PINHOLE SPECT FOR IMAGING IN-111 IN THE HEAD

With the development of targeted radiotherapy techniques, quantitation of radionuclides that emit high-energy photons (>140 keV) by gamma ca mera scintigraphy has become increasingly important in external imagin g applications. The radionuclide In-ill (171 and 245 keV) has been use d experimentally with monoclonal antibodies and receptor specific phar maceuticals to obtain pre-treatment information for various types of b rain tumors. Conventional protocols for imaging In-ill utilize paralle l-hole collimators designed for medium energy (ME) applications. The p erformance of ME collimators suffers from decreased spatial resolution and/or sensitivity. Septal penetration can also lead to image degrada tion. Pinhole collimation can offer improved spatial resolution and/or sensitivity compared with ME collimators when imaging In-ill in objec ts the size of the head or smaller, especially when restricting the fi eld-of-view to regions near the central plane. Simulation and experime ntal phantom studies have been used to investigate pinhole SPECT for i maging In-ill in the head. Chang attenuation and dual-window scatter s ubtraction compensation methods have been evaluated for potential accu racy in pinhole geometry. Results have shown improved image quality wi th pinhole collimation with a less than or equal to 15% quantitative a ccuracy in phantom studies. We demonstrate that pinhole SPECT is a via ble alternative to ME collimator imaging of In-ii 1 in objects the siz e of the head.