Combined laser Doppler and laser speckle imaging for real-time blood flow measurements

Laser Doppler (LDI) and laser speckle imaging (LSI) are two optical non-invasive techniques that are used to obtain 2D maps of blood flow in biological tissues. Each of these techniques has some benefits and drawbacks for measuring the blood flow. LSI is a true real-time imaging technique, but less sensitive to changes of flow parameters such as speed and concentration. In contrast, LDI has superior measurement accuracy but it is not a real-time technique. Recently we have developed a blood-flow imaging system that combines both imaging modalities with a gain in speed and accuracy. Using a single integrating CMOS image sensor for measuring both the Doppler signal spectrum and the image speckle contrast flow-map images are produced. In LDI mode, the flow map refresh rate is 1.2 seconds per 256x256 pixels image. In LSI mode the frame rate is 10 flow-map images per second. We present the basic design and in-vivo performance of this new hybrid imaging system. Subsequently, we discuss the potential of the new instrument for future implementations into clinical research.