Lesion radioactivity concentration estimation using dual modality gamma ray/X-ray imaging

Although the use of dedicated gamma cameras in scintimammography permits closer access to the breast and improved spatial resolution relative to conventional gamma cameras, the task of quantifying the radiotracer concentration in the lesion relative to that in the surrounding breast tissue remains challenging because of the lesion-depth-dependent effects of attenuation and collimator blur. We are developing a dual modality scanner that combines digital x-ray mammography and a dedicated gamma camera on a common upright gantry. Here we present the results of a phantom study evaluating the use of the dual modality system for quantifying radioactivity in breast lesions. In addition to assessment of lesion activity, lesion volume estimates are necessary to quantify lesion radioactivity concentration. We have used multiple view x-ray imaging as a means of estimating lesion volume. Using phantom experiments, we have empirically derived a formula for correction of the measured z dimension of the lesion. The error obtained in quantification of lesion activity is approximately 10%. Lesion volume can be assessed with an accuracy comparable to that of lesion activity assessment using five x-ray views. These results suggest that the error in lesion concentration assessment is approximately 14%.