T selective π Echo-Planar Imaging for porous media MRI.

The π Echo Planar Imaging (PEPI) method has recently been modified to permit proton density imaging of fluids in porous media with moderate T and short T signal components. In many applications, it is desirable to discriminate multiple T components within each image voxel. T selective imaging is explored in this paper through adiabatic inversion as a magnetization preparation with PEPI readout. When prior information of the sample relaxation times is known, responses of different species to broadband adiabatic inversion pulses can be predicted by Bloch equation simulation. Different relaxation components can be acquired by combining the images with and without inversion preparation pulses. T weighting can be easily introduced in the PEPI sequence by shifting the spatial encoding gradients based on its spin echo nature. T decay curves can be extracted for each image voxel from a series of T weighted images and spatially resolved T distributions can be generated. This method is reliable but slow. The two methods were implemented to image porous media samples with PEPI the common basis of spatial resolution. The results of both methods agree remarkably well.