Laser Doppler perfusion imaging of synovial tissues using red and near infra-red lasers

A new laser Doppler perfusion imaging (LDI) system was evaluated by comparing it with the well-established radiolabelled microsphere technique for measuring blood flow in the rabbit knee joint capsule. In this study two laser sources (635 and 835 nm) were compared at three scan speeds (50, 10 and 4 ms/pixel). With blood flow to the rabbit hindlimb controlled via a peristaltic pump, the comparison of LDI and microsphere measurement techniques yielded highly significant correlations for both laser sources (r = 0.9; p = 0.0001; 14 measurements in 7 animals). Comparison of the three scan speeds demonstrated acceptable agreement without significant bias between measurements, suggesting that the inevitable narrowing of the bandwidth at the fastest scan speed does not cause significant deterioration of the signal. The flux values obtained with 635 and 835 nm laser sources were linearly related (r = 0.93, p = 0.0001; 66 measurements in 12 animals), although there was a small but significant bias for higher values with the 635-nm laser (mean ratio of flux values 1.06, 95% confidence interval 1.01-1.12). These results validate the use of LDI with either wavelength laser for the assessment of joint capsule perfusion.