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Simultaneous 3D localization of multiple MR-visible markers in fully reconstructed MR images: proof-of-concept for
Gregor Thörmer1, Nikita Garnov, Michael Moche
1Department of Diagnostic and Interventional Radiology, Leipzig University Hospital, Leipzig, Germany.
Purpose:
To determine whether a greatly reduced spatial resolution of fully reconstructed projection MR images can be used for the simultaneous 3D localization of multiple MR-visible markers and to assess the feasibility of a subsecond position tracking for clinical purposes.
Materials And Methods:
Miniature, inductively coupled RF coils were imaged in three orthogonal planes with a balanced steady-state free precession (SSFP) sequence and automatically localized using a two-dimensional template fitting and a subsequent three-dimensional (3D) matching of the coordinates. Precision, accuracy, speed and robustness of 3D localization were assessed for decreasing in-plane resolutions (0.6-4.7 mm). The feasibility of marker tracking was evaluated at the lowest resolution by following a robotically driven needle on a complex 3D trajectory.
Results:
Average 3D precision and accuracy, sensitivity and specificity of localization ranged between 0.1 and 0.4 mm, 0.5 and 1.0 mm, 100% and 95%, and 100% and 96%, respectively. At the lowest resolution, imaging and localization took ≈350 ms and provided an accuracy of ≈1.0 mm. In the tracking experiment, the needle was clearly depicted on the oblique scan planes defined by the markers.
Conclusion:
Image-based marker localization at a greatly reduced spatial resolution is considered a feasible approach to monitor reference points or rigid instruments at subsecond update rates.
