Implementation and first results of the fully suspended cone beam CT and SPECT system for dedicated breast imaging

Stand-alone cone beam CT and SPECT systems capable of complex sinusoidal acquisition trajectories have previously been developed for dedicated breast imaging and used in early clinical studies. The fully-3D motions of the SPECT system can view into the chest wall and throughout the breast volume. The polar tilting capability of the CT system has shown a marked improvement in sampling into the chest wall, with comparable <;6 mGy total dose delivered to the volume as with a circular orbit, while eliminating cone beam artifacts because of the fully-3D acquisitions. A hybrid SPECT-CT system, with each individual modality capable of independently traversing complex trajectories around a pendant breast, was recently designed and the practical implementation of this design is presented here. The CT system consists of a 40×30 cm
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CsI(Tl) flat panel imager and an x-ray tube with a 16° W-anode angle, placed on opposing ends of the completely suspended gantry. A linear stage mechanism utilizing a pulley and cabling was implemented to tilt the suspended gantry within 0.02° positioning error about the 3D center of rotation; the fully-3D SPECT system with 16×20 cm
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CZT detector is nested inside the suspended CT gantry, oriented perpendicular to the CT source-detector pair. Both sub-systems are positioned on an azimuthal rotation stage enabling spherical trajectories. Initial imaging results demonstrate that additional off-axis projection views of various phantoms, allowed by the ±15° polar tilting of the CT system, facilitate more complete sampling and markedly improved reconstructions. To date, this is the first implementation of a fully-3D positioning hybrid SPECT-CT system that we are aware of, and could have various applications in diagnostic or therapeutic breast imaging.