Evaluation of sinus/edge corrected ZTE-based attenuation correction in brain PET/MRI

Evaluation of sinus/edge corrected ZTE-based attenuation correction in brain PET/MRI:

Purpose: In brain positron emission tomography/magnetic resonance imaging (PET/MRI), the major challenge of zero-echo-time (ZTE)-based attenuation correction (ZTAC) is the misclassification of air/tissue/bone mixtures or their boundaries. Our study aimed to evaluate a sinus/edge corrected (SEC) ZTAC (ZTAC_SEC), relative to an "uncorrected (UC)" ZTAC (ZTAC_UC) and a computed tomography (CT) atlas-based attenuation correction (ATAC). Materials and Methods: Whole-body fluorodeoxyglucose PET/MRI scans were performed for twelve patients, following PET/CT scans. Only data acquired at a bed station that includes the head were employed for this study. Only data acquired at a bed station that included the head were employed for this study. Using PET data from PET/MRI, ZTAC_UC, ZTAC_SEC, ATAC and reference CT-based attenuation correction (CTAC) were applied to PET attenuation correction. For ZTAC_UC, the bias-corrected and normalized ZTE was converted to pseudoCT with air (-1000 HU for ZTE < 0.2), soft-tissue (42 HU for ZTE > 0.75), and bone (-2000*(ZTE-1) + 42 HU for 0.2 ≤ ZTE ≤ 0.75). Afterwards, in the pseudoCT, sinus/edges were automatically estimated as a binary mask through morphological processing and edge detection. In the binary mask, the overestimated values were rescaled below 42 HU for ZTAC_SEC. For ATAC, the atlas deformed to MR in-phase was segmented to air, inner-air, soft-tissue, and continuous bone. For the quantitative evaluation, PET mean uptake values were measured in twenty 1 ml volumes-of-interest distributed throughout brain tissues. The PET uptakes were compared using a paired t-test. An error histogram was employed to show the distribution of voxel-based PET uptake differences. Results: Compared to CTAC, ZTAC_SEC achieved the overall PET quantification accuracy (0.2±2.4%, P = 0.23) similar to CTAC, in comparison with ZTAC_UC (5.6±3.5%, P < 0.01) and ATAC (-0.9±5.0%, P = 0.03). Specifically, a substantial improvement with ZTAC_SEC (0.6±2.7%, P < 0.01) was found in cerebellum region, in comparison with ZTAC_UC (8.1±3.5%, P < 0.01) and ATAC (-4.1±4.3%, P < 0.01). The histogram of voxel-based uptake differences demonstrated that ZTAC_SEC reduced the magnitude and variation of errors substantially, compared to ZTAC_UC and ATAC. Conclusion: Sinus/edge corrected ZTAC can provide an accurate PET quantification in brain PET/MRI, comparable to the accuracy achieved by CTAC, particularly in the cerebellum.



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