| Summary: | Magnetopneumography (MPG) is a non-invasive technique of measuring occupationally acquired pulmonary dust. Most industrially generated dusts and fumes contain ferro- or ferrimagnetic particles which, after being exposed to a magnetising field, exhibit some degree of remanent magnetisation. By magnetising the thorax of an occupationally exposed subject in an external magnetising field and measuring the thoracic remanent magnetic fields using a SQUID (Superconducting QUantum Interference Device) magnetometer, information on the total lung dust burden and lung dust distribution may be obtained. The work described here concentrates on subjects who have been occupationally exposed to asbestos over extended periods as laggers at a local power station. Initial calibration of the response of the SQUID system was carried out using phantom measurements. Qualitative information regarding a subject's pulmonary dust burden and distribution is described and a comparison of the measured dust distributions with diseased tissue locations as shown by established medical imaging techniques such as Computerised Tomography (CT) and x-radiography is performed. The phenomenon of relaxation, which describes the variation in thoracic remanent magnetic field with time is also investigated. A physical interpretation of the phenomenon is given and the characteristic parameters relating to the severity of disease, and to gross localised pathological tissue changes are discussed. A mathematical model of the problem is described and computational simulations of both the whole lung phantoms, and human subjects are carried out. In this manner, a direct comparison between measurement and theory can be made. Finally, using <i>post mortem</i> lung samples known to contain asbestos fibres, a direct comparison between information derived from electron microscopy and MPG is made in order to assess the sensitivity and reliability of measurements made using the magnetometric technique.
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