Fast chemical shift mapping with multiecho balanced SSFP

Abstract

A method is proposed that provides spectroscopic images with high spatial resolution and moderate spectral resolution at very short total data acquisition times. Balanced steady-state free precession (bSSFP, TrueFISP, FIESTA, b-FFE) is combined with a multiecho readout gradient and frequency-sensitive reconstruction such as Fourier reconstruction known from echo-planar spectroscopic imaging (EPSI) or matrix inversion. Balanced SSFP imaging requires short repetition times to minimize banding artefacts, thereby restricting the achievable frequency resolution. Two-dimensional (2D) high-resolution spectroscopic images were produced of three 1H resonances (water, acetone and fat) on phantoms and water/fat separation in vivo within 1-2 s. Additionally, fast 31P spectroscopic images were acquired from a phantom consisting of two resonances within 195 ms. Frequency-sensitive reconstruction of multiecho bSSFP data can provide spectroscopic images with high spatial and temporal resolution while the frequency resolution is moderate at around 100 Hz. The method can also separate more than three resonances, allowing for hetero-nuclei metabolite mapping, for example 13C and 31P.