Distance between laser head and skin does not influence skin blood flow values recorded by laser speckle imaging.

BACKGROUND: Laser Speckle contrast imaging (LSCI) allows non-contact, real-time recording of cutaneous blood flow (CBF). Different distances from laser-head to skin (distances(L-S)) can be chosen by the operator to perform these recordings. We aimed to evaluate the impact of different Distances(L-S) on the analysis of rest blood flow and post-occlusive reactive hyperemia (PORH). METHODS: Four distances(L-S) (10, 15, 20, and 30 cm) were evaluated in a random order in 11 healthy subjects. We analyzed the concordance between each recording at each distance(L-S). We compared CBF results (absolute values and cutaneous vascular conductance (CBF divided by mean arterial pressure)) obtained for each distance(L-S). The intra-subject coefficients of variation due to distances(L-S) (intra-CV, in%) were also studied. RESULTS: The mean "r" (standard deviation) cross-correlation coefficient was 0.99 (0.00) between each CBF trace issued from different distance(L-S). Both kinds of CBF results, at rest and for PORH peak, show non-significant differences when the distance(L-S) is modified. The intra-CV varies from 5.9% to 8.6% at rest and from 5.6% to 9.1% for the PORH peak. CONCLUSION: Distance(L-S) neither influences SBFR at rest, nor at peak post-occlusive hyperemia in the 10-30 cm interval using LSCI.

Increasing the "region of interest" and "time of interest", both reduce the variability of blood flow measurements using laser speckle contrast imaging.

OBJECTIVE: Both spatial variability and temporal variability of skin blood flow are high. Laser speckle contrast imagers (LSCI) allow non-contact, real-time recording of cutaneous blood flow on large skin surfaces. Thereafter, the observer can define different sizes for the region of interest (ROI) in the images to decrease spatial variability and different durations over which the blood flow values are averaged (time of interest, TOI) to decrease temporal variability. We aimed to evaluate the impact of the choices of ROI and TOI on the analysis of rest blood flow and post occlusive reactive hyperemia (PORH). METHODS: Cutaneous blood flow (CBF) was assessed at rest and during PORH. Three different sizes of ROI (1mm(2), 10mm(2) and 100mm(2)), and three different TOI (CBF averaged over 1s, 15s, and 30s for rest, and over 1s, 5s and 10s for PORH peak) were evaluated. Inter-subjects and intra-subjects coefficient of variations (inter-CV and intra-CV) were studied. RESULTS: The inter-subject variability of CBF is about 25% at rest and is moderately improved when the size of the ROI increases (inter-CV=31%, for 1s and 1mm(2) versus inter-CV=23%, for 15s and 100mm(2)). However, increasing the TOI does not improve the results. The variability of the PORH peak is lower with an inter-CV varying between 11.4% (10s and 100mm(2)) and 21.6% (5s and 1mm(2)). The lowest intra-CV for the CBF at rest was 7.3% (TOI of 15s on a ROI of 100mm(2)) and was 3.1% for the PORH peak (TOI of 10s on a ROI of 100mm(2)). CONCLUSION: We suggest that a size of ROI larger than 10mm(2) and a TOI longer than 1s are required to reduce the variability of CBF measurements both at rest and during PORH peak evaluations at the forearm level. Many technical aspects such as comparison of laser speckle contrast imaging and laser Doppler imaging or the effect of skin to head distance on recorded values with LCSI are required to improve future studies using this fascinating clinical tool.