Initial Development of a Dual-Modality SPECT-CT System for Dedicated Mammotomography

Dual-modality systems offer great promise in improving detection and evaluation of cancer through enhancement of the visual quality and quantitative accuracy of radionuclide imaging. A compact SPECT-CT system for dedicated 3D breast imaging is in development. The SPECT components include a 16times20cm² CZT-based compact gamma camera with 2.5mm square pixels, attached to a goniometer with polar positioning capability. The CT component includes a heavily filtered W-target X-ray source producing a quasi-monochromatic cone beam and CsI(Tl) digital detector. Both systems are coupled to a common rotation stage and have a common field of view. The CT system has a stationary polar orientation, and is laterally offset from the center of rotation for imaging pendant uncompressed breasts that are larger than the detector´s field of view. The constraints and performance of this initial configuration are being investigated. Previous measurements with combined system components show that optimal placement is limited by physical constraints rather than signal cross-contamination. Results on a combined system show that emission projection images are contaminated by X-ray scatter photons resulting in the reconstructed emission images having a higher signal level. Emission contamination also increases noise in the transmission image resulting in reducing the SNR in reconstructed CT images. Having both modalities on a single gantry is expected to simplify data acquisition, SPECT-CT image registration, and necessary image corrections.