Whole-brain snapshot CEST imaging at 7 T using 3D-EPI.

PURPOSE: The aim of this work is to develop a fast and robust CEST sequence in order to allow the acquisition of a whole-brain imaging volume after a single preparation block (snapshot acquisition). METHODS: A 3D-CEST sequence with an optimized 3D-EPI readout module was developed, which acquires the complete k-space data following a single CEST preparation for 1 saturation offset. Whole-brain mapping of the Z-spectrum with 2 mm isotropic resolution is achieved at 68 saturation frequencies in 5 minutes (4.33 s per offset). We analyzed the B1 distribution in order to optimize B1 correction and to provide accurate CEST quantification across the whole brain. RESULTS: We obtained maps for 3 different CEST contrasts from 4 healthy subjects. Based on our B1 distribution analysis, we conclude that 3 B1 sampling points allow for sufficient compensation of B1 variations across most of the brain. Two brain regions, the cerebellum and the temporal lobes, are difficult to quantify at 7 T due to very low B1 that was achieved in these regions. CONCLUSIONS: The proposed sequence enables robust acquisition of 2 mm isotropic whole-brain CEST maps at 7 Tesla within a total scan time of 16 minutes.