Measurement of macrophage motility as decay of the magnetic lung field (relaxation) after particle alignment by pulse magnetization. b1 = B(1 min.)/B0 and b5 = B(5 min.)/B0 denote the relative decay of the initial phase (after 1 min.) and of the slow phase (after five min.). The curves represent the mean relaxation behavior in healthy subjects, of patients with sarcoidosis (SAR), with interstitial lung fibrosis (IPF), and with chronic obstructive bronchitis (COB).