Simulation-based Partial Volume Correction for CT-Guided PET/ SPECT imaging of Nasal Cavity Bone

Paranasal sinus cancers account for 3% of all head and neck cancers. Of these cases, only 15% cases are ethmoid sinus cancers (Harari et al., 2014). Cancer in these regions may spread rapidly to the adjacent areas, especially as the early disease is frequently asymptomatic (Bleehen NM, 1972). Ethmoid cancers are locally advanced at presentation and are difficult to cure, with 5-year disease-free survival rates of 30–50%. Because of the anatomic constraints and patterns of local spread, the inclusion of these tumors with those arising in the head and neck region and nasal fossa may be misleading (Waldron et al., 1998). Different imaging modalities can be used to diagnose ethmoid sinus cancer, such as Positron Emission Tomography (PET), Single-Photon Emission Computed Tomography (SPECT), Computed Tomography (CT), and Magnetic Resonance Imaging (MRI). PET and SPECT can provide important functional and molecular information, but they have considerable partial volume effects (PVEs), in which radiotracer activity in small structures appears blurred into nearby tissue, thereby degrading quantitative accuracy. These PVEs can be reduced if full anatomical information (fAI) is available about the spatial extent of the structure, e.g. of a tumor. A less investigated – but perhaps clinically more frequent – scenario is if only partial anatomical information (pAI) is available. Consider for example a tumor in the ethmoid bone. Even if the tumor is not visible on CT, the ethmoid bone is visible, and the visible spatial extent of the ethmoid bone places some limit on the spatial extent of the tumor. In this study, the impacts of CT partial anatomical information in the ethmoid and vomer bones are investigated and are compared to full anatomical information and to no anatomical information. The studies are performed for PET-like imaging (6-mm spatial resolution) and SPECT-like imaging (12-mm spatial resolution). Results: Compared with no anatomical information (as in OSEM reconstructed images), PET/SPECT images reconstructed with anatomical information (pAI) have reduced PVEs, as gauged by visual inspection and RMS errors, albeit not to the same extent as images reconstructed with full anatomical information (fAI). Keywords: Ethmoid sinus cancers, CT anatomy information, PET, SPECT, partial volume effect, image reconstruction