Objective: To test the accuracy of point- and plane- registration of real-time sonography fused with MRI in a phantom.
Methods: A sonography prototype system (LOGIQ, GE Healthcare) with incorporated software for fusion imaging was used to test three methods of co-registration in a phantom: near and far points and plane registration. Three well-defined points were used to measure the accuracy. Accuracy was calculated as root mean square deviation (RMSD), measured in millimeters, and the time required to complete the registration was registered. Two observers, one with prior knowledge to the system, each did 30 co-registrations for each method, adding up to 180 co-registrations. The statistical significance of the difference between the methods and the observers was calculated using analysis of variance (two-way ANOVA).
Results: Co-registration was significantly more accurate when co-registering at the measuring points than when using points away from the measuring points or planes (p<0.0001). The mean calculated RMSD in the first series (co-registration from measuring points) was 1.3 mm (95% CI: 1.1-1.5 mm), in the second series (co-registration from points away from measuring points) 4.0 mm (95% CI: 3.2-4.8 mm), in the third series (co-registration from planes) 3.8 mm (95% CI: 3.2-4.4 mm).
Conclusion: Image fusion involving real-time sonography has a high accuracy and is easy to use in a phantom. Working within the area given by the co-registration points optimizes the accuracy.