Turbid-Polyurethane Phantom for Microscopy A. L. Dayton and S. A. Prahl BME Dept., Oregon Health & Science University, Portland, OR ABSTRACT 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 diffuse reflectance and transmission measurements followed by an inverse adding doubling method. At 488 nm the total attenuation coefficient 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 coefficient was estimated accurately, however in the high absorbing grid, the total attenuation coefficient was underestimated by image analysis techniques. keywords: Polyurethane, Phantom, Reflectance Mode Confocal Microscopy 1. INTRODUCTION Polyurethane phantoms have many advantages as calibration standards. Pogue and Patterson’s review 1 of optical phantoms compared the various materials commonly used for optical phantoms. Polyurethane is advantageous for several reasons: it is solid, permanent, machinable, and durable. When compared to epoxy resins, polyurethane has similar characteristics but has a shorter pot life of 30 minutes. It has also been shown that anthraquinone dyes are stable for at least a year in cured polyurethane. 2 Reflectance mode confocal microscopy has been used by many to image cells and tissues, 3, 4, 5, 6 and some have measured the optical properties of tissue this way. 7 This paper explores some of the challenges of using reflectance mode confocal imaging to measure optical properties. 2. PHANTOM PREPARATION The phantoms were created as described in Moffitt et al. 2 However, the phantom described in this work was inlaid with three dimensional absorption heterogeneities. Briefly, the first phase was to create the bulk of the phantom with known background optical properties. The second phase was to mill troughs into the background phantom. The third phase was to fill the voids with polyurethane having different optical properties. 2.1 Phase 1. Background Polyurethane Polyurethane (BJB Enterprises, Inc.) was made from two components; component A was unreacted polyurethane and component B was catalyst, Figure 2. An absorber, india ink (PRO ART, Beaverton, OR), was mixed with component A and a scatterer, titanium dioxide, TiO 2 , (Sigma, St. Louis MO) was mixed with component B. Each component was then placed in a vacuum chamber for degassing, the solutions were held at a reduced pressure until all air bubbles were drawn out of solution. The two components, A:B, were then mixed together in a 100:85 weight ratio respectively. After mixing, the uncured polyurethane was degassed again and then cast into a mold. To simulate a tissue with low background absorption, an absorption coefficient of about 1cm -1 and a reduced scattering coefficient between 6 and 12 cm -1 was desired. India ink was added to component A at a concentration of 0.0025 mL g and a sonicated TiO 2 in ethanol stock (4.93 mg mL ) was added to component B at a concentration of 0.014 mL g . A phantom approximately 6 cm in diameter and 3mm thick was cast; integrating sphere measurements were made on this phantom. In addition, a square phantom approximately, 6 × 6 × 1 cm, this served as the bulk of the 3 dimensional phantom. Further author information: (Send correspondence to S.A.P.) S.A.P.: E-mail: prahl@bme.ogi.edu, Telephone: (503) 216-2197, 9205 SW Barnes Rd., Portland, OR 97225, USA Design and Performance Validation of Phantoms Used in Conjunction with Optical Measurements of Tissue, edited by Robert J. Nordstrom, Proc. of SPIE Vol. 6870, 687006, (2008) · 1605-7422/08/$18 · doi: 10.1117/12.764010 Proc. of SPIE Vol. 6870 687006-1 2008 SPIE Digital Library -- Subscriber Archive Copy