Browsing by Subject "Implants"

Now showing 1 - 3 of 3

Open Access
Fracture of femoral neck: Analysis of new implant models with a slit and without a slit by the finite element method
(WHO Office in Azerbaijan, 2017) Jafarov, A. A.; Ozer, Z.; Alizadeh, Ch. A.; Mammadov, A. M.
During fractures of the neck of the femur (PBHB) for the completion of postoperative fusion, there is a need for stable fixation - interfragmental immobility. The stability of used implants in a living person is difficult to calculate. For this purpose, the analysis is carried out using the finite element method (the final analysis of the limited elements). The aim of this study is to study the features of the proposed new hip implant with finite element analysis. Based on the digital geometry of the anatomy of the femur, a 3D model of the femur was developed. Stress and strain, obtained with the help of the computer program ANSYS as a result of loads on the head of the thigh, were investigated by the finite element analysis method. Based on the Pawel classification, 3 groups of femoral neck fracture models were created, corresponding to the fracture angles closer to 30, 50 and 70 degrees (type 1, type 2 and type 3). In each group, the corresponding implants are analyzed in 2 types: without a slit and with a slit. For the spongiform bone, the UTS (Ultimate Tensile Stres) is defined as 20 MPA, and for the cortical bone, 150 MPA. In all analyzes, the force loaded in the vertical direction onto the head of the computer model of the femur was calculated to be 4000 N. Given that the slits on the surface of the implant can cross waves, homogeneously distribute the force and pressure throughout the entire implant, on the basis of this, a decrease in pressure on the surface of the bone tissue was observed. It is believed that this process can increase the stability of the implant and minimize the level of damage to the bone tissue.
Open Access
Magnetic resonance imaging assisted by wireless passive implantable fiducial e-markers
(Institute of Electrical and Electronics Engineers, 2017) Gokyar, S.; Alipour, A.; Unal, E.; Atalar, Ergin; Demir, Hilmi Volkan
This paper reports a wireless passive resonator architecture that is used as a fiducial electronic marker (e-marker) intended for internal marking purposes in magnetic resonance imaging (MRI). As a proof-of-concept demonstration, a class of double-layer, sub-cm helical resonators were microfabricated and tuned to the operating frequency of 123 MHz for a three T MRI system. Effects of various geometrical parameters on the resonance frequency of the e-marker were studied, and the resulting specific absorption rate (SAR) increase was analyzed using a full-wave microwave solver. The B1 + field distribution was calculated, and experimental results were compared. As an exemplary application to locate subdural electrodes, these markers were paired with subdural electrodes. It was shown that such sub-cm self-resonant e-markers with biocompatible constituents can be designed and used for implant marking, with sub-mm positioning accuracy, in MRI. In this application, a free-space quality factor ( Q -factor) of approximately 50 was achieved for the proposed resonator architecture. However, this structure caused an SAR increase in certain cases, which limits its usage for in vivo imaging practices. The findings indicate that these implantable resonators hold great promise for wireless fiducial e-marking in MRI as an alternative to multimodal imaging.
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.