An in-vivo approach to quantify in-MRI head motion tracking accuracy: comparison of markerless optical tracking versus fat-navigators.

PURPOSE

Head-motion tracking and correction remains a key area of research in MRI, but the lack of rigorous evaluation approaches hinders their optimization and comparison. This study introduces an in-vivo framework to assess head-motion tracking methods and compares a markerless optical system (MOS) to a fat-signal navigator (FatNav).

METHODS

Six participants underwent 3T brain MRI using a T1-weighted (T1w) pulse-sequence with a fat-navigator module. Participants performed head-rotations of 2° or 4°, each visually guided by MOS feedback around a single primary axis (X or Z). MOS and FatNav estimations were evaluated against T1w-images rigid-registration, as gold-standard, across seven different head positions.

RESULTS

The MOS outperformed FatNav in tracking primary head-rotations and unintentional translations, while FatNav showed marginally better accuracy to subtle secondary rotations. Neck-masking of fat-navigators further improved FatNav estimates of pitch rotations. The quality of T1w-images collected motionless and with head-rotations of 2° and 4° were also investigated. The MOS outperformed FatNav in restoring image fidelity, evidenced by higher structural similarity index, peak signal-to-noise ratio and focus measure. However, image quality evaluation lacked sensitivity to subtle improvements in FatNav with neck-masking.

CONCLUSION

The proposed in-vivo framework enables direct quantitative evaluation of intra-MRI head-motion tracking methods. MOS outperformed FatNav in estimating primary head rotations and unintentional translations, with a moderate FatNav advantage for small unintentional secondary rotations. Quality assessment of the motion-corrected images confirmed the superiority of MOS in practice. However, it proved less sensitive than direct comparison of movement estimates in detecting the nuanced improvements of FatNav with neck-masking.