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Bardwell Speltz LJ, Lee SK, Shu Y, Tarasek MR, Trzasko JD, Foo TKF, Bernstein MA. Modeling and measurement of lead tip heating and resonant length for implanted, insulated wires. Magn Reson Med 2024; 92:1714-1727. [PMID: 38818673 DOI: 10.1002/mrm.30145] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2023] [Revised: 04/15/2024] [Accepted: 04/18/2024] [Indexed: 06/01/2024]
Abstract
PURPOSE To study implant lead tip heating because of the RF power deposition by developing mathematical models and comparing them with measurements acquired at 1.5 T and 3 T, especially to predict resonant length. THEORY AND METHODS A simple exponential model and an adapted transmission line model for the electric field transfer function were developed. A set of wavenumbers, including that calculated from insulated antenna theory (King wavenumber) and that of the embedding medium were considered. Experiments on insulated, capped wires of varying lengths were performed to determine maximum temperature rise under RF exposure. The results are compared with model predictions from analytical expressions derived under the assumption of a constant electric field, and with those numerically calculated from spatially varying, simulated electric fields from body coil transmission. Simple expressions for the resonant length bounded between one-quarter and one-half wavelength are developed based on the roots of transcendental equations. RESULTS The King wavenumber for both models more closely matched the experimental data with a maximum root mean square error of 9.81°C at 1.5 T and 5.71°C at 3 T compared to other wavenumbers with a maximum root mean square error of 27.52°C at 1.5 T and 22.01°C for 3 T. Resonant length was more accurately predicted compared to values solely based on the embedding medium. CONCLUSION Analytical expressions were developed for implanted lead heating and resonant lengths under specific assumptions. The value of the wavenumber has a strong effect on the model predictions. Our work could be used to better manage implanted device lead tip heating.
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Affiliation(s)
- Lydia J Bardwell Speltz
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
- Mayo Clinic Graduate School of Biomedical Sciences, Mayo Clinic, Rochester, Minnesota, USA
| | - Seung-Kyun Lee
- Technology and Innovation Center, GE HealthCare, GE Research, Niskayuna, New York, USA
| | - Yunhong Shu
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
| | - Matthew R Tarasek
- Technology and Innovation Center, GE HealthCare, GE Research, Niskayuna, New York, USA
| | | | - Thomas K F Foo
- Technology and Innovation Center, GE HealthCare, GE Research, Niskayuna, New York, USA
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Zulkarnain NIH, Sadeghi-Tarakameh A, Thotland J, Harel N, Eryaman Y. A workflow for predicting radiofrequency-induced heating around bilateral deep brain stimulation electrodes in MRI. Med Phys 2024; 51:1007-1018. [PMID: 38153187 PMCID: PMC10922480 DOI: 10.1002/mp.16913] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Revised: 10/04/2023] [Accepted: 12/10/2023] [Indexed: 12/29/2023] Open
Abstract
BACKGROUND Heating around deep brain stimulation (DBS) in magnetic resonance imaging (MRI) occurs when the time-varying electromagnetic (EM) fields induce currents in the electrodes which can generate heat and potentially cause tissue damage. Predicting the heating around the electrode contacts is important to ensure the safety of patients with DBS implants undergoing an MRI scan. We previously proposed a workflow to predict heating around DBS contacts and introduced a parameter, equivalent transimpedance, that is independent of electrode trajectories, termination, and radiofrequency (RF) excitations. The workflow performance was validated in a unilateral DBS system. PURPOSE To predict RF heating around the contacts of bilateral (DBS) electrodes during an MRI scan in an anthropomorphic head phantom. METHODS Bilateral electrodes were fixed in a skull phantom filled with hydroxyethyl cellulose (HEC) gel. The electrode shafts were suspended extracranially, in a head and torso phantom filled with the same gel material. The current induced on the electrode shaft was experimentally measured using an MR-based technique 3 cm above the tip. A transimpedance value determined in a previous offline calibration was used to scale the shaft current and calculate the contact voltage. The voltage was assigned as a boundary condition on the electrical contacts of the electrode in a quasi-static (EM) simulation. The resulting specific absorption rate (SAR) distribution became the input for a transient thermal simulation and was used to predict the heating around the contacts. RF heating experiments were performed for eight different lead trajectories using circularly polarized (CP) excitation and two linear excitations for one trajectory. The measured temperatures for all experiments were compared with the simulated temperatures and the root-mean-squared errors (RMSE) were calculated. RESULTS The RF heating around the contacts of both bilateral electrodes was predicted with ≤ 0.29°C of RMSE for 20 heating scenarios. CONCLUSION The workflow successfully predicted the heating for different bilateral DBS trajectories and excitation patterns in an anthropomorphic head phantom.
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Affiliation(s)
- Nur Izzati Huda Zulkarnain
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, 55455, USA
| | - Alireza Sadeghi-Tarakameh
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, 55455, USA
| | - Jeromy Thotland
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, 55455, USA
| | - Noam Harel
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, 55455, USA
| | - Yigitcan Eryaman
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, 55455, USA
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Petzold J, Schmitter S, Silemek B, Winter L, Speck O, Ittermann B, Seifert F. Towards an integrated radiofrequency safety concept for implant carriers in MRI based on sensor-equipped implants and parallel transmission. NMR IN BIOMEDICINE 2023; 36:e4900. [PMID: 36624556 DOI: 10.1002/nbm.4900] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Revised: 10/11/2022] [Accepted: 01/04/2023] [Indexed: 06/15/2023]
Abstract
To protect implant carriers in MRI from excessive radiofrequency (RF) heating it has previously been suggested to assess that hazard via sensors on the implant. Other work recommended parallel transmission (pTx) to actively mitigate implant-related heating. Here, both ideas are integrated into one comprehensive safety concept where native pTx safety (without implant) is ensured by state-of-the-art field simulations and the implant-specific hazard is quantified in situ using physical sensors. The concept is demonstrated by electromagnetic simulations performed on a human voxel model with a simplified spinal-cord implant in an eight-channel pTx body coil at 3 T . To integrate implant and native safety, the sensor signal must be calibrated in terms of an established safety metric (e.g., specific absorption rate [SAR]). Virtual experiments show that E -field and implant-current sensors are well suited for this purpose, while temperature sensors require some caution, and B 1 probes are inadequate. Based on an implant sensor matrix Q s , constructed in situ from sensor readings, and precomputed native SAR limits, a vector space of safe RF excitations is determined where both global (native) and local (implant-related) safety requirements are satisfied. Within this safe-excitation subspace, the solution with the best image quality in terms of B 1 + magnitude and homogeneity is then found by a straightforward optimization algorithm. In the investigated example, the optimized pTx shim provides a 3-fold higher mean B 1 + magnitude compared with circularly polarized excitation for a maximum implant-related temperature increase ∆ T imp ≤ 1 K . To date, sensor-equipped implants interfaced to a pTx scanner exist as demonstrator items in research labs, but commercial devices are not yet within sight. This paper aims to demonstrate the significant benefits of such an approach and how this could impact implant-related RF safety in MRI. Today, the responsibility for safe implant scanning lies with the implant manufacturer and the MRI operator; within the sensor concept, the MRI manufacturer would assume much of the operator's current responsibility.
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Affiliation(s)
- Johannes Petzold
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
- Biomedical Magnetic Resonance, Otto von Guericke University Magdeburg, Magdeburg, Germany
| | - Sebastian Schmitter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Berk Silemek
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Lukas Winter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Oliver Speck
- Biomedical Magnetic Resonance, Otto von Guericke University Magdeburg, Magdeburg, Germany
| | - Bernd Ittermann
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Frank Seifert
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
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Bhusal B, Bhattacharyya P, Baig T, Jones S, Martens M. Effect of inter-electrode RF coupling on heating patterns of wire-like conducting implants in MRI. Magn Reson Med 2022; 87:2933-2946. [PMID: 35092097 DOI: 10.1002/mrm.29177] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2021] [Revised: 12/16/2021] [Accepted: 01/09/2022] [Indexed: 11/05/2022]
Abstract
PURPOSE In this study, the effects of RF coupling on the magnitude and spatial patterns of RF-induced heating near multiple wire-like conducting implants (such as simultaneous electrical stimulation of stereoelectroencephalography electrodes) during MRI were assessed. METHODS Simulations and experimental measurements of RF-induced temperature increases near partially immersed wire-like conductors were performed using a phantom with a transmit/receive head coil on a 3T MRI system. The conductors consisted of either a pair of wires or a single simultaneous electrical stimulation of stereoelectroencephalography electrode with multiple contacts, and the locations and lengths of the conductors were varied to study the effect of electromagnetic coupling on RF-induced heating. RESULTS The temperature increase near a wire within the phantom was dependent not only on its own location and length, but also on the locations and lengths of the other partially immersed wires. In the configurations that were studied, the presence of a second implant could increase the heating near the tip of the conductor by as much as 95%. CONCLUSION The level of RF-induced heating during an MR scan is affected significantly by RF coupling when more than one wire-like implant is present. In some of the configurations studied, the heating was increased by the presence of a second conductor partially immersed in the phantom. Thus, RF coupling is an important factor to consider in the assessment of safety issues for MRI when multiple implants are present.
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Affiliation(s)
- Bhumi Bhusal
- Department of Radiology, Northwestern University, Chicago, Illinois, USA
| | | | - Tanvir Baig
- Department of Radiation Oncology, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA
| | - Stephen Jones
- Imaging Institute, Cleveland Clinic, Cleveland, Ohio, USA
| | - Michael Martens
- Department of Physics, Case Western Reserve University, Cleveland, Ohio, USA
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Zheng J, Yang R, Wang Q, Guo R, Xu J, Shou X, Kainz W, Chen J. Reducing MRI RF-induced heating for the external fixation using capacitive structures. Phys Med Biol 2020; 65:155017. [PMID: 32460252 DOI: 10.1088/1361-6560/ab9706] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This paper presents a generic method to reduce the radiofrequency (RF) induced heating of external fixation devices during the magnetic resonance imaging (MRI) procedure. A simplified equivalent circuit model was developed to illustrate the interaction between the external fixation device and the MRI RF field. Carefully designed mechanical structures, which utilize capacitive reactance from the circuit model, were applied to the external fixation device to mitigate the coupling between the external fixation device and the MRI RF field for RF-induced heating reduction. Both numerical and experimental studies were performed to demonstrate the validity of the circuit model and the effectiveness of the proposed method. By adding capacitive structures in both the clamp-pin and rod-clamp joints, the peak specific absorption rate averaged in 1 gram (SAR1g) near the pin tips were reduced from 760.4 W kg-1 to 12.0 W kg-1 at 1.5 T and 391.5 W kg-1 to 25.2 W kg-1 at 3 T from numerical simulations. Experimental results showed that RF-induced heating was reduced from 7.85 °C to 1.01 °C at 1.5 T and from 16.70 °C to 0.32 °C at 3 T for the external fixation device studied here. The carefully designed capacitive structures can be used to detune the coupling between the external fixation device and the MRI fields to reduce the RF-induced heating in the human body for both 1.5 T and 3 T MRI systems. However, as RF-induced heating is very device and design specific all devices must be thoroughly tested based on its final design.
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Affiliation(s)
- Jianfeng Zheng
- Dept. of Electrical and Computer Engineering, University of Houston, Houston, TX, 77204-4005, United States of America
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Winter L, Seifert F, Zilberti L, Murbach M, Ittermann B. MRI‐Related Heating of Implants and Devices: A Review. J Magn Reson Imaging 2020; 53:1646-1665. [DOI: 10.1002/jmri.27194] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Revised: 04/29/2020] [Accepted: 04/30/2020] [Indexed: 12/11/2022] Open
Affiliation(s)
- Lukas Winter
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Frank Seifert
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Luca Zilberti
- Istituto Nazionale di Ricerca Metrologica Torino Italy
| | - Manuel Murbach
- ZMT Zurich MedTech AG Zurich Switzerland
- Institute for Molecular Instrumentation and Imaging (i3M) Universidad Politécnica de Valencia (UPV) Valencia Spain
| | - Bernd Ittermann
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
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Özen AC, Silemek B, Lottner T, Atalar E, Bock M. MR safety watchdog for active catheters: Wireless impedance control with real-time feedback. Magn Reson Med 2020; 84:1048-1060. [PMID: 31961965 DOI: 10.1002/mrm.28153] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Revised: 11/29/2019] [Accepted: 12/09/2019] [Indexed: 12/13/2022]
Abstract
PURPOSE To dynamically minimize radiofrequency (RF)-induced heating of an active catheter through an automatic change of the termination impedance. METHODS A prototype wireless module was designed that modifies the input impedance of an active catheter to keep the temperature rise during MRI below a threshold, ΔTmax . The wireless module (MR safety watchdog; MRsWD) measures the local temperature at the catheter tip using either a built-in thermistor or external data from a fiber-optical thermometer. It automatically changes the catheter input impedance until the temperature rise during MRI is minimized. If ΔTmax is exceeded, RF transmission is blocked by a feedback system. RESULTS The thermistor and fiber-optical thermometer provided consistent temperature data in a phantom experiment. During MRI, the MRsWD was able to reduce the maximum temperature rise by 25% when operated in real-time feedback mode. CONCLUSION This study demonstrates the technical feasibility of an MRsWD as an alternative or complementary approach to reduce RF-induced heating of active interventional devices. The automatic MRsWD can reduce heating using direct temperature measurements at the tip of the catheter. Given that temperature measurements are intrinsically slow, for a clinical implementation, a faster feedback parameter would be required such as the RF currents along the catheter or scattered electric fields at the tip.
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Affiliation(s)
- Ali Caglar Özen
- Department of Radiology, Medical Physics, Medical Center - University of Freiburg, Freiburg, Germany.,Faculty of Medicine, University of Freiburg, Freiburg, Germany.,German Consortium for Translational Cancer Research Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Berk Silemek
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey.,Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Thomas Lottner
- Department of Radiology, Medical Physics, Medical Center - University of Freiburg, Freiburg, Germany
| | - Ergin Atalar
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey.,Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey
| | - Michael Bock
- Department of Radiology, Medical Physics, Medical Center - University of Freiburg, Freiburg, Germany
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Acikel V, Silemek B, Atalar E. Wireless control of induced radiofrequency currents in active implantable medical devices during MRI. Magn Reson Med 2019; 83:2370-2381. [DOI: 10.1002/mrm.28089] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 10/16/2019] [Accepted: 10/29/2019] [Indexed: 11/09/2022]
Affiliation(s)
| | - Berk Silemek
- National Magnetic Resonance Research Center (UMRAM) Bilkent University Ankara Turkey
| | - Ergin Atalar
- National Magnetic Resonance Research Center (UMRAM) Bilkent University Ankara Turkey
- Department of Electrical and Electronics Engineering Bilkent University Ankara Turkey
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Missoffe A, Barbier T, Felblinger J. Finite difference transmission line model for the design of safe multi-section cables in MRI. MAGMA (NEW YORK, N.Y.) 2019; 32:449-459. [PMID: 30783887 DOI: 10.1007/s10334-019-00744-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2018] [Revised: 02/07/2019] [Accepted: 02/08/2019] [Indexed: 06/09/2023]
Abstract
OBJECTIVE To show the relevance of a simple finite difference transmission line model to help design safe implanted cables in 1.5T MRI's using the multi-section cable approach. MATERIALS AND METHODS The transfer function and heating under a given incident field predicted by the finite difference model for two-section cables are compared to full-wave and experimental results. The finite difference model was then used to design a three-section cable considering the phase effects. RESULTS The differences between the predicted transfer function given by the transmission line model with the full-wave results and the experimental results are, respectively, less than 10% and less than 5%. The predicted heating differed by less than 7% with the full-wave results and less than 25% with the experimental results. The optimum lengths of the three-section cable reduces by 51% the worst case heating at the electrodes compared to the best case unique section wire. DISCUSSION The multi-section cable design can reduce the heating of cables in MRI taking into account phase effects. The finite difference transmission line model presented is a simple valuable tool to estimate the worst case heating of simple multi-section cables.
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Affiliation(s)
- Alexia Missoffe
- IADI (Université de Lorraine-INSERM), Bâtiment Recherche, CHRU de Nancy Brabois, Rue du Morvan, 54511, Vandoeuvre Cedex, France.
| | - Thérèse Barbier
- IADI (Université de Lorraine-INSERM), Bâtiment Recherche, CHRU de Nancy Brabois, Rue du Morvan, 54511, Vandoeuvre Cedex, France
- Axon Cable R&D, Montmirail, France
| | - Jacques Felblinger
- IADI (Université de Lorraine-INSERM), Bâtiment Recherche, CHRU de Nancy Brabois, Rue du Morvan, 54511, Vandoeuvre Cedex, France
- CIC 1433 INSERM, CHRU, Nancy, France
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Özen AC, Lottner T, Bock M. Safety of active catheters in MRI: Termination impedance versus RF‐induced heating. Magn Reson Med 2018; 81:1412-1423. [DOI: 10.1002/mrm.27481] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 06/08/2018] [Accepted: 07/15/2018] [Indexed: 11/06/2022]
Affiliation(s)
- Ali Caglar Özen
- Department of Radiology, Medical Physics, Medical Center ‐ University of Freiburg, Faculty of Medicine University of Freiburg Freiburg Germany
- German Cancer Consortium Partner Site Freiburg, German Cancer Research Center (DKFZ) Heidelberg Germany
| | - Thomas Lottner
- Department of Radiology, Medical Physics, Medical Center ‐ University of Freiburg, Faculty of Medicine University of Freiburg Freiburg Germany
| | - Michael Bock
- Department of Radiology, Medical Physics, Medical Center ‐ University of Freiburg, Faculty of Medicine University of Freiburg Freiburg Germany
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Bhusal B, Bhattacharyya P, Baig T, Jones S, Martens M. Measurements and simulation of RF heating of implanted stereo-electroencephalography electrodes during MR scans. Magn Reson Med 2018; 80:1676-1685. [DOI: 10.1002/mrm.27144] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2017] [Revised: 01/26/2018] [Accepted: 01/31/2018] [Indexed: 12/18/2022]
Affiliation(s)
- Bhumi Bhusal
- Department of Physics; Case Western Reserve University; Cleveland Ohio USA
| | - Pallab Bhattacharyya
- Imaging Institute, Cleveland Clinic; Cleveland Ohio USA
- Radiology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University; Cleveland Ohio USA
| | - Tanvir Baig
- Department of Physics; Case Western Reserve University; Cleveland Ohio USA
| | - Stephen Jones
- Imaging Institute, Cleveland Clinic; Cleveland Ohio USA
- Epilepsy Center, Cleveland Clinic; Cleveland Ohio USA
| | - Michael Martens
- Department of Physics; Case Western Reserve University; Cleveland Ohio USA
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Silemek B, Acikel V, Oto C, Alipour A, Aykut ZG, Algin O, Atalar E. A temperature sensor implant for active implantable medical devices for in vivo subacute heating tests under MRI. Magn Reson Med 2017; 79:2824-2832. [DOI: 10.1002/mrm.26914] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2017] [Revised: 08/17/2017] [Accepted: 08/17/2017] [Indexed: 11/09/2022]
Affiliation(s)
- Berk Silemek
- National Magnetic Resonance Research Center (UMRAM)Bilkent UniversityAnkara Turkey
| | - Volkan Acikel
- Aselsan, REHIS Power Amplifier TechnologiesAnkara Turkey
| | - Cagdas Oto
- Department of AnatomyAnkara UniversityAnkara Turkey
| | - Akbar Alipour
- National Magnetic Resonance Research Center (UMRAM)Bilkent UniversityAnkara Turkey
- Department of Electrical and Electronics EngineeringBilkent UniversityAnkara Turkey
| | - Zaliha Gamze Aykut
- Department of Molecular Biology and GeneticsBilkent UniversityAnkara Turkey
| | - Oktay Algin
- National Magnetic Resonance Research Center (UMRAM)Bilkent UniversityAnkara Turkey
- Department of RadiologyAtaturk Training and Research HospitalAnkara Turkey
| | - Ergin Atalar
- National Magnetic Resonance Research Center (UMRAM)Bilkent UniversityAnkara Turkey
- Department of Electrical and Electronics EngineeringBilkent UniversityAnkara Turkey
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