Towards a quantitative in vivo evaluation of venous blood echogenicity: image processing versus subjective assessment.

PURPOSE Spontaneous blood echogenicity in vein ultrasound images may be a marker for an increased erythrocyte aggregability, but a reliable quantitative evaluation method is a prerequisite for its use in clinical studies. We compared a simple scoring system of blood echogenicity intensity and pattern, with automatic image analysis. MATERIAL AND METHODS 157 femoral and popliteal vein digitized ultrasound sequences were reviewed by two independent observers who chose an image, delimited an area of interest (ROI), and graded blood echogenicity intensity and pattern, using a four class score. Each observer reviewed the images selected by the other, without and with ROI. The computer calculated first and second order parameters describing echo intensity and spatial organization. RESULTS Inter-observer reproducibility of subjective assessment was poor (Kappa<0.5), whereas the automatically calculated ROI average gray level intensity relatively to the whole image (tau(1)) effectively separated all grades of intensity. No parameter effectively separated patterns. CONCLUSION Tau(1) is a simple parameter for the in vivo evaluation of blood echogenicity intensity. It should be evaluated in standardized conditions for clinical hemorheology studies in correlation with in vitro erythrocyte aggregation measurements.