We propose a comprehensive protocol for the performance assessment of photon migration instruments. The protocol has been developed within the European Thematic Network MEDPHOT (optical methods for medical diagnosis and monitoring of diseases) and is based on five criteria: accuracy, linearity, noise, stability, and reproducibility. This protocol was applied to a total of 8 instruments with a set of 32 phantoms, covering a wide range of optical properties.

A solid tissue phantom made of agar, Intralipid and black ink is described and characterized. The preparation procedure is fast and easily implemented with standard laboratory equipment. An instrumentation for time-resolved transmittance measurements was used to determine the optical properties of the phantom. The absorption and the reduced scattering coefficients are linear with the ink and Intralipid concentrations, respectively. A systematic decrease of the reduced scattering coefficient dependent on the agar content is observed, but can easily be managed. The phantom is highly homogeneous and shows good repeatability among different preparations. Moreover, agar inclusions can be easily embedded in either solid or liquid matrixes, and no artefacts are caused by the solid-solid or solid-liquid interfaces. This allows one to produce reliable and realistic inhomogeneous phantoms with known optical properties, particularly interesting for studies on optical imaging through turbid media.

Different approaches for absorption and scattering spectroscopy of living tissues are discussed. In particular, a unique system for time-resolved reflectance and transmittance spectroscopy is presented, capable of acquiring in vivo absorption and scattering spectra of diffusive media between 600 and 1000 nm. A review of typical spectra obtained from a variety of tissue structures is shown, including female breast, forearm, abdomen, and forehead. A second-level analysis of the measured spectra permits an estimation of the concentrations of the key tissue absorbers , as well as of the Mie-equivalent scattering radii. Further, absorption and scattering spectra can be used to estimate the penetration depth of light in tissues as a function of wavelength, which is a crucial parameter in view of the possible application of optical in vivo molecular imaging in clinical diagnosis. Finally, an example of the applicability of the methodology to other biological media such as fruits and vegetables is shown.

Breast cancer is the most common cancer of women and the second leading cause of death after cardiovascular disease in many countries. About one in eight women will be diagnosed with this disease during their lifetimes in the United States and in European countries.^1,2 Early diagnosis of breast cancer is essential to ensure a high chance of survival for the affected women. Therefore, an important task is to provide diagnostic tools with high sensitivity for early detection of breast cancer and high specificity to avoid false positive results.

In recent years, diffuse optical spectroscopy (DOS) is advancing as a promising tool for noninvasive quantification of tissue constituents in pathological diagnostics.¹ 2. 3. ^{– 4} Traditionally, in vivo diffuse optical measurements have been performed, at most, in the 600- to 1100-nm window.⁵ 6. ^{– 7} This is due to high hemoglobin absorption below 600 nm and dominant water absorption combined with lack of suitable detection technology above 1100 nm. Furthermore, studies are most often performed below 900 nm, where more conventional and cheaper detectors are available. However, recent investigations emphasize the advantage of high penetration depth and enhanced constituent specificity in the short wave infrared (SWIR) 1100- to 1700-nm range.⁸ 9. ^{– 10} Importantly, the lack of systematic characterization of tissue constituents in the SWIR range prevents its widespread use for in vivo applications.