Usefulness of amide proton transfer images in the diagnosis of malignant glioma comparison of APT images and 11C-methionine-positron emission tomography.

IntroductionAmide proton transfer (APT) imaging is one of the imaging methods in Magnetic Resonance Imaging (MRI). It is a molecular imaging technique that visualizes contrast based on the concentration or exchange rate of amide groups of amino acids, which increases in tumors. Methionine-positron emission tomography (MET-PET), on the other hand, has been found to be useful in the imaging diagnosis of glioma because of its clear contrast in the accumulation of tumor cells. In this study, we compared APT and MET-PET on the basis of pathological diagnostic results and backwardly examined whether APT is useful for the imaging diagnosis of glioma.MethodForty-six patients with malignant glioma (World Health Organization 2016 (WHO2016) Grade: GII/III/IV) and suspected pseudoprogression who underwent APT and MET-PET were included in the study. For APT, APT signals were measured in the tumor region of interest, and for MET-PET, 370 MBq was administered to measure the tumor-to-normal tissue ratio (TNR).ResultIn the correlation verification, the actual APT and TNR were correlated with 2.22 ± 1.01 and 2.58 ± 1.5, respectively (r = 0.6, p < 0.001). The accuracy of the differentiation between GII/III/IV (32 patients) and suspected pseudoprogression (14 patients) by actual APT measurements was verified with a sensitivity of 91% and specificity of 100% at a cutoff value of 1.81. In the validation of malignancy diagnosis, the measured APT value of GII (6 cases) was 2.18 ± 0.43 and the TNR was 3.53 ± 2.12, the measured APT value of GIII (11 cases) was 2.67 ± 0.69 and TNR was 2.81 ± 0.72, and the measured APT value of GIV (15 cases) was 2.99 ± 0.61 and the TNR was 3.44 ± 1.28. The APT measured value and TNR differed significantly in malignancy diagnoses, with higher grades having higher values. Genetic diagnosis validation revealed that the oligodendroglioma group (GII/III: 10 cases) had an APT of 2.37 ± 0.66 and a TNR of 3.52 ± 1.41, while the astrocytoma group (GII/III: 7 cases) had an APT of 2.67 ± 0.45 and a TNR of 2.41 ± 0.87.ConclusionAPT may be comparable to MET-PET in differentiating suspected pseudoprogression and in diagnosing malignancy. Patients with an actual APT of 1.81 or higher should be considered for a treatment plan, whereas follow-up may be an option for those with an APT of 1.81. Although the TNR tends to be higher in the oligodendroglioma group (GII/III), APT, which is not affected by the blood-brain barrier, has less variability in actual measurements and is useful for the imaging diagnosis of glioma.