Today, the main focus of the Program in Non-Fourier and RF-Encoding is the development of the PSF-Choice method. PSF-Choice is a truly hybrid imaging method that combines the simplicity of Fourier encoding with the flexibility of non-Fourier encoding (slide 22). PSF-Choice is especially useful for applications such as spectroscopic imaging (slide 29) in which only a very few phase encodes are acquired and ringing artifact can be a serious problem. PSF-Choice combines partial 2D RF excitations with standard phase-encoding gradients. In fact, with this method, phase encoding proceeds as usual and reconstruction in PSF-Choice encoding directions involves a simple Fourier transform.
In PSF-Choice, however, a unique RF excitation is performed on each new encode such that over multiple excitations, a "virtual" excitation profile (slide 10) with the desired shape (which is usually Gaussian) results. The point-spread-function (or PSF) of the reconstructed result depends only on the RF "virtual" excitation profile. With this approach, arbitrarily shaped PSF’s such as Gaussians can be achieved, eliminating ringing artifact due to the side lobes associated with the sinc-shaped PSF of standard Fourier encoding.
PSF-Choice has been applied to MR spectroscopic imaging in the prostate where lipid contamination of spectra due to ringing artifact can be a serious problem. PSF-Choice was initially implemented in only one MR spectroscopic direction; however, current work is focusing on a practical 2-dimensional implementation with echo-planar readouts being used for the third dimension (slide 43). PSF Choice Slides (pdf)
