Clinical Evaluation of a New 99mTc-MAA Kit for Lung Scanning

Lung scanning has been recognized as a clinically useful technique for portraying macroscopic pulmonary perfusion defects since it was first reported by Wagner in 1964 (1 ). A number of radiopharmaceuticals have been proposed to assess pulmonary perfusion. Although 1 3 1 I imposes many limitations as a radiotagging agent, the use of iodinated macroaggregated albumin (I-MAA) has received wide acceptance as the agent of choice. The desirability of 9 9 m Tc as a scanning agent, especially for static imaging systems, has long been recognized and leads to the ultimate development of 9 9 m Tc-tagged human albumin microspheres (Tc-HAM) (2). Technetium-99m-labeled macroaggregated albumin (Tc-MAA), although desirable, has not been exploited for lung scanning because of the technical requirements encountered during its preparation (3). Recently, a lyophilized macroaggregated albumin kit (Macrotec) for preparing Tc-MAA has undergone field trials by E.R. Squibb & Sons. Preparation of Tc-MAA from this kit yields a stable product which on standing may be used without resuspension and rewashing the tagged particles to remove sequestered technetium. Preparation and clinical evaluation of the Macrotec kit was undertaken in our laboratories from July 1972 to February 1973 and is the subject of this report.