Potential of a high-frequency correlation method to study skin blood flow

Background/aims: The vast number of existing dedicated techniques proves th at skin blood flow estimation is an unsolved problem. Specificities of cuta neous vascularization (very low blood velocity, noisy environment, complexi ty of the vascularization architecture) result in the unsuitability of conv entional ultrasonic Doppler techniques (long acquisition time, low spatial resolution). The object here was to present a high-frequency time-domain co rrelation method. In particular, the difficulties of adaptating this type o f measurement (data processing, hardware problem) are pointed out. Methods: Radio-frequency (RF) backscattered signals, obtained with a modifi ed Version of a home-made 20 MHz skin imaging system, are studied. Time shi fts between successive windowed sections of the RF signals are determined b y the mean of the crosscorrelation algorithm. A realignment procedure (to r emove the artefacts caused by the movements of the patient and the manipula tor) and a stationary echo cancelling procedure (to remove the signals comi ng from the cutaneous tissues and to permit the detection of very small ves sels) are used. Results: In vitro results show that velocity measurements as low as 0.1 mm/ s are attainable with a 80 mu m axial resolution, and blood vessels of 100 mu m are detectable. Our technique has also been validated by means of in v ivo experiment on an erysipelas located on a human leg. In this way, a 180- mu m-diameter blood Vessel has been detected on a M-mode RF image and the c orresponding velocity profile has been obtained. Conclusion: Further improvements can be expected, and the level of performa nce obtained in vitro in this work should be also attainable in vivo and sh ould then provide an effective tool for skin physiology and pathology.