On model-based MR spectroscopic imaging

In this paper, we analyze the model-based reconstruction framework in MR spectroscopic imaging and derive an exact expression for the reconstruction error. Based on the insight provided by the analysis, we propose two modifications: (a) we introduce a new echo-planar imaging sequence to acquire more Fourier samples in the same scan duration, since increasing the number of Fourier samples will decrease the bias in the reconstructions. We then use the model-based framework to effectively compensate for the corresponding loss in signal to noise ratio/measurement, (b) we observe that model misfit can affect the reconstructions in constrained imaging much more seriously than standard Fourier reconstruction. We propose a data adaptive basis selection procedure to reduce the misfit, without significantly increasing the noise variance. Both these improvements together enable high-resolution reconstructions that are more robust and with fewer artifacts as compared to reduced encoding, without increasing the scan time.