Browsing by Author "Elahi, B."

Now showing 1 - 3 of 3

Open Access
Reconfigurable MRI coil technology can substantially reduce RF heating of deep brain stimulation implants: First in-vitro study of RF heating reduction in bilateral DBS leads at 1.5 T
(Public Library of Science, 2019-08) Golestanirad, L.; Kazemivalipour, Ehsan; Keil, B.; Downs, S.; Kirsch, J.; Elahi, B.; Pilitsis, J.; Wald, L. L.
Patients with deep brain stimulation (DBS) implants can significantly benefit from magnetic resonance imaging (MRI), however access to MRI is restricted in these patients because of safety concerns due to RF heating of the leads. Recently we introduced a patient-adjustable reconfigurable transmit coil for low-SAR imaging of DBS at 1.5T. A previous simulation study demonstrated a substantial reduction in the local SAR around single DBS leads in 9 unilateral lead models. This work reports the first experimental results of temperature measurement at the tips of bilateral DBS leads with realistic trajectories extracted from postoperative CT images of 10 patients (20 leads in total). A total of 200 measurements were performed to record temperature rise at the tips of the leads during 2 minutes of scanning with the coil rotated to cover all accessible rotation angles. In all patients, we were able to find an optimum coil rotation angle and reduced the heating of both left and right leads to a level below the heating produced by the body coil. An average heat reduction of 65% was achieved for bilateral leads. When considering each lead alone, an average heat reduction of 80% was achieved. Our results suggest that reconfigurable coil technology introduces a promising approach for imaging of patients with DBS implants.
Open Access
Reconfigurable MRI technology for low-SAR imaging of deep brain stimulation at 3T: application in bilateral leads, fully-implanted systems, and surgically modified lead trajectories
(Elsevier, 2019) Kazemivalipour, Ehsan; Keil, B.; Vali, A.; Rajan, S.; Elahi, B.; Atalar, Ergin; Wald, L.; Rosenow, J.; Pilitsis, J.; Golestanirad, L.
Patients with deep brain stimulation devices highly benefit from postoperative MRI exams, however MRI is not readily accessible to these patients due to safety risks associated with RF heating of the implants. Recently we introduced a patient-adjustable reconfigurable coil technology that substantially reduced local SAR at tips of single isolated DBS leads during MRI at 1.5 T in 9 realistic patient models. This contribution extends our work to higher fields by demonstrating the feasibility of scaling the technology to 3T and assessing its performance in patients with bilateral leads as well as fully implanted systems. We developed patient-derived models of bilateral DBS leads and fully implanted DBS systems from postoperative CT images of 13 patients and performed finite element simulations to calculate SAR amplification at electrode contacts during MRI with a reconfigurable rotating coil at 3T. Compared to a conventional quadrature body coil, the reconfigurable coil system reduced the SAR on average by 83% for unilateral leads and by 59% for bilateral leads. A simple surgical modification in trajectory of implanted leads was demonstrated to increase the SAR reduction efficiency of the rotating coil to >90% in a patient with a fully implanted bilateral DBS system. Thermal analysis of temperature-rise around electrode contacts during typical brain exams showed a 15-fold heating reduction using the rotating coil, generating <1C temperature rise during ∼4-min imaging with high-SAR sequences where a conventional CP coil generated >10C temperature rise in the tissue for the same flip angle.
Open Access
RF heating of deep brain stimulation implants during MRI in 1.2 T vertical scanners versus 1.5 T horizontal systems: a simulation study with realistic lead configurations
(Institute of Electrical and Electronics Engineers, 2020) Kazemivalipour, Ehsan; Vu, J.; Lin, S.; Bhusal, B.; Nguyen, B. T.; Kirsch, J.; Elahi, B.; Rosenow, J.; Atalar, Ergin; Golestanirad, L.
Patients with deep brain stimulation (DBS) implants are often denied access to magnetic resonance imaging (MRI) due to safety concerns associated with RF heating of implants. Although MR-conditional DBS devices are available, complying with manufacturer guidelines has proved to be difficult as pulse sequences that optimally visualize DBS target structures tend to have much higher specific absorption rate (SAR) of radiofrequency energy than current guidelines allow. The MR-labeling of DBS devices, as well as the majority of studies on RF heating of conductive implants have been limited to horizontal close-bore MRI scanners. Vertical MRI scanners, originally introduced as open low-field MRI systems, are now available at 1.2 T field strength, capable of high-resolution structural and functional imaging. No literature exists on DBS SAR in this class of scanners which have a 90° rotated transmit coil and thus, generate a fundamentally different electric and magnetic field distributions. Here we present a simulation study of RF heating in a cohort of forty patient-derived DBS lead models during MRI in a commercially available vertical openbore MRI system (1.2 T OASIS, Hitachi) and a standard horizontal 1.5 T birdcage coil. Simulations were performed at two major imaging landmarks representing head and chest imaging. We calculated the maximum of 0.1g-averaged SAR (0.1g-SAR Max ) around DBS lead tips when a B 1 + = 4 μT was generated on an axial plane passing through patients body. For head landmark, 0.1g-SAR Max reached 220±188 W/kg in the 1.5 T birdcage coil, but only 14±11 W/kg in the OASIS coil. For chest landmark, 0.1g-SAR Max was 24±17 W/kg in the 1.5 T birdcage coil and 3±2 W/kg in the OASIS coil. A paired two-tail t-test revealed a significant reduction in SAR with a large effect-size during head MRI (p <; 1.5×10 -8 , Cohen's d = 1.5) as well as chest MRI (p <; 6.5×10 -10 , Cohen's d = 1.7) in 1.2 T Hitachi OASIS coil compared to a standard 1.5 T birdcage transmitter. Our findings suggest that open-bore vertical scanners may offer an untapped opportunity for MRI of patients with DBS implants.