Three-Dimensional Digital Sonomicrometry: Comparison with Biplane Radiography

This paper describes a three-dimensional (3D) digital sonomicrometry approach for locating and tracking 3D objects. A commercial digital sonomicrometry system was employed to measure scalar distances between omnidirectional sonomicrometers. 3D coordinates were then derived using the statistical technique of multidimensional scaling (MDS). 3D digital sonomicrometry was directly compared with biplane radiography of the ultrasound crystals for estimation of 3D distances in static phantoms and in vivo using an experimental canine preparation. An excellent correlation (r=0.992) was seen when comparing intercrystal distances derived from biplane radiography and sonomicrometry 3D coordinate data in the gel phantom. A Bland-Altman analysis shows that the average difference in coordinate determined distance between these two different methodologies was only 0.63±0.46 mm, over a range of inter-crystal distances of 3.14 to 17.28 mm. In the in vivo canine preparation, the correlation between the sonomicrometry derived and biplane derived distances was also excellent (r=0.992) with a slope of 1.05 and an intercept of 0.06. The Bland-Altman analysis shows that the average difference in coordinate determined distance between these two different methodologies was only 0.78±0.74 mm, over a range of inter-crystal distances of 2.90 to 27.66 mm. We have demonstrated the feasibility of accurately measuring scalar distances using 3D digital sonomicrometry. Digital sonomicrometry combines high spatial and temporal resolution with availability and portability to accurately measure distances in a closely packed array of implanted piezoelectric crystals.