Nuclear magnetic resonance is a diagnostic procedure, based on the principles of magnetic resonance.

(PWI - Perfusion Weighted Imaging) Perfusion MRI techniques (e.g. PRESTO - Principles of Echo Shifting using a Train of Observations) are sensitive to microscopic levels of blood flow. Contrast enhanced relative cerebral blood volume (rCBV) is the most used perfusion imaging. Both, the ready availability and the T2* susceptibility effects of gadolinium, rather than the T1 shortening effects make gadolinium a suitable agent for use in perfusion imaging. Susceptibility here refers to the loss of MR signal, most marked on T2* (gradient echo)-weighted and T2 (spin echo)-weighted sequences, caused by the magnetic field-distorting effects of paramagnetic substances.
T2* perfusion uses dynamic sequences based on multi or single shot techniques. The T2* (T2) MRI signal drop within or across a brain region is caused by spin dephasing during the rapid passage of contrast agent through the capillary bed. The signal decrease is used to compute the relative perfusion to that region. The bolus through the tissue is only a few seconds, high temporal resolution imaging is required to obtain sequential images during the wash in and wash out of the contrast material and therefore, resolve the first pass of the tracer. Due to the high temporal resolution, processing and calculation of hemodynamic maps are available (including mean transit time (MTT), time to peak (TTP), time of arrival (T0), negative integral (N1) and index.
An important neuroradiological indication for MRI is the evaluation of incipient or acute stroke via perfusion and diffusion imaging. Diffusion imaging can demonstrate the central effect of a stroke on the brain, whereas perfusion imaging visualizes the larger 'second ring' delineating blood flow and blood volume. Qualitative and in some instances quantitative (e.g. quantitative imaging of perfusion using a single subtraction) maps of regional organ perfusion can thus be obtained.
Echo planar and potentially echo volume techniques together with appropriate computing power offer real time images of dynamic variations in water characteristics reflecting perfusion, diffusion, oxygenation (see also Oxygen Mapping) and flow.
Another type of perfusion MR imaging allows the evaluation of myocardial ischemia during pharmacologic stress. After e.g., adenosine infusion, multiple short axis views (see cardiac axes) of the heart are obtained during the administration of gadolinium contrast. Ischemic areas show up as areas of delayed and diminished enhancement. The MRI stress perfusion has been shown to be more accurate than nuclear SPECT exams. Myocardial late enhancement and stress perfusion imaging can also be performed during the same cardiac MRI examination.

A term describing the degree, to which precessing nuclear spins are synchronous.

Philips Medical System is the diagnostics business of Royal Philips Electronics of the Netherlands, one of the world's biggest electronics companies and Europe's largest. Philips is quoted on the NYSE (symbol: PHG), London, Frankfurt, Amsterdam and other stock exchanges. On October 19, 2001, Philips Medical Systems completed a 3-year acquisition strategy through its purchase of Marconi Medical Systems. Marconi Medical Systems offered leading multislice CT, MRI, and Nuclear Gamma Camera systems to medical institutions around the world. As well as new 3.0T developments, Philips is also in collaboration with researchers at the University of Nottingham, with the intention of developing an ultrahigh field strength clinical 7.0T whole body MR system.

MRI Scanners:

0.23T to 1.0T:
1.5T:
3.0T to 7.0T:
Hybrid Scanners:

A measure of the non-spherical distribution of electrical charge possessed by nuclei with a nuclear spin number greater than 1/2. The resulting interaction with electric field gradients in the molecule can lead to a shortening of relaxation times and a broadening of spectral lines.