Fast and numerically stable Mie solution of EM near field and absorption for stratified spheres

2022 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Olivér Csernyava ◽  
Bálint Péter Horváth ◽  
Zsolt Badics ◽  
Sándor Bilicz
Keyword(s):  
Near Field ◽  
Human Head ◽  
Approximate Model ◽  
Head Model ◽  
Wave Regime ◽  
Content Type ◽  
Precise Calculation ◽  
Linearly Polarized ◽  
Numerical Instabilities ◽  
Computational Resources

Purpose The purpose of this paper is the development of an analytic computational model for electromagnetic (EM) wave scattering from spherical objects. The main application field is the modeling of electrically large objects, where the standard numerical techniques require huge computational resources. An example is full-wave modeling of the human head in the millimeter-wave regime. Hence, an approximate model or analytical approach is used. Design/methodology/approach The Mie–Debye theorem is used for calculating the EM scattering from a layered dielectric sphere. The evaluation of the analytical expressions involved in the infinite sum has several numerical instabilities, which makes the precise calculation a challenge. The model is validated through an application example with comparing results to numerical calculations (finite element method). The human head model is used with the approximation of a two-layer sphere, where the brain tissues and the cranial bones are represented by homogeneous materials. Findings A significant improvement is introduced for the stable calculation of the Mie coefficients of a core–shell stratified sphere illuminated by a linearly polarized EM plane wave. Using this technique, a semi-analytical expression is derived for the power loss in the sphere resulting in quick and accurate calculations. Originality/value Two methods are introduced in this work with the main objective of estimating the final precision of the results. This is an important aspect for potentially unstable calculations, and the existing implementations have not included this feature so far.

Development and validation of a new finite element human head model

2018 ◽  
Vol 35 (1) ◽  
pp. 477-496 ◽  
Author(s):  
Fábio A.O. Fernandes ◽  
Dmitri Tchepel ◽  
Ricardo J. Alves de Sousa ◽  
Mariusz Ptak
Keyword(s):  
Finite Element ◽  
Design Methodology ◽  
Human Head ◽  
Design Tool ◽  
Head Model ◽  
Accident Reconstruction ◽  
Research Groups ◽  
Content Type ◽  
Development And Validation ◽  
The Brain

Purpose Currently, there are some finite element head models developed by research groups all around the world. Nevertheless, the majority are not geometrically accurate. One of the problems is the brain geometry, which usually resembles a sphere. This may raise problems when reconstructing any event that involves brain kinematics, such as accidents, affecting the correct evaluation of resulting injuries. Thus, the purpose of this study is to develop a new finite element head model more accurate than the existing ones. Design/methodology/approach In this work, a new and geometrically detailed finite element brain model is proposed. Special attention was given to sulci and gyri modelling, making this model more geometrically accurate than currently available ones. In addition, these brain features are important to predict specific injuries such as brain contusions, which usually involve the crowns of gyri. Findings The model was validated against experimental data from impact tests on cadavers, comparing the intracranial pressure at frontal, parietal, occipital and posterior fossa regions. Originality/value As this model is validated, it can be now used in accident reconstruction and injury evaluation and even as a design tool for protective head gear.

A near-field spherical layered human head model for stroke detections

2015 ◽  
Author(s):  
Dong Huang ◽  
Hong-Li Peng ◽  
Xing Li ◽  
Weiqing Jin ◽  
Junfa Mao
Keyword(s):  
Near Field ◽  
Human Head ◽  
Head Model ◽  
Human Head Model

scholarly journals Neural silences can be localized rapidly using noninvasive scalp EEG

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Alireza Chamanzar ◽  
Marlene Behrmann ◽  
Pulkit Grover
Keyword(s):  
Center Of Mass ◽  
Cost Effective ◽  
Human Head ◽  
Head Model ◽  
Cortical Function ◽  
Scalp Eeg ◽  
Localization Algorithms ◽  
Important Benefit ◽  
Eeg Recordings ◽  
Detection And Localization

AbstractA rapid and cost-effective noninvasive tool to detect and characterize neural silences can be of important benefit in diagnosing and treating many disorders. We propose an algorithm, SilenceMap, for uncovering the absence of electrophysiological signals, or neural silences, using noninvasive scalp electroencephalography (EEG) signals. By accounting for the contributions of different sources to the power of the recorded signals, and using a hemispheric baseline approach and a convex spectral clustering framework, SilenceMap permits rapid detection and localization of regions of silence in the brain using a relatively small amount of EEG data. SilenceMap substantially outperformed existing source localization algorithms in estimating the center-of-mass of the silence for three pediatric cortical resection patients, using fewer than 3 minutes of EEG recordings (13, 2, and 11mm vs. 25, 62, and 53 mm), as well for 100 different simulated regions of silence based on a real human head model (12 ± 0.7 mm vs. 54 ± 2.2 mm). SilenceMap paves the way towards accessible early diagnosis and continuous monitoring of altered physiological properties of human cortical function.

scholarly journals Levels of detail analysis of microwave scattering from human head models for brain stroke detection

PeerJ ◽  
2017 ◽  
Vol 5 ◽  
pp. e4061 ◽  
Author(s):  
Awais Munawar Qureshi ◽  
Zartasha Mustansar
Keyword(s):  
Scattering Problem ◽  
Human Head ◽  
Computational Time ◽  
Head Model ◽  
Microwave Scattering ◽  
Levels Of Detail ◽  
Realistic Head Model ◽  
Different Types ◽  
Brain Stroke ◽  
Brain Tissues

In this paper, we have presented a microwave scattering analysis from multiple human head models. This study incorporates different levels of detail in the human head models and its effect on microwave scattering phenomenon. Two levels of detail are taken into account; (i) Simplified ellipse shaped head model (ii) Anatomically realistic head model, implemented using 2-D geometry. In addition, heterogenic and frequency-dispersive behavior of the brain tissues has also been incorporated in our head models. It is identified during this study that the microwave scattering phenomenon changes significantly once the complexity of head model is increased by incorporating more details using magnetic resonance imaging database. It is also found out that the microwave scattering results match in both types of head model (i.e., geometrically simple and anatomically realistic), once the measurements are made in the structurally simplified regions. However, the results diverge considerably in the complex areas of brain due to the arbitrary shape interface of tissue layers in the anatomically realistic head model.After incorporating various levels of detail, the solution of subject microwave scattering problem and the measurement of transmitted and backscattered signals were obtained using finite element method. Mesh convergence analysis was also performed to achieve error free results with a minimum number of mesh elements and a lesser degree of freedom in the fast computational time. The results were promising and the E-Field values converged for both simple and complex geometrical models. However, the E-Field difference between both types of head model at the same reference point differentiated a lot in terms of magnitude. At complex location, a high difference value of 0.04236 V/m was measured compared to the simple location, where it turned out to be 0.00197 V/m. This study also contributes to provide a comparison analysis between the direct and iterative solvers so as to find out the solution of subject microwave scattering problem in a minimum computational time along with memory resources requirement.It is seen from this study that the microwave imaging may effectively be utilized for the detection, localization and differentiation of different types of brain stroke. The simulation results verified that the microwave imaging can be efficiently exploited to study the significant contrast between electric field values of the normal and abnormal brain tissues for the investigation of brain anomalies. In the end, a specific absorption rate analysis was carried out to compare the ionizing effects of microwave signals to different types of head model using a factor of safety for brain tissues. It is also suggested after careful study of various inversion methods in practice for microwave head imaging, that the contrast source inversion method may be more suitable and computationally efficient for such problems.

A study of human head vibrations using time-averaged holography

1983 ◽  
Vol 58 (5) ◽  
pp. 729-733 ◽  
Author(s):  
Heinz-E. Hoyer ◽  
Jurgen Dorheide
Keyword(s):  
Holographic Interferometry ◽  
Human Head ◽  
Temporal Region ◽  
Human Cadaver ◽  
Resonant Frequencies ◽  
Content Type ◽  
Deformation Measurements ◽  
Fine Print

✓ Intact human cadaver heads were subjected to vibrations. The resonant frequencies over a range of 500 to 3000 Hz were determined. Vibration patterns at three frequencies were presented by means of time-averaged holography. The displacements were quantified and the highest amplitudes were found in the temporal region. Antinode centers were found superimposed on the squamatic suture. This method of holographic interferometry allows sensitive deformation measurements to be taken on intact human heads or skulls.

Ultrasound-guided stereotaxic biopsy using a new apparatus

1986 ◽  
Vol 65 (4) ◽  
pp. 550-554 ◽  
Author(s):  
Mitchel S. Berger
Keyword(s):  
Tissue Sample ◽  
Near Field ◽  
Ct Scanner ◽  
Ultrasound Guided ◽  
Content Type ◽  
Delayed Hemorrhage ◽  
Stereotaxic Biopsy ◽  
Time Required ◽  
Immunodeficiency Syndrome ◽  
Burr Holes

✓ A skull-mounted apparatus is described for use with ultrasound probes 16 mm in diameter (5.0-MHz probes for near-field and 7.5-MHz probes for far-field lesions). The system permits ultrasound-guided stereotaxic biopsy of intracranial lesions through a burr hole in awake or anesthetized patients. This apparatus has been used in 19 patients for biopsy of central nervous system lesions 1.5 to 5 cm in diameter and for drainage of abscess cavities and cysts. The time required to obtain a tissue sample after incision of the skin ranged from 25 to 40 minutes. The only complication was a delayed hemorrhage in a patient with acquired immunodeficiency syndrome. The advantages of this method over those guided by computerized tomography (CT) include less time required for the entire procedure, immediate confirmation of the biopsied target by imaging the echogenic needle track, assessment of cyst or abscess drainage, and detection of hemorrhage within minutes after biopsy. The apparatus may be especially useful in pediatric patients because it obviates the need for general anesthesia during transport to and from the CT scanner. This ultrasound-guided system does not require a craniotomy, craniectomy, or two separate burr holes.

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