Microcirculatory changes identified by photoacoustic microscopy in patients with complex regional pain syndrome type I after stellate ganglion blocks

We developed second-generation (G2) optical-resolution photoacoustic microscopy (OR-PAM). Incorporation of a novel acoustic detection scheme improved upon the sensitivity of our first-generation (G1) system by 18.4 dB, deepening the in vivo tissue penetration to 1.2 mm at 570 nm. Moreover, translating the imaging head instead of the living object accelerated the scanning speed by a factor of 5, widening the field of view within the same acquisition time. Mouse ears, as well as mouse brains with intact craniums, were imaged in vivo in both total concentration and oxygen saturation of hemoglobin.

We have developed a novel phase-resolved optical coherence tomography (OCT) and optical Doppler tomography (ODT) system that uses phase information derived from a Hilbert transformation to image blood flow in human skin with fast scanning speed and high velocity sensitivity. Using the phase change between sequential scans to construct flow-velocity imaging, this technique decouples spatial resolution and velocity sensitivity in flow images and increases imaging speed by more than 2 orders of magnitude without compromising spatial resolution or velocity sensitivity. The minimum flow velocity that can be detected with an axial-line scanning speed of 400 Hz and an average phase change over eight sequential scans is as low as 10 microm/s, while a spatial resolution of 10 microm is maintained. Using this technique, we present what are to our knowledge the first phase-resolved OCT/ODT images of blood flow in human skin.

The cutaneous microcirculation is organized as two horizontal plexuses. One is situated 1-1.5 mm below the skin surface and the other is at the dermal-subcutaneous junction. Ascending arterioles and descending venules are paired as they connect the two plexuses. From the upper layer, arterial capillaries rise to form the dermal papillary loops that represent the nutritive component of the skin circulation. There are sphincter-like smooth muscle cells at the point where the ascending arterioles divide to form the arteriolar component of the upper horizontal plexus. At the dermal-subcutaneous junction, there are collecting veins with two cusped valves that are oriented to prevent the retrograde flow of blood. Laser Doppler flowmetry has demonstrated vasomotion of red cell flux localized to the sites of ascending arterioles. The simultaneous recording by laser Doppler flowmetry of red cell flux and the concentration of moving red blood cells from individual sites allows one to construct topographic maps of these two values. These two maps, based on initial studies using correlative skin biopsies, can define 1 mm3 volumes of skin that are predominantly arteriolar in composition, venular in composition, or essentially devoid of all microvascular elements. The electron and light microscopic features that define the microvascular segments, when coupled with that ability of laser Doppler flowmetry to define the predominant microvascular segments under the probe, allow one to study both the mechanisms of normal physiologic states and the pathogenetic mechanisms underlying pathologic skin disorders in which the microvasculature plays a predominant role.