Time domain algorithm for whole field laser Doppler perfusion imaging

Recently, various groups have developed wide field laser Doppler perfusion imaging systems based on high speed camera's. The limiting factor for the frame rate and measurement duration in whole field laser Doppler perfusion imaging is the speed of transfer and analysis of data. We present an algorithm for calculating perfusion estimations with much lower demands for data storage and computational effort than the conventional FFT-based method. Our algorithm works in the time domain and estimates perfusion through simple time differentiations and multiplications of speckle image values. The algorithm is partly based on mathematical reasoning, and partly on a hypothesis that cannot be proven with rigorous mathematics. We will compare our algorithm with the frequency-domain counterpart for phantom studies involving static and dynamic media, and in vivo experiments on human skin. It is found that both algorithms, applied on the same dataset, approximately give the same perfusion estimations. The random differences are similar to the random variations found in tissue perfusion. Systematic differences between the algorithms smaller than 15% are found. The algorithm is currently twice as fast as the FFT-counterpart. Another advantage is that our algorithm can be included in a moving average scheme, where a new perfusion value can be determined based on the previous value and a small number of new raw speckle images.