Feasibility of scintigraphy in exercise‐induced pulmonary haemorrhage detection and quantification: preliminary studies

Summary We hypothesised that scintigraphic imaging of the lungs following injection of 99m Tc labelled red blood cells ( 99m Tc‐RBC) in the exercising horse might enable exercise‐induced pulmonary haemorrhage (EIPH) quantification. Ideally, to favour detection of bleeding, circulating 99m Tc‐RBC not involved in the haemorrhage should be removed from the circulation quickly. Altering RBC during labelling to stimulate splenic uptake of 99m Tc‐RBC may encourage this. In order to investigate this hypothesis, 99m Tc‐RBC distribution was followed for 1 h in 2 groups of horses. Group 1 was injected i.v., at rest, with radioactive nondenatured RBC ( 99m Tc‐NDRBC); Group 2 received labelled RBC partly denatured by heating ( 99m Tc‐HDRBC). In Group 2 , splenic uptake was higher at all times and radioactivity in the lung was proportionally higher and decreased less quickly than in Group 1. Hence, the time‐consuming 99m Tc‐HDRBC labelling technique did not demonstrate any advantage over the easier 99m Tc‐NDRBC labelling procedure. Additionally, the feasibility of scintigraphic visualisation of a small amount of pulmonary bleeding was confirmed with the following trial: using an endoscope, a radioactive solution mimicking 50 ml of bleeding was deposited at the usual site of EIPH in a live horse. The radioactivity recorded in that area was compared to the one obtained in the same region in Group 1 and 2. The activity measured 20 min post endoscopy corresponded to 33% of the activity obtained in Group 1 vs. 8% in Group 2 at that timing. Once again, there was no advantage of using 99m Tc‐HDRBC vs. 99m Tc‐NDRBC. These results demonstrated that small amounts of bleeding might potentially be detected with scintigraphy; they also suggest that the limiting factor for detecting small amounts of bleeding may be the level of lung background radioactivity.