Chris Van Hoof

• PhD
• Vice President R&D at imec - OnePlanet

Introduction Prevention of hemodynamic complications during hemodialysis remains challenging. Although whole body bioimpedance is well established in fluid status assessment, its use for dynamic or continuous recordings is limited. A segmental approach may serve this purpose better. This study investigates which body segment is best targeted to mea...

Background The human gastrointestinal (GI) tract is challenging to examine due to its intricate structure and inaccessibility. Current diagnostic methods are either invasive, like endoscopy, or offer a limited view, such as faecal tests. Endoscopy capsules allow for a visual inspection of the whole GI tract but still require uncomfortable bowel pre...

Chronic widespread pain remains a complex and incompletely understood condition. To complement existing pain assessment strategies, this study explored the ecological validity of unobtrusively captured daily life physiological signals as indicators of pain. Therefore, we collected physiological data using a wearable wristband from 46 patients with...

The molecular sensing of protein and DNA molecules with nanopore sensor arrays necessitates high-speed readout interfaces. This leads to high output data rates, while only a very small portion of the recorded data contains useful translocation data. The high data rate creates a bottleneck for the design of high-density arrays of nanopores. This art...

Photoplethysmography (PPG) has emerged as a highly convenient and non-invasive technique for assessing heart rate and its variability in wearable health monitoring devices. However, a drawback lies in the energy demand of PPG systems which consequently increases the average power consumption of the wearable devices integrated with PPG sensors. In t...

Ultrasound (US) as a wireless power transfer methodology has drawn considerable attention from the implantable medical devices (IMD) research community. Beamforming (BF) using an external transducer array patch (ETAP) has been proposed as a robust localization scheme to find a mm-sized IMD inside the human body. However, for applications focusing o...

Advancements in integrated circuit (IC) technology have accelerated the miniaturization of body-worn sensors and systems, enabling long-term health monitoring. Wearable electrocardiogram (ECG), finger photoplethysmogram (PPG), and wrist-worn PPG have shown great success and significantly improved life quality. Chest-based PPG has the potential to e...

Background and Objectives The number of people with dementia is expected to triple to 152 million in 2050, with 90% having accompanying behavioral and psychological symptoms (BPSD). Agitation is among the most critical BPSD and can lead to decreased quality of life of people with dementia and their caregivers. This paper aims to explore objective q...

Background and Aims Hemodialysis patients face a high hemodynamic variability in blood pressure and fluid status, which contributes to their cardiovascular mortality. Currently, intradialytic hemodynamic monitoring has to rely on cuff-based blood pressure measurements. During the interdialytic interval, no monitoring system is applied. An interesti...

italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Background Pulse wave velocity (PWV) is a marker of arterial stiffness and local measurements could facilitate its widescale clinical use. However, confluence of incident and early reflected waves leads to biased spatiotemporal PWV estimates. Objectiv...

Repeated single-point measurements of thoracic bioimpedance at a single (low) frequency are strongly related to fluid changes during hemodialysis. Extension to semi-continuous measurements may provide longitudinal details in the time pattern of the bioimpedance signal, and multi-frequency measurements may add in-depth information on the distributio...

Holographic imaging captures an interference pattern, effectively encoding an object‘s properties such as size, shape and refractive index in the hologram. Lens-free holographic imaging offers a scalable solution with large field of view to analyze microparticles or cells in high-throughput biological imaging applications. We studied characterizati...

This pilot study aimed to test a comprehensive experience sampling method (ESM) protocol for investigating the relationship between stress and personality functioning (PF) in the daily lives of outpatients diagnosed with borderline personality disorder (BPD). Participants (N = 22) responded to a 32‐item ESM questionnaire 10 times a day for 1 week w...

Repeated single-point measurements of thoracic bioimpedance at single (low)-frequency are strongly related to fluid changes during hemodialysis. Extension to semi-continuous measurements may provide longitudinal details in the time pattern of the bioimpedance signal, and multifrequency measurements may add in-depth information on the distribution b...

Chronic pain is a complex and personal condition that imposes a substantial burden on both individuals and society. Potentially, wearable technology could enable continuous monitoring of pain in real-world settings, offering insights into the complex relationship between physiological states and chronic pain. In this pilot study, we evaluated the p...

Background Agitation is a critical behavioral and psychological symptom of dementia, leading alone to increased caregiver burden, more frequent hospitalization, and earlier institutionalization. The results presented here provide preliminary insights into one facet of multimodal agitation detection, specifically analyzing the relationship between h...

This paper presents a high-speed readout interface suitable for nanopore-FET (NPFET) sensor arrays, which are being explored for high-throughput DNA or protein sequencing applications. The readout interface utilises a novel architecture that can simultaneously perform recording and automatic background calibration to compensate for offset and drift...

Background and objectives Monitoring electrodermal activity (EDA) in daily life requires effective handling of low-quality segments, which are common in ambulatory EDA data. Although several low-quality handling methods have been implemented, systematic comparison of these methods, which requires a large annotated dataset, is lacking. Methods Ther...

In contrast to whole-body bioimpedance, which estimates fluid status at a single point in time, thoracic bioimpedance applied by a wearable device could enable continuous measurements. However, clinical experience with thoracic bioimpedance in patients in dialysis is still limited. In order to test the reproducibility of whole-body and thoracic bio...

Electrophysiology, which is the study of the electrical properties of biological tissues and cells, has become indispensable in modern clinical research, diagnostics, disease monitoring and therapeutics. In this paper we present a brief history of this discipline and how integrated circuit design shaped electrophysiology in the last few decades. We...

Background and Aims In contrast to portable whole-body bioimpedance, which estimates fluid status at a single point in time, thoracic bioimpedance applied by a wearable device could enable continuous measurements. However, clinical experience with thoracic bioimpedance in patients in dialysis is still limited. The aim of this study is to test the r...

Speckle Plethysmography (SPG) and Photoplethysmography (PPG) are different biophotonics technologies that allow for measurement of haemodynamics. As the difference between SPG and PPG under low perfusion conditions is not fully understood, a Cold Pressor Test (CPT—60 s full hand immersion in ice water), was used to modulate blood pressure and perip...

Speckle Plethysmography (SPG) and Photoplethysmography (PPG) are different biophotonics technologies that allow for measurement of hemodynamics. As the difference between SPG and PPG under low perfusion conditions is not fully understood, a Cold Pressor Test (CPT) was used to modulate blood pressure and peripheral circulation. A custom-built setup...

Stressful life experiences may jeopardize the healthy development of children. To improve interventions, more knowledge is needed on the perception of stress by children. In adults, stress is regarded as a state of low valence and high arousal. It is unclear whether children perceive stress similarly. In the current study, 35 children of the genera...

Objective: The goal was to compare Speckle plethysmography (SPG) and Photoplethysmography (PPG) with non-invasive finger Arterial Pressure (fiAP) regarding Pulse Wave Morphology (PWM) and Pulse Arrival Time (PAT). Methods: Healthy volunteers (n = 8) were connected to a Non-Invasive Blood Pressure (NIBP) monitor providing fiAP pulse wave and PPG fro...

Electrodermal activity (EDA) reflects changes in electrical conductivity of the skin via activation of the sympathetic nervous system. Ambulatory EDA measurements bring multiple challenges regarding quality assessment and response detection. A signal quality indicator (SQI) is one method to overcome these. This study aimed to investigate the transf...

In proteomics, the need to precisely examine the protein compounds of small samples, requires sensitive analytical methods which can separate and enrich compounds with high precision. Current techniques require a minimal analysis time to obtain satisfactory compound separation where longer analysis time means better separation of compounds. But, mo...

Fundamental neuroscience research and high-performance neuro-prostheses require large-scale brain interfaces with ever-greater spatial resolution across a large cortex coverage, which cannot be achieved with current passive (micro) electrocorticography (ECoG) technologies. In this article, we present an active micro-electrocorticography ( $\mu $ E...

Background and Objectives Agitation, a critical behavioral and psychological symptom in dementia, has a profound impact on a patients’ quality of life as well as their caregivers’. Autonomous and objective characterization of agitation with multimodal systems has the potential to capture key patient responses or agitation triggers. Research Design...

Background Chronic stress and depressive symptoms have both been linked to increased heart rate (HR) and reduced HR variability. However, up to date, it is not clear whether chronic stress, the mechanisms intrinsic to depression or a combination of both cause these alterations. Subclinical cases may help to answer these questions. In a healthy work...

A backside illumination (BSI) silicon-based CMOS image sensor (CIS) with three transfer gates is designed and optimized for near-infrared (NIR) fluorescence lifetime imaging microscopy (FLIM) applications. A three-tap design is considered for a more efficient fluorescence acquisition, avoiding sample damage and photobleaching. A thick silicon subst...

Background: Although both speckle plethysmography (SPG) and photoplethysmography (PPG) examine pulsatile changes in the vasculature using opto-electronics, PPG has a long history, whereas SPG is relatively new and less explored. The aim of this study was to compare the effects of integration time and light-source coherence on signal quality and wav...

The ability to objectively measure aspects of performance and behavior is a fundamental pillar of digital health, enabling digital wellness products, decentralized trial concepts, evidence generation, digital therapeutics, and more. Emerging multimodal technologies capable of measuring several modalities simultaneously and efforts to integrate inpu...

A backside-illuminated (BSI) near-infrared enhanced silicon single-photon avalanche diode (SPAD) for time-of-flight (ToF) light detection and ranging applications is presented. The detector contains a 2 $\mu$m wide multiplication region with a spherically-uniform electric field peak enforced by field-line crowding. A charge-focusing electric field...

A backside-illuminated (BSI) near-infrared (NIR)-enhanced silicon single-photon avalanche diode (SPAD) for time-of-flight (ToF) light detection and ranging applications is presented. The detector contains a 2- $\boldsymbol {\mu }\text{m}$ -wide multiplication region with a spherically uniform electric field peak enforced by field-line crowding. A...

Changes in respiratory rate have been found to be one of the early signs of health deterioration in patients. In remote environments where diagnostic tools and medical attention are scarce, such as deep space exploration, the monitoring of the respiratory signal becomes crucial to timely detect life-threatening conditions. Nowadays, this signal can...

UNSTRUCTURED The ability to objectively measure aspects of performance and behavior is a fundamental pillar of digital health, enabling digital wellness products, decentralized trial concepts, evidence generation, digital therapeutics, and more. Emerging multimodal technologies capable of measuring several modalities simultaneously and efforts to i...

This paper presents a low power, high dynamic range (DR), light-to-digital converter (LDC) for wearable chest photoplethysmogram (PPG) applications. The proposed LDC utilizes a novel 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order noise-shaping slope architecture, directly converting...

Technological advancements and miniaturization of wearable sensors have enabled long-term pervasive physiological monitoring. Wrist-worn photoplethysmography (PPG) sensors, although quite popular owing to their form factor, suffer from poor signal quality in ambulatory settings due to motion artifacts. This affects the reliable estimation of vital...

Continuous and non-invasive cardiovascular monitoring has gained attention due to the miniaturization of wearable devices. Particularly, wrist-worn photoplethysmography (PPG) sensors present an alternative to electrocardiogram recording for heart rate (HR) monitoring as it is cheaper and non-intrusive for daily activities. Yet, the accuracy of PPG...

Background: Respiratory sinus arrhythmia (RSA) is a form of cardiorespiratory coupling. Its quantification has been suggested as a biomarker to diagnose different diseases. Two state-of-the-art methods, based on subspace projections and entropy, are used to estimate the RSA strength and are evaluated in this paper. Their computation requires the s...

A Monte Carlo simulation method for the transport and multiplication of carriers in electric fields is presented. The method is based on the stochastic scattering and free flight of electrons and holes in silicon. The simulation technique employs a nonparabolic single-band model for the energy dispersion relation, providing good accuracy for high e...

An ultra-small-area, low-power analog front-end (AFE) for high-density neural recording is presented in this brief. It features an 11-bit incremental delta-sigma analog-to-digital converter ( $\Delta \Sigma $ ADC) enhanced with an offset-rejecting event-driven input biasing network. This network avoids saturation of the ADC input caused by leakage...

In this paper, a computational performance analysis is presented of a wide-field time-gated fluorescence lifetime imaging microscope (FLIM) using practically realizable properties of the laser, sample, and a three-tap time-gated CMOS image sensor. The impact of these component-level properties on the accuracy and the precision of the measurement re...

Background: Abnormalities of heart rate (HR) and its variability are characteristic of major depressive disorder (MDD). However, circadian rhythm is rarely taken into account when statistically exploring state or trait markers for depression. Methods: A 4-day electrocardiogram was recorded for 16 treatment-resistant patients with MDD and 16 age- an...

Background and Aims Blood pressure (BP) variability is an important cardiovascular risk factor that contributes to the high burden of cardiovascular mortality in hemodialysis (HD) patients. Ultrafiltration rate (UFR) and plasma refill rate modify the extracellular volume (ECV), which is a major determinant of the systolic BP. Segmental bioimpedance...

A near-infrared (NIR) enhanced silicon single-photon avalanche diode (SPAD) fabricated in a customized 0.13 $\mu$m CMOS technology is presented. The SPAD has a depleted absorption volume of approximately 15 $\mu$m x 15 $\mu$m x 18 $\mu$m. Electrons generated in the absorption region are efficiently transported by drift to a central active avalanche...

Currently, nearly 6 in 10 US adults are suffering from at least one chronic condition. Wearable technology could help in controlling the health care costs by remote monitoring and early detection of disease worsening. However, in recent years, there have been disappointments in wearable technology with respect to reliability, lack of feedback, or l...

Impedance pneumography has been suggested as an ambulatory technique for the monitoring of respiratory diseases. However, its ambulatory nature makes the recordings more prone to noise sources. It is important that such noisy segments are identified and removed, since they could have a huge impact on the performance of data-driven decision support...

A near-infrared (NIR) enhanced silicon single-photon avalanche diode (SPAD) fabricated in a customized $0.13~\mu \text{m}$ CMOS technology is presented. The SPAD has a depleted absorption volume of approximately $15\,\,\mu \text{m}\,\,\times 15\,\,\mu \text{m}\,\,\times 18\,\,\mu \text{m}$ . Electrons generated in the absorption region are effi...

Objective: Over the last two decades, radar-based contactless monitoring of vital signs (heartbeat and respiration rate) has raised increasing interest as an emerging and added value to health care. However, until now, the flaws caused by indoor multipath propagation formed a fundamental hurdle for the adoption of such technology in practical heal...

The recording of biopotential signals using techniques such as electroencephalography (EEG) and electrocardiography (ECG) poses important challenges to the design of the front-end readout circuits in terms of noise, electrode DC offset cancellation and motion artifact tolerance. In this paper, we present a 2 <sup xmlns:mml="http://www.w3.org/1998/M...

BACKGROUND There are 1.1 billion smokers worldwide and each year more than 8 million die prematurely because of cigarette smoking. Encouragingly, more than half of current smokers make a serious quit every year. Nonetheless, 90% of unaided quitters relapse within the first 4 weeks due to the lack of limited access to cost-effective and efficient sm...

Background: There are 1.1 billion smokers worldwide, and each year, more than 8 million die prematurely because of cigarette smoking. More than half of current smokers make a serious quit every year. Nonetheless, 90% of unaided quitters relapse within the first 4 weeks of quitting due to the lack of limited access to cost-effective and efficient s...

formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> $Objective:$ This study demonstrates a novel method for pulse arrival time (PAT) segmentation into cardiac isovolumic contraction (IVC) and vascular pulse transit time to approximate central pulse wave velocity (PWV). $Methods:$ 10 subjects (38±10...

The electrocardiogram (ECG) is an important diagnostic tool for identifying cardiac problems. Nowadays, new ways to record ECG signals outside of the hospital are being investigated. A promising technique is capacitively coupled ECG (ccECG), which allows ECG signals to be recorded through insulating materials. However, as the ECG is no longer recor...

Background and objective Long-term electrocardiogram monitoring comes at the expense of signal quality. During unconstrained movements, the electrocardiogram is often corrupted by motion artefacts, which can lead to inaccurate physiological information. In this situation, automated quality assessment methods are useful to increase the reliability o...

Background: Pulse wave velocity (PWV) is an established marker of arterial stiffness [1]. Local PWV estimates, however, are affected by confluence of incident and reflected waves, biasing the spatiotemporal propagation of the systolic foot (SF) in the distension waveform [2,3]. We, therefore, propose a Double Gaussian Propagation Model (DGPM) to es...

Accurate image reconstruction in color lens-free imaging has proven challenging. The color image reconstruction of a sample is impacted not only by how strongly the illumination intensity is absorbed at a given spectral range, but also by the lack of phase information recorded on the image sensor. We present a compact and cost-effective approach of...

Cardiac rehabilitation (CR) is a highly recommended secondary prevention measure for patients with diagnosed cardiovascular disease. Unfortunately, participation rates are low due to enrollment and adherence issues. As such, new CR delivery strategies are of interest, as to improve overall CR delivery. The goal of the study was to obtain a better u...

Monolithically integrated GaAs p-i-n diodes are demonstrated on 300-mm Si (001) substrates using a nanoridge-engineering approach. Deep-level transient spectroscopy (DLTS) is used to perform defect analysis for nanoridge and planar GaAs diodes. The point defect, EL2 with NT≃3×1014cm−3, is observed for nanoridge p-i-n diodes. A methodology is develo...

Remote home monitoring via wearables is rapidly gaining popularity, thanks to ever more complex vital signs recording and data analytics that are embedded into single devices. True system-on-chips (SoCs) push the envelope of power and form factor, while wearables are becoming more common-place, novel health sensing paradigms appear. Non-contact sen...

UNSTRUCTURED Currently, nearly 6 in 10 US adults are suffering from at least one chronic condition. Wearable technology could help in controlling the health care costs by remote monitoring and early detection of disease worsening. However, in recent years, there have been disappointments in wearable technology with respect to reliability, lack of f...

The gastro-intestinal (GI) tract is a very important part of the human digestive system but remains largely inaccessible for unobtrusive monitoring. Ingestible electronic devices are a very interesting concept to address this need. This paper discusses the current state of ingestible electronic devices and explores the potential they hold to provid...

Background: Haemodialysis (HD) patients are burdened by frequent fluid shifts which amplify their comorbidities. Bioimpedance (bioZ) is a promising technique to monitor changes in fluid status. The aim of this study is to investigate if the thoracic bioZ signal can track fluid changes during a HD session. Methods: Prevalent patients from a singl...

Accurately monitoring and modeling smoking behavior in real life settings is critical for designing and delivering appropriate smoking-cessation interventions through mHealth applications. In this paper, we inspect smoking patterns based on data collected from 52 volunteers during a 4-week period of their everyday lives. These data are acquired by...

Cardiovascular diseases (CVD) are often characterized by their multifactorial complexity. This makes remote monitoring and ambulatory cardiac rehabilitation (CR) therapy challenging. Current wearable multimodal devices enable remote monitoring. Machine learning (ML) and artificial intelligence (AI) can help in tackling multifaceted datasets. Howeve...

We present a new image reconstruction method for color lens-free imaging (CLFI) using optimized phase estimation. This method accurately preserves sample color and delivers high-quality images useful for e.g. imaging of pathology slides.

This paper presents a low-power fully differential optical sensor interface amplifier for photoplethysmography (PPG) and near infrared spectroscopy (NIRS) recordings. The proposed amplifier employs a stacked current reuse input stage that provides a DC biasing voltage for the photodiode, reducing the parasitic capacitance. The output stage exploits...

Research on heart rate (HR) estimation using wrist-worn photoplethysmography (PPG) sensors have progressed rapidly owing to the prominence of commercial sensing modules, used widely for lifestyle monitoring. Reported methodologies have been fairly successful in mitigating the effect of motion artifacts (MA) in ambulatory environment for HR estimati...

This paper presents a low power, high dynamic range (DR), reconfigurable light-to-digital converter (LDC) for photoplethysmogram (PPG) and near-infrared spectroscopy (NIRS) sensor readouts. The proposed LDC utilizes a current integration and a charge counting operation to directly convert the photocurrent to a digital code. This LDC consists of a l...

Vignetting in camera lenses is generally seen as something to avoid. For spectral cameras with thin-film interference filters, however, we argue that vignetting can be an advantage. When illuminated by focused light, the bandwidth of interference filters increases with the chief-ray angle, causing position-dependent smoothing of the spectra. We sho...

BACKGROUND Chronic stress is increasing in prevalence and it is associated with several physical and mental disorders. Assessment of chronic stress is mostly performed by administrating questionnaires. Despite being convenient and valid tools, questionnaires do not inform on the detrimental effects of chronic stress on physiological functioning, wh...

Background Chronic stress is increasing in prevalence and is associated with several physical and mental disorders. Although it is proven that acute stress changes physiology, much less is known about the relationship between physiology and long-term stress. Continuous measurement of vital signs in daily life and chronic stress detection algorithms...

Background: Local carotid pulse wave velocity (PWV) estimation is challenging due to a complex anatomy and associated wave reflections [1]. Wave interference is both blood pressure (BP) and position dependent, hence causing nonlinearity in the spatiotemporal PWV estimation [2]. In lack of beat-to-beat quality assessment [3], we propose a method to...

Background: Carotid artery tracking has high clinical relevance for the investigation of arterial stiffness indicators like Pulse Wave Velocity (PWV). However, current tracking systems are unreliable and/or not fully automated [1,2]. In this work we propose a novel wall tracking algorithm for long-term ultrasonic recordings, featuring automated bea...

In a normally functioning eye, the iris controls the pupil diameter to regulate the amount of light reaching the retina. Various iris deficiencies exist, manifesting as defects in the iris or an absence of one which result in too much light reaching the retina. Some iris deficiencies, such as aniridia or leiomyoma, can be mitigated with fixed or ad...

Thin-film interference filters can be illuminated by a circular aperture at different angles. Each situation produces a different transmittance spectrum. We present an analytical model that, for small tilt angles, predicts the change in transmittance for an arbitrary position of the filter in three-dimensional space. The model is extended to take i...

BACKGROUND Cardiac rehabilitation (CR) is known for its beneficial effects on functional capacity and is therefore highly recommended as a secondary prevention measure in cardiovascular diseases. In addition, a larger increase in functional capacity is accompanied by better clinical outcomes. However, not all patients respond in a similar way to CR...

Background Cardiac rehabilitation (CR) is known for its beneficial effects on functional capacity and is a key component within current cardiovascular disease management strategies. In addition, a larger increase in functional capacity is accompanied by better clinical outcomes. However, not all patients respond in a similar way to CR. Therefore, a...