(IR) Inversion recovery is an MRI technique, which can be incorporated into MR imaging, wherein the nuclear magnetization is inverted at a time on the order of T1 before the regular imaging pulse-gradient sequences. The resulting partial relaxation of the spins in the different structures being imaged can be used to produce an image that depends strongly on T1. This may bring out differences in the appearance of structures with different T1 relaxation times. Note that this does not directly produce an image of T1. T1 in a given region can be calculated from the change in the MR signal from the region due to the inversion pulse compared to the signal with no inversion pulse or an inversion pulse with a different inversion time. This sequence involves successive 180° and 90° pulses. The inversion recovery sequence is specified in terms of three parameters, inversion time (TI), repetition time (TR) and echo time (TE).

See also Inversion Recovery Sequence and FLAIR.

The subacute risks and side effects of magnetic and RF fields (for patients and staff) have been intensively examined for a long time, but there have been no long-term studies following persons who have been exposed to the static magnetic fields used in MRI. However, no permanent hazardous effects of a static magnetic field exposure upon human beings have yet been demonstrated.
Temporary possible side effects of high magnetic and RF fields:
The results of some animal and cellular studies suggest the possibility that electromagnetic fields may act as co-carcinogens or tumor promoters, but the data are inconclusive. Up to 45 tesla, no important effects on enzyme systems have been observed. Neither changes in enzyme kinetics, nor orientation changes in macromolecules have been conclusively demonstrated.
There are some publications associating an increase in the incidence of leukemia with the location of buildings close to high-current power lines with extremely low-frequency (ELF) electromagnetic radiation of 50-60 Hz, and industrial exposure to electric and magnetic fields but a transposition of such effects to MRI or MRS seems unlikely.
Under consideration of the MRI safety guidelines, real dangers or risks of an exposure with common MRI field strengths up to 3 tesla as well as the RF exposure during the MRI scan, are not to be expected.

For more MRI safety information see also Nerve Conductivity, Contraindications, Pregnancy and Specific Absorption Rate.

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

This effect is an additional electrical charge generated by ions in blood (loaded particles) moving perpendicular to the magnetic field. At 1.5 T, no significant changes are expected; at 6.0 T a 10% blood pressure change is expected. A blood pressure increase is predicted theoretically for a field of 10 T. This is claimed to be caused by interaction of induced electrical potentials and currents within a solution, e.g. blood, and an electrical volume force causing a retardation in the direction opposite to the fluid flow. This decrease in blood flow-velocity must be compensated for by an elevation in pressure.
Static magnetic field gradients of 0.01 T/cm (100 G/cm) make no significant difference in the membrane transport processes. The influence of a static magnetic field upon erythrocytes is not sufficient to provoke sedimentation, as long as there is a normal blood circulation.

The magnetohydrodynamic effect which results from a voltage occurring across a vessel in a magnetic field, is irrelevant at the field strengths used.

Porphyrins occur naturally in plants and animals. All porphyrin molecules feature an aromatic macrocycle ring with a central binding site. This site accommodates transition metals, which are held in place by inward-facing nitrogen atoms. Metalloporphyrins have usually a low toxicity and a potential of a selective uptake in tumors or necrosis. These properties are advantageous for a use as MRI tumor specific agents with positive enhancement. These contrast agents enhance tumors on T1 weighted sequences, which are isointense to surrounding tissues. Porphyrin-based compounds have also necrosis avid properties; they can depict the extent of myocardial infarction as defined by histopathology.
Metalloporphyrins are also used in photodynamic therapy of tumors. The compounds contain a 'lone star' metal atom at the center of the ring and are 'bigger than the average porphyrin'. They contain five N atoms in the central chelating core and this allows them to form complexes with large trivalent lanthanide metals, which have useful cancer therapy properties.

See also Classifications, Characteristics, etc., Gadophrin, MnIIITPPS4, Necrosis Avid Contrast Agent.

(NSF) Nephrogenic systemic fibrosis is a rare and highly debilitating disorder that involves extensive thickening and hardening of the skin with fibrotic nodules and plaques.
MRI contrast media have very low side effects, but accumulating data indicate that gadolinium-based contrast agents increase the risk for the development of NSF among patients with severe renal insufficiency or renal dysfunction due to the hepato-renal syndrome or in the perioperative liver transplantation period.
Due to this reason, gadolinium contrast agents are now considered contraindicated in patients with an estimated glomerular filtration rate fewer than 30 mL/min/1.73m². In these patients, avoid use of gadolinium-based contrast agents unless the diagnostic information is essential and not available with non-contrast enhanced magnetic resonance imaging (MRI).

Recognized or possibly associated factors for NSF:
When administering a gadolinium-based contrast agent, do not exceed the recommended dose and allow a sufficient period of time for elimination of the contrast medium from the body prior to any readminstration. Screen all patients for renal dysfunction by obtaining a history and/or laboratory tests.

See also Contrast Medium, Adverse Reaction, MRI Risks, MRI Safety, Ionic Intravenous Contrast Agents, Nonionic Intravenous Contrast Agents, and Contraindications.