3D Phantom insert for verification of image registration for SPECT/CT and PET/CT

Objectives To develop a vendor independent phantom insert for evaluating image registration accuracy between CT and either SPECT or PET images. This insert should be easy to prepare and setup, require short acquisition times, and yield high contrast images of the SPECT/PET and CT targets.

Methods The basic component of this phantom is a 20 mm diameter cylinder that is casted using a clear urethane material with a 1 mm diameter channel that runs the length of the cylinder (150 mm). The 1 mm diameter channel is filled with a radioactive solution and the ends are capped. Due to the solid surround the contrast of the line when reconstructed axially is excellent. Also, inserted into the 1 mm channel is a 0.016” diameter steel wire that runs the length of the channel. This wire surrounded by the radioactive solution provides a high contrast CT target spatially equivalent to the SPECT/PET data. Multiple line sources can be inserted into a holder where each line is orthonal to each of three reconstructed images planes; transaxial, coronal and sagittal. The congruence of location and thickness of the CT and SPECT/PET images can then easily be compared in a single plane or 3D view.

Results Three plane reconstructed data of the three line source insert yield images with point source like targets of the CT and SPECT/PET data for quick visual evaluation of registration accuracy for x,y, and z axis shifts. Data are presented on a number of PET/CT and SPECT/CT systems.

Conclusions This three line source insert provides a simple independent tool for evaluating registration of hybrid imaging systems. This insert can be used in existing cylindrical SPECT or PET phantoms, or imaged separately, and provides a rigorous method for checking 3D registration