Motion reduction for quantitative brain sodium MR imaging with a navigated flexible twisted projection imaging...

Area of Science:

• Magnetic Resonance Imaging
• Biophysics
• Medical Physics

Background:

• Quantitative measurement of tissue sodium concentration (TSC) is vital for assessing tissue cell volume fraction, aiding in monitoring tumor treatment responses and neurodegeneration.
• Sodium MRI (SMRI) faces challenges due to low signal detection sensitivity and the need for long repetition times, though techniques like twisted projection imaging (TPI) have reduced acquisition times.
• Patient motion, even in cooperative subjects, can significantly degrade the accuracy of quantitative SMRI.

Purpose of the Study:

• To enhance the robustness of quantitative sodium MRI by minimizing the impact of patient motion.
• To develop a motion correction strategy for quantitative SMRI without increasing acquisition time.

Main Methods:

• A novel method was developed involving spatial encoding of a lower-resolution navigator echo after the main quantitative image data acquisition, using flexTPI readout trajectories.
• Navigator images, acquired at higher temporal (∼1 min) but lower spatial (8 mm) resolution, were used to extract translational and rotational motion parameters assuming rigid-body motion.
• These motion parameters were then applied to align k-space data during the acquisition of quantitative images, correcting for subject movement.

Main Results:

• The proposed method significantly reduced image blurring caused by random head motion up to 7° between navigator acquisitions.
• The navigator echo acquisition occurred at no additional time penalty, maintaining the overall efficiency of the quantitative SMRI.
• Successful alignment of k-space data based on navigator-derived motion parameters demonstrated the effectiveness of the correction technique.

Conclusions:

• The developed navigator-based motion correction method improves the accuracy and robustness of quantitative sodium MRI.
• This technique offers a practical solution to motion artifacts in SMRI, enhancing its utility in clinical and research applications.
• The approach enables more reliable TSC measurements, supporting better diagnostic and prognostic capabilities in various medical conditions.