Comparison of multipole and mean value methods to quantify dust in human lungs: Simulating the magnetopneumography procedure

Abstract

Magnetopneumography (MPG) can quantify the retention of magnetisable particles in the lung acquired, for instance, in welding work. MPG is non-invasive and is used in occupational health, industrial hygiene and lung physiology. Following a brief magnetisation, the remanent magnetic field is mapped with magnetometers outside the thorax. There is no unique analytical inverse solution to this class of magnetostatic problem, and various inverse methods have been proposed. In the present study, the influence of variations in size and shape of the lungs and chest, magnetic measurement noise, positional noise and spatial dust distribution are investigated in five inverse methods. The mean value of the field map, calibrated against a lung phantom, is the commonly used method. Lung and chest size influence the mean value method solutions strongly. Correction for chest size reduces these errors, but bias errors and sensitivity to the deposition pattern remains a problem. A multipolar expansion, including dipolar, quadrupolar and octopolar moments, yields best results overall, provided the single-to-noise ratio is sufficient. This inverse solution is unbiased, requires no calibration with phantom lung models and serves to minimise errors due to inter-individual differences in anatomy and to inhomogeneous retention of inhaled dust.

Study of stomach motility using the relaxation of magnetic tracers

“…Measurements of magnetic fields produced by magnetic particles inside human organs can give useful information for both diagnosis and basic studies. Techniques have been developed to estimate the iron concentration in the liver (Farrel et al 1983, Fischer et al 1989, Engelhardt et al 1995 and lungs (Forsman et al 1995). This approach can be used to study gastrointestinal motility when a magnetic test meal or a magnetic marker is ingested (Miranda et al 1992, 1997, Baffa et al 1995, Daghastanli et al 1998, Oliveira et al 1996, Di Luzio et al 1989, Basile et al 1992, Weitschies et al 1991.…”

Multiple Layer Scanning in Magnetopneumography

“…The gradiometer's probes are, in our application, just above the bed, nevertheless, quite usually some sensors are even placed below the subject [9]. The gradiometer is fixed to a portal that is separate from the movable scanning bed in order to isolate any mechanical vibrations, see Fig.…”

“…However, the field variations during the step-by-step scans (several minutes for all the nodes) bias the field-maps considerably. These make the inversion difficult [4], [9], [10]. Furthermore, the difference between the signals (the "gradient") does not uniquely describe the measured field and additionally there is the nonuniqueness of the inversion of the general magneto-static problem [13]- [17].…”

Partial independence of bioelectric and biomagnetic fields and its implications for encephalography and cardiography

“…Features of the magnetic field from stimulus and action currents in the isolated rabbit heart are not consistent with the simple current dipole model, because of the complicated electrical anisotropy of the tissue [3, 7, 14, 24]. The application of multipole modeling to magnetopneumography [8] has shown that multipolar expansions including dipolar, quadrupolar and octupolar moments are optimal for the characterization of magnetisable particle retention in the lung. In magnetogastrography, multipole models are important for the characterization of abnormal electrical activation patterns in the stomach due to gastroparesis and ischemia [15].…”