Clinical experience with oblique views in pulmonary perfusion camera-imaging in normal and pathological anatomy.

Abstract

Pulmonary perfusion patterns resulting from the use of commercially available MAA 131I imaging procedures have been used widely in the last five years in an attempt to identify significant perfusion defects associated with pulmonary emboli. Few studies have addressed themselves to methods of better demonstrating significant defects as well as anatomical variants capable of producing false defects. The question as to what represents a significant perfusion defect as compared to a normal variant frequently arises. Corresponding lesions on radiographs, when present, help corroborate the finding of perfusion defects in the radiopharmaceutical procedures. Often, however, there is significant question as to whether a defect is real in the absence of corroborative data. As with other radiopharmaceutical organ-imaging procedures, one would like to view abnormalities on at least two views in order to make a positive diagnosis of perfusion defects. With this approach in mind most investigators obtain anterior and posterior views of the lungs. Because the lung, however, is a distended, thick organ the focal lengths of most collimators used with conventional rectilinear scanners are such that posterior lesions may not be seen anteriorly and vice versa unless they are massive. With the gamma scintillation camera, the best “view” is immediately on the surface of the straight-bore collimator with resolution becoming less with depth of the organ from the surface. We have investigated a means to delineate perfusion defects better by utilizing the gamma camera, with which one readily obtains oblique views. In this paper we review our experience with oblique pulmonary camera-imaging in 160 patients during 1967. Methods A dose of 300 µCi of MAA 131I is slowly injected intravenously, with the patient in the supine position and breathing normally. Imaging is begun immediately. Most of our pulmonary perfusion studies are accomplished with the gamma camera, although infrequently rectilinear scanning is performed. The gamma camera lends itself particularly well to the proposed procedures. Each view can be completed with good detail in four to five minutes. A total of the eight required views, anterior, posterior, and obliques of each lung, can be accomplished in thirty-five to forty-five minutes, the time required for an anterior and posterior scan with the rectilinear scanner. Positioning is accomplished first by means of a special “microscopic stage” type stretcher top which was designed by our laboratory. This apparatus allows for accurate rapid positioning (Fig. 1). With each corresponding straight view of the lung, the imaging head of the gamma camera is rotated to the maximum of 40° obtainable with the instrument, and oblique views are taken. All of the pulmonary perfusion camera images obtained in this manner in 1967 were reviewed in order to determine the value of the oblique view in the interpretation of the studies.