Accuracy of electrical field measurement using the flexible Schottky diode sheet at 433 MHz

Rhoon, Gerard C. van; Ameziane, A.; Lee, W. M.; Heuvel, D. J. Van Der; Klinkhamer, H. J.; Barendrecht, C.; Volenec, K; Rietveld, P. J. M.

doi:10.1080/0265673021000035226

Cited by 5 publications

(6 citation statements)

References 9 publications

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“…Our work also suggests further innovations for directly measuring and monitoring E-fields [57]–[59], temperature changes induced by the radiofrequency fields in interventional MRI [60] as well as developments of B 1 + phase mapping techniques at ultrahigh fields and its application for in vivo electrical conductivity and permittivity mapping [61]. Driving the proof-of-principle demonstrated in this study closer to the clinical scenario requires real time feedback capabilities to manage temperature measurements and RF power/RF control simultaneously [23].…”

Section: Discussionmentioning

confidence: 82%

Design and Evaluation of a Hybrid Radiofrequency Applicator for Magnetic Resonance Imaging and RF Induced Hyperthermia: Electromagnetic Field Simulations up to 14.0 Tesla and Proof-of-Concept at 7.0 Tesla

et al. 2013

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This work demonstrates the feasibility of a hybrid radiofrequency (RF) applicator that supports magnetic resonance (MR) imaging and MR controlled targeted RF heating at ultrahigh magnetic fields (B0≥7.0T). For this purpose a virtual and an experimental configuration of an 8-channel transmit/receive (TX/RX) hybrid RF applicator was designed. For TX/RX bow tie antenna electric dipoles were employed. Electromagnetic field simulations (EMF) were performed to study RF heating versus RF wavelength (frequency range: 64 MHz (1.5T) to 600 MHz (14.0T)). The experimental version of the applicator was implemented at B0 = 7.0T. The applicators feasibility for targeted RF heating was evaluated in EMF simulations and in phantom studies. Temperature co-simulations were conducted in phantoms and in a human voxel model. Our results demonstrate that higher frequencies afford a reduction in the size of specific absorption rate (SAR) hotspots. At 7T (298 MHz) the hybrid applicator yielded a 50% iso-contour SAR (iso-SAR-50%) hotspot with a diameter of 43 mm. At 600 MHz an iso-SAR-50% hotspot of 26 mm in diameter was observed. RF power deposition per RF input power was found to increase with B0 which makes targeted RF heating more efficient at higher frequencies. The applicator was capable of generating deep-seated temperature hotspots in phantoms. The feasibility of 2D steering of a SAR/temperature hotspot to a target location was demonstrated by the induction of a focal temperature increase (ΔT = 8.1 K) in an off-center region of the phantom. Temperature simulations in the human brain performed at 298 MHz showed a maximum temperature increase to 48.6C for a deep-seated hotspot in the brain with a size of (19×23×32)mm3 iso-temperature-90%. The hybrid applicator provided imaging capabilities that facilitate high spatial resolution brain MRI. To conclude, this study outlines the technical underpinnings and demonstrates the basic feasibility of an 8-channel hybrid TX/RX applicator that supports MR imaging, MR thermometry and targeted RF heating in one device.

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Section: Discussionmentioning

confidence: 82%

Design and Evaluation of a Hybrid Radiofrequency Applicator for Magnetic Resonance Imaging and RF Induced Hyperthermia: Electromagnetic Field Simulations up to 14.0 Tesla and Proof-of-Concept at 7.0 Tesla

et al. 2013

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“…Although, compared to flat-phantom EFS measurements, the distributions obtained in this publication show much higher SAR gradients and therefore heat conduction might have somewhat more influence, by comparing the thermography results to the fiber probe measurement we could show that this influence remains low. By using the Schottky-diode E-field sheet [26] [25] we performed E-field measurements that can be performed at low power thus dynamic SAR steering with the prototype can be assessed. A major drawback of this equipment is its low resolution because it was designed for superficial hyperthermia applicator assessments in flat phantoms were the fields are more gradual.…”

Section: Resultsmentioning

confidence: 99%

“…For fast measurements, which also enables studying the prototypes dynamic behavior, we performed SAR measurements also with the E-field Schottky diode sheet, that is described in Kaatee et al [25] and Van Rhoon et al [26]. Hereto, two sheets were positioned between both halves of the prototype ( Figure 3).…”

Section: E-field Schottky-diode Sheetmentioning

confidence: 99%

“…all distributions can be measured using one single disposition of the experimental setup. Without calibration their accuracy is 6% [26], however when airgaps are present close to the diodes this accuracy is reduced due to lower sensitivity. A main disadvantage of the current design of the sheet is its poor spatial resolution for measurements at 433MHz, i.e.…”

Section: E-field Schottky-diode Sheetmentioning

confidence: 99%

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Electromagnetic Head-And-Neck Hyperthermia Applicator: Experimental Phantom Verification and FDTD Model

Paulides

Bakker

Rhoon

2007

International Journal of Radiation Oncology*Biology*Physics

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Purpose: Experimental verification of the feasibility of focussed heating in the neck region by an array of two rings of six electromagnetic antennas. We further measured the dynamic specific absorption rate (SAR) steering possibilities of this setup and compared these SAR patterns to simulations. Methods and Materials: By a specially constructed laboratory prototype head and neck applicator, including a neck mimicking cylindrical muscle phantom, we performed SAR measurements by electric-field Schottky-diode sheet measurements and, using the power-pulse technique, by fiberoptic thermometry and infra-red (IR) thermography. Using phase-steering, we also steered the SAR distribution in radial and axial directions. All measured distributions where compared to predictions by a finite-difference time-domain (FDTD)-based electromagnetic simulator. Results: A central 50% iso-SAR focus of 35mm (±3mm) in diameter and around 100mm (±15mm) in length are obtained for all investigated settings. Further, this SAR focus can be steered towards the desired location in radial and axial direction with an accuracy of ∼5mm. SAR distributions as measured by all three experimental methods are well predicted by the simulations. Conclusions: We conclude that focussed heating in the neck is feasible and that this focus can effectively be steered in both radial and axial direction. For quality assurance (QA) measurements we conclude that the Schottky-diode sheet provides the best compromise between effort, speed and accuracy, though a more specific and improved design is warranted.

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“…The diode sheet consists of 8 Â 8 diodes of which the resolution is 2.5 Â 2.5 cm 2 /diode and is explained in detail by Kaatee et al 15 and Van Rhoon et al 16 . For the measurement of SAR x and SAR y in both phantoms, antenna element 8 is supplied with an input power of 30 W only, whereas all other antenna elements are terminated with 50 loads.…”

Section: Sar Distribution Of a Single Antenna Element At Different Dementioning

confidence: 99%

Assessment of the performance characteristics of a prototype 12-element capacitive contact flexible microstrip applicator (CFMA-12) for superficial hyperthermia

Lee

Gelvich²,

Baan

et al. 2004

International Journal of Hyperthermia

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The electrical performance of the CFMA-12 operating at 433 MHz is assessed under laboratory conditions using a RF network analyser. From measurements of the scattering parameters of the CFMA-12 on both a multi-layered muscle- and fat/muscle-equivalent phantom, the optimal water bolus thickness, at which the transfer of the energy to the phantom configuration is maximal, is determined to be approximately 1 cm. The SAR distribution of the CFMA-12 in a multi-layered muscle-equivalent phantom is characterized using Schottky diode sheets and a TVS-600 IR camera. From the SAR measurements using the Schottky diode sheets it is shown that the contribution of the E(x) component to the SAR (SAR(x)) is maximal 7% of the contribution of the E(y)component to the SAR (SAR(y)) at different layers in both phantom configurations. The complete SAR distribution (SAR(tot)) at different depths is measured using the power pulse technique. From these measurements, it can be seen that SAR(y)at a depth of 0 cm in the muscle-equivalent phantom represents up to 80% of SAR(tot). At 1 and 2 cm depth, SAR(y) is up to 95% of SAR(tot). Therefore, in homogeneous muscle-equivalent phantoms, E(y) is the largest E-field component and measurement of SAR(y) distribution is sufficient to characterize SAR-steering performance of the CFMA-12. SAR steering measurements at 1 cm depth in the muscle-equivalent phantom show that the SAR maximum varies by 40% (1 SD) around the average value of 38.8 W kg(-1) (range 10-65 W kg(-1)) between single antenna elements. The effective fieldsize (E(50)) varies by 14% (1 SD) around the average value of 19.1 cm(2).

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Accuracy of electrical field measurement using the flexible Schottky diode sheet at 433 MHz

Cited by 5 publications

References 9 publications

Design and Evaluation of a Hybrid Radiofrequency Applicator for Magnetic Resonance Imaging and RF Induced Hyperthermia: Electromagnetic Field Simulations up to 14.0 Tesla and Proof-of-Concept at 7.0 Tesla

Design and Evaluation of a Hybrid Radiofrequency Applicator for Magnetic Resonance Imaging and RF Induced Hyperthermia: Electromagnetic Field Simulations up to 14.0 Tesla and Proof-of-Concept at 7.0 Tesla

Electromagnetic Head-And-Neck Hyperthermia Applicator: Experimental Phantom Verification and FDTD Model

Assessment of the performance characteristics of a prototype 12-element capacitive contact flexible microstrip applicator (CFMA-12) for superficial hyperthermia

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