(USPIO) The class of the ultrasmall superparamagnetic iron oxide includes several chemically and pharmacologically very distinct materials, which may or may not be interchangeable for a specific use. Some ultrasmall SPIO particles (median diameter less than 50nm) are used as MRI contrast agents (Sinerem®, Combidex®), e.g. to differentiate metastatic from inflammatory lymph nodes. USPIO shows also potential for providing important information about angiogenesis in cancer tumors and could possibly complement MRI helping physicians to identify dangerous arteriosclerosis plaques.
Because of the disadvantageous large T2*//T1 ratio, USPIO compounds are less suitable for arterial bolus contrast enhanced magnetic resonance angiography than gadolinium complexes. The tiny ultrasmall superparamagnetic iron oxides do not accumulate in the RES system as fast as larger particles, which results in a long plasma half-life. USPIO particles, with a small median diameter (less than 10 nm), will accumulate in lymph nodes after an intravenous injection by e.g. direct transcapillary passage through endothelial venules. Once within the nodal parenchyma, phagocytic cells of the mononuclear phagocyte system take up the particles.
As a second way, USPIOs are subsequently taken up from then interstitium by lymphatic vessels and transported to regional lymph nodes. A lymph node with normal phagocytic function takes up a considerable amount and shows a reduction of the signal intensity caused by T2 shortening effects and magnetic susceptibility. Caused by the small uptake of the USPIOs in metastatic lymph nodes, they appear with less signal reduction, and permit the differentiation of healthy lymph nodes from normal-sized, metastatic nodes.

See also Superparamagnetic Contrast Agents, Superparamagnetic Iron Oxide, Very Small Superparamagnetic Iron Oxide Particles, Blood Pool Agents, Intracellular Contrast Agents.

This line specifies the perimeter around a MR scanner within which the static magnetic fields are higher than five gauss. Five gauss and below are considered 'safe' levels of static magnetic field exposure for the general public.
Due to the physical properties of magnetic fields, the magnetic flux, which penetrates the useful volume of the magnet will return through the surroundings of the magnet to form closed field lines. Depending on the magnet construction, the returning flux will penetrate large open spaces (unshielded magnets) or will be confined largely to iron yokes or through secondary coils (shielded magnets).

This line specifies the perimeter around a MR scanner within which the static magnetic fields are higher than five gauss. Five gauss and below are considered 'safe' levels of static magnetic field exposure for the general public.
Portable devices requiring a separation distance between the device and the MR magnet, should not be considered 'MR Safe', 'MR Compatible', or intended for use in the MR environment. Typically the 5 gauss line is the only location where the static magnetic field strength is specified around a MR scanner. Therefore, labeling specifying a separation distance between the MR magnet and the device to ensure safe or proper operation of the device should be avoided.

See also the related poll result: 'In 2010 your scanner will probably work with a field strength of'

This superparamagnetic oral contrast agent consists of large iron oxide particles, coated with insoluble material. Abdoscan® particles have a mean diameter no less than 300 nm. Gastrointestinal superparamagnetic contrast agents are used for negative bowel enhancement.

Abdoscan® was approved in Europe but was taken off the market in 2000, and all sales stopped by the end of 2002.

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.