Conventional x-ray/scintillation mammography does not provide the depth information necessary to quantify the location and concentration of lesion activities in breast tissue. Our group is developing a novel tomographic dual modality system that will provide 3D structural and functional information of the breast. Because of constraints on the gantry geometry and acquisition time, only a limited number of views on one side of the breast can be acquired. In addition, the scatter and attenuation of gamma rays by breast tissue is a major problem for the reconstruction. We present an expectation-maximization (EM) method which naturally takes into account all the factors of noise, limited views, scatter, and attenuation. In a preliminary phantom study our quantification technique obtained results agreeing well with the ground truth.