Sequential and Hybrid PET/MRI Acquisition in Follow-Up Examination of Glioblastoma Show Similar Diagnostic Performance

SIMPLE SUMMARY: Reliable differentiation between true tumor progression and treatment-related changes is a challenging situation in the management of glioma patients. Both amino-acid PET and perfusion MRI, as well as their combination, play a central role in this decision. In clinical practice, PET and MRI are usually acquired at two separate time points, so the question arises if and how this affects their diagnostic performance. In our study, we investigated a unique cohort of 38 glioblastoma patients (IDH wild-type), who received both a PET–MRI (with simultaneous acquisition of FET-PET and DSC perfusion) as well as an MRI exam with DSC perfusion within a month of each other. For all global and local image metrics, and importantly also for the diagnostic performance, we found no significant difference between the simultaneous and sequential acquisition of PET and MRI. These results are reassuring for routine clinical management and support further investigation into advanced, multi-parametric models for improving personalized decision-making in neuro-oncology when PET and MRI are not acquired simultaneously. ABSTRACT: Both positron emission tomography (PET) and magnetic resonance imaging (MRI), including dynamic susceptibility contrast perfusion (DSC-PWI), are crucial for treatment monitoring of patients with high-grade gliomas. In clinical practice, they are usually conducted at separate time points. Whether this affects their diagnostic performance is presently unclear. To this end, we retrospectively reviewed 38 patients with pathologically confirmed glioblastoma (IDH wild-type) and suspected tumor recurrence after radiotherapy. Only patients who received both a PET–MRI (where DSC perfusion was acquired simultaneously with a FET-PET) and a separate MRI exam (including DSC perfusion) were included. Tumors were automatically segmented into contrast-enhancing tumor (CET), necrosis, and edema. To compare the simultaneous as well as the sequential DSC perfusion to the FET-PET, we calculated Dice overlap, global mutual information as well as voxel-wise Spearman correlation of hotspot areas. For the joint assessment of PET and MRI, we computed logistic regression models for the differentiation between true progression (PD) and treatment-related changes (TRC) using simultaneously or sequentially acquired images as input data. We observed no significant differences between Dice overlap (p = 0.17; paired t-test), mutual information (p = 0.18; paired t-test) and Spearman correlation (p = 0.90; paired t-test) when comparing simultaneous PET–MRI and sequential PET/MRI acquisition. This also held true for the subgroup of patients with >14 days between exams. Importantly, for the diagnostic performance, ROC analysis showed similar AUCs for differentiation of PD and TRC (AUC simultaneous PET: 0.77; AUC sequential PET: 0.78; p = 0.83, DeLong’s test). We found no relevant differences between simultaneous and sequential acquisition of FET-PET and DSC perfusion, also regarding their diagnostic performance. Given the increasing attention to multi-parametric assessment of glioma treatment response, our results reassuringly suggest that sequential acquisition is clinically and scientifically acceptable.