Magic sandwich echo relaxation mapping of anisotropic systems

The main objective of this article was (i) to refocus the residual dipolar and quadrupolar interactions in anisotropic tissues employing magic sandwich echo (MSE) imaging and to compare the results with that of conventional spin-echo (SE) imaging, and (ii) to quantify MSE relaxation and dispersion characteristics in bovine Achilles tendon and compare with spin-lattice relaxation time constant in the rotating frame (T_1ρ). Magic sandwich echo weighted images are ∼75-100% higher in signal-to-noise ratio than the corresponding T₂-weighted images. Magic sandwich echo relaxation times varied from 13±2 to 19±3 ms (mean±S.D.), depending upon the structural location of tendon. T₂ relaxation times only varied from 4±1 to 10±3 ms (mean±S.D.) on the same corresponding locations. Magic sandwich echo provides ∼100% enhancement in relaxation times compared to T₂. Preliminary results based on bovine Achilles tendon and cartilage specimens suggest that the MSE technique has potential for refocusing residual dipolar as well as quadrupolar interactions in anisotropic systems and yields higher intensities than conventional SE imaging as well as T_1ρ-encoded imaging, especially at low-burst pulse amplitudes (250 and 500 Hz).