Cross-section scattering is a measure of the scattering strength of a point scatterer. The scattering strength is dependent on the size of the scatterer, the density and compressibility of the scatterer and the surrounding medium, and the ultrasound wavelength.
If a transducer emits ultrasound with a total acoustic power of P, and the power is assumed to be uniform distributed over the US beam cross-sectional area, then the ultrasound intensity at a certain range, is defined by:
I = P/A
where I is the intensity, and A is the cross-sectional beam area at that range.
A point scatterer located in the ultrasound beam at this range, will scatter the ultrasound with a total acoustic power of Ps, defined by:
Ps = I s
where s is the scattering cross-section of the point scatterer.

(MI) The mechanical index is an estimate of the maximum amplitude of the pressure pulse in tissue. It is an indicator of the likelihood of mechanical bioeffects (streaming and cavitation). The mechanical index of the ultrasound beam is the amount of negative acoustic pressure within a ultrasonic field and is used to modulate the output signature of US contrast agents and to incite different microbubble responses.
The mechanical index is defined as the peak rarefactional pressure (negative pressure) divided by the square root of the ultrasound frequency.
The FDA ultrasound regulations allow a mechanical index of up to 1.9 to be used for all applications except ophthalmic (maximum 0.23). The used range varies from 0.05 to 1.9.
At low acoustic power, the acoustic response is considered as linear. At a low MI (less than 0.2), the microbubbles undergo oscillation with compression and rarefaction that are equal in amplitude and no special contrast enhanced signal is created. Microbubbles act as strong scattering objects due to the difference in impedance between air and liquid, and the acoustic response is optimized at the resonant frequency of a microbubble.
At higher acoustic power (MI between 0.2-0.5), nonlinear oscillation occurs preferentially with the bubbles undergoing rarefaction that is greater than compression. Ultrasound waves are created at harmonics of the delivered frequency. The harmonic response frequencies are different from that of the incident wave (fundamental frequency) with subharmonics (half of the fundamental frequency), harmonics (including the second harmonic response at twice the fundamental frequency), and ultra-harmonics obtained at 1.5 or 2.5 times the fundamental frequency. These contrast enhanced ultrasound signals are microbubble-specific.
At high acoustic power (MI greater than 0.5), microbubble destruction begins with emission of high intensity transient signals very rich in nonlinear components. Intermittent imaging becomes needed to allow the capillaries to be refilled with fresh microbubbles. Microbubble destruction occurs to some degree at all mechanical indices. A mechanical index from 0.8 to 1.9 creates high microbubble destruction. The output signal is unique to the contrast agent.

A piezoelectric crystal changes the physical dimensions when subjected to an electric field. When deformed by external pressure, an electric field is created across the crystal. Piezoelectric ceramic and crystals are used in ultrasound transducers to transmit and receive ultrasound waves.
The piezoelectric crystal in ultrasound transducers has electrodes attached to its front and back for the application and detection of electrical charges. The crystal consists of numerous dipoles, and in the normal state, the individual dipoles have an oblique orientation with no net surface charge.
In ultrasound physics, an electric field applied across the crystal will realign the dipoles and results in compression or expansion of the crystal, depending on the direction of the electric field. For the transmission of a short ultrasound pulse, a voltage spike of very short duration is applied, causing the crystal to initially contract and then vibrate for a short time with its resonant frequency.

See also Composite Array, Transducer Pulse Control, and Temporal Peak Intensity.

(TRUS) Transrectal sonography (also called transrectal ultrasonography, transrectal echography (TRE), endorectal ultrasound (ERUS or EUS)) is an ultrasound procedure used to examine the prostate gland, the rectum or bladder.
A small, lubricated transducer placed into the rectum releases sound waves, which create echoes as they enter the region of interest. A computer creates a picture called a sonogram.
TRUS is commonly used for guidance during a prostate needle biopsy and may be used to deliver brachytherapy and monitor cancer treatment. Transrectal ultrasonography detects enlargement, tumors and other abnormalities of the prostate, rectal polyps, rectal cancer, perianal infection, and sphincter muscle injuries. TRUS is also performed on male patients with infertility to view the prostate and surrounding structures and on patients with suspected bladder conditions or disease to view the bladder.

See also Transurethral Sonography, Endoscopic Ultrasound, Pelvic Ultrasound, Rectal Probe, Biplane Probe, Endocavitary Echography and High Intensity Focused Ultrasound.

[This entry is marked for removal.]

From Acusphere Inc
AI-700 (trade name Imagify™) is an US contrast agent, usable for myocardial perfusion undergoing regulatory FDA approval. The synthetic polymers used in AI-700 (perflubutane polymer microspheres) do not break during the ultrasound imaging procedure. The used perfluorocarbon filling gas is less soluble in water and therefore has the propensity to stay inside the contrast agent particles. As a result, a higher concentration of gas is delivered to the myocardium over a longer period of time, thereby enabling AI-700 to target the broader application of myocardial perfusion assessment.
Imagify is a dry powder consisting of small, porous microparticles filled with perfluoropropane. These microparticles are made of a synthetic biodegradable polymer, called poly (D, L-lactide co-glycolide), or PLGA, that has been used in other drug delivery systems approved by the FDA.
The composition and structure of the phospholipid containing microparticles and the properties of the perfluorocarbon gas slow the rate at which the gas dissolves and prevent the microparticles from being quickly broken down. The powder is to suspend in sterile water and injected by a single intravenous injection prior to ultrasound imaging.

In 2009, Acusphere Inc received feedback from the Food and Drug Administration (FDA) to their New Drug Application (NDA) stating that another clinical trial would be required for U.S. approval, this one demonstrating that Imagify with ultrasound is superior to ultrasound without Imagify.
In June 2004, Acusphere entered into a Collaboration, License and Supply Agreement with Nycomed Danmark APS for the European development and marketing rights to Acusphere's lead product candidate AI-700.
Acusphere's focus will be on preparing the Marketing Authorization Application (MAA) for filing in Q4 2010, building upon the work that the previous partner, Nycomed, had done, in concert with the NDA.


In 2008 the FDA panel rejected the regulatory application for AI-700 (Imagify™) because of safety concerns.