Detectability of contrast agents for confocal reflectance imaging of skin and microcirculation

Abstract

Confocal reflectance microscopy of skin and other tissues in vivo is currently limited to imaging at the cellular, nuclear and general architectural levels due to the lack of microstructure-specific contrast. Morphologic and functional imaging at specific organelle and microstructure levels may require the use of exogenous contrast agents in small (nontoxic) concentrations, from which weakly backscattered light must be detected in real time. We report an analysis based on Mie theory to predict detectability, in terms of signal-to-background and signal-to-noise ratios, of reflectance contrast agents within skin and microcirculation. The analysis was experimentally verified by detectability of (a) intravenously injected polystyrene microspheres that enhance the contrast of dermal microcirculation in Sprague-Dawley rats, and (b) acetic acid-induced compaction of chromatin that enhances nuclear morphology in normal and cancerous human skin. Such analyses and experiments provide a quantitative basis for developing the opto-biochemical properties and use of contrast agents and for designing confocal instrumentation to enable real-time detectability in vivo.

In Vivo Confocal Scanning Laser Microscopy of a Series of Congenital Melanocytic Nevi Suggestive of Having Developed Malignant Melanoma

“…19,20,[26][27][28][29][30] Melanin and melanosomes provide strong cytoplasmic contrast for the light source and therefore consistently appear bright on confocal microscopy, allowing for visualization of pigmented cells. 17,18 Langley et al 29 evaluated 40 melanocytic neoplasms by CSLM and proposed criteria to distinguish nevi from melanoma. However, the specificity or sensitivity of their criteria has not been tested yet, and it seems premature to apply them for diagnosis.…”

Automated detection of malignant features in confocal microscopy on superficial spreading melanoma versus nevi

“…Previous studies showing bright contrast of melanocytes in amelanotic melanoma suggest that contrast may arise from nonmelanized melanosomes that are 0.6 to 1.2 μm and/or clinically unapparent melanin in premelanosomes. 35,36 Though the mechanism of contrast is melanosomes (0.7×0.3 μm), 37 one important limitation of PM detection is the failure to differentiate pagetoid melanocytes from other pagetoid cells, in particular Langerhans cells, a notoriously difficult distinction with RCM, since they appear similar to pagetoid melanocytes. 38 Multispectral, 39 photoacoustic, 40 and/or angular resolved 39 microscopy show promise to specify Langerhans cells by identifying backscattering from Birbeck granules versus melanin granules in PMs.…”

Similar but Different: How Reflectance Confocal Microscopy May Help in the Diagnosis of Pink Lesions

“…In such lesions, melanocytes and pigmented keratinocytes appear very bright compared with background tissue, rendering a distinctive contrast to architectural and cellular details. Most recently, some publications reported RCM features observed in pink, hypopigmented, or amelanotic lesions; in those entities, the reflectance is provided by melanosomes and intracellular organelles of approximately 500 nm in diameter, especially in the background of a completely amelanotic tissue surrounding the tumor [6][7][8][9][10][11] .…”