(CHI) Contrast harmonic imaging is an ultrasound technique to improve the measurement of blood perfusion or capillary blood flow. Based on the nonlinear properties of contrast agents, CHI transmits at the fundamental frequency but receives at the second harmonic. Contrast enhanced echo signals contain significant energy components at higher harmonics (bubbles acts as harmonic oscillators), while tissue echoes do not. Caused by that contrast signal can be separated from tissue echoes by the characteristic signal.
In combination with the pulse inversion technique, CHI promises very high contrast agent sensitivity with high spatial resolution.

See also Ultrasound Contrast Agent Safety and Hemoglobin.

(CEUS) Contrast agents increase the reflection of ultrasonic energy, improve the signal to noise ratio and caused by that the detection of abnormal microvascular and macrovascular disorders. Contrast enhanced ultrasound is used in abdominal ultrasound (liver sonography) as well as in cerebrovascular examinations e.g., for an accurate grading of carotid stenosis. The used contrast agents are safe and well tolerated.

The quality of the enhancement depends on:
The additional use of ultrasound contrast agents (USCAs) may overcome typical limitations like poor contrast of B-mode imaging or limited sensitivity of Doppler techniques. The development of new ultrasound applications (e.g., blood flow imaging, perfusion quantification) depends also from the development of pulse sequences for bubble specific imaging. In addition, contrast enhanced ultrasound improves the monitoring of ultrasound guided interventions like RF thermal ablation.

See also Contrast Enhanced Doppler Imaging, Contrast Harmonic Imaging, Contrast Imaging Techniques and Contrast Pulse Sequencing.

Many different contrast imaging techniques have been developed. Most are either variations, hybrids, or combinations of the following ultrasound techniques:

See also Coherent Contrast Imaging, Ultrasound Picture and Targeted Contrast Imaging.

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The earliest introduction of vascular ultrasound contrast agents (USCA) was by Gramiak and Shah in 1968, when they injected agitated saline into the ascending aorta and cardiac chambers during echocardiographic to opacify the left heart chamber. Strong echoes were produced within the heart, due to the acoustic mismatch between free air microbubbles in the saline and the surrounding blood.