Abstract
PurposeIn this paper we compared two different 3D ultrasound (US) modes (3D free-hand mode and 3D wobbler mode) to see which is more suitable to perform the 3D-US/3D-US registration for clinical guidance applications. The typical errors with respect to their impact on the final localization error were evaluated step by step.MethodsMulti-point target and Hand-eye calibration methods were used for 3D US calibration together with a newly designed multi-cone phantom. Pointer based and image based methods were used for 2D US calibration. The calibration target error was computed by using a different multi-cone phantom. An egg-shaped phantom was used as ground truth to compare distortions for both 3D modes along with the measurements of the volume. Finally, we compared 3D ultrasound images acquired by 3D wobbler mode and 3D free-hand mode with respect to their 3D-US/3D-US registration accuracy using both, phantom and patient data. A theoretical step by step error analysis was performed and compared to empirical data.ResultsTarget registration errors based on the calibration with the 3D Multi-point and 2D pointer/image method have been found to be comparable (∼1mm). They both outperformed the 3D Hand-eye method (error >2mm). Volume measurements with the 3D free-hand mode were closest to the ground truth (around 6% error compared to 9% with the 3D wobbler mode). Additional scans on phantoms showed a 3D-US/3D-US registration error below 1 mm for both, the 3D free-hand mode and the 3D wobbler mode, respectively. Results with patient data showed greater error with the 3D free-hand mode (6.50mm − 13.37mm) than with the 3D wobbler mode (2.99 ± 1.54 mm). All the measured errors were found to be in accordance to their theoretical upper bounds.ConclusionWhile both 3D volume methods showed comparable results with respect to 3D-US/3D-US registration for phantom images, for patient data registrations the 3D wobbler mode is superior to the 3D free-hand mode. The effect of all error sources could be estimated by theoretical derivations.
Highlights
Three dimensional (3D) ultrasound (US) imaging is a promising approach for fast and non invasive visualisation in clinical environment
Target registration errors based on the calibration with the 3D Multi-point and 2D pointer/ image method have been found to be comparable (*1mm)
Volume measurements with the 3D free-hand mode were closest to the ground truth
Summary
Three dimensional (3D) ultrasound (US) imaging is a promising approach for fast and non invasive visualisation in clinical environment. Compared to two dimensional (2D) images, the 3D presentation of the entire structure of an organ allows for a more intuitive orientation, repeatability of region of interest (ROI), and fusion with other 3D image modalities [1]. In this research study we compared two particular 3D-US reconstruction methods having in mind applications in image guidance [4, 5]. Our sample in-vivo images are abdominal prostate images because US-guided prostate therapy and US-guided prostate biopsy are among the most common applications for image guidance [6, 7, 8]
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