P15.12.A Amine CEST contrast in gliomas to measure metabolic treatment effect at 7T

Abstract

Abstract Background Chemical exchange saturation transfer (CEST) is an imaging technique that generates contrast based on proton exchange between water and a solute pool of interest. CEST is sensitive to molecules containing amine groups such as glutamate and creatine. Since creatine is a crucial metabolite in cellular metabolism and deregulation in cellular bioenergetics is a hallmark of cancer, CEST could be relevant for glioma imaging, specifically when evaluating treatment response. No clear consensus has been established on its use, therefore we wanted to preliminarily investigate the presence of amine CEST contrast in the contrast enhanced (CE) and non-enhanced (NE) lesions of gliomas, and to assess whether treated tumors would display different CEST contrast compared to treatment naïve tumors. Material and Methods We prospectively scanned 12 glioma patients on a whole-body 7 Tesla Philips Achieva MRI scanner (7 treated glioblastomas; 4 treatment naïve glioblastomas; 1 treatment naïve low-grade astrocytoma). Treatment included surgical resection, chemotherapy and radiotherapy. All patients gave informed consent. CEST images were post-processed, including corrections for B0 and B1 inhomogeneities. The CEST Z-spectra and magnetization transfer ratio (MTR) asymmetry were calculated per voxel. To retrieve the CEST values within the tumor lesions and contralateral white matter for normalization, segmentations were manually delineated on the clinical T2-FLAIR or post contrast 3D-T1. Results Overall we observed a relative increase of amine CEST contrast in the CE (MTRasym: Mean (x̄)=1.32; Standard deviation (σ)= 0.28) compared to a relative decrease (MTRasym: x̄=1.20; σ= 0.35) in the NE lesion. When evaluating the results from the CE and NE lesions for treated and treatment naïve groups individually, we observed a slightly different trend. In the treatment group, the CE lesions showed a higher amine CEST contrast (MTRasym: x̄=1.38; σ= 0.30) than the NE (MTRasym: x̄ = 1.11; σ = 0.302). In contrast, in the treatment naïve group, the CE lesion showed a slightly lower CEST contrast (MTRasym: x̄ = 1.23; σ=0.21) than in the NE group (MTRasym: x̄ = 1.29; σ= 0.38). Conclusion Our results show different amine CEST contrast trends between treated and treatment naïve groups when comparing CE and NE lesions. This suggests that treatment may have an effect on tumor tissue bioenergetics affecting the concentration of creatine. Nevertheless, future work is necessary to verify our results in a larger group of patients.