Design Considerations for Radiofrequency Whole-Body and Head Coils
Read Description
Alternatively, full-orthogonal excitation of the coil, if possible, would mitigate this design challenge, especially if high-Q operation cannot be guaranteed. In this contribution a field theoretical technique for the optimization of the capacitive coupling is introduced and applied to the birdcage configuration as representative of TEM coils. A fairly general analysis of these coils is also introduced and/or revisited, which underlies the proposed technique and offers simple analytic design equations. Simulation results are presented to validate the considered approach. The presented analysis deals with the homogeneously filled coils and therefore does not consider the B+1 inhomogeneities caused by the loading. The latter will be the subject of future publications.
Portable Microwave Head Imaging System Using Software-Defined Radio and Switching Network
Read Description
This paper proposes a portable microwave head imaging system that can easily be taken to the patient. The system utilises a novel combination of a software-defined radio and solid-state switching network to collect the imaging data, and operates in the frequency band of 0.85 – 2 GHz. It can capture input signals over a range of approximately 106 dB, which is suitable for detecting realistic brain injuries. The concept has been validated through experimental data collection and confocal image generation, and was capable of producing images in less than a minute. A simplified head phantom was developed for gathering the verification data and proved that the system was capable of locating targets with dielectric properties similar to brain tumours and bleeds. The presented design is highly accessible, achieved through being small, light, and inexpensive: key factors that could help save lives in time-critical medical emergencies.
Subject-specific, Non-invasive Helmet-restraint RF Coil for Awake, Non-human Primate MR Imaging
Read Description
In this work, an RF coil holder was integrated into the design of a subject-specfic helmet to place the coil in closest distance to the head for improved signal-to-noise ratio (SNR). Additive manufacturing was used to print the helmet based upon CT images of the subject. A single channel transmit/receive loop coil was designed using electromagnetic simulations loaded with a voxel-based monkey head model. The Rhesus macaque used in this study underwent behavioral training based on positive reinforcement before engaging in MR imaging. Imaging was performed using the helmet coil which was successful in immobilizing the macaque head in an awake, unanesthetized subject. Results showed improved SNR by approximately 28% compared to a loop coil used with an implanted head post, and minimal motion artifact in structural imaging. The non-invasive helmet coil eliminates the need for permanently implanting monkeys with a headpost, provides the necessary head immobilization, and allows the use of more subjects for neuroimaging studies.
NanoNeuroRFID: A Wireless Implantable Device Based on Magnetoelectric Antennas
Read Description
Electromagnetic-based wireless devices are big in size because of their large antenna, which must be larger than onetenth of the wavelength of the operational frequency. Ultrasound-based wireless devices, in addition to their low data rate, have a massive loss in the skull and need an intermediate electromagnetic transceiver under the skull. Furthermore, almost all state-ofthe- art wireless devices use micro-electrodes for neuronal recording, which are not reliable in long-term monitoring applications because of direct contact between the tissue and metal electrodes. In this paper, we propose a novel wireless and ultra-compact implantable device termed NanoNeuroRFID. At the core of this device there is a Magnetoelectric (ME) antenna array. ME antennas are smart and ultra-miniaturized (<200μm diameter), and can perform multiple tasks: 1) They can harvest electromagnetic energy to power the NanoNeuroRFID system. Their limit of detection for RF magnetic fields is 40pT. 2) They can sense quasi-static neuronal magnetic fields as small as 200pT without a direct contact to the tissue, allowing a long lifetime and reliable neural recording. 3) They can communicate with an external transceiver, and their operational frequency could be 10s to 100s of MHz where tissue loss is small.
Unintentional RF Energy Transfer During Tonsillectomy: An In Vitro Investigation
Read Description
To validate our hypothesis, in vitro studies are performed in a ground beef phantom with sensors measuring: a) the unwanted current coupled to the mouth retractor, and b) the unwanted temperature rise in the tissues that surround the retractor. The simulated surgery was performed using two separate surgical techniques: monopolar electrosurgery and coblation. Results indicate that unintentional RF energy transfer is indeed a real issue. During electrosurgery, peak-to-peak unwanted currents vary from 80.53 to 181.48 mA for typical power levels ranging from 10W to 30W. Tissue temperature unintentionally increases by 1.3°C and 1.8°C, respectively. Coblation indicates smaller coupling effects, with peak-to-peak currents on the mouth retractor capped at 12.33 mA for a typical 7 W setting. Concurrently, tissue temperature is reduced by 0.73°C, as attributed to the saline solution inherent to coblation. As the first of its kind, this study illuminates possible causes of post-tonsillectomy dysgeusia and intends to trigger future studies. The ultimate goal is safe and complication-free tonsillectomies
A Layered Pork Model for Subdermal Antenna Tests at 433 MHz
Read Description
Objectives: The objectives of this work are to create a simple biological test bed for subdermal implantable antennas that includes the normal expected variation of the tissues Technology or Method: A layered model using pork products with skin, pork fat or lard, and pork loin or ground pork is used. Results: The ex vivo porcine tissues are similar to in vivo human tissues. Pork fat and loin have more variability than lard and ground pork but are more difficult to imbed subdermal antennas in. This model provides an easy to use platform for testing subdermal antennas in the lab. This test bed was developed for 433 MHz, the ISM band closest to the MedRadio band (402-405 MHz). Initial tests are demonstrated on a two-wire passive system for focusing power within the muscle region.
