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Magnetic hyperthermia
Magnetic hyperthermia is the ever-promising "fourth leg" of cancer treatment. This thermotherapy It is based on the fact that magnetic nanoparticles can transform electromagnetic energy from an external high-frequency field to heat. As a consequence, if magnetic nanoparticles are put inside a tumor and the whole patient is placed in an alternating magnetic field of well-chosen amplitude and frequency, only the tumor temperature would rise. The elevation of temperature may enhance tumor oxygenation and radio- and chemosensitivity, thus shrinking tumors. As well, this experimental cancer treatment has also been investigated for the aid of other ailments, such as bacterial infections. The technique is also of great value in many other applications from drug-delivery in medicine to the polymer industry.
Numerous clinical trials worldwide have studied hyperthermia in combination with radiation therapy and/or chemotherapy. But up to now only the company MagForce AG has received EU-wide regulatory approval for treatment of brain tumors. Active research is done to test and develop this technique further. The benefits of the application of a nanotechnological approach, as compared to conventional treatments, are expected to be accompanied by a direct health service cost reduction and improvement of the quality of life of the patients.
==Generalities and definition==
Many magnetic materials display a magnetic hysteresis when subjected to a magnetic field that alternates direction. The area enclosed in this hysteresis cycle represents the irreversible work, which is dissipated in the environment as thermal energy. This heat is very undesirable in many industrial applications, though it turns profitable in magnetic hyperthermia. This power is often called the "Specific Absorption Rate" (''SAR'') and it is usually expressed in watts per gram of nanoparticles. For a given material is then simply ''SAR'' = ''Af'', where ''A'' is the area of the hysteresis loop and ''f'' the sweeping frequency of the magnetic field. ''A'' is expressed in J/g and is also called the "specific losses" of the material. Note that this expression for ''SAR'' is a definition; the difficulty lies in finding ''A''. Indeed, as is explained in more detail below, ''A'' depends non-trivially on all the properties of the magnetic nanoparticles, including their effective magnetic anisotropy K (which comprises the magnetocrystalline anisotropy but also other contributions such as shape, strain, surface, etc.), their volume ''V'', the temperature ''T'', the frequency of the magnetic field ''f'', its amplitude ''H''max, and on the concentration of the nanoparticles.〔J. Carrey, B. Mehdaoui, M. Respaud, J. Appl. Phys. 109, 083921 (2011).〕 Those intimately entwined ingredients can be summarized in a hyperthermia ''trilemma'', similarly to the issues encountered in magnetic recording.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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