Motion-corrected ²³ Na MRI of the human brain using interleaved ¹ H 3D navigator images

To evaluate the feasibility of motion correction for sodium (²³ Na) MRI based on interleaved acquired 3D proton (¹ H) navigator images.

A 3D radial density-adapted sequence for interleaved ²³ Na/¹ H MRI was implemented on a 7 Tesla whole-body MRI system. The ¹ H data obtained during the ²³ Na acquisition were used to reconstruct 140 navigator image volumes with a nominal spatial resolution of (2.5 mm)³ and a temporal resolution of 6 s. The motion information received from co-registration was then used to correct the ²³ Na image dataset, which also had a nominal spatial resolution of (2.5 mm)³ . The approach was evaluated on six healthy volunteers, whose motion during the scans had different intensities and characteristics.

Interleaved acquisition of two nuclei did not show any relevant influence on image quality (SNR of 13.0 for interleaved versus 13.2 for standard ²³ Na MRI and 176.4 for interleaved versus 178.0 for standard ¹ H MRI). The applied motion correction increased the consistency between two consecutive scans for all examined volunteers and improved the image quality for all kinds of motion. The SD of the differences ranged between 2.30% and 6.96% for the uncorrected and between 2.13% and 2.67% for the corrected images.

The feasibility of interleaved acquired ¹ H navigator images to be used for retrospective motion correction of ²³ Na images was successfully demonstrated. The approach neither affected the ²³ Na image quality nor elongated the scan time and can therefore be an important tool to improve the accuracy of quantitative ²³ Na MRI.