Phantom study of a new hand-held γ-imaging probe for radio-guided surgery

In recent years, hand-held mini γ-cameras have been increasingly used to perform scintigraphic imaging during surgery. The aim of the present work was to evaluate the physical characteristics of a new high-sensitivity hand-held mini γ-camera through specific phantom measurements. To characterize the performances of the imaging probe Guardian2 hand-held γ-camera, we measured its sensitivity and depth transmission curve, the extrinsic spatial resolution and spatial linearity, the spatial uniformity, and the count-rate linearity. We also estimated its whole image quality through the contrast-to-noise ratio of four hot spheres (internal diameters ranging from 4.9 to 9.8 mm). The sensitivity of the imaging probe Guardian2 γ-camera was 204 counts/s/MBq; it had a high spatial resolution (2.5 mm FWHM at contact) and optimal linearity of counts (Pearson's coefficient, R=0.999). The integral uniformity was 12.0% in the useful field of view (FOV) and 8.8% in the central FOV, whereas the differential uniformity was 5.7% in the useful FOV and 4.0% in the central FOV. The system was able to detect and distinguish all four small spheres used for the whole quality test. The contrast-to-noise ratio was evaluated both at contact with the collimator and with a 5-cm-thick interposed Plexiglas slab. The γ-imaging probe that we evaluated demonstrated good performance, confidently allowing its use for specific clinical applications in radio-guided surgery.