Switchable skin window induced by optical clearing method for dermal blood flow imaging.

Optical imaging techniques have shown tremendous potential for assessing cutaneous microcirculation, but the imaging depth and contrast is limited by the strong scattering of skin. Current skin windows have to be fulfilled by surgical operation and suffer from some side effects. In this study, a switchable skin window was developed by topical application of an optical clearing agent (OCA) and saline on rat skin in vivo. The validity of the skin window was evaluated by the laser speckle contrast imaging technique, and the safety of OCA to the body was tested through histologic examinations. The results indicated that administration of OCA or saline on rat skin in vivo can open or close the window of skin repeatedly for three days. With the repair effect of hyaluronic acid and Vaseline, it is able to repeatedly visualize the dermal blood vessels and flow distribution. Long-term observation shows that there is no abnormal reflection in micro-structure, body weight, organ coefficients, histopathologic lesions, or toxic reactions compared with a control group. This switchable window will provide an effective tool not only for cutaneous microcirculation with laser speckle contrast imaging, but also for diagnosis and treatment of peripheral vascular diseases, including tumor research with various optical imaging techniques.

Error analysis of ratiometric imaging of extracellular pH in a window chamber model.

Ratiometric fluorescence-imaging technique is commonly used to measure extracellular pH in tumors and surrounding tissue within a dorsal skin-fold window chamber. Using a pH-sensitive fluorophore such as carboxy SNARF-1 one can measure pH distributions with high precision. However, it is often observed that the measured pH is lower than expected, with a bias that varies from one image to another. A comprehensive analysis of possible error sources is presented. These error sources include photon noise, estimator bias, instrument errors, temperature, and calibration errors from biological factors.

Modified skin-window technique in cynomolgus macaques (Macaca fasicularis) for assessing neutrophil extravasation.

Alterations in neutrophil extravasation are seen in disease states and in response to therapeutics. To investigate neutrophil extravasation during the acute inflammatory response, a skin-window technique used in humans was adapted for use in cynomolgus macaques (Macaca fasicularis). Modulation of neutrophil extravasation was attempted with systemic methotrexate and local application of the anaphylatoxin recombinant C5a (rC5a). On day 1, skin windows were created in 4 ketamine-anesthetized monkeys on both forearms by mildly abrading the skin and then overlaying the abrasions with filter paper either saturated in saline or rC5a for 6 h. At 2.5 h prior to generation of new skin windows on day 2, the monkeys received 4.5 mg methotrexate IM, and skin windows and treatment with saline or rC5a were repeated on new forearm sites on each monkey. All papers were analyzed for albumin, neutrophil number, and the neutrophil chemoattractant IL8. Day 1 albumin levels did not differ between groups, indicating consistent abrasion. Methotrexate given prior to the day 2 abrasions reduced neutrophil extravasation and IL8 levels compared with those on day 1. rC5a partially abrogated the methotrexate-induced reduction in neutrophil extravasation and IL8 production. The skin-window technique was well tolerated by the monkeys and successfully accommodated measurement of changes in neutrophil extravasation in response to inflammatory modulators.