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 camera scintigraphy has become increasingly important in external imaging applications. The radionuclide In-111 (171 and 245 keV) has been used experimentally with monoclonal antibodies and receptor specific pharmaceuticals to obtain pre-treatment information for various types of brain tumors. Conventional protocols for imaging In-111 utilize parallel-hole collimators designed for medium energy (ME) applications. The performance of ME collimators suffers from decreased spatial resolution and/or sensitivity. Septal penetration can also lead to image degradation. Pinhole collimation can offer improved spatial resolution and/or sensitivity compared with ME collimators when imaging In-111 in objects the size of the head or smaller, especially when restricting the field-of-view to regions near the central plane. Simulation and experimental phantom studies have been used to investigate pinhole SPECT for imaging In-111 in the head. Chang attenuation and dual-window scatter subtraction compensation methods have been evaluated for potential accuracy in pinhole geometry. Results have shown improved image quality with pinhole collimation with a ⩽15% quantitative accuracy in phantom studies. We demonstrate that pinhole SPECT is a viable alternative to ME collimator imaging of In-111 in objects the size of the head