Abstract:

Purpose of Z-string-beads phantom design is to high precision calibration define the spatial relationship between the ultrasound (US) image plane and an external tracking device attached to the US probe. The phantom consists of accurately located beads and two layers of Z-string planar arrays. The beads can rapidly guide the user to accurate probe orientation for imaging when the US image plane is coincident with the beads plane. Then calculate all scales of every two distances between two neighboring imaging points of all beads in the scan plane, and select the special method to correct the manual coordinates of the imaging points according to the scales of distances between two beads in the phantom coordinate system. The calibration parameters are calculated by matching of homologous points in the image and the magnetic tracking device. Thus the 2-D US image can be converted into 3-D US coordinates. The results show that this method can improve the calibration efficiency the calibration procedure faster than other more complex methods and the calibration precision and reconstruction accuracy of the 3-D US system are similar to those. The material and the construction of the phantom are simplified and can reduce the interactions during the phantom imaging, so an efficient and rapid 3-D calibration method for freehand 2-D US is obtained. The calibration experiments are demonstrated with a magnetic locator, but the method could be suitable for other tracking devices.

Key words: 3D location, 3-D ultrasound freehand scanning, guided phantom, magnetic tracking, ultrasound image calibration