Ultrasound Evaluation of the Lower Extremity Veins

Imaging of experimental venous thrombus by means of Doppler and CEUS techniques in dogs

Venous thrombosis has been widely studied in humans, but not in dogs. This study was designed to evaluate a venous thrombus in dogs, from creation to solution, by means of various ultrasonographic techniques. Nine healthy Beagle dogs were included in the study. The venous thrombus was formatted by puncturing the lumen of the external jugular veins and then, the veins were examined with B-mode, color Doppler, pulsed-wave Doppler, and contrast-enhanced ultrasound (CEUS) techniques, at regular intervals, within 210-270 min after venipuncture. Haemodynamic parameters were calculated at two different locations, before and after the site of the thrombus formation. The existence of a thrombus was confirmed by CEUS technique. Thrombus volume and echogenicity were evaluated. The results showed that the visualization of the venous thrombus by color Doppler modality was not feasible in some veins. The blood volume was the parameter that could more precisely indicate the presence or absence of a thrombus. In cases where thrombus volume was less than 0.001 cm3, it was impossible to detect its presence using haemodynamic parameters. The CEUS imaging depicted accurately the size and shape of an anechoic venous thrombus, even when its volume was 0.001cm3.

Comparison of a Pocket-Sized Versus a Full-Sized Ultrasound System in the Diagnosis of Proximal Lower Limb Acute Deep Vein Thrombosis

This study assessed the performance of a pocket-sized ultrasound system for the diagnosis of proximal lower limb acute deep vein thrombosis (DVT) compared to a full-sized ultrasound system. Patients who needed urgent lower limb sonograms for acute DVT were invited for the study. In each examination, the investigator scanned the patient using the pocket-sized system and then repeated the scan using the full-sized system. The sensitivity, specificity, and accuracy of the pocket-sized system were determined in reference to the full-sized system. The venous segments that failed to be visualized using the two systems were compared. One hundred lower limbs comprising 500 venous segments were examined. There were four venous segments, including two mid and two lower femoral veins in two patients who failed to be visualized using both systems. The sensitivity, specificity, and accuracy for diagnosing proximal lower limb acute DVT were 100% (95% confidence interval [CI], 94.94%–100%), 100% (95% CI, 99.05%–100%), and 100% (95% CI, 99.19%–100%), respectively. The pocket-sized ultrasound system and the full sized-ultrasound system demonstrated a comparable performance in detecting acute DVT in the leg.

Ultrasonic colour Doppler imaging

Ultrasonic colour Doppler is an imaging technique that combines anatomical information derived using ultrasonic pulse-echo techniques with velocity information derived using ultrasonic Doppler techniques to generate colour-coded maps of tissue velocity superimposed on grey-scale images of tissue anatomy. The most common use of the technique is to image the movement of blood through the heart, arteries and veins, but it may also be used to image the motion of solid tissues such as the heart walls. Colour Doppler imaging is now provided on almost all commercial ultrasound machines, and has been found to be of great value in assessing blood flow in many clinical conditions. Although the method for obtaining the velocity information is in many ways similar to the method for obtaining the anatomical information, it is technically more demanding for a number of reasons. It also has a number of weaknesses, perhaps the greatest being that in conventional systems, the velocities measured and thus displayed are the components of the flow velocity directly towards or away from the transducer, while ideally the method would give information about the magnitude and direction of the three-dimensional flow vectors. This review briefly introduces the principles behind colour Doppler imaging and describes some clinical applications. It then describes the basic components of conventional colour Doppler systems and the methods used to derive velocity information from the ultrasound signal. Next, a number of new techniques that seek to overcome the vector problem mentioned above are described. Finally, some examples of vector velocity images are presented.