Experimental scatter- and attenuation “free” SPECT/PET imaging using a novel sandwich phantom design

The technique is based on the assumption that a selected physical property of a 3D object can be represented by a series of thin 2D-sheets. The authors have applied this approach for imaging of radioactive objects, with, and “without” disturbing effects from photon scattering and attenuation. Experimental SPECT-images, built-up, essentially by primary photons, have been obtained by stacking sheets of radioactivity distributions into 3D structures with air or low density material (μ=0.0068 cm^-1 for 140 keV photons) in between. Digitized sections of the 3D Hoffman rCBF-, the Jaszczak hot-rod and a cylindrical phantom were printed out on 0.1 mm thick paper sheets using radioactive ink. These sheets were stacked in air, low-density material or between polystyrene plates to form sampled 3D versions of each phantom. SPECT was performed with the sheets perpendicular to the central axis of the camera. The scatter contribution was negligible when the sheets were stacked in air or in low-density material. The attenuation losses with low-density material stacking were about 14%. The technique is extremely flexible and allows accurate experimental validation of scatter and attenuation correction methods in objects with arbitrary activity distributions. It may also be applied for absolute calibration of SPECT (and possibly PET) data