Interference is the interplay of two or more waveforms. When two or more waves with equal frequency and wavelength interfere, a new wave is created whose amplitude at any point in time and space is the sum of the amplitudes of the original waves at the same point in time and space. Constructive interference occurs when two waves of equal frequency are in phase. The amplitudes will always be in the same direction, and the waves will combine to produce a stronger one. Two equally strong waves with the same amplitude that are 180° out of phase will cancel each other out.

See also Interference Artifact.

Interference artifacts occur if decreasing of the echo amplitude is not exponential with penetration depth caused by inhomogeneous tissue layers and fluid or air-filled regions. If ultrasound waves have opposite phases, i.e. if the phase difference is 180°, their amplitudes will always be in opposite directions and their sum is a weaker wave. This is destructive interference and artifacts occur.

Huygens principle states that an expanding sphere of waves behaves as if each point on the wave front were a new source of radiation of the same frequency and phase. The principle explains how a flat ultrasound transducer can transmit a narrow ultrasound beam, which in the near field is confined to the dimensions of the transducer surface.
Spherical wavelets are emitted from numerous point sources on the transducer surface. They interfere to form a narrow, slightly converging beam of ultrasound in the near field. The wavefronts in the beam are nearly parallel. A precondition for this interference is that the transducer surface is much larger than the ultrasound wavelength.

See also Interference Artifact.

An undesirable background interference or disturbance that affects image quality.
The noise is commonly characterized by the standard deviation of signal intensity in the image of a uniform object (phantom) in the absence of artifacts. The measured noise may depend on the particular phantom used due to variable effects. Noisy images appear when the signal to noise ratio is too low. There are various noise sources in any electronic system, including Johnson noise, shot noise, thermal noise.

See also Interference Artifact.

California-based research and development company. Alliance Pharmaceutical Corporation. The principal activities of the Company is identifying, designing, and developing novel medical products. The Company is engaged in development of scientific discoveries into medical products and licensing these products to multinational pharmaceutical companies in exchange for fixed payments and royalty or profit sharing payments. The Company has developed three innovative products through initial clinical (human) trials. The products are Oxygent™, Liquivent and Imavist™. The Company's strategy is to identify potential new medical products though its own efforts and scientific collaborations with researchers and clinicians in universities and medical centers. In Dec 2000 the company acquired Molecular Biosystems Inc a developer of intravenous ultrasound contrast agent for the heart.

'September 20, 2001 Alliance Pharmaceutical Corp. announced that it has won a favorable Final Judgment from the United States Patent and Trademark Office's Board of Patent Appeals and Interferences regarding claims in U.S. Patent No. 5,558,854, which is owned by Nycomed Imaging, AS. The Final Judgment determined that claims made in the Nycomed patent with respect to 'microbubbles' that contain perfluorohexane filling gas are invalid and are therefore unpatentable.'
June 04, 2010, the company announced in their quartzerly report: 'We no longer have working capital to fund our operations. Because adequate funds have not been available to us in the past, we have already delayed our Oxygent development efforts and have eliminated our other product development programs.'

Ultrasound Contrast Agents: