  Two different dynamic decoupling strategies, the classic CPMG and the more
recently proposed UDD protocol are compared in the context of magnetic
resonance imaging (MRI). Both sequences were implemented on a 3T human MRI
system and relaxometry was performed for a variety of tissue-mimicking agar and
agarose gels. We find that CPMG provides moderately better decoupling than
\UDD. The results are consistent with experimental noise spectra obtained from
\textit{in vivo} spectroscopy results, which suggest that the type of noise
spectra obtained would favor \CPMG. Theoretical coherence pathway analysis
further suggests that \UDD\ is more susceptible to systematic errors due to
static magnetic and radio-frequency field inhomogeneity or imperfect excitation
and refocusing pulse profiles.
