Impact of [¹¹C]methionine PET with Bayesian penalized likelihood reconstruction on glioma grades based on new WHO 2021 classification

The uptake of [¹¹C]methionine in positron emission tomography (PET) imaging overlapped in earlier images of tumors. Bayesian penalized likelihood (BPL) reconstruction increases the quantitative values of tumors compared with conventional ordered subset-expectation maximization (OSEM). The present study aimed to grade glioma malignancy based on the new WHO 2021 classification using [¹¹C]methionine PET images reconstructed using BPL.

We categorized 32 gliomas in 28 patients as grades 2/3 (n = 15) and 4 (n = 17) based on the WHO 2021 classification. All [¹¹C]methionine images were reconstructed using OSEM + time-of-flight (TOF) and BPL + TOF (β = 200). Maximum standardized uptake value (SUV_max) and tumor-to-normal tissue ratio (T/N_max) were measured at each lesion.

The mean SUV_max was 4.65 and 4.93 in grade 2/3 and 6.38 and 7.11 in grade 4, and the mean T/N_max was 7.08 and 7.22 in grade 2/3 and 9.30 and 10.19 in grade 4 for OSEM and BPL, respectively. The BPL significantly increased these values in grade 4 gliomas. The area under the receiver operator characteristic (ROC) curve (AUC) for SUV_max was the highest (0.792) using BPL.

The BPL increased mean SUV_max and mean T/N_max in lesions with higher contrast such as grade 4 glioma. The discrimination power between grades 2/3 and 4 in SUV_max was also increased using [¹¹C]methionine PET images reconstructed with BPL.