This PDF file contains the front matter associated with SPIE Proceedings Volume 8583, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Over the past decade, we developed near-infrared fluorescence (NIRF) devices for non-invasive lymphatic imaging using microdosages of ICG in humans and for detection of lymph node metastasis in animal models mimicking metastatic human prostate cancer. To validate imaging, a NIST traceable phantom is needed so that developed “first-inhumans” drugs may be used with different luorescent imaging platforms. In this work, we developed a QDots 800 based fluorescent solid phantom for installation and operational qualification of clinical and preclinical, NIRF imaging devices. Due to its optical clearance, polyurethane was chosen as the base material. Titanium dioxide was used as the scattering agent because of its miscibility in polyurethane. QDots 800 was chosen owing to its stability and NIR emission spectra. A first phantom was constructed for evaluation of the noise floor arising from excitation light leakage, a phenomenon that can be minimized during engineering and design of fluorescent imaging systems. A second set of phantoms were constructed to enable quantification of device sensitivity associated with our preclinical and clinical devices. The phantoms have been successfully applied for installation and operational qualification of our preclinical and clinical devices. Assessment of excitation light leakage provides a figure of merit for “noise floor” and imaging sensitivity can be used to benchmark devices for specific imaging agents.

Simulations of light propagation in biological tissues are a useful method in detector development for tissue spectroscopy. In practice most attention is paid to the adequate description of tissue structures and the ray trace procedure. The surrounding light source geometry, such as output window, reflector and casing is neglected. Instead, the description of the light source is usually reduced to incident beam paths. This also applies to detectors and further surrounding tissue connected sensor geometry. This paper discusses the influence of a complex and realistic description of the light source and detector geometry with the ray tracing software ASAP (Breault Research Organization). Additionally simulations include the light distribution curve in respect to light propagation through the tissue model. It was observed that the implementation of the geometric elements of the light source and the detector have direct influence on the propagation paths, average photon penetration depth, average photon path length and detected photon energy. The results show the importance of the inclusion of realistic geometric structures for various light source, tissue and sensor scenarios, especially for reflectance measurements. In reality the tissue surrounding sensor geometry has a substantial impact on surface and subsurface reflectance and transmittance due to the fact that a certain amount of photons are prevented from leaving the tissue model. Further improvement allows a determination of optimal materials and geometry for the light source and sensors to increase the number of light-tissue-interactions by the incident photons.

For the reconstruction of physiological changes in specific tissue layers detected by optical techniques, the exact knowledge of the optical parameters μ_a, μ_s and g of different tissue types is of paramount importance. One approach to accurately determine these parameters for biological tissue or phantom material is to use a double-integrating-sphere measurement system. It offers a flexible way to measure various kinds of tissues, liquids and artificial phantom materials. Accurate measurements can be achieved by technical adjustments and calibration of the spheres using commercially available reflection and transmission standards. The determination For the reconstruction of physiological changes in specific tissue layers detected by optical techniques, the exact knowledge of the optical parameters μ_a, μ_s and g of different tissue types is of paramount importance. One approach to accurately determine these parameters for biological tissue or phantom material is to use a double-integrating-sphere measurement system. It offers a flexible way to measure various kinds of tissues, liquids and artificial phantom materials. Accurate measurements can be achieved by technical adjustments and calibration of the spheres using commercially available reflection and transmission standards. The determination of the optical parameters of a material is based on two separate steps. Firstly, the reflectance ρ_s, the total transmittance T_s^T and the unscattered transmittance T_s^C of the sample s are measured with the double-integrating-sphere setup. Secondly, the optical parameters μ_a, μ_s and g are reconstructed with an inverse search algorithm combined with an appropriate solver for the forward problem (calculating ρ_s, T_s^T and T_s^C from μ_a, μ_s and g) has to be applied. In this study a Genetic Algorithm is applied as search heuristic, since it offers the most flexible and general approach without requiring any foreknowledge of the fitness-landscape. Given the challenging preparation of real tissue samples it comes as no surprise that these are subject to various uncertainties. In order to perform a robust parameter reconstruction samples of different thickness are used. This adds a further, strong restriction to the potential results from the heuristic reconstruction algorithm.

We describe a stable and reproducible liquid tissue mimicking phantom optimized for applications involving both ultrasound and light waves. The phantom has optical and acoustic properties similar to soft biological tissue. The base material is Glycerol. The TiO2 is added to the Glycerol as scattering particles. An absorbing dye is added to obtain desired absorptions in the Near IR range. The phantom's optical absorption was measured by Spatially Resolved Spectroscopy (SRS). In addition, the optical properties were calculated based on the spatial decay of an acousto-optic signal generated in the phantom, and were compared to those obtained with SRS.

Photoacoustic tomography (PAT) is an emerging modality that combines the high contrast of optical imaging, with the spatial resolution and penetration depth of ultrasound, by exploiting the photoacoustic effect. As with any new imaging modality, reliable physical phantoms are needed to: calibrate instruments; validate performance; optimize signal-to-noise; perform routine quality control; and compare systems. Phantom materials for testing small animal PAT systems should also mimic both the optical and acoustic properties of soft tissue, while for calibration purposes should be resistant to degradation over long time periods. We show here that polyvinyl chloride plastisol (PVCP) phantoms enable calibration and performance validation using two PAT systems with distinct designs (Visualsonics Vevo LAZR and Endra Nexus 128) across a wavelength range of 680 nm – 950 nm. Inclusions between 2 and 3.2 mm in diameter were fabricated from PVCP using a range of dye concentrations (0 % to 0.256 % Black Plastic Color, BPC) in a custom mold. A calibration phantom was imaged repeatedly on both systems, over time scales of minutes, hours and days, to assess system stability. Both systems demonstrated good reproducibility over time, with the coefficient of variation in the measured signal-to-noise ratio (SNR) being less than 15% over the course of 30 days. Imaging performance was optimized by plotting SNR as a function of different system parameters. The visualization of objects embedded in optically absorbing and scattering backgrounds was also assessed. PVCP is easy to work with and provides stable phantoms for assessing PAT system performance.

Resolution is an important figure of merit for imaging systems. We designed, fabricated and tested an optical phantom consisting of a block of SU-8 with bars etched into its surface. This phantom mimics the simplicity of the 1951 Air Force test chart but can characterize both the axial and lateral resolution of optical coherence tomography systems. The phantom was successfully used to find the axial and lateral resolutions of multiple OCT systems.

We propose and validate the design of inhomogeneous phantoms for diffuse optical imaging purposes using totally absorbing objects embedded in a diffusive medium. From Monte Carlo simulations, we show that a given or desired perturbation strength caused by an realistic absorbing inhomogeneity of a certain absorption and volume can be approximately mimicked by a small totally absorbing object of a so-called Equivalent Black Volume (Equivalence Relation). This concept can be useful to design realistic inhomogeneous phantoms using a set of black objects with different volumes. Further, it permits to grade physiological or pathological changes on a reproducible scale of equivalent black volumes, thus facilitating the performance assessment of clinical instruments. We have also provided a plot to derive the Equivalent Black Volume yielding the same effect of a realistic absorption object.

Tissue phantoms are important tools to calibrate and validate light propagation effects, measurements and diagnostic test in real biological soft tissue. We produce low cost phantoms using standard commercial jelly, distillated water, glycerol and a 20% lipid emulsion (Oliclinomel N7-1000 ®) was used in place of the usual Intralipid®. In a previous work we designed a protocol to elaborate high purity phantoms which can be used over months. We produced three different types of phantoms regarding the lipid emulsion – glycerol - gelatin – water composition: Pure gelatin phantoms, lipid in glycerol, and lipid in gelatin phantoms were produced and different concentrations of the lipid emulsion were used to study optical propagation properties of diffusive mixtures. Besides, 1.09 μm poly latex spheres in distilled water were used to produce reference phantoms. In order to use all the phantom sides, the phantoms were produced in disposable spectrometer cuvettes, designed for fluorescence studies. Measurements were performed using an OceanOptics 4000 channels spectrophotometer and integrating spheres. For the scattering measurements a homemade goniometer with a high resolution angular scale was used and the scattering detector was a linear array of optical fibers, with an angular collimator, connected to the spectrophotometer. White LED was used as light source, and the 6328.8 nm HeNe Laser was used for calibration. In this work we present characterization measurements for gelatin and microspheres phantoms using spectral reflectance, diffuse and direct spectral transmittance, and angle scattering measurements. The results of these measurements and their comparison are presented.

We developed a stable, reproducible three-dimensional optical phantom for the evaluation of a wide-field endoscopic molecular imaging system. This phantom mimicked a human esophagus structure with flexibility to demonstrate body movements. At the same time, realistic visual appearance and diffuse spectral reflectance properties of the tissue were simulated by a color matching methodology. A photostable dye-in-polymer technology was applied to represent biomarker probed “hot-spot” locations. Furthermore, fluorescent target quantification of the phantom was demonstrated using a 1.2mm ultrathin scanning fiber endoscope with concurrent fluorescence-reflectance imaging.

Methodologies to fabricate a solid optical tissue phantom (OTP) mimicking epidermal thin-layer have been developed for in vitro human skin experiment. However, there are cumbersome and time-consuming efforts in fabrication process such as a custom-made casting and calculation of solvent volume before curing process. In a previous study, we introduced a new methodology based on spin coating method (SCM) which is utilized to fabricate a thin-layer OTP analogous to epidermal thickness. In this study, a double layer solid OTP which has epidermal and dermal layers was fabricated to mimic the morphological and optical similarity of human tissue. The structural characteristic and optical properties of fabricated double layer OTP were measured using optical coherence tomography and inverse adding doubling algorithms, respectively. It is expected that the new methodology based on the SCM may be usefully used in the fabrication of double layer OTP.

We document our latest work in developing a new eye model with a solid-state cornea and liquid filled anterior chamber designed for demonstrating, validating and comparing anterior chamber ophthalmic Optical Coherence Tomography (OCT) instruments, corneal topographers, and Scheimpflug cameras. Anterior chamber eye model (ACEM) phantoms can serve a variety of purposes, including demonstrating instrument functionality and performance in both the clinic and exhibit hall, validating corneal layer thickness measurements from different commercial instruments and as an aide for the R and D engineer and field service technician in the development and repair of instruments, respectively. The ideal eye model for OCT, the optical cross-sectional imaging modality, would have a volumetric morphology and scattering and absorption properties similar to that of normal human cornea. These include a multi-layered structure of equivalent thickness to nominal human corneal layers, including an epithelium layer, a stroma with appropriate backscattering properties, and an endothelium. A filled and sealed tissue phantom relieves the user of constant cleaning and maintenance associated with the more common water bath model eyes. Novel processes have been developed to create corneal layers that closely mimic the reflectance and scattering coefficients of the real layers of the cornea, as imaged by spectral bandwidth of OCT.

Fluorescence intensity is often standardized by comparing the unknown sample signal to that of a reference solution with a known concentration of a reference fluorophore. To use this technique for in vivo fluorescence reflectance measurements standardization, a reference sample that also mimics the scattering and absorption properties of the tissue would need to be used. A simpler approach to fluorescence reflectance measurements standardization is to express the intensity of the measured fluorescence as a ratio of the excitation irradiance to the fluorescence radiance. This ratio of radiometric quantities can be measured by normalizing the measured fluorescence image to a reflectance image acquired with a reflection standard at the excitation wavelength (without the emission filter). Instruments could be calibrated to report their intensity results using this dimensionless ratio. The calibration could also be transferred from a reference calibrated instrument to other instruments through the use of fluorescence phantoms. Reporting fluorescence intensity measurements using this dimensionless ratio will ease instrument standardization and comparison of fluorescence reflectance results between instruments, vendors and applications.

Novel protocols were developed and applied in the European project “nEUROPt” to assess and compare the performance of instruments for time-domain optical brain imaging and of related methods of data analysis. The objective of the first protocol, “Basic Instrumental Performance”, was to record relevant basic instrumental characteristics in a direct way. The present paper focuses on the second novel protocol (“nEUROPt” protocol) that was devoted to the assessment of sensitivity, spatial resolution and quantification of absorption changes within inhomogeneous media. It was implemented with liquid phantoms based on Intralipid and ink, with black inclusions and, alternatively, in two-layered geometry. Small black cylinders of various sizes were used to mimic small localized changes of the absorption coefficient. Their position was varied in depth and lateral direction to address contrast and spatial resolution. Two-layered liquid phantoms were used, in particular, to determine depth selectivity, i.e. the ratio of contrasts due to a deep and a superficial absorption change of the same magnitude. We introduce the tests of the “nEUROPt” protocol and present exemplary results obtained with various instruments. The results are related to measurements with both types of phantoms and to the analysis of measured time-resolved reflectance based on time windows and moments. Results are compared for the different instruments or instrumental configurations as well as for the methods of data analysis. The nEUROPt protocol is also applicable to cw or frequency-domain instruments and could be useful for designing performance tests in future standards in diffuse optical imaging.