ZTE imaging of tight sandstone rocks at 9.4 T — Comparison with standard NMR analysis at 0.05 T

Analysis of ZTE MRI application to sandstone and carbonate

“…Some NMR methods are not new to geological media characterization, but NMR's evolving versatility offers significant advantages. For instance, time‐domain NMR (TD‐NMR) data can be collected at low‐field strength (0.05 T) 1,3,4 . With this low field, the induced internal gradients that compromise NMR signals at higher field strength are minimized.…”

“…However, TD‐NMR spectra are known to have poor signal‐to‐noise ratios (S/N). The low field can also make it challenging to detect signals with very short (ns) transverse‐relaxation times ( T 2 ) 1,3 . Despite these drawbacks, TD‐NMR often serves as complimentary technique to MRI methods in that the former can determine volume of water within the sample, T 2 relaxation distributions and diffusion measurements on a relatively fast timescale.…”

“…Despite these drawbacks, TD‐NMR often serves as complimentary technique to MRI methods in that the former can determine volume of water within the sample, T 2 relaxation distributions and diffusion measurements on a relatively fast timescale. Single‐point imaging (SPI) can be performed at low magnetic field, but requires long acquisition times and is often impractical especially for high‐resolution imaging 3,5 …”

“…Zero Echo Time (ZTE) is a pulse sequence that has been used for image collection of a variety of porous media. This pulse sequence uses a smaller excitation flip angle (5°), constant gradients and radial k ‐space encoding techniques 1,3,4,8‐10 . When compared to the more common pulse sequences that use 90°‐flip angles, the 5°‐flip angle used in ZTE allows for a much shorter pulse time, leading to less relaxation of the magnetization before the receiver is switched on.…”

“…This technique has been used in multiple fields such as imaging tissues with T 2 value on the μs scale in animal bones and human teeth 2,9,10 . The ZTE pulse sequence has also been applied to image porous media such as dolomite, reef reservoirs and sandstone 1,3,4,10 …”