title: [Magnetic resonance--historical and theoretical basis].
abstract: Magnetic resonance (MR) imaging is a fast developing modality that has become an indispensable diagnostic tool at numerous disease states. The first MR imager in Norway was installed in 1986; by the end of 1999 Norway will have a total of 39 units, approximately one unit per 114,000 inhabitants. MR technique uses radiowaves and magnetic fields, and no ionising radiation is involved. Imaging is based on the fact that all biological tissues are magnetized when placed in a strong, static magnetic field. Short radiofrequency pulses set the tissue magnetic vector into rotation, and the vector induces electric currents in a receiver coil. The electric signals are spatially encoded by means of magnetic field gradients, thus enabling image reconstruction by means of Fourier transformation. The signal intensities can be made dependent on several tissue parameters, thus creating several unique image contrast possibilities.
authors.affiliation: Røntgen-Radiumavdelingen, Rikshospitalet, Oslo. h.j.smith@rh.uio.no
authors.forename: H J
authors.initials: HJ
authors.lastname: Smith
authors.forename: K I
authors.initials: KI
authors.lastname: Gjesdal
mesh_terms: D001921:Brain / Q000473:pathology; D003287:Contrast Media; D049673:History, 20th Century; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000266:history / Q000379:methods / Q000706:statistics & numerical data; D009664:Norway; D011522:Protons; D012449:Safety; D014059:Tongue / Q000473:pathology
chemical_list: D003287:Contrast Media; D011522:Protons