Magnetism in Medicine: A Handbook
Language: English
Pages: 511
ISBN: 3527402217
Format: PDF / Kindle (mobi) / ePub
This is the first reference work to be published in this growing field of medical physics. The authors are well-known specialists form Germany, the U.S., Japan and Scandinavia. A description of an aspect of magnetism in life sciences with great practical impact: Magnetism in Medicine. It is a manual for researchers in this field as well as for those who apply modern methods based on magnetism in medical practise.
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magnetization distribution tries to decrease the corresponding magnetization and hence is called the demagnetizing field [and its magnetostatic energy, Eq. (1.62) – the demagnetizing energy]. The concept of magnetic charges also enables us to determine in which cases there is no demagnetizing energy – we should simply avoid the appearance of such charges, because they create the demagnetizing field and this field always (according to Eq. 1.62) carries energy with them. Magnetic charges (Eq. 1.63)
Biomagnetic Fields Magnetic induction of biomagnetic fields and of environmental magnetic field disturbances as well as the magnetometer resolution. (Courtesy J. Vrba). Fig. 2.1. Neuromagnetic signals (MEG) are much weaker. The largest field intensity of a normal awake brain is due to spontaneous activity. The so-called alpha rhythm, which is observed over the posterior regions of the head, is about 1 pT in amplitude. Typical evoked fields – somatosensory, auditory or visually evoked responses –
the reviews of Stroink (1993) and Nenonen (1994), and the textbooks of Malmivuo and Plonsey (1995) or Gulrajani (1998), may be consulted. 2.3.2.2 Single Current Dipole in an Infinite Homogeneous Conductive Medium As a first approximation, the active, distributed cardiac sources can be grouped into a single current dipole, representing the total ‘‘vector of electrical activity’’ or 167 168 2.3 Cardiomagnetism Fig. 2.33. (a) Locus of the total current dipole vector, P, during the cardiac
approximation, the cardiac activity can be represented by a single-current dipole embedded in an infinite or semi-infinite homogeneous conductive medium. The resulting equivalent current dipole (ECD) inverse solution can be considered a first-order estimate of the source parameters. This source model is adequate when estimating, for instance, the location of the initial activation of the ventricle via an accessory pathway in patients with WPW syndrome, or the onset of an ectopic beat originating
Luborsky et al., 1964). Fig. 1.5. or pieces of wire from bales of hay. In order to prevent these sharp objects from damaging the stomach and intestinal walls, the cows are forced to swallow a ‘‘cow magnet’’, a 7 cm-long and 1 cm-diameter rod Alnico magnet covered with an anticorrosive plastic coating. The cow magnet remains in one of the cow’s stomachs, where it attracts any steel or iron objects that pass by, rendering them nondangerous and preventing the so-called ‘‘hardware disease’’. The
