Quantifying breast density with a cone-beam breast CT

Volumetric breast density was evaluated using a simulated cone beam breast CT with 80 kVp. The breast was modeled as a cylinder with background tissue composition of 20% glandular and 80% adipose. Various objects with different sizes and tissue compositions were embedded. Ray-tracing algorithm was utilized to obtain projection images in a full rotation without considering scatter, beam hardening and imaging noise. Filtered backprojection was adopted for image reconstruction with high quality. Reconstructed images had flat profiles except at large cone angle of 8.6 degrees to 10 degrees. They were calibrated using known linear attenuation coefficients of two image contrast objects. A 3D mapping of tissue densities could be directly computed within 5% error. Tissue volumes were obtained by counting voxels in appropriate attenuation coefficient ranges. Results of contrast objects were consistent with true volumes within 10% error. However, cone angle artifact decreased pixel values, and a reduction algorithm was required for accurate tissue assessment at large cone angles. This study indicates the possibility of excellent quantitative breast density measurements and volume assessments with cone-beam breast CT.