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, that 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 's' sones has loudness 10 log2 s + 40 phons.

See also Acoustic Noise.

From Siemens Medical Systems;
with the introduction of this system, it is possible to perform contrast MR angiography for abdominal, thoracic and neck vessels from the origins to the circle of Willis. The system also has many newer features including functional imaging, spectroscopy, advanced body, ortho- and neuroimaging.

Vibrations of the gradient coil support structure create sound waves. These are caused by the interactions of the magnetic field created by pulses of the current through the gradient coil with the main magnetic field in a manner similar to a loudspeaker coil. The sounds made by the scanner vary in volume and tone with the type of procedure being performed.
Sound pressure is reported on a logarithmic scale called sound-pressure level, expressed in decibel (dB) referenced to the weakest audible 1 000 Hz sound pressure of 2 * 10^-5 pascal (20 micropascal). Sound level meters contain filters that simulate the ear's frequency response. The most commonly used filter provides what is called 'A' weighting, with the letter 'A' appended to the dB units, i.e. dBA.
MRI system noise levels increase with field strength. Disposable earplugs and/or headphones for the patient are recommended in high-field systems. Noise-canceling systems and special earphones are available, and active acoustic control systems were developed, e.g. softtone, pianissimo. A sequence with low noise gradient pulses is also called 'whisper sequence'.

See also Phon and Decibel.

Texas-based university research group. Current projects include: 'Multi-Modal Molecular Imaging Agents' or 'Micro-Fluidics and Nanosensing'. For example, the research group is evaluating Ln-PK-11195 as a bimodal imaging contrast agent for brain cancer detection by MRI and fluorescence.
Please see their Current Projects Abstracts for complete coverage.

The range of diagnostics and imaging systems of Siemens Medical Systems covers ultrasound, nuclear medicine, angiography, magnetic resonance, computer tomography and patient monitoring. Siemens is one of the three leading MRI manufacturers, which together account for approximately 80 percent of the MRI machines installed worldwide. Siemens currently offers the Allegra 3T MRI, which is for head scanning only, but the company will also be launching the Trio MRI, a 3T whole body scanner.
Siemens has formed partnerships with more than ten research institutions and private practitioners to define a comprehensive MRI examination and compare MR to currently established cardiovascular modalities, thereby defining optimal diagnosis and treatment.

MRI Scanners:

0.2T to 1.0T:
1.5T:
3.0T to 7.0T:
Hybrid Scanners:
Mobile Solutions: