Clean demarcation of cartilage tissue 23Na by inversion recovery

Abstract

Monitoring the sodium concentration in vivo using 23 Na MRI can be an important tool for assessing the onset of tissue disorders. Practical clinical 23 Na MRI methods furthermore often do not allow one to use sufficiently small voxel sizes such that only the tissue of interest is seen, but a large signal contamination can arise from sodium in synovial fluid. Here we demonstrate that applying an inversion recovery (IR) technique allows one to distinctly select either the cartilage-bound or the free sodium for visualization in an image. The results are validated both ex vivo and in vivo.

Selective detection of ordered sodium signals by a jump-and-return pulse sequence

“…1(b)). This feature makes the QJR sequence more favorable for MRI than other 23 Na contrast methods, such as the inversion recovery (IR) [14] and quadrupolar filter by nutation (QFN) [15], which excite both the central and satellite peaks. On the other hand, the QJR sequence rather selects a narrow range of the quadrupolar coupling constants, compared with the IR and QFN methods (see Fig.…”

“…Hence, the sodium concentration in the cartilage can be a direct reporter of degenerative joint diseases such as OA and DDD. Techniques for modifying 23 Na contrast have been developed in order to cleanly separate ordered sodium ions (in cartilage) from free sodium ions (in non-cartilage tissues) on high-resolution 23 Na images both in vivo and ex vivo [12,13,15,14]. In a recent communication, we presented a new 23 Na contrast based on a pulse sequence optimally exciting the central peak of ordered sodium ions [16].…”

T1-Weighted Sodium MRI of the Articulator Cartilage in Osteoarthritis: A Cross Sectional and Longitudinal Study

“…Fluid suppression via inversion recovery in sodium sequences [13] can effectively remove the confounding synovial fluid signal, though at the penalty of reduced SNR in the cartilage signal. The sodium concentration in the fluid is about half that of the cartilage, even so, fluid suppression does result in higher sodium values [16].…”

“…Current sodium MRI methods [10–12] have focused on sodium-density weighted imaging, requiring long TRs in order to assure full T1 recovery of all species. Further, inversion-recovery (IR) based sodium MRI has now been explored to remove the synovial fluid component [13–15] which can affect the measured cartilage sodium concentration by the partial voluming effect of the low resolution achievable in sodium MRI. The major drawback of these IR methods are a 40% loss of SNR [15], or equivalently half the SNR efficiency [16], which requires twice the scan time in order to recover the lost SNR.…”

Reduction of inhomogeneity effects in triple-quantum-filtered sodium imaging

“…These reagents are toxic, however, and cannot be applied to studies with humans. A second, non-invasive approach utilizes differences of relaxation rates in different physiological compartments for selective signal suppression via inversion recovery [7,8]. In this case, only one type of environment with one specific decay rate of the 23 Na transversal magnetization can be suppressed at once and regions with similar decay rates might be unintentionally suppressed.…”