Tracked ultrasound calibration studies with a phantom made of LEGO® bricks

Consortium research supervisor: Gabor Fichtinger PURPOSE: Real-time tracked ultrasound imaging is a non-invasive and safe approach to facilitate needle-based interventions such as biopsy, drug delivery and surgical ablation. These procedures require a degree of accuracy maintained by an accurate and consistent spatial and temporal calibration that relates the image pixels of the ultrasound to the coordinate system of the tracked probe. In this study, spatial calibration of tracked ultrasound was compared by using a calibration phantom made of LEGO® bricks [1] and two 3-D printed N-wire phantoms METHODS: The accuracy and variance of calibrations were compared under a variety of operating conditions. Twenty trials were performed using an electromagnetic tracking device with a linear probe and three trials were performed using varied probes, varied tracking devices and the three aforementioned N-wire phantoms shown in figure 1. The accuracy and variance of spatial calibrations found through the standard deviation and error of the 3-D image reprojection were used to compare the calibrations produced from the phantoms. CONCLUSION: Given that the phantom made of LEGO® bricks is significantly less expensive, more readily available, and more easily modified than precision-machined N-wire phantoms, it prompts to be a viable calibration tool especially for quick laboratory research and proof of concept implementations of tracked ultrasound navigation