High-speed laser Doppler imaging of blood flow in biological tissue
Laser Doppler Imaging (LDI) is a non-invasive optical technique used for assessing the blood flow in biological tissue. This technique allows visualizing 2D distribution of blood flow over an extended area of tissue, e.g. human skin. We have developed a new high-speed instrument for full-field blood flow laser Doppler imaging. The new imager delivers high-resolution flow images every 0.7 to 11 seconds, depending on the number of points in the acquired time-domain signal (32-512 points) and the image resolution (256×256 or 512×512 pixels). This new imaging modality utilizes a digital integrating CMOS image sensor to detect Doppler signals in a plurality of points over the area illuminated by a divergent laser beam of a uniform intensity profile. The integrating property of the detector improves the signal-to-noise ratio of the measurements, which results in high-quality flow images. We made a series of measurements in vitro to test the performance of the system in terms of bandwidth, SNR, etc. Subsequently we give some examples of flow-related images measured on human skin, thus demonstrating the performance of the imager in vivo. The perspectives for future implementations of the imager for clinical and physiological applications will be discussed.