Effect of sinus attenuation in MR-based attenuation correction in 18F-FDG brain PET/MR

Attenuation correction is essential for image quantification in PET. At minimum, bone, soft tissue and air need to be included in MR-based attenuation correction (MRAC) of the head. Additional tissue classes might be beneficial to improve the accuracy of MRAC further. We studied the attenuation effect of nasal sinuses in MRAC by four attenuation maps and by assessment of regional PET quantification.MR-based attenuation maps using 0.151 cm−1, CT template-based, 0.100 cm−1, 0.060 cm−1 for sinus attenuation coefficients were created. A volume of interest (VOI) analysis of MRAC reconstructed PET data was conducted. Relative difference against PET data reconstructed with CT-based attenuation correction (CTAC) was calculated. Bias ratio images across the subject group were studied.The mean relative difference in the whole brain to CTAC reconstructed PET for each of the methods were as follows: -2.88 %, -3.16 %, -3.17 % and -3.42 %. The difference to CTAC reconstructed PET was not statistically significant (p>0.05) with any of the methods. The bias ratio images showed the largest differences in sinus region while gray matter activity remained largely unchanged. The maximum differences between the methods were 1.46 % and 2.35 % in the Cerebellum and in Gyrus Rectus.Therefore, when investigating only the changes in the gray matter radioactivity in neurodegenerative diseases, there is no critical need to account for sinus attenuation for MRAC of the head in 18F-FDG brain PET/MR.