Niels Kuster

ETH Zurich | ETH Zürich · Department Information Technology and Electrical Engineering

Objective: Non-invasive brain stimulation (NIBS) methodologies, such as transcranial electric (tES) are increasingly employed for therapeutic, diagnostic, or research purposes. The concurrent presence of active/passive implants can pose safety risks, affect the NIBS delivery, or generate confounding signals. A systematic investigation is required t...

Objective: Develop an efficient method for simulating evoked compound action potential (eCAP) signals from complex nerves to help optimize and interpret eCAP recordings; validate it through comparison with measured vagus nerve eCAP recordings; elucidate the subtle interplay giving rise to specific eCAP signal shapes and magnitudes. Approach: We dev...

Spinal cord stimulation (SCS) is a well-established treatment for the management of certain chronic pain conditions. More recently, it has also garnered attention as a means of modulating neural activity with the goal of restoring lost autonomic or sensory-motor function. Personalized modeling and treatment planning are critical aspects of safe and...

A spinal cord injury (SCI) causes immediate and sustained hemodynamic instability that threatens neurological recovery and impacts quality of life. Here, we establish the clinical burden of chronic hypotensive complications due to SCI and expose the ineffective treatment of these complications with conservative measures. To address this clinical bu...

As the size and complexity of network simulations accessible to computational neuroscience grows, new avenues open for research into extracellularly recorded electric signals. Biophysically detailed simulations permit the identification of the biological origins of the different components of recorded signals, the evaluation of signal sensitivity t...

Objective: Non-invasive brain stimulation (NIBS) methodologies, such as transcranial electric (tES) and magnetic stimulation are increasingly employed for therapeutic, diagnostic, or research purposes. The concurrent presence of active or passive implants can pose safety risks, affect the NIBS delivery, or generate confounding signals. A systematic...

Resource-efficient and robust validation of systems designed to measure a multi-dimensional parameter space is an unsolved problem as it would require millions of test permutations for comprehensive validation coverage. In the paper, an efficient and comprehensive validation approach based on a Gaussian Process (GP) model of the test system has bee...

Deep brain stimulation (DBS) via implanted electrodes is used worldwide to treat patients with severe neurological and psychiatric disorders. However, its invasiveness precludes widespread clinical use and deployment in research. Temporal interference (TI) is a strategy for non-invasive steerable DBS using multiple kHz-range electric fields with a...

Purpose Radiofrequency (RF) exposure during MR examination is limited by IEC 60601‐2‐33 to prevent thermal hazards to patients. These limits are also the basis to derive the maximum induced field for the demonstration of MR safety of implants per ISO/TS 10974 (2018). One limit is the head‐averaged specific absorption rate (SAR), for which the head...

A confined electron laser is a “wiggled” electron beam confined by the ponderomotive forces inside an electromagnetic cavity. The ponderomotive forces counteract the beam expansion due to space-charge forces, thereby enabling lasing at low energies. In this Letter we show the possibility of lasing at a wavelength of approximately 4 nm in the soft-x...

Objective . Craniospinal compliance (CC) is an important metric for the characterization of space-occupying neurological pathologies. CC is obtained using invasive procedures that carry risks for the patients. Therefore, noninvasive methods for acquiring surrogates of CC have been proposed, most recently based on changes in the head’s dielectric pr...

Regulators require that wireless power transfer (WPT) systems and other strong magnetic field sources are compliant with the basic restrictions (BR) defined as the limits of the fields induced in the human body, i.e., the induced electric field/current density/specific absorption rate limits. This can be achieved by demonstrating compliance with th...

Temporal interference stimulation (TIS) is a new form of transcranial electrical stimulation (tES) that has been proposed as a method for targeted, non-invasive stimulation of deep brain structures. While TIS holds promise for a variety of clinical and non-clinical applications, little data is yet available regarding its effects in humans. To infor...

Monitoring intracranial pressure (ICP) and craniospinal compliance (CC) is frequently required in the treatment of patients suffering from craniospinal diseases. However, current approaches are invasive and cannot provide continuous monitoring of CC. Dynamic exchange of blood and cerebrospinal fluid (CSF) between cranial and spinal compartments due...

Resource-efficient and robust validation of complex measurement system that would require millions of test permutations for comprehensive coverage is an unsolved problem. In the paper, a general, robust, trustworthy, efficient, and comprehensive validation approach based on a Gaussian Process Interpolation (GPI)-model of the test-system has been de...

This study investigates the absorption of the induced E‐field in homogeneous biological tissue exposed to highly localized field sources in proximity of the body, such as the charged tips of antennas, where E‐field coupling dominates. These conditions are relevant for compliance testing of modern mobile phones where exposure is evaluated at small s...

Temporal interference (TI) is a strategy for non-invasive steerable stimulation of neurons deep in the brain using multiple kHz-range electric fields with a difference frequency within the range of neural activity. Here we report the validation of the TI stimulation concept in humans. We used electric field modelling and measurements in a human cad...

Exposure assessment of wireless devices operating at ≥6 GHz requires measurement of power density (PD) from a distance of 2 mm ( $\geq \lambda $ /25) from the surface of the device (reactive near field) to the far field with minimal uncertainties. The challenges are field distortion and backscattering by the probe, spatial resolution, sensitivity,...

The constant increase in the required user capacity and the evolution of wireless network technologies impact the exposure that users experience from wireless networks. This paper evaluates various 5G network topologies regarding human exposure, mobile communication quality, and sustainability. We assess human exposure, based on a novel Exposure Ra...

Objective: The clinical management of several neurological disorders benefits from the assessment of intracranial pressure and craniospinal compliance. However, the associated procedures are invasive in nature. Here, we aimed to assess whether naturally occurring periodic changes in the dielectric properties of the head could serve as the basis fo...

Purpose Healthy tissue hotspots are a main limiting factor in administering deep hyperthermia cancer therapy. We propose an optimization scheme that uses time-multiplexed steering (TMPS) among minimally correlated (nearly) Pareto-optimal solutions to suppress hotspots without reducing tumor heating. Furthermore, tumor heating homogeneity is maximiz...

Epidural electrical stimulation (EES) targeting the dorsal roots of lumbosacral segments restores walking in people with spinal cord injury (SCI). However, EES is delivered with multielectrode paddle leads that were originally designed to target the dorsal column of the spinal cord. Here, we hypothesized that an arrangement of electrodes targeting...

Fifth generation networks (5G) will be associated with a partial shift to higher carrier frequencies, including wavelengths comparable in size to insects. This may lead to higher absorption of radio frequency (RF) electromagnetic fields (EMF) by insects and could cause dielectric heating. The yellow fever mosquito (Aedes aegypti), a vector for dise...

Using an open-ended coaxial probe and a vector network analyzer is a conventional technique for noninvasive and broadband measurement of dielectric permittivity. The method is widely applied to characterize bulk material and liquids and has recently been extended to thin sheet material samples. However, it is commonly believed that the method is no...

Purpose: To characterize and quantify the induced radiofrequency (RF) E-fields and B1+rms fields in patients undergoing magnetic resonance (MR) examinations; to provide guidance on aspects of RF heating risks for patients with and without implants; and to discuss some strengths and limitations of safety assessments in current ISO, IEC, and ASTM st...

Low-Intensity Focused Ultrasound Stimulation (LIFUS) holds promise for the remote modulation of neural activity, but an incomplete mechanistic characterization hinders its clinical maturation. Here we developed a computational framework to model intramembrane cavitation (a candidate mechanism) in multi-compartment, morphologically structured neuron...

Compact coherent x-ray sources have been the focus of extensive research efforts over the past decades. As a result, several novel schemes like optical and nano-undulators for generating x-ray emissions in ‘table-top’ setups are proposed, developed, and assessed. Despite the extensive efforts in the past decades, there exists no operational FEL bas...

Several recent theoretical dosimetric studies above 6 GHz apply generic layered skin models. For this frequency range, new experimental phantoms for over-the-air performance of wireless devices were proposed that simulate the impedance matching effects of the stratum corneum layer (SCL) with a low-loss coating layer. The aim of this study was to ve...

We present a simulation study investigating the feasibility of electrical impedance tomography (EIT) as a low cost, noninvasive technique for hyperthermia (HT) treatment monitoring and adaptation. Temperature rise in tissues leads to perfusion and tissue conductivity changes that can be reconstructed in 3D by EIT to noninvasively map temperature an...

The Data and Resource Center (DRC) of the NIH-funded SPARC program is developing databases, connectivity maps, and simulation tools for the mammalian autonomic nervous system. The experimental data and mathematical models supplied to the DRC by the SPARC consortium are curated, annotated and semantically linked via a single knowledgebase. A data po...

Purpose The risks of RF‐induced heating of active implantable medical device (AIMD) leads during MR examinations must be well understood and realistically assessed. In this study, we evaluate the potential additional risks of broken and abandoned (cut) leads. Methods First, we defined a generic AIMD with a metallic implantable pulse generator (IPG...

The introduction of new dosimetric quantities, in particular, epithelial or absorbed power density for frequencies above 6 GHz, in exposure guidelines and safety standards requires the development of new experimental assessment procedures for compliance testing. In this study, we propose to approximate the peak spatial-average absorbed power densit...

Compact coherent x-ray sources have been the focus of extensive research efforts over the past decades. As a result, several novel schemes like optical and nano-undulators for generating x-ray emissions in "table-top" setups are proposed, developed, and assessed. Despite the extensive efforts in the past decades, there exists no operational FEL bas...

Objective: Low-intensity transcranial ultrasound stimulation (TUS) is a promising non-invasive brain stimulation (NIBS) technique. TUS can reach deeper areas and target smaller regions in the brain than other NIBS techniques, but its application in humans is hampered by the lack of a straightforward and reliable procedure to predict the induced ul...

The Data and Resource Center (DRC) of the NIH-funded SPARC program is developing databases, connectivity maps and simulation tools for the mammalian autonomic nervous system. The experimental data and mathematical models supplied to the DRC by the SPARC consortium are curated, annotated and semantically linked via a single knowledgebase. A data por...

Convex formulations can be used to reduce the local specific absorption rate enhancement by active medical implants of radiofrequency fields in magnetic resonance examinations while minimizing the loss of image quality. This paper demonstrates that such an optimization methodology, previously presented for strictly computational models, can be exte...

The latest electromagnetic safety guidelines define transmitted or epithelial power density as the basic restriction above 6 GHz. In this note, we derive an approximation for a conservative transmission coefficient for quasi plane wave incidence as a function of the frequency for the normal component of the Poynting vector with respect to the evalu...

We present a novel patient-specific fluid-solidgrowth framework to model the mechanobiological state of clinically detected intracranial aneurysm (IA) and simulate its evolution. The artery and IA sac are modelled as fibre-reinforced composites which account for the undulation distribution of collagen fibres: the adventitia of the healthy artery is...

Low-Intensity Focused Ultrasound Stimulation (LIFUS) holds promise for the remote modulation of neuronal activity, but an incomplete mechanistic characterization hinders its clinical maturation. Here, we developed a computational framework to model intramembrane cavitation in multi-compartmental, morphologically-realistic neuronal representations,...

Over-the-air (OTA) performance evaluations of devices operating at frequencies greater than 6 GHz are typically performed in the compact antenna test ranges (CATRs) with head and hand phantoms. However, existing specific anthropomorphic mannequin (SAM) head phantoms do not meet the quiet zone and weight restrictions of CATRs. In this study, we inve...

Neuromodulation is a new therapeutic pathway to treat inflammatory conditions by modulating the electrical signalling pattern of the autonomic connections to the spleen. However, targeting this subdivision of the nervous system presents specific challenges in translating nerve stimulation parameters. Firstly, autonomic nerves are typically embedded...

In this article, we discuss numerical aspects related to the accuracy and the computational efficiency of numerical dosimetric simulations, performed in the context of human exposure to static inductive charging systems of electric vehicles. Two alternative numerical methods based on electric vector potential and electric scalar potential formulati...