Human Brain Scanning with Radioiodinated Macroaggregates of Human Serum Albumin

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Abstract
WHEN MACROAGGREGATES of human serum albumin (MAA), 10 microns or more, are injected into the antecubital vein, they are immediately filtered out by the pulmonary arterial capillary bed of the lung. Several favorable reports have appeared in the literature (1–3, 7) of using radioactive MAA in lung scanning for the detection of regional pulmonary arterial flow deficits. Taplin and his group (5) attested to the safety of intracarotid injections in brain scanning in dogs. Thompson (6) in similar experiments with a large number of dogs was unable to produce any deleterious effects with as much as 1,600 mg of macroaggregated albumin. On the basis of this preliminary animal work we embarked on a program of brain scanning in selected patients by intracarotid injection of I131_MAA. Method and Material The I131_MAA was obtained from Charles E. Frosst & Co., Montreal, and the particles ranged in size from 5 to 30 microns, averaging about 15 microns. Between 50 and 100 micro curies of l131_MAA were administered in a volume of 10 ml NaCl buffered with equal volumes of 0.2N sodium hydroxide and 0.2N acetic acid. A 100-microcurie dose contains about 4 mg albumin. The patient was prepared in the usual manner for a carotid injection, and the material was administered by syringe through a 20-gauge needle. Immediately afterward the needle was withdrawn, and compression was applied to the puncture site long enough to prevent the formation of a hematoma. Some patients were scanned following cerebral angiography; the I131_MAA was injected through the same needle or catheter left in place, and thereby a second carotid puncture was avoided. Lateral and frontal scans were obtained immediately after hemostasis was assured. A 19–hole lead focusing collimator associated with a 1.5 × 3–in. diameter scintillation crystal was used, and the automatic scintillation scanner was set to accept the full width of the 360 kv photopeak. The background cut-off was determined by the count rate over the cheek (external carotid circulation). Potassium iodide tablets (0.3 g) were administered the day before, the day of, and the day after the brain scan to block the thyroid gland when possible. Results The count rate over the brain was about 1,500 cpm per 100-microcurie test dose. Activity over the cheek varied between 15 and 25 per cent of the brain activity, and this represents a division of blood flow between the external and internal carotid arteries. In 3 patients the biological half-life of the macroaggregates in the brain was determined to be approximately two hours. Because of a theoretical hazard in injecting particulate matter and producing a transient capillary embolism, all 15 subjects were carefully examined clinically before and after the administration of I131_ MAA.

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