Age determination of experimental venous thrombi by ultrasonic tissue characterization

Abstract

The ability of ultrasonic tissue characterization based on radiofrequency signal processing to detect compositional differences in thrombi of varying ages was evaluated in vivo. Methods: Thrombi were produced in 49 jugular veins of 26 anesthetized 18 to 20 kg pigs by partial ligation and application of direct electric current. Thrombi were imaged 30 minutes after formation and 1, 7, and 14 days later with a color Doppler ultrasound scanner that identified the thrombi, and acqnired radio frequency data for ultrasonic tissue characterization analysis. Ultrasonic tissue characterization used two parameters from the normalized power spectrum, slope, and intercept, which are related to scatterer size, scatterer concentration, and acoustic-impedance differences between scatterers and surrounding medium. Previous in vitro studies demonstrated that lower slope and higher intercept values correlated with greater cellularity and more-dense fibrin mesh. Histologic examination was performed for each time period. The values of slope and intercept for each timed observation were compared by a multilinear discriminant analysis. Results: There were no statistical differences between day 0 and day 1. Statisticallysignificant differences in ultrasonic tissue characterization parameters were seen between all other time intervals withp values < 0.01. Older thrombi tended to demonstrate higher slope and lower intercept values. These ultrasonic tissue characterization changes correlated with a red cell and fibrin-mesh density reduction, which was confirmed by histologic findings and was indicative of partial spontaneous thrombolysis. The degree of spontaneous thrombolysis provides an estimate of the age of thrombi. Conclusion: Ultrasonic tissue characterization is capable of distinguishing age differences in thrombi in an animal model and has the potential for noninvasive application in clinical diagnosis.

The distinctive structure and composition of arterial and venous thrombi and pulmonary emboli

“…The tail region of this venous thrombus, like the emboli, contained more fibrin and fewer RBCs than the other segments. These results are consistent with experiments in an animal model showing that the composition of venous thrombi change over time 42 . Initially RBCs were the predominant constituent of thrombi, but later fibrin increased in the head and tail, while the body was composed primarily of RBCs, in striking agreement with our findings.…”

Venous Duplex Imaging for the Diagnosis of Acute Deep Venous Thrombosis

“…In our experience and that of oth ers, only 50% of the cases with venogram-doc umented DVT have thrombus visualized by VDI. It has been demonstrated that very acute thrombi are echogenic and subse quently become anechoic after approximately 4 days [ 19.20], Other studies have also shown that the echogenicity of in vitro clot changes over time [21], These investigators have shown that clot is echogenic for the first 24-96 h after formation, but then becomes pro gressively anechoic owing to the breakdown of red blood cells and their replacement in the clot by fibrin. This natural fibrinolytic process liquifies thrombus: therefore, it loses its echo genicity.…”

Elastography techniques in the evaluation of deep vein thrombosis

“…Initial investigations into assessing clot age focused on US characteristics of the clot (32). Histological evaluation of clots of varying age have demonstrated marked increases in fibroblasts and collagen production as clots age.…”