Out-of-Plane Needle Placements Using 3D Augmented Reality Protractor on Smartphone: An Experimental Phantom Study

Purpose To evaluate the accuracy of needle placement using a three-dimensional (3D) augmented reality (AR) protractor on smartphones (AR Puncture). Materials and Methods An AR protractor that can be rotated in three directions against the CT plane with angle guidance lines for smartphones was developed. The protractor center can be adjusted to an entry point by manually moving the smartphone with the protractor center fixed at the center of the screen (Fix-On-Screen) or by image tracking with a printed QR code placed at an entry point (QR-Tracking). Needle placement was performed by viewing a target line in the tangent direction with the Bull’s eye method. The needle placement errors placed by four operators in six out-of-plane directions in a phantom using a smartphone (iPhone XR, Apple, Cupertino, CA, USA) were compared with two registration methods. Results No significant difference in the average needle placement error was observed between the Fix-On-Screen and QR-Tracking methods (5.6 ± 1.7 mm vs. 6.1 ± 2.9 mm, p = 0.475). The average procedural time of the Fix-On-Screen method was shorter than that of the QR-Tracking method (71.0 ± 23.9 s vs. 98.4 ± 59.5 s, p = 0.042). Conclusion The accuracies of out-of-plane needle placements using the 3D AR protractor with the two registration methods were equally high, with short procedure times. In clinical use, the Fix-On-Screen registration method would be more convenient because no additional markers are required.