The fabrication of a stable, reproducible optical imaging phantom is critical to the assessment and optimization of optical imaging systems. In this study, we present a novel design of optical phantom based on metal-doped glass-ceramics. The matrix was doped with nickel ions to imitate the absorption of haemoglobin, and scattering levels representative of tissue were induced through controlled crystallisation in the glass-based phantom at elevated temperature. Our glass-based optical phantom can provide controlled levels of optical scattering and absorption to mimic the optical properties of human tissues with excellent optical homogeneity, and potentially long-term stability and reproducibility.

Refractive index (RI) measurements are highly dependent on environmental conditions, which are often not reported, resulting in non-traceable measurements. Additionally, the RI of buffer solutions, such as phosphate-buffered saline (PBS), is unknown. We built a new optical set-up based on the minimum deviation angle to traceably measure the RI of solids and liquids under controlled environmental conditions. We measured the RI of fused silica, 1.470091, and PBS, 1.344599, at 405 nm, 20.00 °C with an expanded uncertainty of 1.4e-6. Our results differ from previously assumed RIs and therefore have practical implications for nanoparticle flow cytometry measurements.

The Medical Devices Regulations (MDR) in Europe have a major impact on medical devices and software developed in research institutes. A strategic program at the University of Twente supports researchers with practical formats of the Investigational Medical Device Dossier IMDD including risk assessment and ethical approval for clinical studies. The R&D facilities have a QMS in the spirit of ISO 9001 and 13485 to ease the transfer to a commercial partner or spin-off company. A maturity scan helps researchers to determine ‘missing’ parts for successful implementation of a medical device to the market. These practical tools accelerate the successful implementation of medtech innovations to the health market.

Current approaches of creating optical phantoms cannot accurately capture the wavelength-dependent properties found in tissue. To address this, we developed a method of producing solid, inorganic phantoms whose wavelength-dependent optical properties can be fit to those of tissue over 370 to 950 nm through the combination of up to twenty different absorbing and scattering pigments. Using this approach, we were able to create and validate spectral phantoms closely matching the optical properties of muscle and nerve tissue, the diffuse reflectance of pale and melanistic skin, and the chromophore concentrations of a computational skin model with varying levels of oxygen saturation.

Pulse sampling fluorescence Lifetime Imaging (PS-FLIm) is a powerful noninvasive technique with applications to basic science and translational clinical research. However, little is known about the photon-economy of PS-FLIm. We report the first study about the photon-economy of PS-FLIm. We found that for in vivo measurements, the photon rate of multispectral PS-FLIm ranges from 1 to 5 GHz (three channels), order of magnitude higher than that of TCSPC and the F-value of PS-FLIm is less performant than that of TCSPC. This study is a first step toward understanding the photon-economy of PS-FLIm and will facilitate the optimization of PS-FLIm for future clinical use.

For high-signal-rate nonlinear microscopy using an analog PMT to detect multiple photons per excitation pulse, the conversion of analog output to photon counts is required to realize quantitative imaging. To enable this ability, we propose a method for photon counting with analog photodetection based on “imaging” of standard dye solutions and a mathematical model of Poisson photon statistics. Using this method, we not only enable the quantification across different types of PMTs from different setups, but also quantify the channel leakage for multichannel or multispectral imaging systems. This method paves the way for analog PMTs in high-signal-rate quantitative imaging of either label-free or labeled samples.

Multiphoton fluorescence imaging allows clinicians to identify early signs of oral cancer at its origin below the tissue surface. The high resolution required for adequate morphological assessment is only possible over a relatively small field of view, however, so an additional co-registered wide field of view, low resolution image is crucial for efficient device operation. To meet this need, we present the design of a handheld intraoral probe that includes a 0.50NA objective for multiphoton imaging and auxiliary cameras for region-of-interest identification. Because multiphoton image quality is most dependent on the high NA objective, we characterize its performance and correlate findings to expected system-level quality. Finally, we show concepts for the design and manufacturing strategy of a compact, monolithic, high NA freeform prism objective optimized for multiphoton imaging in the oral cavity.

There is increased interest in use of multiple optical imaging/sensing modalities together as a means to potentially improve diagnostic outcomes. This presentation will review aspects of analysis methods that have been employed when evaluating diagnostic potential of multimodal imaging. It will include discussion of our own current/previous approaches and a thorough commentary on the methods employed in the literature with literature review focusing on multimodal diagnostic imaging. This review includes investigational as well as clinical modalities, and beyond optical imaging to other modalities. Strategies and specific recommendations for consideration of analyses during the development of multimodal approaches will be presented.

Facial masks are assumed to provide protection against aerosols and droplets but can leak due to poor fit which reduces the effectiveness against transmission of Covid19. A theoretical model was developed to predict the leakage around facial mask and the results were compared to leakage measurements using thermal imaging on various facial mask types. All tested masks showed leakage of exhaled air along the gaps at the rim of the mask due to the high resistance of the mask filter material. The experimental data was relatively in good agreement with the theoretical ‘simplified’ model. Common types of facial masks are not effective in filtering aerosols but do block droplets.

3D cell models that are induced to interact and grow in a 3D environment are formed up to several hundred micrometers. Since cells grow in all directions, an imaging system that can show molecular images using fluorescence as well as morphological structures without damaging the structure of the cell model is needed. We have developed a multimodal optical microscopy imaging system that combines extended depth of focus-optical coherence microscopy (EDOF-OCM) and two-photon fluorescence microscopy (TPFM) for more accurate measurement of 3D cells. This imaging system was able to acquire merged images without moving the spheroids, and the efficiency of the imaging systems was compared using optical coherence tomography (OCT), OCM, and confocal fluorescence microscopy(CFM).

The emerging clinical use of fluorescent agents has led to a shift in intraoperative imaging practices that overcome the limitations of human vision, thereby improving treatment outcomes in applications such as perfusion assessment and positive margins in tumor resection. As the field of fluorescence-guided surgery (FGS) expands, there is a wider range of imaging systems that are indicated for the same uses, such that there is a compelling need for standards and methods that enable system characterization and intersystem comparisons. Here we present methods for the radiometric characterization of FGS imaging systems using a calibrated solid-state emitter to enable the conversion of imager-specific responses to SI-traceable units.

Phantoms play a critical role in the development of biophotonics techniques. There is currently a lack of solid phantoms relevant to the emerging field of upconverting nanoparticles (UCNP) for biophotonics application. This work intends to showcase a range of UCNP-based phantom models and manufacturing recipe to bridge the gap and accelerate the development of UCNP-based biophotonics applications. A total of 24 phantoms were classified into 4 different categories: homogeneous, multilayer, tumour inclusion and UCNP background phantoms were manufactured and an example use case was explored. The optical properties (absorption, reduced scattering and UCNP emission) of these phantoms were found to be stable over a period of 4 months with CV < 4%. With the recent advances in the use of UCNP for biophotonics, we believe our recipe and tools will play a pivotal role in the growth of the UCNP for biophotonics applications.

Recent controversial studies reporting racial bias in pulse oximetry measurements have highlighted the need for well-validated, objective techniques for assessing skin pigmentation. To address the increased interest in classification of skin using visible to near infrared reflectance measurements, we provide a thorough critical review of melanometers – devices that estimate melanin content – and skin colorimeters. This review focuses on working mechanisms and assessing the degree to which scientific data supports the use of these devices. Additionally, we describe approaches for standardization and relevant emerging optical techniques.

The major optical absorbers in tissue are melanin and oxy/deoxy-hemoglobin, but the impact of skin tone and pigmentation on biomedical optics is still not completely understood or adequately addressed. Melanin largely governs skin tone with higher melanin concentration in subjects with darker skin tones. Recently, there has been extensive debate on the bias of pulse oximeters when used with darker subjects. Photoacoustic (PA) imaging can measure oxygen saturation similarly as pulse oximeters and could have value in studying this bias. More importantly, it can deconvolute the signal from the skin and underlying tissue. Here, we studied the impact of skin tone on PA signal generation, depth penetration, and oximetry. Our results show that subjects with darker skin tones exhibit significantly higher PA signal at the skin surface, reduced penetration depth, and lower oxygen saturation compared to subjects with lighter skin tones. We then suggest a simple way to compensate for these signal differences. More recently, we have developed 3D-bioprinted skin-mimicking phantoms with skin colors ranging across the Fitzpatrick scale. These tools can help understand the impact of skin phototypes on biomedical optics. Synthetic melanin nanoparticles of different sizes (70–500 nm) and clusters were fabricated to mimic the optical behavior of melanosome. The absorption coefficient and reduced scattering coefficient of the phantoms are comparable to real human skin. We further validated the melanin content and distribution in the phantoms versus real human skins via photoacoustic (PA) imaging. The PA signal of the phantom could be improved by (i) increasing melanin size (>1,000-fold), (ii) increasing clustering (2–10.5-fold), and (iii) increasing concentration (1.3–8-fold). We then used multiple biomedical optics tools (e.g., PA, fluorescence imaging and photothermal therapy) to understand the impact of skin tone on these modalities. These well-defined 3D-bioprinted phantoms may have value in translating biomedical optics and reducing racial bias.

Photoacoustic Imaging (PAI) devices enable deep mapping of blood oxygen saturation (SO2), but recent studies have suggested potential degraded accuracy of pulse oximeters and other optical oximetry technologies in patients with darker skin. To assess PAI oximetry robustness to skin pigmentation level, we developed a test method to quantify PAI oximetry performance using different skin-mimicking polyvinyl chloride (PVCP) phantoms with fluid channels containing blood at various SO2 levels. Varying phantom skin absorption significantly modified spectral coloring artifacts and SO2 accuracy. This test method can enable device design optimization to help ensure high device performance for all patients.

Optical devices for monitoring individuals’ physiology are becoming omnipresent with the advent of wearable and point-of-care (POC) devices capable of photoplethysmography and pulse oximetry. These devices can also provide unique opportunities for managing obesity. We have conducted a pilot human study to characterize the obese optical properties and their connection to body mass index (BMI – a metric of obesity). We have shown computationally and experimentally that obesity is an important biological variable that cannot be ignored when developing optics-based instrumentation. We will report on our recent findings and propose strategies to improve wearable functionality.

A prediction model based on artificial neural networks was built to quantify changes in blood oxygen saturation of the internal jugular vein (dSijvO2) from diffuse reflectance measured at five wavelengths. The model was trained by Monte Carlo simulations with various tissue optical coefficients and subject-specific tissue structure determined by ultrasound imaging. Errors in dSijvO2 estimated from simulated data are below 2.2% and independent of the initial oxygen saturation. The model was further validated by excellent agreements between modeled and measured in-vivo reflectance spectra from a healthy volunteer undergoing hyperventilation, and the quantified trend of dSijvO2 followed expectations during and after hyperventilation. The proposed method is promising to provide non-invasive quantification of dSijvO2.

Pulse oximetry represents the universal application of optics in modern medicine. However, recent studies have raised concerns regarding the potential impact of confounding factors like variable skin pigmentation and blood content on blood oxygen saturation measurement accuracy. Tissue-mimicking phantom testing offers a low-cost solution for characterizing device performance and potential error sources. Phantom manufacturing literature for pulse oximetry on the human finger was reviewed. Studies were categorized, and relevant optical and mechanical properties were summarized and implemented toward a preliminary phantom for optimal biological relevance using molding and 3D printing. Gaps, recommendations, and strategies were presented for continued phantom development.

We present experimental results using ex-vivo human blood in a setup built to mimic the scattering and flow properties of retinal vasculature. This system controls sources of imaging variability to assist with extracting the core physical principles required to better understand in-vivo OCT, doppler OCT, and SLO data. The setup consists of a flow system which is able to manipulate the blood oxygenation level/flow velocity and interchangeable silicone-elastomer capillaries which acts as an optical window to the flow medium. Here, we reproduce the well-known hour-glass profile in an OCT B-scan cross-section of our phantom capillary, typically seen in small-diameter vasculature.

Recent clinical studies have shown that abnormal retinal blood is associated with many ocular diseases such as age-related macular degeneration, glaucoma, and diabetic retinopathy. Several ocular imaging techniques have been developed to measure retinal blood flow both invasively and non-invasively, including optical coherence tomography angiography (OCTA), erythrocyte mediated angiography (EMA), laser speckle imaging (LSI) and adaptive optics - scanning laser ophthalmoscopy (AO-SLO). Here we present a simple, compact, well-controlled clinical flow phantom model which allows flow evaluation across several techniques to aid in the clinical diagnosis of ocular diseases with abnormal blood flow.