Theoretical limitations in the immunodiagnostic imaging of cancer with computed tomography and nuclear scanning

In order to help assess the feasibility of using immunologically tagged agents to render tumors detectable with current computed tomographic and nuclear scanners, mathematical formulations were developed to determine the theoretical limits of tumor detection relative to size and depth of the lesions. The results of our analysis suggest that visualization with computed tomography of a tiny tumor (1 sq mm, cross-sectional area) would require binding in the order of 2 x 10(5) iodine atoms/antigenic site, while imaging of a very large (900-sq mm) tumor would require approximately 10(4) atoms/site. Very low energy scanners might reduce these discouraging estimates by an order of 10(2). The immunological imaging of tumors with nuclear scanning appears quite feasible from our formulations, as has been demonstrated by others clinically. Small (1-sq cm) and deep (greater than or equal to 5-cm) tumors appear detectable with uptake ratios of the order of 5 or higher, which seem to be attainable currently. Smaller and deeper tumors require much higher uptake ratios to be detected.