Doppler Ultrasound
Doppler or Vascular ultrasound is a technique for visualising arteries and veins in the body using sound waves. The basic principles of ultrasound are described at the ultrasound webpage. There are several different ultrasound modes or techniques that are used in examining blood vessels. Two dimensional ultrasound images directly visualise the vessel walls and lumen and can demonstrate plaques causing narrowings in arteries, dilatations of arteries known as aneurysms, clots within the blood vessels etc. Duplex scans use the Doppler principle to study the velocity, direction and character of flowing blood through the vessels. Echoes returning from a moving target experience a shift in frequency that is proportional to the velocity of blood flow. The frequency shift can be analysed by the systems computer to estimate the velocity of blood flow. Narrowings in arteries are associated with increased velocities and therefore an estimate of the severity of a narrowing can be obtained from the velocity of blood flow recorded at the site of narrowing. Colour Doppler mode superimposes Doppler information on the two dimensional images by colour coding flowing blood according to the direction and velocity of flow. This provides an instantaneous graphic display of the character of blood flowing through a vessel. A new technique known as 'B' flow imaging directly visualises flowing blood in a vessel lumen by amplifying signals from moving targets. Using a combination of the above techniques it is possible to document the presence and severity of narrowings and complete occlusions, the presence of blood clot in the vessels, the extent and size of aneurysms or varicosities, the presence of abnormal connections between arteries and veins and any anatomic variations in vascular anatomy. The examination is performed by a specifically trained ultrasonographer. A report is issued to the referring doctor by the radiologist or physician on site.
