Clinical evaluation of ZTE attenuation correction for brain FDG-PET/MR imaging—comparison with atlas attenuation correction

Abstract

Accurate attenuation correction (AC) on PET/MR is still challenging. The purpose of this study was to evaluate the clinical feasibility of AC based on fast zero-echo-time (ZTE) MR imaging by comparing it the default atlas-based AC on a clinical PET/MR scanner. Methods: We recruited 10 patients with malignant diseases not located on the brain. In all patients, a clinically-indicated whole-body ¹⁸F-FDG-PET/CT was acquired. In addition, a head PET/MR scan (GE SIGNA TOF-PET/MR) was performed voluntarily. For each patient, two AC maps were generated from the MR images. One was Atlas-AC, derived from T1-weighted LAVA-FLEX images (clinical standard). The other was ZTE-AC, derived from proton-density-weighted ZTE images by applying tissue segmentation and assigning continuous attenuation values to the bone. The AC map generated by PET/CT was used as silver standard. Based on each AC map, PET images were reconstructed from identical raw data on the PET/MR scanner. All PET images were normalized to the SPM5 PET template. After that, these images were qualified visually and quantified in 67 volumes-of-interest (VOIs; automated anatomical labeling (AAL), atlas). Relative differences (%diff) and absolute relative differences (|%diff|) between PET images based on each AC were calculated. FDG uptake in all 670 VOIs and generalized merged VOIs were compared using paired t-test. Results: Qualitative analysis shows that ZTE-AC was robust to patient variability. Nevertheless, misclassification of air and bone in mastoid and nasal areas led the overestimation of PET in the temporal lobe and cerebellum (%diff of ZTE-AC; 2.46±1.19% and 3.31±1.70%, respectively). The |%diff| of all 670 VOIs on ZTE was improved by approximately 25% compared to Atlas-AC (ZTE-AC vs. Atlas-AC; 1.77±1.41% vs. 2.44±1.63%, P < 0.01). In two out of seven generalized VOIs, |%diff| on ZTE-AC were significantly smaller than Atlas-AC (ZTE-AC vs. Atlas-AC; Insula and cingulate, 1.06±0.67% vs. 2.22±1.10%, P < 0.01; central structure, 1.03±0.99% vs. 2.54±1.20%, P < 0.05). Conclusion: The ZTE-AC could provide more accurate AC than clinical Atlas-AC by improving the estimation of head skull attenuation. The misclassification in mastoid and nasal areas must be addressed to prevent the overestimation of PET in regions near the skull base.