With the development of multilayer models for the analysis of quantitative spectroscopic techniques, there is a need
to generate controlled and stable phantoms capable of validating these new models specific to the particular
instrument performance and/or probe geometry. Direct applications for these multilayer phantoms include
characterization or validation of depth penetration for specific probe geometries or describing layer specific
sensitivity of optical instrumentation.
We will present a method of producing interchangeable silicone phantoms that vary in thickness from 90 microns up
to several millimeters which can be combined to produce multilayered structures to mimic optical properties of
physiologic tissues such as skin. The optical properties of these phantoms are verified through inverse addingdoubling
methods and the homogeneous distribution of optical properties will be discussed.
We describe the development of a rapid, noncontact imaging method, modulated imaging (MI), for quantitative, wide-field characterization of optical absorption and scattering properties of turbid media. MI utilizes principles of frequency-domain sampling and model-based analysis of the spatial modulation transfer function (s-MTF). We present and compare analytic diffusion and probabilistic Monte Carlo models of diffuse reflectance in the spatial frequency domain. Next, we perform MI measurements on tissue-simulating phantoms exhibiting a wide range of l* values (0.5 mm to 3 mm) and (µ/µa) ratios (8 to 500), reporting an overall accuracy of approximately 6% and 3% in absorption and reduced scattering parameters, respectively. Sampling of only two spatial frequencies, achieved with only three camera images, is found to be sufficient for accurate determination of the optical properties. We then perform MI measurements in an in vivo tissue system, demonstrating spatial mapping of the absorption and scattering optical contrast in a human forearm and dynamic measurements of a forearm during venous occlusion. Last, metrics of spatial resolution are assessed through both simulations and measurements of spatially heterogeneous phantoms.
Currently the only method for positively identifying malignant melanoma involves invasive and often undesirable biopsy
procedures. Available <i>ex-vivo</i> data indicates increased vascularization in the lower regions of excised melanoma, as
compared to dysplastic nevi. The ability to interrogate this region of tissue <i>in-vivo</i> could lead to useful diagnostic
information. Using a newly developed fiber based superficial probe in conjunction with a steady-state frequency-domain
photon migration (SSFDPM) system, we can probe the upper 1-2 mm of tissue, extracting functional information in the
near infrared (650-1000 nm) range. To test the resolution and detection range of the superficial probe in this context,
deformable silicone phantoms have been fabricated that simulate normal skin with melanocytic lesions. These phantoms
consist of a two-layered matrix with the optical properties of normal light skin, containing several cylindrical inclusions
that simulate highly absorbing pigmented lesions such as melanoma. These inclusions are varied in depth, diameter, and
optical properties in order to fully test the probe's detection capabilities. It was found that, depending on absorption, we
can typically probe to a depth of 1.0-1.5 mm in an inclusion, likely reaching the site of angiogenesis in an early-stage
melanoma. Additionally, we can successfully interrogate normal tissue below lesions 1.5mm deep when absorption is
about 0.4/mm or less. This data indicates that the superficial probe shows great promise for non-invasive diagnosis of
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.