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Although diagnostic and therapeutic decisions in patients with vascular disease are guided primarily by the history and physical examination, the use of non-invasive investigations has increased significantly in recent years, mainly as a result of technological advances in ultrasonography. This article describes the main investigative techniques.Handheld pencil Doppler being used to measure ankle brachial pressure indexIn the simplest form of ultrasonography, ultrasound is transmitted as a continuous beam from a probe that contains two piezoelectric crystals. The transmitting crystal produces ultrasound at a fixed frequency (set by the operator according to the depth of the vessel being examined), and the receiving crystal vibrates in response to reflected waves and produces an output voltage. Conventional B mode (brightness mode) ultrasonography records the ultrasound waves reflected from tissue interfaces, and a two dimensional picture is built up according to the reflective properties of the tissues.### Doppler ultrasonographyUltrasound signals reflected off stationary surfaces retain the same frequency with which they were transmitted, but the principle underlying Doppler ultrasonography is that the frequency of signals reflected from moving objects such as red blood cells shifts in proportion to the velocity of the target. The output from a continuous wave Doppler ultrasonograph is usually presented as an audible signal, so that a sound is heard whenever there is movement of blood in the vessel being examined.Left: Doppler velocity waveforms:( a ) triphasic waveform in normal artery; ( b ) biphasic waveform, with increased velocity, through a mild stenosis;( c ) monophasic waveform, with greatly increased velocity, through tight stenosis; and ( d ) dampened monophasic waveform, with reduced velocity, recorded distal to tight stenosis. Right:Anatomical chart used to record position of stenoses, showing three stenoses with velocity increases of 7×, 4×, and 3× compared with adjacent unaffected arteries### Pulsed ultrasonographyContinuous wave ultrasonography provides little scope for restricting the area of …

ABC of arterial and venous disease: Non-invasive methods of arterial and venous assessment