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

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PURPOSE: Dephasing gradients can be introduced within a variety of gradient-echo pulse sequences to delineate local susceptibility changes ("White-Marker" phenomenon), e.g., for the visualization of metallic interventional devices which are otherwise difficult to display. We investigated dephased balanced steady-state free precession (d-bSSFP) and compared it with similar contrast techniques: dephased RF-spoiled fast low-angle shot (d-FLASH) and dephased steady-state free precession (d-SSFP). METHODS: = 0.55 T. Model accuracy was evaluated by comparing the measured artifact size (for TEs between 3.4 ms and 50 ms) and the signal magnitude to the model prediction. RESULTS: While positive contrast artifacts for d-FLASH and d-SSFP are axisymmetric with respect to the generating object, for d-bSSFP, a point-symmetric susceptibility artifact arises for a cylindrical needle due to the characteristic signal formation. The observed d-bSSFP artifact size was in accordance with the model (error < 1 mm). Measured (predicted) cumulated artifact signal was 1.13 ± 0.07 (1.27) times higher and 5.9 ± 0.4 times higher than the d-SSFP and d-FLASH cumulated artifact signal, respectively. In contrast to d-SSFP, the d-bSSFP artifact was robust against banding artifacts. CONCLUSION: d-bSSFP contrast is well described by the introduced model. Positive contrast artifacts show higher cumulated signal magnitude, symmetry, and homogeneity compared with d-FLASH and d-SSFP and can therefore improve device visualization and potentially device localization.

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