Uniqueness in multispectral constant-wave epi-illumination imaging.

Multispectral tissue imaging based on optical cameras and continuous-wave tissue illumination is commonly used in medicine and biology. Surprisingly, there is a characteristic absence of a critical look at the quantities that can be uniquely characterized from optically diffuse matter by multispectral imaging. Here, we investigate the fundamental question of uniqueness in epi-illumination measurements from turbid media obtained at multiple wavelengths. By utilizing an analytical model, tissue-mimicking phantoms, and an in vivo imaging experiment we show that independent of the bands employed, spectral measurements cannot uniquely retrieve absorption and scattering coefficients. We also establish that it is, nevertheless, possible to uniquely quantify oxygen saturation and the Mie scattering power-a previously undocumented uniqueness condition.

Three-dimensional imaging of whole mouse models: comparing nondestructive X-ray phase-contrast micro-CT with cryotome-based planar epi-illumination imaging.

In this study, we compare two evolving techniques for obtaining high-resolution 3D anatomical data of a mouse specimen. On the one hand, we investigate cryotome-based planar epi-illumination imaging (cryo-imaging). On the other hand, we examine X-ray phase-contrast micro-computed tomography (micro-CT) using synchrotron radiation. Cryo-imaging is a technique in which an electron multiplying charge coupled camera takes images of a cryo-frozen specimen during the sectioning process. Subsequent image alignment and virtual stacking result in volumetric data. X-ray phase-contrast imaging is based on the minute refraction of X-rays inside the specimen and features higher soft-tissue contrast than conventional, attenuation-based micro-CT. To explore the potential of both techniques for studying whole mouse disease models, one mouse specimen was imaged using both techniques. Obtained data are compared visually and quantitatively, specifically with regard to the visibility of fine anatomical details. Internal structure of the mouse specimen is visible in great detail with both techniques and the study shows in particular that soft-tissue contrast is strongly enhanced in the X-ray phase images compared to the attenuation-based images. This identifies phase-contrast micro-CT as a powerful tool for the study of small animal disease models.