ABSTRACT
Background: Three-dimensional (3D) observation techniques are useful for understanding organ microcirculation. Optical coherence tomography (OCT) is one of the 3-D imaging techniques and is increasingly applied for tissue microcirculatory studies. Objective: This article reviews the current and prospective usages of OCT in microcirculation. Methods: OCT is an optical technique to obtain tomographic images of highly scattering media like living tissues by means of coherence gating, whose spatial resolution is down to 10 μm. It is also capable of obtaining velocity profiles of blood flow by use of Doppler frequency shift (Doppler OCT). Results: The OCT technique has been applied for observation of microvessels in rat skin, hamster dorsal skin, rat brain etc. Small microvessels down to 20 μm have been detected with the aid of Doppler OCT. Doppler OCT also revealed that the blood flow in microvessels is a quasi-steady laminar flow. The OCT signal from the cerebral cortex was found to change following neural activation, probably reflecting the functional hyperemia. Conclusion: The OCT technique combined with Doppler OCT technique has a great potential for in vivo observation of 3-D structures of microvessels and blood flow distribution. Further OCT is expected to be a depth-dependent imaging tool for the study of brain function.
ABSTRACT
Background: Information of the three dimensional (3D) structure of vascular smooth muscle cells (VSMCs) is essential for understanding the regulatory mechanism of blood flow in the microvascular system. objective: To examine the 3D structure of individual VSMCs in rabbit mesenteric arterioles, using confocal laser scanning microscopy. Methods: Japanese white rabbits were anesthetized with urethane and α-chlorase. After intravital observation of the mesenteric microcirculation under a videomicroscope, the intestine with mesentery was extracted and perfused and fixed with paraformaldehyde under a static pressure (100 mmHg). A section of the mesentery was isolated from the intestine and spread out to simulate the in vivo geometry of the the vascular network. The mesenteric section was stained with fluorescein anti-smooth muscle myosin antibody and rhodamine-labeled anti-rabbit Ig antibody. The samples were observed using confocal laser microscopy, and the 3D images were reconstructed by means of sliced images. The cross-sectional image was re-sliced to measure two axes of the best-fitting ellipse. Single VSMCs were picked out from the vascular wall using the continuity law of density distribution of vessel wall. Results: The cross-sectional shapes of arterioles were not circular but elliptical. The aspect ratio (major to minor axis) of the best-fitting ellipse was in the range from 0.3 to 0.7 for 28 arterioles (diameters: 10-30 μm). On the 3D image of VSMCs, the cell width ranged from 2.2 to 4.5 μm. The cells were classified into round and spindle types. The cell width of round shape was significantly larger than that of spindle shape. The VSMCs appeared to arrange circumferentially and tightly along the cross-section along the axis of vessel. The mean length of single VSMCs was approximately 1.2 times of the circumferential length of the arteriole. This cellular arrangement may have influence on the distribution of mechanical stress by VSMC-induced myogenic force. Conclusion: Confocal laser microscopy is useful for quantitative analysis of the 3D arrangement of individual VSHCs.