A logarithmic measure of sound loudness closely related to the decibel. The unit decibel is used for objective measurements, that means, they measure the actual pressure of the sound waves as recorded using a microphone. The unit phon is used for subjective measurements, which means, measurements made using the ears of a human listener.
A sound has the loudness 'p' phon if it seems to the listener to be equal in loudness to the sound of a pure tone of the frequency 1 kilohertz and strength 'p' decibel. A measurement in phons will be similar to a measurement in decibel, but not identical, since the perceived loudness of a sound depends on the distribution of frequencies in the sound as well as the pressure of the sound waves. In the U.S., sound loudness is frequently measured in sones rather than phons: a sound of loudness x sones has loudness 10 log2 x + 40 phons.

See also Acoustic Noise.

From Bracco Diagnostics, Inc.
SonoVue® was first launched in October 2001 and is now available in all European countries.
SonoVue is a second generation USCA, designed and optimized with regard to the resistance to pressure. SonoVue is an example of an important family of microbubbles whose membrane consists of phospholipids. SonoVue microbubbles are filled with sulfur hexafluoride (SF6), a gas which has a low solubility and diffuses slowly in blood for the gaseous phase of the microbubbles.
In particular, the SonoVue microbubbles, thanks to the high flexibility of their shell, are strongly echogenic in a wide range of frequencies and acoustic pressure and therefore can be used with both destructive and conservative contrast bubble specific imaging methods.

See also Coherent Contrast Imaging.

The main advantage of ultrasound is that certain structures can be observed without using radiation. However, ultrasound is energy and there are ultrasound safety regulations, because two bioeffects of ultrasound are heat and cavitation. Ultrasound is a mechanical energy in which a pressure wave travels through tissue. Reflection and scattering back to the transducer are used to form the image. As sound energy is transmitted through the tissue, some energy is reflected and some power is absorbed.
Possible physical effects with ultrasound:
The ultrasound safety is based on two indices, the mechanical index (MI) and the thermal index (TI). The WFUMB guidelines state that ultrasound that produces temperature rises of less than 1.5°C may be used without reservation. They also state that ultrasonic exposure causing temperature rises of greater than 4°C for over 5 min should be considered potentially hazardous. This leaves a wide range of temperature increases which are within the capability of diagnostic ultrasound equipment to produce and for which no time limits are recommended. However, it has not been determined that medical ultrasound causes any adverse reaction or deleterious effect.
The American Institute of Ultrasound in Medicine states that as of 1982, no independently confirmed significant biologic effects had been observed in mammalian tissue below (medical usage) 100mW/cm2.

See also Ultrasound Regulations and Ultrasound Radiation Force.

Albunex and Infoson, used mainly in cardiac evaluations, are first generation one-pass-only contrast agents and have been replaced by the new-generation contrast media. Albunex and Infoson are the same sonicated human serum albumin microbubbles. Infoson is licensed and manufactured in Europe, while Albunex was produced in the USA.
Albunex, an air-filled microbubble with a denatured albumin shell (modified from air-filled albumin microspheres prepared from sonicated 5% human serum albumin), was the first FDA-approved contrast agent, but is no longer in production.
Cardiac shunts and valve regurgitations are often evaluated with Color Doppler Imaging (CDI), which also improved with injections of Albunex, but this agent is pressure-sensitive and does not recirculate. It is effectively a one-pass-only agent, limiting its clinical efficacy.

See also First generation USCA, Echocardiography and Contrast Enhanced Ultrasound.

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.