Transmission Imaging with a Compact Gamma Camera: Initial Results for Mammotomography
A dedicated single photon emission prototype imaging system is intended for fully 3D Application Specific Emission and Transmission Tomography (ASETT), where one specific application is dedicated breast imaging. In breast imaging, this dual-modality system may be useful for (1) improving detectability of low contrast lesions with x-ray CT imaging, (2) emission quantification using the transmission images, and (3) better interpretation of the reconstructed emission data by facilitating objective region selection. Each imaging component needs independent development, optimization and characterization. The prototype SPECT component using a NaI(Tl) based gamma camera has been built and initially evaluated with small, low contrast breast lesions; resolution and sampling issues are under investigation with the arbitrary orbits possible with the hemispherical positioning capability. This emission component has been demonstrated to be a novel and viable approach to dedicated mammotomography with high lesion signal-to-noise and contrast. Geometrical feasibility studies are investigated herein for transmission mammotomography. The studies use the emission gamma camera with 2×2×6 mm3 crystals with and without detector collimation, with single photon 99mTc 140 keV sources for the pendant breast geometry. Transmission data are acquired with simple vertical axis of rotation (with 0° polar tilt, 360° azimuthal acquisition). Phantom measurements are made with acrylic/air mini-rod and mini-tube resolution phantoms, and an anthropomorphic breast phantom containing 0.6 and 1.0 cm diameter water-filled, acrylic lesions. All data were reconstructed with ordered subsets expectation maximization. Initial transmission images are also shown with a recently acquired digital flat-panel x-ray detector illuminated with a nuclear source. This detector is intended for use in the final design of the dedicated x-ray transmission instrument.
