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Comparison of the Scintillation Camera with a Conventional Rectilinear Scanner Using Technetium-99m Pertechnetate in a Tumor Brain Phantom^1,2

Minneapolis, Minnesota

ABSTRACT

Critical physical factors which limit the ability of a scintiphotographic system to demonstrate intracerebral space-occupying lesions are 1) volume of the lesion, 2) location within the brain, 3) the tumor-brain radioactive concentration ratio, 4) absolute concentration of radioactivity in the tumor and 5) type and amount of radionuclide tracer agent injected. Our study emphasizes the importance of the first three factors in evaluating in vitro methods of brain tumor detection. A water ^99mTc brain tumor phantom was used to compare scintiphotograms Obtained with the scintillation camera and the conventional rectilinear scaner. "Pseudotumor" volumes and tumor-brain radioactive concentration ratios were found to relate inversely in a straight line manner when plotted on log-log graph paper if one uses limits of resolution as defined in this study. It was found that pseudotumors near the midline of the phantom brain were more difficult to visualize than those in a more lateral position. Using optimal instrument settings, "pseudotumor" volumes which were barely detectable were 0.6 cc and 50 cc and required tumor-brain concentration ratios of 20:1 and 1.3:1 respectively to be visualized in a lateral position, provided the technical factors had been adjusted to optimal settings.

Our results compare favorably with other workers investigating the resolvability of pseudotumors with respect to their size and their radioactivity as compared to the surrounding media.

Both the conventional rectilinear scanner and the scintillation camera showed similar resolving characteristics when the same pseudotumor-brain phantom systems were used. If optimal camera settings are used, the examination times for both the rectilinear scanner and the camera are very nearly equal. One practical advantage of the scintillation camera over the conventional scanner is that the camera detector may be moved with ease to a variety of diferent positions.

Caution must be exercised when attempting to transfer data from phantom studies such as this to actual clinical studies of the human brain because of obvious differences between the complex anatomical structures of the brain and the relatively simple materials used in the tumor-brain phantom.

FOOTNOTES

¹ From the Nuclear Medicine Clinic, University of Minnesota Hospitals, the Dept. of Radiology of the Univ. of Minnesota Medical School and the Veterans Administration Hospital, Minneapolis, Minn.

² Supported by funds from the Graduate School, University of Minnesota, The American Cancer Society (Institutional Grant), and the United States Public Health Service(#CA-0332-07).