Darkfield orthogonal polarized spectral imaging for studying endovascular laser-tissue interactions in vivo-a preliminary study

Abstract

Due to the limited number of suitable intravital microscopy techniques, relatively little is known about the opto-thermal (endo)vascular responses to selective photothermolysis, used as a default treatment modality for superficial vascular anomalies such as port wine stains, telangiectasias, and hemangiomas. In this preliminary study we present a novel microscopy technique for studying (endo)vascular laser-tissue interactions in vivo, in which conventional orthogonal polarized spectral (OPS) imaging is combined with darkfield (DF) illumination. DFOPS imaging of rat mesenteric vasculature irradiated at increasing powers revealed the following (tissular) responses: formation of translucent aggregates, retrograde flow, gradual and immediate hemostasis, reinstatement of flow, vessel disappearance, and perivascular collagen damage. DFOPS imaging therefore constitutes a useful tool for examining (endo)vascular events following selective photothermolysis. W. Groner, J. W. Winkelman, A. G. Harris, C. Ince, G. J. Bouma, K. Messmer, and R. G. Nadeau, "Orthogonal polarization spectral imaging: a new method for study of the microcirculation," Nat. Med. 5, 1209-1212 (1999

Laser-induced primary and secondary hemostasis dynamics and mechanisms in relation to selective photothermolysis of port wine stains

“…Thirdly, photocoagulation is associated with protein denaturation [48,49] that embodies conformational rearrangements and cross-linking/aggregation of unfolded/misfolded proteins [50] and corollary amyloid fibril formation [51]. There is increasing evidence that misfolded proteins/amyloids activate platelets via CD42b [52] and initiate the contact activation pathway through the auto-activation of fXII by anionic surfaces [53].…”

Thrombosis versus thermal coagulum formation as a result of endovenous laser treatment: Biochemistry versus photophysics

“…Consequently, the erythrocytes undergo primary and secondary thermal coagulation that leads to thermal coagulum formation 20,21 ( Figure 1). Second, thermal coagula generated in vitro and in vivo appear black, [28][29][30] as is the case for the structure shown in Figure 4, 19 although this may also have been a result of carbonization. Conversely, a thrombus composed of mainly fibrin (EDTA is a calcium chelator that inhibits platelet activation, precluding platelets to partake in thrombosis) would appear colorless, as one observes during serum preparation using clotting tubes.…”

“…First, however, it is imperative to address endovascular laser-tissue interactions from a mechanistic perspective, as summarized in Figure 1. 4,7,[20][21][22][23][24][25][26][27][28][29][30][31] Endovascular laser-tissue interactions are essentially composed of a photophysical and a biochemical component, whereby the biochemical component occurs in response to the photophysical component. 17,18 The photophysics that underlie laser-tissue interactions encompass the conversion of radiant energy (i.e., laser light) to heat by endogenous chromophores such as hemoglobin and water.…”

“…The mechanisms related to photothermal processes are illustrated for red blood cells 4,[20][21][22] and for the vascular wall [23][24][25][26][27] as a function of temperature. At the biochemical level, the laser-induced formation of a thermal coagulum 28,29 triggers primary and secondary hemostasis 30 involving platelets and coagulation factors, respectively, culminating in the formation of a thrombus. ELTinduced endothelial damage, comprising endothelial cell activation, necrosis, and denudation, mainly leads to secondary hemostasis, as coagulation constitutes the predominant route to thrombus formation for this type of damage profile in low-flow veins.…”

‘Go with the flow ’: A review of methods and advancements in blood flow imaging

“…In OPS imaging, the tissue embedding the microcirculation is illuminated with polarised green light [60,133,[141][142][143]. As in the case of PS imaging, backscattered (and thus depolarised) light is projected onto a CCD camera after it passes an analyzer.…”