Positive susceptibility-based contrast imaging with dephased balanced steady-state free precession

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Medical Device Visualization
• Artifact Characterization

Background:

• Dephasing gradients enhance visualization of metallic interventional devices by delineating local susceptibility changes.
• Traditional gradient-echo sequences face challenges in displaying metallic implants due to susceptibility artifacts.

Purpose of the Study:

• To investigate dephased balanced steady-state free precession (d-bSSFP) for improved visualization of metallic devices.
• To compare d-bSSFP with dephased RF-spoiled fast low-angle shot (d-FLASH) and dephased steady-state free precession (d-SSFP).

Main Methods:

• Formulated a signal model to describe positive contrast in d-bSSFP.
• Verified the model using an MR-compatible aspiration needle in a water phantom at 0.55 T.
• Evaluated model accuracy by comparing measured and predicted artifact size and signal magnitude.

Main Results:

• d-bSSFP generates point-symmetric susceptibility artifacts, unlike the axisymmetric artifacts of d-FLASH and d-SSFP.
• The observed d-bSSFP artifact size closely matched model predictions (error < 1 mm).
• d-bSSFP artifacts exhibited significantly higher cumulated signal magnitude (1.13-5.9 times) and robustness against banding artifacts compared to d-SSFP and d-FLASH.

Conclusions:

• The developed signal model accurately describes d-bSSFP contrast.
• d-bSSFP produces positive contrast artifacts with superior signal magnitude, symmetry, and homogeneity.
• These characteristics enhance metallic device visualization and localization capabilities.