Methods and Limits for Micro Scale Blood Vessel Flow Imaging in Scattering Media by Optical Feedback Interferometry: Application to Human Skin

Abstract

At the micrometric scale, vessels or skin capillaries network architecture can provide useful information for human health management. In this paper, from simulation to in vitro, we investigate some limits and interests of optical feedback interferometry (OFI) for blood flow imaging of skin vascularization. In order to analyze the tissue scattering effect on OFI performances, a series of skin-tissue simulating optical phantoms have been designed, fabricated and characterized. The horizontal (2D) and vertical (depth penetration) sensing resolution of the OFI sensor have been estimated. The experimental results that we present on this study are showing a very good accordance with theoretical models. In the case of a skin phantom of 0.5 mm depth with a scattering coefficient from 0 to 10.8 mm-1, the presented OFI system is able to distinguish a pair of micro fluidic channels (100 µm × 100 µm) spaced by 10 µm. Eventually, an in vivo test on human skin is presented and, for the first time using an OFI sensor, a 2D blood flow image of a vein located just beneath the skin is computed.

Keywords: imaging; micro scale blood flow; optical feedback interferometry.

Figure 1

Schematic configuration of a laser under feedback with an attenuating medium placed between the laser and the target.

Figure 2

Skin phantoms characterization setup for total transmission measurements, diffuse reflection measurements and collimated transmission measurements.

Figure 3

Measured scattering coefficient of the phantoms versus titanium oxide concentration

Figure 4

Schematic diagram of the velocity measurement with the skin phantom placed between the lens and the target which is a rotating disk.

Figure 5

Zero moment versus square of unscattered transmission for fabricated phantoms.

Figure 6

Photography of the microfluidic chip with the serpentine 100 µm square section channels and spacing ranging from 10 to 1400 µm. The red rectangular describes the actual scanning area.

Figure 7

Power reflected by the channels full of milk for a phantom with a total transmission for g = 0.5: from top solid line (red solid line sample 1) to bottom blue solid (sample 10).

Figure 8

Power reflected by the channels full of milk for a phantom with a total transmission for g = 0.8: from top solid line (red solid line sample 1) to bottom blue solid (sample 10).

Figure 9

Power reflected by the channels full of milk for a phantom with a total transmission for g = 0.95: from top solid line (red solid line sample 1) to bottom blue solid (sample 10).

Figure 10

Experimental set up for OFI (Optical Feedback Interferometry) 2D resolution characterization.

Figure 11

Experimentalresults for OFI 2D resolution.

Figure 12

Zero moment obtained for skin phantom number 5 with different thickness at the rates 10, 30, 50 µL/min.

Figure 13

(a) Photography of the scanning zone (the red thick line represents the position of the vein, the blue thin line represents the transverse scanning line), (b) evolution of the zeroth moment and (c) spectra of different pixels along the scan line transverse to the superficial vein).