TC-99(M)-HMPAO AND TC-99(M)-DTPA RADIOAEROSOL CLEARANCE MEASUREMENTS IN IDIOPATHIC PULMONARY FIBROSIS

The clearance rate of an inhaled aerosol of a lipophilic complex, Tc-9 9(m)-hexamethylpropyleneamine oxime (Tc-99(m)-HMPAO), was compared wit h that of a hydrophilic complex, Tc-99(m)-diethylenetriamine pentaacet ate (Tc-99(m)-DTPA), in nine normal subjects and in eight patients wit h idiopathic pulmonary fibrosis (IPF). Data were acquired as follows. The subjects were placed supine with their back against the scintillat ion camera and breathed aerosol for 2 min; pulmonary radioactivity was then monitored for 30 min. A time-activity curve (TAC) was generated from the region of interest (ROI) over the periphery of each lung fiel d and a computer program was then used to calculate percentage clearan ce per minute ((k) over bar) in each lung. The mean (+/- S.E.M.) rate of clearance of Tc-99(m)-DTPA ((k) over bar = 1.31 +/- 0.13% min(-1)) was not significantly different from that of Tc-99(m)-HMPAO ((k) over bar = 1.32 +/- 0.27% min(-1), P>0.25) in the normal subjects. However, Tc-99(m)-DTPA clearance was 1.91 +/- 0.27% min(-1) and 9PTcm-HMPAO cl earance 0.78 +/- 0.17% min(-1) in eight patients with IPF (P<0.001, Tc -99(m)-DTPA vs Tc-99(m)-HMPAO). By regression analysis using a multipl icative model, both values correlated fairly [r = -0.71, y = exp (0.08 - 0.85 ln x); P<0.005], with a change in clearance rate in the opposi te direction in all eight patients. The results of our study demonstra te that the pulmonary clearance of Tc-99(m)-HMPAO is different from th at of Tc-99(m)-DTPA in IPF.