Attenuation compensation for breast tissue in combined CT/SPECT devices dedicated to mammography

The usefulness to generate attenuation maps from computed tomography (CT) system for compensation of photon attenuation in single photon emission computed tomography (SPECT) mammographic evaluation is discussed. The present investigation is part of a general project intended to perform co-registration of functional and morphological information. The experimental apparatus consists of a quasi-monochromatic X-ray computed tomography and a high resolution compact gamma camera. The projection data are reconstructed using filtered backprojection to form the X-ray CT image, which is then properly scaled to produce an estimate of the attenuation map at the energy of the emission nuclide. The scaling is done following a two phases model of the breast tissue which takes into account the realistic average composition of the basic components. It is shown that both for simulations and measurements, the attenuation maps, generated from the CT images, estimate accurately the attenuation of breast in the reconstructed SPECT evaluations.