Abstract
Purpose: Three-dimensional (3D) intraoperative ultrasound may be easier
to interpret when used in combination with less noisy preoperative
image data such as CT. The purpose of this study was to evaluate
the use of preoperative image data in a 3D ultrasound-based navigation
system specially designed for minimally invasive abdominal surgery.
A prototype system has been tested in patients with aortic aneurysms
undergoing clinical assessment before and after abdominal aortic
stent-graft implantation. Methods: All patients were first imaged
by spiral CT followed by 3D ultrasound scanning. The CT volume was
registered to the patient using fiducial markers. This enabled us
to compare corresponding slices from 3D ultrasound and CT volumes.
The accuracy of the patient registration was evaluated both using
the external fiducial markers (artificial landmarks glued on the
patient's skin) and using intraoperative 3D ultrasound as a measure
of the true positioning of anatomic landmarks inside the body. Results:
The mean registration accuracy on the surface was found to be 7.1
mm, but increased to 13.0 mm for specific landmarks inside the body.
CT and ultrasound gave supplementary information of surrounding structures
and position of the patient's anatomy. Fine-tuning the initial patient
registration of the CT data with a multimodal CT to intraoperative
3D ultrasound registration (e.g., mutual information), as well as
ensuring no movements between this registration and image guidance,
may improve the registration accuracy. Conclusion: Preoperative CT
in combination with 3D ultrasound might be helpful for guiding minimal
invasive abdominal interventions
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