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Lung Scanning Following Radioaerosol Inhalation²

Los Angeles, California

ABSTRACT

The development of a safe technique for visualizing the lower respiratory tract by chest scanning following inhalation of suitable radioaerosols is described. The aerosolization equipment and test agents are readily available. Filtration of the exhaled air and channeling it to a vented hood or to the outside atmosphere prevents contamination of the examining room and personnel. Normally, inhaled radioactive particles smaller than 1–2 µ are evenly distributed throughout the lungs and penetrate to the distal alveoli. Inhalation and intravenous lung scans have nearly identical patterns in normal subjects. The inhalation scan pattern represents the distribution of airborne particles deposited throughout the lower respiratory tract, but the amount of radioactivity in any given portion of the lung is not always proportional to air flow to that region. Aerosol deposition is related to factors other than diffusion, such as particle size, sedimentation, impaction, concentration of aerosol and the rate of air movement. When inhalation is performed with the subject in the lateral position, greater amounts of aerosol are deposited in the superior lung, where ventilation and perfusion are reduced. With partial bronchial obstruction, increased deposition of radioaerosol may occur at the obstruction site and the region beyond usually shows reduced levels of radioactivity. Complete bronchial obstruction is readily detectable in the inhalation scan as an area devoid of radioactivity. A normal lung image indicates patency of the lower respiratory passages.

The radioaerosol inhalation scanning procedure is a useful adjunct to bronchography in the assessment of airway patency. It may be employed safely when bronchography is contraindicated as in patients with impaired pulmonary function. Additional applications of the inhalation scanning procedure are mentioned.

FOOTNOTES

² These studies were supported by Contract AT(04-1)-GEN-12 between the U.S. Atomic Energy Commission and the University of California at Los Angeles, and by a grant-in-aid from Abbott Laboratories, North Chicago, Illinois.

¹ From the Laboratory of Nuclear Medicine and Radiation Biology, School of Medicine, University of California at Los Angeles; and the Department of Radiology, Los Angeles County Olive View Hospital, Olive View, Calif.