ULTRASONIC TISSUE CHARACTERIZATION OF BLOOD DURING STASIS AND THROMBOSIS WITH A REAL-TIME LINEAR-ARRAY BACKSCATTER IMAGING-SYSTEM

Background: The use of B-mode ultrasound in the diagnosis of thrombosis is still limited by problems that include transducer-related artifacts, the influence of system electronics on image formation, and the subjective nature of image interpretation. In this study we used a novel quantitative vascular imaging method based on the measurement of ultrasonic integrated backscatter to detect changes in the scattering from blood under conditions of stasis and coagulation. Methods: Thrombi were created in excised sections of porcine aortae and imaged in a water tank over 2 h with a clinical integrated backscatter imaging system equipped with a 7.5 MHz linear-array transducer. Similar backscatter imaging was performed on anticoagulated whole blood that was allowed to remain quiescent for 2 h. Imaging was also performed on anticoagulated blood to which hetastarch was added to accelerate red cell aggregation. Results: The integrated backscatter from thrombus increased by 19.4 +/- 2.1 dB from baseline. Blood that remained static but did not clot showed an increase in integrated backscatter of 12.6 +/- 0.9 dB; this increase was immediately and completely reversed by restirring. The addition of hetastarch produced a marked increase in scattering of 29.0 +/- 1.6 dB, and this value also returned to baseline after the blood was restirred. The increase in integrated backscatter after the addition of hetastarch was significantly greater than that observed for thrombosis, which in turn was greater than that for static blood. Conclusion: Quantitative integrated backscatter imaging of blood during stasis and coagulation is feasible using a clinically applicable real-time integrated backscatter imager. Ultrasonic tissue characterization of thrombi may provide data on thrombus age, composition, and stability, which may assist diagnosis and treatment.