International audienceThis study was designed to characterize the blood clotting process in vitro by following changes in its acoustic properties. High frequency (from 20 to 45 MHz) ultrasound parameters were measured both in double transmission (sound velocity) and backscattering (backscatter coefficient, integrated backscatter coefficient and effective scatterer size) mode. Whole blood samples were collected from healthy volunteers. The protocol to initiate the coagulation process is describe. During the blood clotting process (two hours' observation), acoustic parameters were measured with 15 seconds time resolution for the transmission parameters and 1 minute for the backscattering parameters. The results clearly showed that changes in several acoustic parameters are able to identify several stages in the in vitro blood clotting process, in particular, red blood cell aggregation and blood solidification

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1. Heme compounds, like hemin, a heme oxygenase-1 inducer, are used in the treatment of acute porphyria treatment. The side-effects of hemin on haemostasis have been reported. To address those effects, in the present study we used a sensitive, high-frequency ultrasound technique to record acoustic velocity and to investigate whole blood clotting in Wistar rats treated chronically with hemin (50 mg/kg per day). 2. The hemin-induced disturbances in haemostasis measured were comparable to the heparin reference treatment, with a significant decrease in clotting velocity in both groups compared with controls (e.g. the time to clot was 40 +/- 5, 53 +/- 13 and 10 +/- 2 min, respectively; P < 0.05). Precautions must be taken when using high doses of hemin or in the treatment of bleeding diseases. 3. Further investigations are required to explore the effects of hemin in thrombosis models, because it could be a promising 'old drug' for the treatment of venous thrombosis in patients.

In previous studies [1] [2], we presented a device capable to simultaneously estimate, during the blood clotting process, HF ultrasound parameters both in double-transmission mode (DT-mode) and in backscattering mode (BS-mode). The integrated BS coefficient (IBC) and the effective scatterer size (ESS) were evaluated between 10 and 30 MHz. In DT-mode, sound velocity was estimated with a 45 MHz transducer.The aim of the present work was to confirm several specific results with human whole blood and to validate the method with an animal model: the rat under anticoagulant therapy. Acoustic velocity was estimated during ex-vivo coagulation process of blood from heparin-treated rats.