Figure 1.

Effects of scatter on resolution for different types of in vivo optical imaging. (a) Laser scanning microscopy images (two-photon) acquired in the living rodent brain (top: green = GFP in NPY neurons, red = Texas Red dextran in capillaries; bottom: blue = SR101 in astrocytes, red = FITC dextran in vessels) [4]. For high-resolution imaging with resolution of the order of micrometres, imaging can only be achieved at depths of a few hundred micrometres where scattering effects can be excluded. (b) Top: camera-based imaging of the exposed rodent brain under 530 nm illumination; bottom: a map of the change in oxy-haemoglobin just following cessation of a 4 s hindpaw stimulus [26]. Resolution is now of the order of tens of micrometres and quantitation is affected by scattering; yet without scattering, this absorption contrast would not be measurable in a reflectance geometry. (c) Photograph of a malignant skin lesion showing haemoglobin and melanin absorption contrast. (d) Epi-fluorescence imaging (top) and white-light image (bottom) of a whole nude mouse. Organs in the mouse at depths of 2–3 mm can be seen, with resolution of the order of 1–3 mm [27]. (e) Optical tomography measurements of the human forearm, acquired by shining light all the way across 7 cm of tissue. Information about the timing of detected photons was incorporated into a diffusion model-based reconstruction to account for the effects of scattering. Images show baseline blood oxygen saturation when the arm was at rest, versus gripping a force transducer [28,29]. Through this thickness of tissue, resolution here is of the order of 1–2 cm.