MR Computer GmbH

Gelsenkirchen, Germany

MR Computer GmbH

Gelsenkirchen, Germany
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Kozlov M.,MR Computer GmbH | Kozlov M.,Max Planck Institute for Human Cognitive and Brain Sciences | Schaefers G.,MR Computer GmbH | Schaefers G.,Institute for Safety Technology GmbH
Proceedings of the 12th IASTED International Conference on Biomedical Engineering, BioMed 2016 | Year: 2016

For insulated stainless steel wires of 1.5 mm in diameter with 0.5 mm insulation thickness, we evaluated the dependence of 64 MHz RF-induced power deposited at a hotspot (p) on: 1) lead length, 2) lead insulating electrical properties, 3) lead surrounding medium. Lead transfer functions (TF) were obtained with 3-D electromagnetic simulations. TF and p depended significantly on electrical properties of the insulation and lead surrounding medium. Increased insulator conductivity resulted in decreased p in most investigated cases. It is impossible to define one test surrounding medium that results in worst case power deposition for all cases: a) different lead lengths; b) different electrical properties of the lead insulator; and c) different tissues surrounding the lead in human body.


Kozlov M.,MR Computer GmbH | Schaefers G.,MR Computer GmbH | Schaefers G.,MRI STaR GmbH
2016 IEEE Conference on Antenna Measurements and Applications, CAMA 2016 | Year: 2016

At 64 and 127 MHz for insulated stainless steel wires with an insulation diameter of 1.46 mm, we evaluated the dependence of RF-induced power deposited at a hotspot (p) on wire and tip electrode diameters. The lead electrical length, the transfer functions obtained with 3-D electromagnetic simulations and the power deposition p significantly depended on wire diameter and substantially on tip electrode diameter. Discrepancy of results was up to 1280% at 64 MHz and up to 3200% at 127 MHz. © 2016 IEEE.


Kozlov M.,MR Computer GmbH | Schaefers G.,MR Computer GmbH | Schaefers G.,MRI STaR GmbH
2016 IEEE Conference on Antenna Measurements and Applications, CAMA 2016 | Year: 2016

At 64 and 127 MHz for eight electrode leads with an insulation diameter of 1.46 mm, we evaluated the dependence of RF-induced power (p) generated by a plane wave incident field at electrodes on: distance between leads, electrical properties of surrounding media. At both frequencies and for all investigated surrounding media three cases were observed: p remained practically unaffected due to presence of the second lead, p was reduced up to 90%, p was increased by as much as 3. © 2016 IEEE.


Grant
Agency: European Commission | Branch: FP7 | Program: MC-ITN | Phase: FP7-PEOPLE-ITN-2008 | Award Amount: 3.71M | Year: 2009

The scope of the present consortium is to provide technology and training for the integration of ultrasound and biophotonics based imaging with magnetic resonance imaging (MRI), Computed Tomography (CT) and Positron Emission Tomography (PET) to define the specs of an Integrated Interventional Imaging Operating System (III OS) aimed at minimal invasive treatment of common life-threatening disorders, e.g., cancer, cardiovascular disease and structural heart defects. Effective therapy of these conditions will require a range of safe surgical and interventional devices used with the necessary visualization and tracking under real-time image guidance. The consortium includes a critical mass of industrial and university research institute partners with high expertise in design, development, and manufacture of these devices and instruments. To ensure medical the safety and economical usability of the system and to allow an optimal integration into the future hospital workflow, 6 university hospitals will contribute their clinical and administrative expertise to the consortium in the fields of Interventional Radiology/Cardiology, Anaesthesia, Oncology, General and Cardiovascular Surgery and preclinical Image guided procedures. The consortium of the IIIOS research and training process includes two Biomedical Technology Societies: DGBMT and SMIT&MEDIS Foundation in Rumania providing expert networking and conference organization. The is involved in the consortium and will play a key role in the exchange of knowledge and expertise to the new member states of the EU through hosting conferences such SMIT 2009 in Sinaia (www.smit2009.com).


Kraff O.,University of Duisburg - Essen | Wrede K.H.,University of Duisburg - Essen | Schoemberg T.,University of Duisburg - Essen | Dammann P.,University of Duisburg - Essen | And 5 more authors.
Medical Physics | Year: 2013

Purpose: The increasing number of clinically oriented MRI studies at 7 T motivates the safety assessment of implants, since many 7 T research sites conservatively exclude all subjects with metallic implants, regardless of type or location. The purpose of this study was to investigate potential RF-induced heating during a 7 T MRI scan using a self-built transmitreceive RF coil in patients with implants used for refixation of the bone flap after craniotomy. Going beyond standard ASTM safety tests, a comprehensive test procedure for safety assessments at 7 T is presented which takes into account the more complex coupling of the electromagnetic field with the human body and the implant as well as polarization effects. Methods: The safety assessment consisted of three main investigations using (1) numerical simulations in simplified models, (2) electric and magnetic field measurements and validation procedures in homogeneous phantoms, and (3) analysis of exposure scenarios in a heterogeneous human body model including thermal simulations. Finally, 7 T in vivo images show the degree of image artifact around the implants. Results: The simulations showed that the field distortions remain localized within the direct vicinity of the implants. A parallel E-field polarization was found to be the most relevant component in creating local SAR deviations, resulting in a 10 increase in 10-g-averaged SAR and 53 in 1-g-averaged SAR. Using a heterogeneous human head model, the implants caused field distortions and SAR elevations in the numerical simulations which were distinctly lower than the maximum local SAR value caused by the RF coil alone. Also, the position of the maximum 10-g-averaged SAR remained unchanged by the presence of the implants. Similarly, the maximum absolute local temperature remained below 39 °C in the thermal simulations. Only minor artifacts from the implants were observed in the in vivo images that would not likely affect the diagnostic image quality in patients. Conclusions: The findings suggested no evidence for noteworthy RF-related heating in humans after craniotomy using the described implants and for the particular RF coil that was used in this study. Here, identical transmit power restrictions apply with or without the implants. For other RF coils, the maximum permissible input power should be reduced by 10 until further simulations may indicate otherwise. © 2013 American Association of Physicists in Medicine.


Kozlov M.,MR Computer GmbH | Schaefers G.,MR Computer GmbH
2015 IEEE International Conference on Microwaves, Communications, Antennas and Electronic Systems, COMCAS 2015 | Year: 2015

The implant model obtained by 3D EM and thermal co-simulation was used to estimate power deposition and temperature rise due to the presence of bare titanium rods placed in a high permittivity medium for uniform and non-uniform 64 MHz incident electric fields. No correlation between power deposition and temperature rise were observed. Worst-case temperature rise for an implant with a fixed diameter and variable length excited by a tangential electric field with constant amplitude can be estimated using the implant thermal model. For other cases further extensive investigations are required. © 2015 IEEE.


Kozlov M.,MR Computer GmbH | Schaefers G.,MR Computer GmbH
2015 IEEE International Conference on Microwaves, Communications, Antennas and Electronic Systems, COMCAS 2015 | Year: 2015

We numerically investigated volume loss density and temperature rise generated due to presence of a titanium rod placed in an ASTM F2182-11a high permittivity medium which was excited by radio frequency (RF) 64 MHz plane waves. 3-D electromagnetic and thermal co-simulations were performed for continuous wave and time-varied excitations. If time variable RF excitation that reaches the limit set by the short duration specific absorption rate limit and the implant thermal time constant is comparable to or less than 10s, RF induced heating on and near an implant during magnetic resonance imaging can be up to factor of 2 higher than RF induced heating caused by continuous RF excitation reaches the limit set by whole body specific absorption rate limit defined by IEC 60601-2-33. If the thermal time constant is significantly longer than 10 s, continuous wave excitation results in a reliable assessment of the maximum temperature rise. © 2015 IEEE.


Lu Z.,University of Missouri | Camps-Raga B.,MR Computer GmBH | Islam N.E.,University of Missouri
Physics Research International | Year: 2012

The concept of a single frequency band, single high-refractive-index metamaterial has been extended and applied in the design of dual frequency band, dual high-refractive-index metamaterials in the THz regime. The structure design consists of twenty five unit cells with a surface area of 250 um by 250 um and a thickness of 5 um. Each cell has metallic structures embedded in a polyimide substrate. The return loss (S-parameter) analysis shows two strong electric responses at two frequency ranges, and the extracted constitutive parameters suggested high values of simultaneous dielectric constant and permeability at these frequencies. Results retrieved from the S-parameters also show high refractive index values. A first peak refractive index of 61.83 was observed at a resonant frequency of 0.384 THz, and another peak refractive index of 19.2 was observed at the resonant frequency 1.416 THz. Analysis show that higher refractive index at the second resonance frequency band is achievable through redesign of the structures, and modifications could lead to a single structure with multiple frequency, multiple high-refractive-index metamaterials that can be put to practical use. © 2012 Zan Lu et al.


Kozlov M.,MR Computer GmbH | Kozlov M.,Max Planck Institute for Human Cognitive and Brain Sciences | Schaefers G.,MR Computer GmbH
Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS | Year: 2015

We numerically investigated power deposition and temperature rise generated due to the presence of a titanium rod placed in a phantom, located inside a 1.5 T coil. The induced power deposition and temperature rise normalized to incident tangential electric field was found to be dependent on distance to the phantom wall. The different dependence of the integral of power deposition over a box surrounded the rod and the temperature rise on American Society for Testing and Materials (ASTM) phantom medium electrical conductivity was observed. The consequences of numerical domain simplification have been analyzed. © 2015 IEEE.


Schmitt S.,Gelsenkirchen University of Applied Sciences | Choli M.,MR Computer GmbH | Overhoff H.M.,Gelsenkirchen University of Applied Sciences
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2015

MRI-guided interventions have gained much interest. They profit from intervention synchronous data acquisition and image visualization. Due to long data acquisition durations, ergonomic limitations may occur. For a trueFISP MRI-data acquisition sequence, a time sparing sub-sampling strategy has been developed that is adapted to amagnetic needle detection. A symmetrical and contrast rich susceptibility needle artifact, i.e. an approximately rectangular gray scale profile is assumed. The 1-D-Fourier transformed of a rectangular function is a sinc-function. Its periodicity is exploited by sampling only along a few orthogonal trajectories in k-space. Because a needle moves during intervention, its tip region resembles a rectangle in a time-difference image that is reconstructed from such sub-sampled k-spaces acquired at different time stamps. In different phantom experiments, a needle was pushed forward along a reference trajectory, which was determined from a needle holders geometric parameters. In addition, the trajectory of the needle tip was estimated by the method described above. Only ca. 4 to 5 % of the entire k-space data was used for needle tip estimation. The misalignment of needle orientation and needle tip position, i.e. the differences between reference and estimated values, is small and even in its worst case less than 2 mm. The results show that the method is applicable under nearly real conditions. Next steps are addressed to the validation of the method for clinical data. © 2015 SPIE.

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