A novel application specific emission tomograph (ASET) for breast imaging
A novel, dedicated and compact single photon ASET dedicated to pendant-breast nuclear medicine-based lesion imaging is developed. The prototype ASET system utilizes a compact gamma camera mounted on a support with variable radius-of-rotation, which is coupled to a polar goniometric cradle, all on an azimuthal vertical axis-of-rotation stage. The combination of radial, polar and azimuthal motions can achieve nearly any contiguous 3D acquisition orbit on an inverted hemispherical domain of the pendant breast reference frame. Tomographic resolution and volume sampling considerations were evaluated with cold rod and disk phantoms imaged with simple orbits, with the projection data reconstructed using an OSEM algorithm which accounts for the arbitrary Euler angles of the camera's vantage. With parallel-beam collimation, the 3.1 mm cold rods were visualized with the smallest radius-of-rotation; increasing polar tilt angle demonstrated insufficient sampling of the Orlov volume for the highly symmetric cold disk phantom, but can be ameliorated by the complex 3D orbits possible with the system. An uncompressed breast phantom containing Tc-99m and 0.6 and 1.0 cm diameter hot lesions was affixed to an anthropomorphic torso phantom with total activity concentration ratios for lesions: breast+body : cardiac+liver of 11:1:19. Despite insufficient sampling with simple orbits about the volume, as well as torso background contamination, the hot lesions were easily visualized on the uniform breast background, yielding signal-to-noise ratios and contrasts which were >9 times higher than for planar data; scatter correction further increased the SNR and contrast improvements. This new, compact, dedicated ASET imaging system has the potential of providing valuable, fully 3D, functional imaging information about small (lt;1cm), otherwise indeterminate breast lesions as an adjunct to diagnostic mammography.
