Advantage of sampling density weighted apodization over postacquisition filtering apodization for sodium MRI of the human brain

Abstract

For sodium imaging of the human brain, Gibbs' ringing can degrade image appearance and confound image analysis; k-space filtering is generally required. In this work, the signal to noise ratio (SNR) advantage of sampling density weighted apodization (SDWA) over uniform k-space sampling with postacquisition filtering apodization (UPFA) is quantified for sodium three-dimensional (3D) twisted projection imaging (TPI) of the human brain. A direct comparison was conducted with the creation of two TPI projection data sets (each with an equal number of projections of equal length): one generating uniform sampling density, and the other a "generalized Hamming" sampling density that conformed to 3D-TPI constraints for full k-space sampling. In this work it is shown theoretically, and then experimentally with sodium imaging of the human brain, that an SNR advantage of 17% is associated with the use of SDWA over UPFA for the filter presented, along with a significant noise-coloring benefit.