Browsing by Subject "Inductive coupling"

Now showing 1 - 4 of 4

Open Access
A catheter tracking method using reverse polarization for MR‐guided interventions
(John Wiley & Sons, Inc., 2007) Celik, H.; Ulutürk, A.; Tali, T.; Atalar, Ergin
To conduct interventional procedures in MRI, reliable visualization of interventional devices such as catheters is necessary. For this purpose, the use of inductively-coupled radio frequency (ICRF) coils has been proposed. Without a wired connection, the signal around the ICRF coil is amplified, enabling catheters to be visualized. The wireless connection allows easy handling of catheters, in some pulse sequences, however, it might be difficult to differentiate the catheters from anatomical background information. In this work, a novel ICRF coil visualization method, which allows separation of the catheter and the anatomical information by using the reverse and forward polarization modes of a coil, is proposed. This method allows images of the anatomy and the catheter to be combined into a color-coded image. First, an ICRF coil with decoupling diodes was constructed; we call this a receive-coupled RF (RCRF) coil. The RF safety profile of the RCRF coil is shown to be better than the ICRF coil. Second, to demonstrate the feasibility of this method, a receive-only birdcage coil without a hybrid coupler was constructed and then connected to a scanner as a two-channel phased-array coil. MR signals acquired from two channels were added after phase adjustments to create the reverse and forward polarization mode images. The reverse polarization mode image contained signal only from the RCRF coil, but the forward polarization mode displayed both anatomical information and the RCRF coil. The performance of this novel tracking method was tested in phantom and animal experiments. Color-coded images demonstrate the feasibility of the method to track catheters using RCRF coils. © 2007 Wiley-Liss, Inc.
Open Access
Development of a distance-independent wireless passive RF resonator sensor and a new telemetric measurement technique for wireless strain monitoring
(Elsevier B.V., 2017) Alipour, A.; Unal, E.; Gokyar, S.; Demir, Hilmi Volkan
We proposed and developed a novel wireless passive RF resonator scheme that enables telemetric strain sensing avoiding the need for calibration at different interrogation distances. The specific architecture of the proposed structure allows for strong inductive coupling and, thus, a higher wireless signal-to-noise ratio. Here, in operation, the frequency scan of the sensor impedance was used to measure simultaneously both the impedance amplitude and resonance frequency. Using this wireless sensor, we further introduced a new telemetric monitoring modality that employs full electrical characteristics of the system to achieve correct strain extraction at any interrogation distance. In principle, any deformation of the sensor structure results in the resonance frequency shift to track strain. However, changing of the interrogation distance also varies the inductive coupling between the sensor and its pick-up antenna at the interrogation distance. Therefore, at varying interrogation distances, it is not possible to attribute an individual resonance frequency value solely to an individual strain level, consequently resulting in discrepancies in the strain extraction if the interrogation distance is not kept fixed or distance-specific calibration is not used. In this work, we showed that by using both the proposed passive sensor structure and wireless measurement technique, strain can be successfully extracted independent of the interrogation distance for the first time. The experimental results indicate high sensitivity and linearity for the proposed system. These findings may open up new possibilities in applications with varying interrogation distance for mobile wireless sensing. © 2017 Elsevier B.V.
Open Access
An inductively coupled ultra-thin, flexible, and passive RF resonator for MRI marking and guiding purposes: Clinical feasibility
(John Wiley & Sons, 2018) Alipour, A.; Gökyar, S.; Algın, O.; Atalar, Ergin; Demir, Hilmi Volkan
Purpose: The purpose of this study is to develop a wireless, flexible, ultra-thin, and passive radiofrequency-based MRI resonant fiducial marker, and to validate its feasibility in a phantom model and several body regions. Methods: Standard microfabrication processing was used to fabricate the resonant marker. The proposed marker consists of two metal traces in the shape of a square with an edge length of 8 mm, with upper and lower traces connected to each other by a metalized via. A 3T MRI fiducial marking procedure was tested in phantom and ex vivo, and then the marker's performance was evaluated in an MRI experiment using humans. The radiofrequency safety was also tested using temperature sensors in the proximity of the resonator. Results: A flexible resonator with a thickness of 115 μm and a dimension of 8 × 8 mm was obtained. The experimental results in the phantom show that at low background flip angles (6-18°), the resonant marker enables precise and rapid visibility, with high marker-to-background contrast and signal-to-noise ratio improvement of greater than 10 in the vicinity of the marker. Temperature analysis showed a specific absorption ratio gain of 1.3. Clinical studies further showed a successful biopsy procedure using the fiducial marking functionality of our device. Conclusions: The ultra-thin and flexible structure of this wireless flexible radiofrequency resonant marker offers effective and safe MR visualization with high feasibility for anatomic marking and guiding at various regions of the body. Magn Reson Med 80:361-370, 2018.
Open Access
Wireless thin-film microwave resonators for sensing and marking
(2017-05) Alipour, Akbar
Rapid progress in wireless microwave technology has attracted increasing interest for high-performance wireless devices. The thin- lm microwave technology is now evolving into the mainstream of applications but signi cant advances are required in resonator architectures and processing for operation in the desired frequency ranges. This dissertation studies the thin- lm microwave technology to develop wireless resonators and describes the core elements that give rise to resonators for high performance in wireless sensing and marking. Speci c to wireless sensing, we proposed and developed a novel wireless microwave resonator scheme that enables telemetric strain sensing avoiding the need for calibration at di erent interrogation distances. In this work, we showed that by using both the proposed sensor architecture and wireless measurement method, strain can be successfully extracted independent of the interrogation distance for the rst time. The experimental results indicate high sensitivity and linearity for the proposed system. This approach enables mobile wireless sensing with varying interrogation distance. For wireless marking, we investigated an ultra-thin, exible, passive radio frequency (RF) based resonator compatible with magnetic resonance imaging (MRI) that successfully was tested in clinic. The ultra-thin and exible architecture of the device o ers an e ective and safe MR visualization and improves the feasibility and reliability of anatomic marking at various surfaces of the body. Results show that, at low background ip angles, the proposed structure enables precise and rapid visibility with high marker-to-background contrast as well as high signal-to-noise ratio (SNR). Also clinical studies have led to a successful biopsy procedure using marking functionality of our device. In another work related to marking, we proposed a new method to enhance local SNR and resolution without disturbing the B1- eld. Here we used our passive RF resonator in the inductively uncoupled mode for endocavity MR imaging. T1- and T2-weighted sequences were employed for phantom and in vivo experiments. The obtained images show the feasibility of the proposed technique to improve the SNR and the resolution in the vicinity of the device. These ndings will allow for new possibilities in applications using wireless sensing and marking approaches shown in this thesis.