This PDF file contains the front matter associated with SPIE Proceedings Volume 6870, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

For much of the past decade, we have developed most of the essential hardware and software components needed for practical implementation of dynamic NIRS imaging. Until recently, however, these efforts have been hampered by the lack of calibrating phantoms whose dynamics substantially mimic those seen in tissue. Here we present findings that document the performance of a dynamic phantom based on use of twisted nematic liquid crystal (LC) technology. Programmable time courses of applied voltage cause the opacity of the LC devices, which are embedded in a background matrix consisting of polysiloxane (silicone) admixed with scattering and absorbing materials, to vary in a manner that mimics the spatiotemporal hemodynamic pattern of interest. Methods for producing phantoms with selected absorption and scattering, internal heterogeneity, external geometry, hardness, and number and locations of embedded LCs are described. Also described is a method for overcoming the apparent limitation that arises from LCs being mainly independent of the illumination wavelength. The results presented demonstrate that: the opacity vs. voltage response of LCs are highly stable and repeatable; the dynamic phantom can be driven at physiologically relevant speeds, and will produce time-varying absorption that follows the programmed behavior with high fidelity; image time series recovered from measurements on the phantom have high temporal and spatial location accuracy. Thus the dynamic phantom can fill the need for test media that practitioners may use to confirm the accuracy of computed imaging results, assure the correct operation of imaging hardware, and compare performance of different data analysis algorithms.

As optical imaging modalities gain acceptance for medical diagnostics and become common in clinical applications, standardized protocols to quantitatively assess optical sensor performance are required to ensure commonality in measurements and to validate system performance. The current emphasis is on the development of 3-dimensional, tissue-simulating artifacts with optical scattering and absorption properties designed to closely mimic biological systems. These artifacts, commonly known as tissue phantoms, can be fairly complex and are tailored for each specific application. In this work, we describe a conceptually simpler, 2-dimensional digital analog to the 3-dimensional tissue phantoms that we call Digital Tissue Phantoms. The Digital Tissue Phantoms are complex, realistic, calibrated, optical projections of medically relevant images with known spectral and spatial content. By generating a defined set of Digital Tissue Phantoms, the radiometric performance of the optical imaging sensor can be quantified, based on the accuracy of measurements of the projected images. The system is dynamically programmable, which means that the same system can be used with different sets of Digital Tissue Phantoms for sensor performance metrics covering a wide range of optical medical diagnostics, from cancer and tumor detection to burn quantification.

Engineered tissue represents a convenient path to providing models for imaging and disease progression. The use of these models or phantoms is becoming increasingly prevalent. While structural characterization of these systems is well-documented, a combination of biochemical and structural knowledge is often helpful. Fourier transform infrared (FTIR) spectroscopic imaging is a rapidly emerging technique that combines the molecular selectivity of spectroscopy with the spatial specificity of optical microscopy. Here, we report on the application of FTIR spectroscopic for analysis of a melanoma model in engineered skin. We first characterize the biochemical properties, consistency and spectral changes in different layers of growing skin. Results provide simple indices for monitoring tissue consistency and reproducibility as a function of time. Second, we introduce malignant melanocytes to simulate tumor formation and growth. Both cellular changes associated with tumor formation and growth can be observed. FTIR images indicate holistic chemical changes during the tumor growth, allowing for the development of automated pathology protocols. FTIR imaging being non-destructive, further, samples remain entirely compatible with downstream tissue processing or staining. We specifically examined the correlation of structural changes, molecular content and reproducibility of the model systems. The development of analysis, integrating spectroscopy, imaging and computation will allow for quality control and standardization of both the structural and biochemical properties of tissue phantoms.

For a number of years, phantoms have been used to optimize device parameters and validate performance in the primary medical imaging modalities (CT, MRI, PET/SPECT, ultrasound). Furthermore, the FDA under the Mammography Quality Standards Act (MQSA) requires image quality evaluation of mammography systems using FDA-approved phantoms. The oldest quantitative optical diagnostic technology, pulse oximetry, also benefits from the use of active phantoms known as patient simulators to validate certain performance characteristics under different clinically-relevant conditions. As such, guidance provided by the FDA to its staff and to industry on the contents of pre-market notification and approval submissions includes suggestions on how to incorporate the appropriate phantoms in establishing device effectiveness. Research at the FDA supports regulatory statements on the use of phantoms by investigating how phantoms can be designed, characterized, and utilized to determine critical device performance characteristics. These examples provide a model for how novel techniques in the rapidly growing field of optical diagnostics can use phantoms during pre- and post-market regulatory testing.

Calibration standards are needed for measurements of tissues in reflectance mode confocal microscopy. We have created a three dimensional turbid polyurethane phantom with a grid of inclusions. The grid had a 10 fold increase in absorption compared to the bulk of the phantom and the same scattering properties. India ink was used as an absorber for the bulk of the phantom, and Epolin 5532 (absorption peak at 500 nm) was used in the grid. Titanium dioxide particles were used as scatterers. The optical properties of the constructed phantoms were characterized with difiuse reflectance and transmission measurements followed by an inverse adding doubling method. At 488nm the total attenuation coeffcient was 40.6 ± 0.3 cm^-1 in the grid and 32.5 ± 0.3 cm^-1 in the bulk of the phantom. The phantom was imaged with reflectance mode confocal microscopy. Image analysis using the Beer-Lambert-Bouguer Law was performed. In the low absorbing bulk of the phantom the total attenuation coeffcient was estimated accurately, however in the high absorbing grid, the total attenuation coeffcient was underestimated by image analysis techniques.

We present a fabrication process for Polydimethylsiloxane (PDMS) tissue simulating phantoms with tunable optical properties to be used for optical system calibration and performance testing. Compared to liquid phantoms, cured PDMS phantoms are easier to transport and use, and have a longer usable life than gelatin based phantoms. Additionally, the deformability of cured PDMS makes it a better option over hard phantoms such as polyurethane optical phantoms when using optical probes which require tissue contact. PDMS has a refractive index of about 1.43 in the near infrared domain which is in the range of the refractive index of tissue. Absorption properties are determined through the addition of india ink, a broad band absorber in the visible and near infrared spectrum. Scattering properties are set by adding titanium dioxide, an inexpensive and widely available scattering agent which yields a wavelength dependent scattering coefficient similar to that observed in tissue in the near infrared. Phantom properties were characterized and validated using a two-distance, broadband frequency-domain photon migration system. Repeatability and predictability for the phantom fabrication process will be presented.

Tissue-simulating gel phantoms have been used in selective laser photothermal interaction. The gelatin phantom provides a uniform tissue-simulating medium for analyzing thermal performance under laser radiation. The gelatin phantom gel is used particularly in measurements of thermal reactions in laser thermology. The gelatin phantom is made from gelatin and Liposyn. A special gel sphere with Indocyanine Green (ICG) laser absorption enhancement dye is embedded in normal gel to simulate the dye-enhanced tumor in normal tissue. The concentration of ICG within the dye sphere is optimized using simulation for selective phototherapy. As a first attempt, the concentration of ICG and laser power density was optimized using a temperature ratio of target tissue versus surrounding tissue. The gel thermal performance is also monitored using MRI thermology imaging technology. The thermal imaging shows in vivo, 3D temperature mapping inside the gel. The study of thermal distribution using gel phantom provides information to guide the future selective laser photothermal thermal therapy.

We developed optical tissue phantoms with a novel combination of matrix and scatterers. These phantoms have a well known scattering microstructure of monodisperse silica microspheres, embedded in elastic silicone. We characterize their mechanical properties and, some of their optical properties. We also validate the control over the density of scatterers achieved with our proposed fabrication technique. The properties obtained are a practical combination of deformability, durability and simplicity of the microstructure. These are illustrated by results on speckle statistics in optical coherence tomography.

Tissue phantoms have been in use for decades in the quality control and calibration of x-ray, computed tomography, magnetic resonance imaging, and positron emission tomography. Such phantoms are necessary in clinical imaging, insuring the accuracy and calibration of acquired images and allowing for artifact correction. In addition, phantoms allow image comparison and/or registration between multiple instruments at different clinics and temporal comparison of the same animal. Recently, optical tissue phantoms have received much attention as it has become apparent that optical imagers pose many of the same requirements for quality control and calibration as clinical imagers. Small animal fluorescence imaging is a rapidly growing field that could benefit greatly from the implementation of a standardized reference phantom. We present our results in developing optical tissue phantoms for quality control and calibration of small animal fluorescence imagers. To accurately simulate in vivo imaging conditions, the phantom provides absorption, scatter, and fluorescence information, in known amounts and varying with spatial distribution. This allows us to monitor day-to-day variability and system response as a function of different optical path components in hyperspectral imaging technologies for small animal fluorescence imaging. The phantom has also enabled us to assess the actual, or practical, sensitivity of a small animal fluorescence imager in terms of imaging a dye concentration through an equivalent tissue depth. By combining an understanding of system response with theoretical optical raytrace modeling, this calibration tool can be applied to the majority of small animal fluorescence imagers currently in production.

A unique tissue phantom is reported here that mimics the optical and acoustical properties of biological tissue and enables testing and validation of a dual-modality clinical diagnostic system combining time-resolved laser-induced fluorescence spectroscopy (TR-LIFS) and ultrasound backscatter microscopy (UBM). The phantom consisted of contrast agents including silicon dioxide particles with a range of diameters from 0.5 to 10 μm acting as optical and acoustical scatterers, and FITC-conjugated dextran mimicking the endogenous fluorophore in tissue. The agents were encapsulated in a polymer bead attached to the end of an optical fiber with a 200 μm diameter using a UV-induced polymerization technique. A set of beads with fibers were then implanted into a gel-based matrix with controlled patterns including a design with lateral distribution and a design with successively changing depth. The configuration presented here allowed the validation of the hybrid fluorescence spectroscopic and ultrasonic system by detecting the lateral and depth distribution of the contrast agents, as well as for coregistration of the ultrasonic image with spectroscopic data. In addition, the depth of the beads in the gel matrix was changed to explore the effect of different concentration ratio of the mixture on the fluorescence signal emitted.

We are investigating the use of ZnS-capped CdSe quantum dot (QD) bioconjugates combined with fluorescence endoscopy for improved early cancer detection in the esophagus, colon and lung. A major challenge in using fluorescent contrast agents in vivo is to extract the relevant signal from the tissue autofluorescence (AF). The present studies are aimed at maximizing the QD signal to AF background ratio (SBR) to facilitate detection. These contrast optimization studies require optical phantoms that simulate tissue autofluorescence, absorption and scattering over the entire visible spectrum, while allowing us to control the optical thickness. We present an optical phantom made of fresh homogenized tissue diluted in water. The homogenized tissue is poured into a clear polymer tank designed to hold a QD-loaded silica capillary in its center. Because of the non-linear effects of absorption and scattering on measured autofluorescence, direct comparison between results obtained using tissue phantoms of different concentration is not possible. We introduce mathematical models that make it possible to perform measurements on diluted tissue homogenates and subsequently extrapolate the results to intact (non-diluted) tissue. Finally, we present preliminary QD contrast data showing that the 380-420 nm spectral window is optimal for surface QD imaging.

Recently, the use of polarized light for medical diagnosis and therapeutic management has seen increased interest due the noninvasive nature of light-tissue interactions. Examples of the use of polarized light include polarization imaging to enhance spatial resolution in turbid media, selective imaging of polarized light to increase surface contrast in tissue, polarization-sensitive optical coherence tomography (PS-OCT), and glucose monitoring. With these emerging applications there is a need for controllable phantoms to validate the emerging techniques; however, this has been done only to a limited degree primarily due to the difficulty in creating controllable phantoms. The primary effects of tissue on the polarization of light are scattering, linear birefringence, and optical activity (circular birefringence). An ideal phantom would exhibit all these effects simultaneously in a controllable fashion. We have achieved this through the use of polyacrylamide gels with polystyrene microspheres added as scattering particles, strain applied to the gels to create birefringence, and sucrose added for optical activity. The phantom methodology has been validated using our polarimetry system. Currently, the phantom system is being used to extend our work in birefringence mapping of the myocardium and to further our work in characterizing tissue.

In biomedical optics applications, the scattering of light by biological tissue is typically mimicked by embedding microparticles such as polystyrene microspheres or TiO₂ within a non-scattering matrix. Such particles are well structured and give rise to uniform optical scattering properties. However, typical biological scatterers are seldom well-organized nor uniformly sized. In this work, we sought to characterize the scattering properties from particles common to many tissues such as collagen fibers, cells, and lipids. These purified particles were suspended and sandwiched between 2 glass cover slips to form disposable phantoms. The phantoms were imaged by optical coherence tomography and reflectance-mode confocal microscopy. From the images, the attenuation and reflectivity of the sample were evaluated by fitting the depth-dependent signal from specified regions of the image to a theoretical model. The fitted attenuation and reflectivity were used to deduce a distribution of local values of the scattering coefficient and anisotropy factor for each phantom. The measured optical properties at the 2 wavelengths differed in ways that can be explained by Mie theory, suggesting that despite their complex structure, typical biological scatterers exhibit some regularity that can potentially be characterized quantitatively.

Preparation of phantoms with reproducible and homogenous optical properties is tricky. The microscopic heterogeneity and macroscopic homogeneity of tissue phantoms were compared using reflectance-mode confocal laser scanning microscopy. Tissue phantoms were prepared using polystyrene microspheres as scattering medium in aqueous and gel matrix. Uniform distribution of microparticles in phantoms was evaluated by confocal imaging. Comparison of the heterogeneity of the phantoms was accomplished based on microscopic optical scattering properties. Distribution of optical properties at the microscopic levels was determined by a simple theory developed based on the depth-dependent decay of the reflectance-mode confocal signal. The variability of these optical properties is correlated to heterogeneity of the phantom. These microscopic properties were compared with macroscopic properties determined by ballistic transmission experiment. This enabled to optimize the phantom preparation procedure.

We have designed and built an imaging elastic scattering spectroscopy endoscopic instrument for the purpose of detecting cancer in vivo. As part of our testing and validation of the system, known targets representing potential disease states of interest were constructed using polystyrene beads of known average diameter and TiO₂ crystals embedded in a two-layer agarose gel. Final construction geometry was verified using a dissection microscope. The phantoms were then imaged using the endoscopic probe at a known incident angle, and the results compared to model predictions. The mathematical model that was used combines classic ray-tracing optics with Mie scattering to predict the images that would be observed by the probe at a given physical distance from a Mie-regime scattering media. This model was used generate the expected observed response for a broad range of parameter values, and these results were then used as a library to fit the observed data from the phantoms. Compared against the theoretical library, the best matching signal correlated well with known phantom material dimensions. These results lead us to believe that imaging elastic scattering can be useful in detection/diagnosis, but further refinement of the device will be necessary to detect the weak signals in a real clinical setting.

Near infrared spectroscopy with diffuse light has been used within magnetic resonance imaging for several years now. The calibration of these hybrid systems requires sophisticated phantoms which have both NIR and MR characteristics, and allow validation of all the resolution, contrast, geometry and anthropomorphic characteristics of the systems and their applications. This paper reviews the range of uses of phantoms in MR and tomography imaging, and discusses key areas of development in NIR phantoms, and then some gelatin based phantoms which have been used in the hybrid system application of breast cancer imaging.

Optical phantoms are widely used for simulating optical properties of biological tissues. Their accurate design and fabrication are important factors in validating and designing biomedical systems. We discuss fabrication and measurement of optical phantoms in ultrasound-modulated optical tomography. The optical properties of the phantoms are measured by an oblique-incidence diffuse reflectance spectrometer, which can accurately measure the wavelength-dependent absorption and reduced scattering coefficients of optical phantoms. In addition, the acoustic properties of the phantoms are discussed.

Measurements of oxygen saturation and flow in the retina can yield information about the eye health and the onset of eye pathologies such as Diabetic Retinopathy. Recently we have realized an instrument capable of measuring oxygenation in the retina using six different wavelengths and capable of measuring blood flow using speckle-based techniques. The calibration of such instrument is particularly difficult due to the layered structure of the eye and the lack of alternative measurement techniques. For this purpose we have realized an in vitro model of the human eye. The artificial eye is composed of four layers: the retina vessels, the choroids, the retinal pigmented epithelium (RPE), and the sclera. The retina vessels are modeled with 150 μm tube connected to a micro-pump delivering 34 μl/min. The micro-tube, the pump, and a blood reservoir were connected in a closed circulatory system; blood oxygenation in the vessel could be modified using an external oxygen reservoir. The optical properties of all other layers were mimicked using titanium dioxide as a scatterer and ink as an absorber. The absorption coefficient μa and the scattering coefficient µs of these layers were independently measured using an integrating sphere. Absorption and scattering coefficient of all layers were modified before experimental measurements and a Monte Carlo program was finally used to model the experimental results.

This study describes the process of design, development and validation of phantoms that mimic the optical properties of human tissue that could be used for performance verification of Diffuse Optical Tomography (DOT) and Diffuse Optical Spectroscopy (DOS) instruments. The process starts with choosing and qualifying the ingredients (hosting matrix, scatterers and absorbers) that allow adjusting of the scattering and absorption coefficients independently and linearly scalable. Results of the evaluation of liquid and solid phantoms are presented. In addition, the study evaluates the reproducibility and long-term stability of the designed phantoms. The results show that some of the phantoms could be reliable references for performance assessment and periodic calibration-validation of the systems, during pre-clinical and clinical stages.

Intralipid is a material widely employed for the preparation of phantoms simulating optical properties of tissues in the field of optical imaging. Two main assumptions underlie the theoretical predictions of their scattering properties: the occurrence of single scattering for any concentrations of Intralipid, thus enabling the use of Mie theory, and a highly anisotropic g-factor giving a forward preferential direction of photon propagation. The importance of precisely estimating the optical properties of such phantoms requires that the accuracy of these assumptions and their range of applicability are very well-assessed. In this paper, we report the first step of an experimental investigation on the scattering properties of Intralipid suspensions at different concentrations. The study is carried out by the joined use of Time-Resolved Transmittance and Dynamic and Static Light Scattering techniques. By the analysis of the angular and temporal dependence of light scattered by Intralipid suspensions, a more reliable description of the scattering process occurring in the samples could be obtained. The results allow us to better elucidate the dependence of scattering properties of suspensions on Intralipid concentrations and composition. This will help in the design and realization of tissue phantoms with more and more reliable optical properties.