The Effect of Including Bone in Dixon-Based Attenuation Correction for ¹⁸F-Fluciclovine PET/MRI of Prostate Cancer.

Abstract

The objective of this study was to evaluate the effect of including bone in Dixon-based attenuation correction for ¹⁸F-fluciclovine PET/MRI of primary and recurrent prostate cancer. <b>Methods:</b>¹⁸F-fluciclovine PET data from 2 PET/MRI studies-one for staging of high-risk prostate cancer (28 patients) and one for diagnosis of recurrent prostate cancer (81 patients)-were reconstructed with a 4-compartment (reference) and 5-compartment attenuation map. In the latter, continuous linear attenuation coefficients for bone were included by coregistration with an atlas. The SUV_max and mean 50% isocontour SUV (SUV_iso) of primary, locally recurrent, and metastatic lesions were compared between the 2 reconstruction methods using linear mixed-effects models. In addition, mean SUVs were obtained from bone marrow in the third lumbar vertebra (L3) to investigate the effect of including bone attenuation on lesion-to-bone marrow SUV ratios (SUVR_max and SUVR_iso; recurrence study only). The 5-compartment attenuation maps were visually compared with the in-phase Dixon MR images for evaluation of bone registration errors near the lesions. <i>P</i> values of less than 0.05 were considered significant. <b>Results:</b> Sixty-two lesions from 39 patients were evaluated. Bone registration errors were found near 19 (31%) of these lesions. In the remaining 8 primary prostate tumors, 7 locally recurrent lesions, and 28 lymph node metastases without bone registration errors, use of the 5-compartment attenuation map was associated with small but significant increases in SUV_max (2.5%; 95% confidence interval [CI], 2.0%-3.0%; <i>P</i> < 0.001) and SUV_iso (2.5%; 95% CI, 1.9%-3.0%; <i>P</i> < 0.001), but not SUVR_max (0.2%; 95% CI, -0.5%-0.9%; <i>P</i> = 0.604) and SUVR_iso (0.2%; 95% CI -0.6%-1.0%; <i>P</i> = 0.581), in comparison to the 4-compartment attenuation map. <b>Conclusion:</b> The investigated method for atlas-based inclusion of bone in ¹⁸F-fluciclovine PET/MRI attenuation correction has only a small effect on the SUVs of soft-tissue prostate cancer lesions, and no effect on their lesion-to-bone marrow SUVRs when using signal from L3 as a reference. The attenuation maps should always be checked for registration artifacts for lesions in or close to the bones.