THE PULMONARY SCAN with radioactive particulate material has been proved to be an effective and easy method to demonstrate the pulmonary blood flow by radioisotope scanning technique.1 The major clinical usefulness has been in the investigation of pulmonary infarcts, but its usefulness is being extended to include investigation of a number of pulmonary problems.2,3
The most common material used for this scanning procedure has been macroaggregated human serum albumin labeled with radioactive iodine (131 I), chromium (51 Cr), or technetium (99m Tc). These particles are nearly completely removed from the circulation by the small vessels in the lungs after intravenous injection and are then broken down to smaller particles which leave the lungs with half-times ranging between five and ten hours.1
Clinical and experimental studies indicate that pulmonary emboli may cause significant physiological changes, with or without symptoms, in human subjects and animals.45 Since radioisotope