Simultaneous quantitative susceptibility mapping (QSM) and R2* for high iron concentration quantification with 3D...

Area of Science:

• Magnetic Resonance Imaging
• Biomedical Engineering
• Medical Physics

Background:

• Quantitative susceptibility mapping (QSM) is crucial for detecting and characterizing iron deposition in tissues.
• High concentrations of iron oxide nanoparticles pose challenges for accurate QSM and R2* measurements due to susceptibility effects.
• 3D ultrashort echo time (UTE) sequences offer potential for improved imaging in such scenarios.

Purpose of the Study:

• To evaluate the echo time dependence of 3D UTE quantitative susceptibility mapping (QSM) and R2* measurements.
• To determine the optimal echo time parameters for accurate QSM and R2* in the presence of high iron concentrations.
• To compare the sensitivity of UTE-QSM and R2* to echo time selection.

Main Methods:

• A phantom study was conducted using a 3D UTE Cones sequence with iron concentrations ranging from 2 to 22 mM.
• Simultaneous QSM processing with morphology-enabled dipole inversion (MEDI) and R2* single exponential fitting were performed.
• The dependence of UTE-QSM and R2* on echo spacing (ΔTE) and first echo time (TE1) was investigated.

Main Results:

• A linear relationship between UTE-QSM and iron concentration was observed up to 22 mM with TE1 = 0.032 ms and ΔTE < 0.1 ms.
• A linear relationship between R2* and iron concentration was observed up to 22 mM only when TE1 < 0.132 ms and ΔTE < 1.2 ms.
• UTE-QSM with MEDI processing demonstrated a strong dependence on ΔTE and TE1, particularly at high iron concentrations.

Conclusions:

• UTE-QSM is more sensitive to echo time selection than R2* measurements.
• Achieving accurate QSM in the presence of high iron concentrations necessitates an ultrashort first echo time (TE1) and a small echo spacing (ΔTE).
• Optimized echo time parameters are critical for reliable quantitative susceptibility mapping in high iron environments.