Certain diseases result in inadequate perfusion of blood in important organs. Examples include the post-infarct myocardium and the kidney distal to an arterial stenosis. Also, malignant angiogenesis allows cancer tumours to grow to a lethal size. In all these areas, information about the blood flow in small vessels is of critical clinical significance. Ultrasound imaging with or without Doppler has become an important clinical tool for assessing vascular structures and blood flow.
Diagnostic ultrasound is non-invasive, inexpensive, widely available and uses no ionizing radiation.
A transducer is used to convert electrical pulses to ultrasound and vice versa. Pulses of ultrasound are directed into the body and allowed to interact with the body structures. A fraction of the ultrasound energy is scattered back towards the transducers. In B-mode imaging a greyscale image is constructed from the amplitude envelope of the backscatter signals. Image contrast arises from the variability of echo strength.