Quantitative abdominal sodium MRI combined with 32-channel proton pTx MRI at 7 Tesla in a large field-of-view

To combine large field-of-view abdominal ${\hspace{0.17em}}^{1}H$ and quantitative sodium ( ${\hspace{0.17em}}^{23}\text{Na}$ ) MRI in the same position at 7 T to enable the quantification of the tissue sodium concentration via ${\hspace{0.17em}}^{23}\text{Na}$ MRI and the anatomical assignment in ${\hspace{0.17em}}^{1}H$ images without repositioning in several tissues and organs at once.

A custom-built ${\hspace{0.17em}}^{23}\text{Na}$ birdcage coil and reference vial setup together with a 32-channel ${\hspace{0.17em}}^{1}H$ pTx array were employed at 7 T to allow dual-nuclei MRI in the same position for a field-of-view (FOV) of $(400\times 400\times 400){\text{mm}}^3$ . $T_1$ relaxation effects in the reference vials and phantom were corrected, $B_1^{+}$ maps were measured, and $B_1^{-}$ maps were simulated to correct the acquired ${\hspace{0.17em}}^{23}\text{Na}$ data in post-processing. These corrections were evaluated in a phantom and then applied in vivo in three healthy volunteers.

In the phantom, it was demonstrated that proton and quantitative sodium MR images share the same large FOV. Phantom measurements showed an improved sodium concentration accuracy after the performed corrections. Large FOV ${\hspace{0.17em}}^{1}H$ and quantitative ${\hspace{0.17em}}^{23}\text{Na}$ in vivo MRI was demonstrated in three healthy volunteers.

This work shows the feasibility of combined ${\hspace{0.17em}}^{1}H$ and quantitative ${\hspace{0.17em}}^{23}\text{Na}$ imaging at 7 T in a large FOV both under free breathing in $\le 47\min$ , laying the ground work for an accurate evaluation of the tissue sodium concentration in several organs at once.