[123I]HIPDM pulmonary imaging demonstrates elastase-induced pulmonary emphysema

Because more than 90 percent of [123I]hydroxyiodobenzyl-propanediamine (HIPDM) is localized in the lung after intravenous injection, the radiopharmaceutical has been proposed as a lung imaging agent. Its potential usefulness for the detection of pulmonary emphysema was evaluated in an animal model of elastase-induced emphysema along with [99mTc]MAA lung perfusion imaging. To induce lung emphysema, Long-Evans rats (200-250 g) were given 400 IU/Kg elastase intratracheally under ether anesthesia. Four weeks after elastase treatment, 15 treated and 15 nontreated rats were paired and simultaneously imaged under a scintillation camera immediately following intravenous injection of 0.25-0.3 mCi[99mTc]MAA. The procedure was repeated 48 hr later using 0.25-0.3 mCi[123I]HIPDM. Activity in the region of interest (ROI) over the lungs was recorded after the injections. Total counts per ROI from each rat were measured and normalized by lung volume. The normalized lung activity ratio of treated/nontreated rats was computed. The mean ratios of HIPDM and MAA were 0.847 and 0.802, respectively. The significant decrease in uptake of both HIPDM (p < 0.021) and of MAA (p < 0.025) in the elastase-treated lungs indicates decrease in functioning vascular endothelium and decrease in number of pulmonary capillary vessels, respectively, reflecting damage in capillaries and small arterioles. The decrease in treated/nontreated ratios lung is consistent with a significant alteration in pulmonary function and a significant increase in mean linear intercept (p < 0.005) in treated lung. Since the imaging reflects pulmonary endothelial receptor function, [123I]HIPDM lung imaging may serve as an alternative diagnostic modality for pulmonary emphysema.