Reducing Noise Induced by Cardiac Pulsatility in Brain Maps of R2* and Magnetic Susceptibility Using Tailored k-space Sampling | JoVE Visualize

Area of Science:

Magnetic Resonance Imaging (MRI)
Medical Physics
Neuroimaging

Background:

Gradient-echo MRI sequences are susceptible to signal instabilities caused by cardiac pulsation.
These instabilities, particularly cardiac-induced noise, can affect the accuracy of R2* and magnetic susceptibility (χ) brain maps.
Accurate R2* and χ mapping is crucial for diagnosing various neurological conditions.

Purpose of the Study:

To introduce and evaluate novel k-space sampling strategies for mitigating cardiac-induced noise in brain R2* and χ maps.
To compare the effectiveness of a Cartesian trajectory with Spiral PRofile (CASPR) acquisition and cardiac triggering against standard linear trajectories.
To assess the impact of these strategies on map variability, scan time, and artifact reduction.

Main Methods:

Two k-space sampling strategies were developed: CASPR, which adapts data acquisition based on local noise levels, and cardiac triggering for real-time synchronization.
Data from 10 healthy volunteers were acquired using both strategies and a standard linear trajectory, with four repetitions for variability assessment.
Variability across repetitions, scan time, and aliasing artifacts from pulsating vessels were quantified and compared.

Main Results:

CASPR significantly reduced the variability of R2* and χ maps across repetitions by 22% and 16% brain-wide, respectively, compared to linear trajectories.
Reductions in variability exceeded 30% in inferior brain regions with CASPR, despite a 14% increase in scan time.
CASPR also effectively reduced aliasing artifacts from pulsating blood vessels, while cardiac triggering showed no significant reduction in map variability.

Conclusions:

The CASPR k-space sampling strategy is effective in mitigating cardiac-induced noise for improved brain R2* and χ mapping in MRI.
CASPR offers enhanced accuracy and reduced artifacts, particularly in brain regions susceptible to pulsatile motion.
Cardiac triggering, in its current implementation, does not provide significant benefits for reducing cardiac-induced noise in these specific MRI parameters.