From Bracco Research SA, Geneva, Switzerland,
BR14 is a new experimental ultrasound contrast agent, consisting of bubbles containing a high molecular weight filling gas enclosed by a flexible phospholipid monolayer shell a few nanometers thick.
This agent shows significant non-linear scattering and agent modification even at low insonation pressures, the detection pulses used did not destroy the contrast bubbles. The results obtained with HPD before the release burst show that the BR14 bubbles are efficient scatterers that can be modified and, thus, detected by low power insonation.

Ultrasound waves are reflected when there is a change in acoustic impedance. The larger the change, the more ultrasound is reflected. Microbubbles have an enormous difference in acoustic impedance as compared to surrounding fluid due to the large differences in density, elasticity and compressibility.
At low acoustic power (mechanical index less than 0.1), the mechanism of ultrasound reflection is that of Rayleigh scattering and the microbubbles may be regarded as point scatterers. The scattering strength of a point scatterer is proportional to the sixth power of the particle radius and to the fourth power of the ultrasound frequency;; the echogenicity of such contrast agent is therefore highly dependent upon particle size and transmit frequency. The backscattered intensity of a group of point scatterers is furthermore directly proportional to the total number of scatterers in the insonified volume. The concentration of the contrast medium is of importance.

See also Backscatter Energy, Cross-section Scattering.

Bubble specific imaging methods rely usually on non-linear imaging modes. These contrast imaging techniques are designed to suppress the echo from tissue in relation to that from a microbubble contrast agent.
Stimulated acoustic emission (SAE) and phase / pulse inversion imaging mode (PIM) are bubble specific modes, which can image the tissue specific phase.
In SAE mode bubble rupture is seen as a transient bright signal in B-mode and as a characteristic mosaic-like effect in velocity 2D color Doppler.
PIM are Doppler modes and detect non-linear echoes from microbubbles. In pulse inversion imaging modes the transducer bandwidth extends, resulting in improved spatial resolution and more contrast.

See also Contrast Pulse Sequencing, Microbubble Scanner Modification, Narrow Bandwidth, Contrast Medium, Dead Zone.

[This entry is marked for removal.]

From POINT Biomedical Corp
CARDIOsphere® is an ultrasound contrast agent for assessment of myocardial perfusion in patients with coronary artery disease composed of highly echogenic bispheres.
PB127 is a new developed microbubble with a bilayer polymer/albumin shell filled with nitrogen gas that has ideal characteristics for power harmonic Doppler. They can be destroyed by high power ultrasound, and spectral decorrelation between ultrasound pulses is maximized by rapid dissolution of the released nitrogen gas.
POINT Biomedical Corp. announced (March 01, 2004) that it has completed two Phase 3 trials of CARDIOsphere®. The Phase 3 trials were designed to evaluate the performance of CARDIOsphere® imaging relative to radionuclide imaging for detecting obstructive coronary artery disease and identifying the anatomic location of perfusion defects.

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.