Harmonic imaging relies on detection of harmonics of the transmitted frequency produced by bubble oscillation. This method is widely available on ultrasound scanners and uses the same array transducers as conventional imaging. A major limitation of the use of ultrasound contrast agents is the problem that signals from the microbubbles are mixed with those from tissue. Echoes from solid tissue and red blood cells are suppressed by harmonic imaging.
In harmonic mode, the system transmits at one frequency, but is tuned to receive echoes preferentially at double that frequency, and the second harmonic echoes from the place of the bubble. Typically, the transmit frequency lies between 1.5 and 3 MHz and the receive frequency is selected by means of a bandpass filter whose center frequency lies between 3 and 6 MHz.
Color Doppler and real-time harmonic spectral Doppler modes have also been implemented and show a level of tissue motion suppression not available in conventional modes.

See also Harmonic B-Mode Imaging, and Harmonic Power Doppler.

(HPD) Harmonic power Doppler is currently one of the most sensitive techniques for detecting ultrasound contrast agents. HPD works by transmitting multiple pulses toward the object to be imaged and detecting the pulse-to-pulse changes in the received echo signals.
Second harmonic bandbass filtering is applied to the received signals to exploit the non-linear behavior of scattering from bubbles (clutter). Harmonic power Doppler operates best at high output levels because of increased contrast destruction, and pulse amplitudes close to the maximum allowed are used much of the time.
With a high mechanical index, non-linear propagation of the sound will cause significant harmonic components from tissue, and the contrast agent to tissue ratio will decrease.
Also called Harmonic Power Angio. See also Multiple Frame Trigger.

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.

Founded in 1991, ImaRx Pharmaceutical Corp. designs, develops and markets pharmaceuticals for medical imaging (MRI, ultrasound and computed tomography) for the radiological imaging industry.
ImaRx Pharmaceutical Corp., announced 1999 that it has been acquired by E.I DuPont de Nemours & Co., Inc. The terms of the acquisition provide a royalty-free licensing arrangement with a newly-formed company, ImaRx LLC ('LLC'), to pursue and develop new products and technologies for drug and gene delivery independent from DuPont. Yamanouchi Pharmaceutical Co. Ltd., ImaRx' licensee for Asian territories for this product, will continue to develop the product in Asia as DuPont's licensee. ImaRx LLC will have ownership of all other targeted and therapeutic products previously owned by ImaRx, including imaging products outside of diagnostic ultrasound imaging and two other imaging products, SonoRx® and LumenHance®, which are both FDA approved and licensed to BRACCO Diagnostics.
See also Lantheus Medical Imaging and Definity®.

Ultrasound Contrast Agents:

The perfect image quality is dependent on some assumptions of the propagation of ultrasound waves in tissues after generating in an imaging system. These assumptions are important for the developing of optimal ultrasound imaging systems.
A lot of steps can be taken to prevent artifacts and to improve image quality, for example beamforming is used to focus the ultrasound beam, and contrast agents decrease the reflectivity of the undesired interfaces or increase the backscattered echoes from the desired regions.

See also Coded Excitation, Validation and Refraction Artifact, Q-Value, Ultrasound Phantom, Dead Zone, Narrow Bandwidth.