Doppler ultrasound is a medical imaging technique for calculating the relative velocity between two points by measuring the frequency shift of a sound wave transmitted from one point to the other, based on the Doppler effect. Continuous or pulsed Doppler is frequently used to examine cardiovascular blood flow. The combination of routine 2D-mode and Doppler ultrasound allows a complete evaluation of the heart's anatomy and function (including the fetal heart). See also Doppler Fluximetry in Pregnancy.
Doppler ultrasound depends on the fact that if a moving object reflects the ultrasound waves, the echo frequencies are changed. A higher frequency is created if the object is moving toward the probe//transducer and a lower frequency if it is moving away from it. How much the frequency is changed depends upon how fast the object is moving. Doppler ultrasound shows the different rates of blood flow in different colors on a monitor in real time.
The major Doppler parameters are the peak systolic velocity and the end-diastolic velocity. The peak systolic velocity ratio compensates the variability between different patients and instrumentations.

Different Doppler and duplex techniques:

Imagent® is an injectable suspension for intravenous administration during a sonogram. This diagnostic contrast agent for enhancement of ultrasound images contains perflexane lipid microspheres. Imagent® US is indicated in the assessment of heart function and perfusion, as well as the detection of tumors and blood flow abnormalities by using gray scale, color Doppler, and harmonic ultrasound imaging techniques.
During the course of its development, the brand name for this product has changed from Imagent to Imavist (between August 2000 and March 2002) back to Imagent. The manufacturer's 06/03/02 press release announcing FDA approval refers to the product as 'Imagent (formerly Imavist),' and the approval notice and monograph posted at the FDA site refers to the product as Imagent.
Jointly developed by Alliance Pharmaceutical Corp and Bayer Schering Pharma AG (Germany). Source: PR Newswire - 10/10/96, 03/31/98, 10/13/99, 03/13/01, 10/08/01; FDA approvals - 05/31/02; Alliance Pharmaceutical press release - 06/03/02.
Currently the production of Imagent® is discontinued.

In 3D ultrasound (US) several 2D images are acquired by moving the probe across the body surface or rotating inserted probes. 3D-mode uses the same basic concept of a 2D ultrasound but rather than take the image from a single angle, the sonographer takes a volume image. The volume image that is displayed on the screen is a software rendering of all of the detected soft-tissue combined by specialized computer software to form three-dimensional images.
The 3D volume rendering technique (VR) does not rely on segmentation (segmentation techniques are difficult to apply to ultrasound pictures) and makes it possible to obtain clear 3D ultrasound images for clinical diagnosis. A 3D ultrasound produces a still image. Diagnostic US systems with 3D display functions and linear array probes are mainly used for obstetric and abdominal applications. The combination of contrast agents, harmonic imaging and power Doppler greatly improves 3D US reconstructions.

3D imaging shows a better look at the organ being examined and is used for:

Fusion 3D imaging methods for generating compound images from two sets of ultrasound images (B-mode and Doppler images) enable the observation of the structural relationships between lesions and their associated blood vessels in three dimensions (maximum intensity projection).

Standard scanners allow visualizing microbubbles on conventional gray scale imaging in large vascular spaces. In the periphery, more sensitive techniques such as Doppler or non-linear gray scale modes must be used because of the dilution of the microbubbles in the blood pool. Harmonic power Doppler (HPD) is one of the most sensitive techniques for detecting ultrasound contrast agents.
Commonly microbubbles are encapsulated or otherwise stabilized to prolong their lifetime after injection. These bubbles can be altered by exposure to ultrasound pulses. Depending on the contrast agent and the insonating pulse, the changes include deformation or breakage of the encapsulating or stabilizing material, generation of free gas bubbles, reshaping or resizing of gas volumes.
High acoustic pressure amplitudes and long pulses increase the changes. However, safety considerations limit the pressure amplitude and long pulses decrease spatial resolution. In addition, lowering the pulse frequency increases destruction of contrast bubbles. However, at low insonation power levels, contrast agent particles resist insonation without detectable changes. Newer agents are more reflective and will usually allow gray scale imaging to be used with the advantages of better spatial resolution, fewer artifacts and faster frame rates.

Feasible imaging methods with advantages in specific acoustic microbubble properties:
Resonating microbubbles emit harmonic signals at double their resonance frequency. If a scanner is modified to select only these harmonic signals, this non-linear mode produces a clear image or trace. The effect depends on the fact that it is easier to expand a bubble than to compress it so that it responds asymmetrically to a symmetrical ultrasound wave. A special array design allows to perform third or fourth harmonic imaging. This probe type is called a dual frequency phased array transducer.

See also Bubble Specific Imaging.

The company is a member of the Bracco Group, a highly innovative health care group and world leader in global integrated solutions for the diagnostic imaging field. The Bracco Group is headquartered in Milan, Italy. Its North American operations consist of Bracco Diagnostics and Bracco Research USA, both located in Princeton, New Jersey. Bracco Diagnostics is one of the fastest growing developers and marketers of diagnostic pharmaceuticals in North America, with products for various imaging applications, including Isovue® (iopamidol) X-ray contrast agent, ProHance®, (gadoteridol), MRI contrast agent, and nuclear medicine products.
Gadoteridol has been available in Europe and the USA for several years. Holder of the Marketing Authorization: Bracco International B.V. - Strawinskylaan 3051 - 1077 ZX Amsterdam The Netherlands. (Contact: Kirk Deeter, Phone: +NL-303-838-8708)

The Bracco Group is the world's leading provider of global diagnostic imaging solutions, with net sales of more than 1 billion euro, of which more than 64% from international sales; it has operations in 115 countries and about 3,500 employees, of whom more than 600 work in R&D. Bracco invests around 15% of its turnover in R&D and has a portfolio of 1,500 patents worldwide. The Bracco Group deploys an integrated approach to diagnostic imaging, with an offer that encompasses contrast media, its core business where it is one of the world's top players, biomedical equipment from Esaote, one of the world's primary producers of magnetic resonance and ultrasonographic medical equipment, contrast media delivery systems from Acist Medical Systems, a top US company in advanced contrast media injection systems, and medical application software from EBIT-AET and Singapore's Volume Interactions, the leading developer of advanced medical software. Bracco has formed a high-level international research network, whose three centers in Milan, Geneva and Princeton study and develop products for the latest-generation diagnostic techniques, from X-rays and computerized axial tomography to magnetic resonance and echo contrast.

Ultrasound Contrast Agents: