Unraveling contributions to the Z‐spectrum signal at 3.5 ppm of human brain tumors

Abstract

AbstractPurposeTo evaluate the influence of the confounding factors, direct water saturation (DWS), and magnetization transfer contrast (MTC) effects on measured Z‐spectra and amide proton transfer (APT) contrast in brain tumors.MethodsHigh‐grade glioma patients were scanned using an RF saturation‐encoded 3D MR fingerprinting (MRF) sequence at 3 T. For MRF reconstruction, a recurrent neural network was designed to learn free water and semisolid macromolecule parameter mappings of the underlying multiple tissue properties from saturation‐transfer MRF signals. The DWS spectra and MTC spectra were synthesized by solving Bloch‐McConnell equations and evaluated in brain tumors.ResultsThe dominant contribution to the saturation effect at 3.5 ppm was from DWS and MTC effects, but 25%–33% of the saturated signal in the gadolinium‐enhancing tumor (13%–20% for normal tissue) was due to the APT effect. The APT# signal of the gadolinium‐enhancing tumor was significantly higher than that of the normal‐appearing white matter (10.1% vs. 8.3% at 1 μT and 11.2% vs. 7.8% at 1.5 μT).ConclusionThe RF saturation‐encoded MRF allowed us to separate contributions to the saturation signal at 3.5 ppm in the Z‐spectrum. Although free water and semisolid MTC are the main contributors, significant APT contrast between tumor and normal tissues was observed.