MRI-guided targeted needle placement during motion using hydrostatic actuators.

BACKGROUND: Magnetic resonance imaging (MRI) has unique advantages for guiding interventions, but the narrow space is a major challenge. This study evaluates the feasibility of a remote-controlled hydrostatic actuator system for MRI-guided targeted needle placement. METHODS: The effects of the hydrostatic actuator system on MR image quality were evaluated. Using a reference step-and-shoot method (SS) and the proposed actuator-assisted method (AA), two operators performed MRI-guided needle placement in targets (n = 12) in a motion phantom. RESULTS: The hydrostatic actuator system exhibited negligible impact on MR image quality. In dynamic targets, AA was significantly more accurate and precise than SS, with mean ± SD needle-to-target error of 1.8 ± 1.0 mm (operator 1) and 1.3 ± 0.5 mm (operator 2). AA reduced the insertion time by 50% to 80% and total procedure time by 25%, compared to SS. CONCLUSIONS: The proposed hydrostatic actuator system may improve accuracy and reduce procedure time for MRI-guided targeted needle placement during motion.

Respiratory Motion Prediction Using Fusion-Based Multi-Rate Kalman Filtering and Real-Time Golden-Angle Radial MRI.

OBJECTIVE: Magnetic resonance imaging (MRI) can provide guidance for interventions in organs affected by respiration (e.g., liver). This study aims to: 1) investigate image-based and surrogate-based motion tracking methods using real-time golden-angle radial MRI; and 2) propose and evaluate a new fusion-based respiratory motion prediction framework with multi-rate Kalman filtering. METHODS: Images with different temporal footprints were reconstructed from the same golden-angle radial MRI data stream to simultaneously enable image-based and surrogate-based tracking at 10 Hz. A custom software pipeline was constructed to perform online tracking and calibrate tracking error and latency using a programmable motion phantom. A fusion-based motion prediction method was developed to combine the lower tracking error of image-based tracking with the lower latency of surrogate-based tracking. The fusion-based method was evaluated in retrospective studies using in vivo real-time free-breathing liver MRI. RESULTS: Phantom experiments confirmed that the median online tracking error of image-based tracking was lower than surrogate-based methods, however, with higher median system latency (350 ms vs. 150 ms). In retrospective in vivo studies, 75 respiratory waveforms of target features from eight subjects were analyzed. The median root-mean-squared prediction error (RMSE) for the fusion-based method (0.97 mm) was reduced (Wilcoxon signed rank test p < 0.05) compared to surrogate-based (1.18 mm) and image-based (1.3 mm) methods. CONCLUSION: The proposed fusion-based respiratory motion prediction framework using golden-angle radial MRI can achieve low-latency feedback with improved accuracy. SIGNIFICANCE: Respiratory motion prediction using the fusion-based method can overcome system latency to provide accurate feedback information for MRI-guided interventions.