Fast whole brain quantitative proton density mapping to quantify metabolites in tumors

Abstract

Introduction Gliomas are the most common primary brain tumors, whose aggressive forms are glioblastomas (high grade gliomas). Common treatment of glioblastomas is concomitant chemotherapy and radiotherapy (RT). Volumes considered for RT are defined from T1 weighted images to which security (but not optimal) margins are added to cover possible tumoral infiltration. In this context, metabolite quantification could be a precious marker to obtain a better delineation of the tumor invasion and a characterization of RT adverse effects in normal brain tissue and in tumor. Metabolic information is brought by spectroscopy imaging. However, intra and inter-subjects comparison could only be achieved with normalized signal CSI maps. The aim of this study is validate a fast method of normalization and to determine quantification in tumors based on CSI normalization for water content. Material and methods 3 sequences (T2*, XEP[1] and DESPOT1 [2]) for the water content determination and CSI sequence were acquired at 3T (Siemens Verio system), on a phantom containing NAA and different concentrations of deuterium and on five healthy volunteers, using a 32-channel receiver head coil. CSI data normalization was realized using the method [3] correcting non-water suppressed CSI by proton-density ( ρ ) MRI. Results Phantom: T1, ρ and absolute concentration of NAA were found similar to theoretical calculations. Volunteers A good agreement was achieved between T1, ρ and absolute concentration of metabolites between published values and mean values found on volunteers in different regions. A patient analysis is in work-in-progress. Conclusion This combination yields to a real benefit for water spectrum correction and could be applied in clinical protocol to obtain signal normalization of metabolites (acquisition time = 9 mn) even in the presence of brain disorder which water content cannot be directly known.