Doppler ultrasonography is medical ultrasonography that employs the Doppler effect to generate imaging of the movement of tissues and body fluids (usually blood),[1] and their relative velocity to the probe. By calculating the frequency shift of a particular sample volume, for example, flow in an artery or a jet of blood flow over a heart valve, its speed and direction can be determined and visualized. Color Doppler or color flow Doppler is the presentation of the velocity by color scale. Color Doppler images are generally combined with grayscale (B-mode) images to display duplex ultrasonography images, allowing for simultaneous visualization of the anatomy of the area.This is particularly useful in cardiovascular studies (sonography of the vascular system and heart) and essential in many areas such as determining reverse blood flow in the liver vasculature in portal hypertension.
Uses
Transcranial
Transcranial Doppler (TCD) and transcranial color Doppler (TCCD) measure the velocity of blood flow through the brain's blood vessels transcranially (through the cranium). These modes of medical imaging conduct a spectral analysis of the acoustic signals they receive and can therefore be classified as methods of active acoustocerebrography.Blood vessels
Vascular ultrasonography helps determine multiple factors within the circulatory system. It can evaluate central (abdominal) and peripheral arteries and veins, it helps determine the amount of vascular stenosis (narrowing) or occlusion (complete blockage) within an artery, it assists in ruling out aneurysmal disease, and it is the main aid to rule out thrombotic events.Kidneys
Doppler ultrasonography is widely used in renal ultrasonography. Renal vessels are easily depicted by the color Doppler technique in order to evaluate perfusion. Applying spectral Doppler to the renal artery and selected interlobular arteries, peak systolic velocities, resistive index, and acceleration curves can be estimated (Figure 4) (e.g., peak systolic velocity of the renal artery above 180 cm/s is a predictor of renal artery stenosis of more than 60%, and a resistive index, which is a calculated from peak systolic and end systolic velocity, above 0.70 is indicative of abnormal renovascular resistance).Heart
Doppler echocardiography is the use of Doppler ultrasonography to examine the heart.[11] An echocardiogram can, within certain limits, produce an accurate assessment of the direction of blood flow and the velocity of blood and cardiac tissue at any arbitrary point using the Doppler effect. One of the limitations is that the ultrasound beam should be as parallel to the blood flow as possible.
