Analysis of laser Doppler perfusion images of experimental irritant skin reactions

Laser Doppler perfusion imaging (LDPI) permits measurement of skin blood flow changes in patch test reactions. It is, as yet, unclear how collected data can best be handled and presented in order to maximize the possible discriminatory advantage of the imaging technique and to make the selection of data for statistical analysis as objective as possible. The aim of the present study was to compare a new software program (LDISOFT) for the analysis of LDPI images with the built-in standard statistical functions in the LDPI system (PIM 1.0). In addition, a modification of the software was used to gather additional data by performing sequential perfusion images.

A dithranol cream was applied under Finn chambers for 30, 60 and 90 min on the ventral forearm skin of three volunteers. Photographic documentation and LDPI recordings were performed immediately after the removal of the Finn chambers and at 24, 48, 72 and 96 h. By the use of the above mentioned software, rectangular and threshold selected regions of interest were used to find an optimal way of calculating the mean perfusion and extent of the reactions.

An LDISOFT threshold of 2 V was adequate and showed agreement (r<0.902, n=78) between mean perfusion analysis performed by LDISOFT (threshold-steered region of interest) and LDPI statistics (rectangular region of interest). The LDISOFT program had the added advantage of comparing application-site size with reaction size. Sequential recordings showed both spatial and temporal perfusion variability.

Utilization of the full potential of LDPI will involve optimization of data analysis and presentation. A more "automated" system for data analysis will reduce bias due to subjective selection of analysis area. Particularly in weaker reactions, in irregular shaped or ring reactions and when there is non-specific background irritation, this may represent an advantage. Averaging of sequential recordings reduced background noise.