Quantification of partial volume effects in salivary glands SPECT images after radiation therapy of head and neck tumors

Introduction: Radical radiation therapy of head and neck cancers may injure the salivary glands and reduce their function. Single-photon emission computed tomography (SPECT) images maybe used to evaluate function post-therapy. However, accurate quantification is hindered by the partial volume effects (PVEs). The present study involved the introduction of a PVEs quantification technique aimed at improved quantification of the salivary glands function. Material and Methods: The parotid and submandibular salivary glands were mimicked with hollow spheres. The left parotid (LP), right parotid (RP), left submandibular (LSM), and right submandibular (RSM) salivary glands had diameters; 16, 14, 11, and 12 mm, respectively. Technetium-99m solution (activity concentration; 300 kBq/mL) filled the salivary glands prior to implanting into a hollow head and neck phantom later filled with the technetium-99m solution (activity concentration; 1440 Bq/mL). A SPECT image was acquired on 128 x 128 matrix size over 30 min and reconstructed using filtered back projection algorithm (Butterworth filter with a cut-off frequency of 0.9 cycles per pixel and an order of 9). Reconstructed images were quantified using ImageJ software. Results: The image counts extracted from the LP, RP, RMS, and LMS salivary glands SPECT images were 672 019, 494 842, 398 091, and 262 908, respectively after the quantification of PVEs, compared to 486 320, 347 534, 272 940, and 175 307 before the quantification of PVEs. The respective quantitative errors were 27%, 29%, 31%, and 33%. Conclusion: Quantification of PVEs allows recovery of image counts spread outside the image pixels leading to improved quantification.