P15.06.B Influence of arterial transit time delays on the differentiation between tumor progression and pseudo-progression in glioblastoma by arterial spin labeling MRI
Authors: van Dorth D , Jiang J , Schmitz-Abecassis B , Croese R J I , Taphoorn M J B , Smits M , Dirven L , de Bresser J , van Osch M J P , Koekkoek J A F 
Published: September 2022

Abstract

Background
Perfusion MRI by Arterial Spin Labeling (ASL) and Dynamic Susceptibility Contrast (DSC) has shown its potential for differentiating tumor progression from pseudo-progression in glioblastoma patients. The ASL scans can be affected by arterial transit time (ATT) delays, which could be caused by treatment effects due to concomitant radiochemotherapy. A prolonged ATT is present as apparent signal increase in the large arteries due to labeled spins still residing within the vasculature, leading to underestimation of tissue perfusion and thus potentially affecting clinical decision-making. The research questions were: 1) Do delayed ATTs lead to a difference in the visual assessment of ASL perfusion (normal/increased) maps compared to DSC-MRI?; 2) Does the radiological evaluation (progression vs. pseudo-progression) of ASL and DSC perfusion maps differ when ATT artifacts are present?; 3) Do delayed ATTs affect the predictive value of ASL-MRI scans 3 months post-radiotherapy for detecting true disease progression?

Material and Methods
This retrospective, single-center study included 68 adult patients with histologically confirmed glioblastoma who received postoperative radio(chemo)therapy. ASL and DSC scans were acquired 3 months post-radiotherapy as part of routine clinical follow-up. The perfusion data were visually scored by a neuroradiologist who determined presence/absence of ATT artifacts and their severity (%), perfusion of the enhancing tumor lesion and the radiological evaluation of tumor progression versus pseudo-progression. Presence of true disease progression was determined by follow-up of clinical data until 9 months post-radiotherapy available for 49/68 patients. Logistic regression was performed with gender, age, treatment type and tumor genetic status as covariates to assess the predictive value of ASL.

Results
In 78% of the patients ATT artifacts were present. No statistically significant association between the agreement of the perfusion maps and presence of ATT artifacts was found, but presence of ATT artifacts lowered the agreement between the DSC and ASL radiological evaluation. The logistic regression analysis showed that the ASL-based radiological score could not predict true disease progression, whereas higher age and unmethylated MGMT gene were associated with progression. Presence of ATT artifacts was not associated with tumor progression.

Conclusion
The presence of delayed ATT in ASL data seems to impact the radiological evaluation of ASL data, steering interpretation towards tumor progression (as compared to the DSC evaluation), whereas in patients without ATT artifacts ASL and DSC provide more similar radiological scores. Therefore, it is highly recommended to consider these artifacts when interpreting ASL perfusion MRI to differentiate between tumor progression and pseudo-progression in glioblastoma patients.