on RF heating of conductive implants have been performed in horizontal close-bore MRI scanners. Vertical MRI scanners which have a 90° rotated transmit coil generate fundamentally different electric and magnetic field distributions, yet very little is known about RF heating of implants in this class of scanners. We performed numerical simulations as well as phantom experiments to compare RF heating of DBS implants in a 1.2T vertical scanner (OASIS, Hitachi) compared to a 1.5T horizontal scanner (Aera, Siemens). METHODS: Simulations were performed on 90 lead models created from post-operative CT images of patients with DBS implants. Experiments were performed with wires and commercial DBS devices implanted in an anthropomorphic phantom. RESULTS: We found significant reduction of 0.1 g-averaged specific absorption rate (30-fold, P < 1 × 10-5 ) and RF heating (9-fold, P < .026) in the 1.2T vertical scanner compared to the 1.5T conventional scanner. CONCLUSION: Vertical MRI scanners appear to generate lower RF heating around DBS leads, providing potentially heightened safety or the flexibility to use sequences with higher power levels than on conventional systems.
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