scholarly journals Reducing RF-induced Heating near Implanted Leads through High-Dielectric Capacitive Bleeding of Current (CBLOC)

2018 ◽  
Author(s):  
Laleh Golestanirad ◽  
Leonardo M Angelone ◽  
John Kirsch ◽  
Sean Downs ◽  
Boris Keil ◽  
...  
Keyword(s):  
Electrically Conductive ◽  
Tissue Heating ◽  
Rf Exposure ◽  
Fold Reduction ◽  
Implanted Medical Devices ◽  
Rf Energy ◽  
Magnetic Resonance Imaging Mri ◽  
Novel Concept ◽  
High Dielectric ◽  
To Receive

AbstractPatients with implanted medical devices such as deep brain stimulation or spinal cord stimulation are often unable to receive magnetic resonance imaging (MRI). This is because once the device is within the radiofrequency (RF) field of the MRI scanner, electrically conductive leads act as antenna, amplifying the RF energy deposition in the tissue and causing possible excessive tissue heating. Here we propose a novel concept in lead design in which 40cm lead wires are coated with a ~1.2mm layer of high dielectric constant material (155 < εr < 250) embedded in a weakly conductive insulation (σ = 20 S/m). The technique called High-Dielectric Capacitive Bleeding of Current, or CBLOC, works by forming a distributed capacitance along the lengths of the lead, efficiently dissipating RF energy before it reaches the exposed tip. Measurements during RF exposure at 64 MHz and 123 MHz demonstrated that CBLOC leads generated 20-fold less heating at 1.5 T, and 40-fold less heating at 3 T compared to control leads. Numerical simulations of RF exposure at 297 MHz (7T) predicted a 15-fold reduction in specific absorption rate (SAR) of RF energy around the tip of CBLOC leads compared to control leads.

scholarly journals RF Exposure Assessment for Various Poses of Patient Assistant in Open MRI Environment

2021 ◽  
Vol 11 (11) ◽  
pp. 4967
Author(s):  
Seon-Eui Hong ◽  
Sukhoon Oh ◽  
Hyung-Do Choi
Keyword(s):  
Rf Coils ◽  
Rf Coil ◽  
Open Mri ◽  
Rf Exposure ◽  
Open Magnetic Resonance Imaging ◽  
Mri Environment ◽  
Rf Energy ◽  
Magnetic Resonance Imaging Mri ◽  
High Level ◽  
Difference Time

In this study, the radio-frequency (RF) energy exposure of patient assistants was assessed for an open magnetic resonance imaging (MRI) system based on numerical computations of the head and body RF coil. Various poses of the patient assistants were defined to see how poorly they affected the RF energy exposure. For the assessments, the peak spatial-averaged specific absorption rate (SAR) levels were carefully compared with each patient assistant pose based on the finite-difference time domain calculations of RF coil models when the patient was placed in such coils in a 0.3 Tesla open MRI system. Overall, the SAR levels of the patient assistant were much lower than those of the patient. However, significantly increased SAR levels were observed under specific conditions, including a larger loop size of the patient assistants’ arms and a closer distance to the RF coils. A comparably high level of SAR to the patient’s body was also found. More careful investigations are needed to prevent the increase of SAR in patient assistants for open MRI systems at higher field strengths.

scholarly journals MRI-Based Multiscale Model for Electromagnetic Analysis in the Human Head with Implanted DBS

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Maria Ida Iacono ◽  
Nikos Makris ◽  
Luca Mainardi ◽  
Leonardo M. Angelone ◽  
Giorgio Bonmassar
Keyword(s):  
Electric Field ◽  
Ex Vivo ◽  
Human Head ◽  
Multiscale Model ◽  
Head Model ◽  
Tissue Heating ◽  
Electromagnetic Simulations ◽  
Anatomical Detail ◽  
Magnetic Resonance Imaging Mri ◽  
Deep Brain

Deep brain stimulation (DBS) is an established procedure for the treatment of movement and affective disorders. Patients with DBS may benefit from magnetic resonance imaging (MRI) to evaluate injuries or comorbidities. However, the MRI radio-frequency (RF) energy may cause excessive tissue heating particularly near the electrode. This paper studies how the accuracy of numerical modeling of the RF field inside a DBS patient varies with spatial resolution and corresponding anatomical detail of the volume surrounding the electrodes. A multiscale model (MS) was created by an atlas-based segmentation using a 1 mm3head model (mRes) refined in the basal ganglia by a 200 μm2ex-vivo dataset. Four DBS electrodes targeting the left globus pallidus internus were modeled. Electromagnetic simulations at 128 MHz showed that the peak of the electric field of the MS doubled (18.7 kV/m versus 9.33 kV/m) and shifted 6.4 mm compared to the mRes model. Additionally, the MS had a sixfold increase over the mRes model in peak-specific absorption rate (SAR of 43.9 kW/kg versus 7 kW/kg). The results suggest that submillimetric resolution and improved anatomical detail in the model may increase the accuracy of computed electric field and local SAR around the tip of the implant.

scholarly journals A 2.77 μW Ambient RF Energy Harvesting Using DTMOS Cross-Coupled Rectifier on 65 nm SOTB and Wide Bandwidth System Design

Electronics ◽  
2019 ◽  
Vol 8 (10) ◽  
pp. 1173
Author(s):  
Thuy-Linh Nguyen ◽  
Yasuo Sato ◽  
Koichiro Ishibashi
Keyword(s):  
Energy Harvesting ◽  
Orthogonal Frequency Division Multiplexing ◽  
Input Power ◽  
Potential Candidate ◽  
Wide Bandwidth ◽  
Rf Energy Harvesting ◽  
Ambient Environment ◽  
Rf Energy ◽  
Rf Signal ◽  
To Receive

This paper proposes a structure of the μ W RF energy harvesting (RFEH) system that is used for scavenging RF power from an ambient environment. A cross-coupled rectifier (CCR) with floating sub-circuit structures was utilized in the application of dynamic threshold MOSFET (DTMOS) on Silicon on Thin Buried Oxide (SOTB) to obtain high drain conductance of the MOSFET. A wide bandwidth matching between antenna and rectifier was designed to receive energy from the orthogonal frequency division multiplexing (OFDM) RF signal with a bandwidth of 15 MHz at 950 MHz band. Realistic measurements with a 950 MHz LTE mobile phone signal from the ambient environment indicate that an average DC output power of 2.77 μ W is harvested with the proposed RFEH system at a level of −19.4 dBm input power. The proposed RFEH system exhibits the best performance when compared to that of other realistic RFEH systems and is a potential candidate for battery-less Internet of Things (IoT) applications.

Rationing Rotational Magnet Cochlear Implant Technology in a Single Payer Healthcare System

2020 ◽  
pp. 000348942094323
Author(s):  
Justyn Pisa ◽  
Colin Andrews ◽  
Jordan B. Hochman
Keyword(s):  
Magnetic Resonance ◽  
Cochlear Implant ◽  
Unit Cost ◽  
Wait Times ◽  
Publicly Funded ◽  
Magnet Technology ◽  
Single Payer ◽  
Number Of Patients ◽  
Magnetic Resonance Imaging Mri ◽  
To Receive

Introduction: In a publicly funded health care system, fiscally responsible management of any program is required. This is especially pertinent as evolving technology and associated incremental costs, places pressure on device availability within a fixed funding envelope. The application of rotational magnet technology and associated escalating surgical wait times must be justified to patients and the single-payer system. We present a single cochlear implant center’s attempt at a rationing schema for magnetic resonance compatible cochlear implantation. Contrasting approaches to rationing care are evaluated and deliberated. Methods: Based on a comparison of magnetic resonance imaging (MRI) rates within the general population to our cochlear implant (CI) cohort, we attempt the development of a decision-making schema that maximizes the number of patients to receive a CI while rationing the distribution of a rotational magnet technology to similarly situated individuals most likely to benefit. Results: We elect to provide rotational magnet technology to select patient cohorts. This is based on the dominant imaging needs of these populations and the probability of requiring recurrent imaging studies. We consider this an ethical approach grounded in the egalitarian principle of equality of opportunity within cohorts of patients. Conclusion: Given finite resources, increasing per unit cost will unavoidably extend wait times for adult patients. Our approach does not afford similar implant devices for all patients, but rather all similarly situated individuals. Therefore, access to a scare medical resource requires program rigor and a formalized policy around candidacy for emergent technology.

scholarly journals Statistical Evaluation of Radiofrequency Exposure during Magnetic Resonant Imaging: Application of Whole-Body Individual Human Model and Body Motion in the Coil

2019 ◽  
Vol 16 (6) ◽  
pp. 1069 ◽  
Author(s):  
Wenli Liu ◽  
Hongkai Wang ◽  
Pu Zhang ◽  
Chengwei Li ◽  
Jie Sun ◽  
...  
Keyword(s):  
Body Motion ◽  
Human Model ◽  
Whole Body ◽  
Patient Specific ◽  
Accurate Estimation ◽  
Modelling Method ◽  
Rf Exposure ◽  
Imaging Application ◽  
Magnetic Resonance Imaging Mri ◽  
The Individual

The accurate estimation of patient’s exposure to the radiofrequency (RF) electromagnetic field of magnetic resonance imaging (MRI) significantly depends on a precise individual anatomical model. In the study, we investigated the applicability of an efficient whole-body individual modelling method for the assessment of MRI RF exposure. The individual modelling method included a deformable human model and tissue simplification techniques. Besides its remarkable efficiency, this approach utilized only a low specific absorption rate (SAR) sequence or even no MRI scan to generate the whole-body individual model. Therefore, it substantially reduced the risk of RF exposure. The dosimetric difference of the individual modelling method was evaluated using the manually segmented human models. In addition, stochastic dosimetry using a surrogate model by polynomial chaos presented SAR variability due to body misalignment and tilt in the coil, which were frequently occurred in the practical scan. In conclusion, the dosimetric equivalence of the individual models was validated by both deterministic and stochastic dosimetry. The proposed individual modelling method allowed the physicians to quantify the patient-specific SAR while the statistical results enabled them to comprehensively weigh over the exposure risk and get the benefit of imaging enhancement by using the high-intensity scanners or the high-SAR sequences.

scholarly journals Successful Treatment of Posttransplant EBV-Associated Lymphoma and Plasmacytoma Solely Localized to the CNS

2012 ◽  
Vol 2012 ◽  
pp. 1-4
Author(s):  
Per Boye Hansen ◽  
Signe Ledou Nielsen
Keyword(s):  
Immune Suppression ◽  
Cervical Vertebra ◽  
B Cell Lymphoma ◽  
Complete Regression ◽  
Barr Virus ◽  
Co Morbidity ◽  
Epstein Barr ◽  
Magnetic Resonance Imaging Mri ◽  
Initiation Of Therapy ◽  
To Receive

Two patients with diabetic nephropathy were diagnosed with primary central nervous system posttransplantEpstein-Barr-virus-associated lymphoproliferative disorder (PTLD) 3 years after renal transplantation. The histological diagnoses of the isolated brain tumors were diffuse large B-cell lymphoma and plasmacytoma. Considerable co-morbidity precluded intensive chemotherapy. The first patient with lymphoid CD20+ PTLD had a partial resection of her tumor performed. She was treated with 4 weekly doses of rituximab, ganciclovir and prednisolone; the posttransplant immune suppression (tacrolimus) was reduced. After 4 weeks of treatment a magnetic resonance imaging (MRI) demonstrated complete regression of the CNS lesion. The patient continues to receive rituximab (every second month), valgangciclovir and low-dose prednisolone. Twenty-two months after initiation of therapy, she is still in complete remission. The second patient was only treated with craniospinal irradiation involving the medulla to the second cervical vertebra and valgangciclovir. Moreover, the posttransplant immune suppression was reduced. A new MRI two months after initiation of therapy showed a complete regression of the lesions in the CNS; this was again demonstrated by a MRI after 19 months. These 2 cases illustrate interesting alternative treatments of PTLD. To our knowledge, an EBV-associated PTLD of plasmacytic origin isolated to the CNS has never been described before.

Effect of a Single Pulsed Shortwave Diathermy Treatment on Extensibility of the Hamstrings

2014 ◽  
Vol 19 (1) ◽  
pp. 6-10 ◽  
Author(s):  
Alicia Martínez-Rodríguez ◽  
Olalla Bello ◽  
Isabel Yañez-Brage
Keyword(s):  
Knee Extension ◽  
Range Of Movement ◽  
Deep Tissue ◽  
Outcome Measurements ◽  
Tissue Heating ◽  
Passive Stretching ◽  
Before And After ◽  
To Receive ◽  
Subjective Level ◽  
Shortwave Diathermy

Context:Lack of extensibility of the hamstrings is manifested by a restricion of knee extension range of motion.Objective:To quantify the effect of a single pulsed shortwave diathermy treatment on extensibility of the hamstrings.Participants:Twenty volunteers with tight hamstrings (< 150° of active knee extension).Intervention:Subjects were randomly allocated to receive either a pulsed shortwave diathermy treatment (experimental group) or a simulated pulsed shortwave diathermy treatment that did not produce a deep tissue heating effect.Main Outcome Measurements:Measurements of active and passive range of movement were recorded before and after the treatment, as well as the subjective level of discomfort perceived during the passive stretching.Results:No statistically signifcant differences were found.Conclusion:A single pulsed shortwave diathermy treatment, without stretching, did not increase hamstring extensibility.

Value generation in B2B contexts: the SMEs’ perspective

2015 ◽  
Vol 27 (3) ◽  
pp. 297-317 ◽  
Author(s):  
Lourdes Pérez ◽  
Jesús Cambra-Fierro
Keyword(s):  
Small Businesses ◽  
Small Firms ◽  
Value Appropriation ◽  
Content Type ◽  
A Value ◽  
Novel Concept ◽  
To Receive ◽  
The Relationship ◽  
Asymmetric Relationships

Purpose – The aim of this paper is to understand the process of value creation in business-to-business (B2B) contexts from the perspective of small- and medium-sized firms (SMEs). Small businesses are challenged to compete and collaborate with larger firms. While the “sharks” dilemma (often the most dangerous sharks also have the most valuable resources) focuses on specific defences, the authors emphasize a value generation perspective. Design/methodology/approach – The concept of asymmetric relationships is taken as a reference and examined using a longitudinal multi-case study. Findings – The authors results demonstrate how small firms not always assume an inferior, defensive position. Ambitious and growth-oriented SMEs learn to collaborate with larger partners and exhibit a proactive attitude towards relationship management. They understand the importance of developing social ties. They foster frequent and informal communication with their customers, favouring personal visits as a means to receive advice for directing their research efforts and exchange information and views. Such ties help them to develop shared plans and goals. Research limitations/implications – In asymmetric relationships, partner selection models should help firms to concentrate their efforts in a reduced group of key partners. These models should include not only economic performance indicators – variables such as flexibility and autonomy – but also innovation and improvement in processes, image, prestige and positioning, access to markets and stability. Originality/value – The authors found insight into a novel concept: dual-value appropriation, where partners do not split the pie of the total value generated, as frequently proposed in the literature, but fully appropriate a different and unique value from the relationship. The authors further highlight the important role played by the committed champions in developing communication and trust.

scholarly journals Culture Medium Geometry: The Dominant Factor Affecting In Vitro RF Exposure Dosimetry

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Alessandra Paffi ◽  
Francesca Apollonio ◽  
Micaela Liberti ◽  
Asher Sheppard ◽  
Giorgi Bit-Babik ◽  
...  
Keyword(s):  
Culture Medium ◽  
Living Cells ◽  
Dominant Factor ◽  
Biological Entity ◽  
Antenna Theory ◽  
Rf Exposure ◽  
Receiving Antenna ◽  
Rf Energy ◽  
Computationally Intensive

Biological experiments that expose living cells or tissues to RF energy must have an aqueous medium to provide essential water, ions, nutrients, and growth factors. However, as we show here, the medium inherently functions as a receiving antenna that conveys RF energy to the biological entity in a manner entirely determined by exposure vessel geometry, orientation to the incident RF flux, frequency, and dielectric properties of the medium. We show for two common experimental arrangements that basic antenna theory can predict electromagnetic energy patterns that agree well with those otherwise obtained by computationally intensive methods that require specialized resources.

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