Open-LIFU Transducer Localization Accuracy Study

This report describes the use of photogrammetric reconstruction for localizing the position of an ultrasonic transducer on a subject, and co-registering the transducer position with the subject's MRI image. Openwater's cell phone application was used to acquire images of a mannequin wearing an Open-LIFU 2X headset at a known position; photogrammetry meshes were reconstructed from those images and co-registered with the mannequin's MRI and with a model of the transducer, determining the transducer position relative to the subject's internal anatomy.

Two reconstruction methods were tested across 30 scans: an online method (Apple Composer Pro) and an offline open-source method (Meshroom / AliceVision). The online method produced average errors of less than 1 mm in the right, anterior, and superior directions; the offline method produced average errors of up to approximately 3 mm. Standard deviations across repeated trials were 1-2 mm for both methods, indicating good repeatability. Both fall within the 1-3 mm range typically reported for clinical neuronavigation systems, supporting phone-based photogrammetry as a sufficient method for subject registration in the Open-LIFU desktop application.