COMPARISON OF MULTIPOLE AND MEAN-VALUE METHODS TO QUANTIFY DUST IN HUMAN LUNGS - SIMULATING THE MAGNETOPNEUMOGRAPHY PROCEDURE

Magnetopneumography (MPG) can quantify the retention of magnetisable p articles in the lung acquired, for instance, in welding work. MPG is n on-invasive and is used in occupational health, industrial hygiene and lung physiology. Following a brief magnetisation, the remanent magnet ic field is mapped with magnetometers outside the thorax. There is no unique analytical inverse solution to this class of magnetostatic prob lem, and various inverse methods have been proposed. In the present st udy, the influence of variations in size and shape of the lungs and ch est, magnetic measurement noise, positional noise and spatial dust dis tribution 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 er rors and sensitivity to the deposition pattern remains a problem. A mu ltipolar expansion, including dipolar, quadrupolar and octopolar momen ts, yields best results overall, provided the signal-to-noise ratio is sufficient. This inverse solution is unbiased, requires no calibratio n with phantom lung models and serves to minimise errors due to inter- individual differences in anatomy and to inhomogeneous retention of in haled dust.