Recently, three-dimensional (3D) rotational x-ray imaging has been combined with navigation technology, enabling direct 3D navigation for minimally invasive image guided interventions. In this study, phantom experiments are used to determine the accuracy of such a navigation set-up for a mobile C-arm with propeller motion. After calibration of the C-arm system, the accuracy is evaluated by pinpointing divots on a special-purpose phantom with known geometry. This evaluation is performed both with and without C-arm motion in between calibration and registration for navigation. The variation caused by each of the individual transformations in the calibration and registration process is also studied. The feasibility of direct navigation on 3D rotational x-ray images for functional endoscopic sinus surgery has been evaluated in a cadaver navigation experiment. Navigation accuracy was approximately 1.0 mm, which is sufficient for functional endoscopic sinus surgery. C-arm motion in between calibration and registration slightly degraded the registration accuracy by approximately 0.3 mm. Standard deviations of each of the transformations were in the range 0.15-0.31 mm. In the cadaver experiment, the navigation images were considered in good correspondence with the endoscopic images by an experienced ENT surgeon. Availability of 3D localization information provided by the navigation system was considered valuable by the ENT surgeon.
[Show abstract][Hide abstract] ABSTRACT: C-arm computed tomography is an option on a C-arm angiographic system capable of acquiring projections while rotating the C-arm around the patient and reconstructing cross-sectional images with improved contrast resolution of 5 to 10 Hounsfield units. Typical abdominal C-arm computed tomographic (CCT) images, however, exhibit artifacts with spatially varying and drifting pixel values. Considering liver tumor oncologic procedures, the aim of this study was to evaluate the accuracy of liver iodine concentration (IC) estimated from CCT images under such challenging conditions.
The proposed method estimates the IC in a region of interest (ROI) using pixel values of CCT images measured at the ROI and a nonenhanced background. Two approaches to measure the background value were tested: one approach, L-BG, measured a corresponding local background value near each ROI, and the other, G-BG, used one global background value for the entire object. The accuracy of estimations using CCT and computed tomographic scanners was evaluated; an elliptical cylinder water phantom with iodine solution inserts and seven patient data sets with transcatheter arterial chemoembolization were used.
With the least "truncation" (the edge of the object being outside the field of view) of 27 mm, the IC was accurately estimated with CCT images (n = 9; root-mean-square error [RMSE], 1.60-1.63 mg/mL; normalized RMSE, 11.8%; r(2) = 0.97; P < .001), with the true concentration ranging from 2.32 to 31.82 mg/mL. With truncations of up to 100 mm (n = 88), the estimation by L-BG remained accurate independent of the amount of truncation (RMSE, 1.58 mg/mL; normalized RMSE, 12.5%; r(2) = 0.06; P = .02), whereas the estimation by G-BG reduced the accuracy (RMSE, 4.61 mg/mL; normalized RMSE, 34.3%; r(2) = 0.10; P = .003). Clinical data (n = 37) showed that the estimation from CCT images using the L-BG method agreed well with that from computed tomographic images (RMSE, 2.86 mg/mL; normalized RMSE, 38.7%; r(2) = 0.76; P < .001).
The liver IC can be accurately estimated with abdominal CCT images.
[Show abstract][Hide abstract] ABSTRACT: C-arm based Cone-Beam CT (CBCT) imaging enables the in-situ acquisition of three dimensional images. In the context of image-guided interventions this technology potentially reduces the complexity of a procedure's workflow. Instead of acquiring the preoperative volumetric images in a separate location and transferring the patient to the interventional suite, both imaging and intervention are carried out in the same location. A key component in image-guided interventions is image to patient registration. The most common registration approach, in clinical use, is based on fiducial markers placed on the patient's skin which are then localized in the volumetric image and in the interventional environment. When using C-arm CBCT this registration approach is challenging as in many cases the small size of the volumetric reconstruction cannot include both the skin fiducials and the organ of interest. In this paper we show that fiducial localization outside of the reconstructed volume is possible if the projection images from which the reconstruction was obtained are available. By replacing direct fiducial localization in the volumetric images with localization in the projection images we obtain the fiducial coordinates in the volume's coordinate system even when the fiducials are outside of the reconstructed region. The approach was evaluated using two anthropomorphic phantoms. When using the projection images all fiducials were localized, including those that were outside the reconstruction volume. The method's maximal localization error as evaluated using fiducials that could be directly localized in the CBCT reconstruction was 0.67 millimeters.
Proceedings of SPIE - The International Society for Optical Engineering 02/2009; 7261. DOI:10.1117/12.811633 · 0.20 Impact Factor
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