(CAI) Color amplitude imaging shows the amplitude of the Doppler signal from moving blood flow. CAI is an ultrasound technique with increased dynamic range and flow sensitivity. The sensitivity of Doppler ultrasound increases markedly in conjunction with the use of vascular contrast agents.

See also Amplitude Map, Amplitude Indicator.

(CCI) A major limitation of the use of ultrasound contrast agents is the problem that signals from the microbubbles are mixed with those from tissue, so that the distribution of the microbubbles is not optimally displayed either in Doppler or gray scale.
Coherent contrast imaging is a high frame rate implementation of inverting the phase of alternate sound pulses and summing the resulting echoes. The symmetrical signals from linear reflectors are cancelled leaving those from non-linear scatterers, with the advantage that the cancellation is performed without the need to transmit two pulses per image line so that bubble destruction is minimized. Coherent contrast imaging yields best results in the vascular phase of phospholipid microbubbles (such as Definity and SonoVue).

See also Coherence.

(CDI) Color Doppler imaging depicts the mean frequency shifts of the Doppler signal. Color [colour, Brit.] Doppler imaging is a method for visualizing direction and velocity of movement, such as of blood flow within the cardiac chambers or blood vessels. The flow direction and velocity information gathered by Doppler ultrasonography is color coded onto a gray scale cross-sectional image. The sensitivity of Doppler ultrasound is increased in conjunction with the use of vascular contrast agents.
Direction and blood flow velocity are coded as colors and shades:
Red - flow coming nearer to the probe.
Blue - flow coming away of the probe.

See also Bi-directional Illumination, Color Map.

(TCD) Transcranial color Doppler sonography allows to evaluate the presence and flow direction of vessels as well as their relationships to surrounding structures.
A disadvantage of cerebrovascular ultrasonography is the attenuation of the ultrasound signal by the skull. The loss of power through the skull is considerable, the signal to noise ratio is poor and so contrast enhanced Doppler imaging is advantageous. The use of ultrasound contrast agents provides a diagnostic window of sufficient duration and imaging quality to improve an evaluation of the cerebral vessels. Contrast TCD also results in visualization of small arteries and veins and greater length of these vessels.

See also A-Mode, Cranial Bone Thermal Index, Transcranial Color Coded Sonography and Transcranial Window.

Cerebrovascular ultrasonography is the best screening tool for the detection of carotid artery stenosis. Transcranial sonography is used in the evaluation of patients with suspected cerebrovascular disease, but a common problem is the attenuation of the ultrasound signal by the skull.
Contrast enhanced ultrasound play a particularly important role in the visualization of the intracranial vessels, and thus improves the accuracy of transcranial Doppler and increases the potential of this technique. The use of microbubbles is helpful for classification of stenosis and for plaque evaluation in patients with poor initial examination. Ultrasound contrast agents avoid misdiagnosing a subtotal stenosis, which is a very important clinical issue.

See also Adventitia, Intima, Periorbital Doppler, and Acoustic Window.