Abstract Poster 7th European Congress of Thermology

Infrared Laser Doppler Imaging - Skin Temperature & Perfusion Studies

Prof. Francis Ring, Royal National Hospital for Rheumatic Diseases, Upper Borough Walls, U.K.

It is generally recognised that skin temperature and skin perfusion are inter-related. When regional blood flow is increased as in inflammation an area of warmer skin can be observed by thermal imaging. Conversely, reduced blood flow observed in the fingers in Raynaud's Phenomenon, will be characterised by areas of reduced temperature, particularly after cold stress. Laser Doppler Imaging, introduced within the last 5 years, produces an image which represents blood flow in the skin. With false colour coding, these images often resemble thermograms, and have been applied to a number of clinical situations which have already been studied by infra red thermal imaging.
A Moor LDI laser Doppler Imager has been used in conjunction with an Agema 782 IR camera IRT, both being remote sensing devices. Images were recorded by both systems in a temperature controlled room at either 20 C or 23 C. The LDl scans a low power laser beam in a raster pattern over the skin. Moving blood in the microvasculature causes a Doppler shift which is processed to build up a colour coded image of blood flow. At the same time a black and white visible light image is formed for comparison. Resolution is dependant on speed of scan, but can be from 0.2mm to 2mm. Real time single point measurements can also be taken. Comprehensive image processing software is provided with the LDI. The area scanned can be varied from 5x5cm at 20cms distance to 50x50cm from 100cm.

Results

A series of experiments have been made on hands from normal and Raynaud's patients. Both IRT and LDI show reduced signal over the finger nails. This results In a higher temperature and blood flow over the palmar finger tips than that measured over the dorsal surface. However, the general distribution of temperature and of blood flow were similar by both methods. One patient with a single cold 2nd finger measured a flux of 11.5 SD3.06 compared with the third finger flux of 20.3 SD 9.84. The contralateral 2nd finger unaffected measured Flux 20 SD 8.75. The thermogram, however showed an equal temperature with fingers 2 and 3 on the affected hand. A patient with Raynauds Phenomenon and cold fingers pre and 10 mins post cold stress (20'C for 1 min.) was measured with LDI. The flux values were almost identical in both readings, with similar temperatures pre and post stress. In other normal hands where reactive hyperaemia occurred post stress, increased flux was found. ln Paged disease of bone in the tibia, there was no agreement between the two methods. The Infra red image showed a significant increase in heat over the actively diseased bone, bot now increase in skin blopd flow. The tibia is known to have high osseous perfusion in this disease, and these results show that the LDI is measuring surface perfusion, whereas lRT is presenting a thermal pattern created by blood flow in the underlying bone. Other experiments have been performed to illustrate blood flux in the arm during different positions. A combination of LDI and IRT can provide enhanced information, and give a dynamic representation of skin blood flow and its relationship to skin temperature.