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OCT is a powerful tool for detection of physiological functions of micro organs underneath the human skin surface, besides the clinical application to ophthalmology, as recently demonstrated by the authors’ group. In particular, dynamics of peripheral vessels can be observed clearly in the time-sequential OCT images. Among the vascular system, only the small artery has two physiological functions both for the elastic artery and for muscle-controlled one. It, therefore, is important for dynamic analysis of blood flow and circulation. In the time-sequential OCT images obtained with 25 frames/sec, it is found that the small artery makes a sharp response to sound stress for contraction and expansion while it continues pulsation in synchronization with the heartbeats. This result indicates that the small artery exhibits clearly the two physiological functions for blood flow and circulation. In response to sound stress, blood flow is controlled effectively by thickness change of the tunica media which consists of five to six layers of smooth muscles. It is thus found that the thickness of the tunica media changes remarkably in response to external stress, which shows the activity of the sympathetic nerve. The dynamic analysis of the small artery presented here will allow us not only to understand the mechanism of blood flow control and also to detect abnormal physiological functions in the whole vascular system.
In this paper, the dynamic analysis of mental sweating
for sound stimulus of a few tens of eccrine sweat glands is performed by the
time-sequential piled-up en-face optical coherence tomography (OCT) images with
the frame spacing of 3.3 sec. In the experiment, the amount of excess sweat can
be evaluated simultaneously for a few tens of sweat glands by piling up of all
the en-face OCT images. Strong non-uniformity is observed in mental sweating
where the amount of sweat in response to sound stimulus is different for each
sweat gland. Furthermore, the amount of sweat is significantly increased in
proportion to the strength of the stimulus.
We demonstrate a high-speed swept-source optical
coherence tomography (SS-OCT) system, which is based on a high-speed
swept light source and a Mach-Zehnder interferometer with a high-speed
photodetector. The light source is an external-cavity laser tuned by a KTN
electro-optic deflector, which exhibits a very fast response and large
deflection. The scanning wavelength range is almost 80 nm up to 200 kHz with a
±400-V deflector driving voltage. The system acquires 1 mm × 1 mm
images consisting of 200 × 200 pixels within few milliseconds. We present
preliminary SS-OCT images of an in-vitro human nail and an in-vivo finger pad.