Investigating novel patient bed designs for use in a hybrid dual modality dedicated 3D breast imaging system
A hybrid SPECT-CT system for dedicated 3D breast cancer imaging (mammotomography) is in development. Using complex 3D imaging acquisition trajectories, the versatile integrated system will be capable of contouring and imaging an uncompressed breast suspended in a 3D volume located below a radio-opaque patient bed, providing co-registered volumetric anatomical and functional information. This study examines tradeoffs involved in the design of the patient bed to satisfy concomitant and competing technical and ergonomie requirements specific to this imaging paradigm. The complementary source-detector arrangement of the CT system is geometrically more restrictive than that of the single detector SPECT system. Additionally, the compact dimensions and size of the CT system components (primarily the x-ray tube) are key constraints on the bed design and so the focus is concentrated there. Using computer-aided design software, several design geometry options are examined to simultaneously consider and optimize the following parameters: image magnification, imaged breast volume, azimuthal imaging span, and patient comfort. Several CT system source to image distances are examined (55-80cm), as well as axial patient tilt up to 35°. An optimal patient bed design for a completely under-bed hybrid imaging system was determined. A 60cm SID, magnification factor of ∼1.5, and patient bed angled at ∼15° provided the optimal dimensions. Additional bed dimensions allow the CT projection beam to nearly entirely image the chest wall, however at the cost of reduced angular sampling for CT. Acquired x-ray mammotomographic image data is used to assess the feasibility of this reduced angle acquisition approach.
