Registering pre- and postresection 3-dimensional ultrasound for improved visualization of residual brain tumor

The goal of this study was to find a registration technique to improve the alignment of ultrasound images taken before and after brain tumor resection. Validation was performed on 16 tumor cases in 2 ways: (1) manually selected tags on pre- and postresection ultrasounds were used to compute the mean Euclidean distance between corresponding points in the 2 volumes before and after registration; and (2) the surgeon was asked to rank and rate the quality of the alignment before and after registration. The mean distance was 2.7 mm after a rigid registration and 1.7 mm after a nonlinear registration. Of 16 cases, the surgeon determined that initially only 2 were satisfactorily aligned; after the rigid registration, 5 were satisfactory, and after the nonlinear registration, 13 were satisfactory. According to both the distance and the ranking metrics, the nonlinear registration approach significantly improved the alignment of the ultrasound images.