Impact of calcification modeling to improve image fusion accuracy for endovascular aortic aneurysm repair.

Since the 1990s, endovascular aortic aneurysm repair (EVAR) has become a common alternative to open surgery for the treatment of abdominal aortic aneurysms (AAAs). To aid the deployment of stent-grafts, fluoroscopic image guidance can be enhanced using preoperative simulation and intraoperative image fusion techniques. However, the impact of calcification (Ca) presence on the guidance accuracy of such techniques is yet to be considered. In the present work, we introduce a guidance tool that accounts for patient-specific Ca presence. Numerical simulations of EVAR were developed for 12 elective AAA patients, both with (With-Ca) and without (No-Ca) Ca consideration. To assess the accuracy of the simulations, the image results were overlaid on corresponding intraoperative images and the overlay error was measured at selected anatomical landmarks. With this approach we gained insight into the impact of Ca presence on image fusion accuracy. Inclusion of Ca improved mean image fusion accuracy by 8.68 ± 4.59%. In addition, a positive correlation between the relative Ca presence and the image fusion accuracy was found (R = .753, p < .005). Our results suggest that considering Ca presence in patient-specific EVAR simulations increases the reliability of EVAR image guidance techniques that utilize numerical simulation, especially for patients with severe aortic Ca presence.

Simultaneous reconstruction of multiple stiff wires from a single X-ray projection for endovascular aortic repair.

PURPOSE: Endovascular repair of aortic aneurysms (EVAR) can be supported by fusing pre- and intraoperative data to allow for improved navigation and to reduce the amount of contrast agent needed during the intervention. However, stiff wires and delivery devices can deform the vasculature severely, which reduces the accuracy of the fusion. Knowledge about the 3D position of the inserted instruments can help to transfer these deformations to the preoperative information. METHOD: We propose a method to simultaneously reconstruct the stiff wires in both iliac arteries based on only a single monoplane acquisition, thereby avoiding interference with the clinical workflow. In the available X-ray projection, the 2D course of the wire is extracted. Then, a virtual second view of each wire orthogonal to the real projection is estimated using the preoperative vessel anatomy from a computed tomography angiography as prior information. Based on the real and virtual 2D wire courses, the wires can then be reconstructed in 3D using epipolar geometry. RESULTS: We achieve a mean modified Hausdorff distance of 4.2 mm between the estimated 3D position and the true wire course for the contralateral side and 4.5 mm for the ipsilateral side. CONCLUSION: The accuracy and speed of the proposed method allow for use in an intraoperative setting of deformation correction for EVAR.

Intraoperative stent segmentation in X-ray fluoroscopy for endovascular aortic repair.

PURPOSE: Fusion of preoperative data with intraoperative X-ray images has proven the potential to reduce radiation exposure and contrast agent, especially for complex endovascular aortic repair (EVAR). Due to patient movement and introduced devices that deform the vasculature, the fusion can become inaccurate. This is usually detected by comparing the preoperative information with the contrasted vessel. To avoid repeated use of iodine, comparison with an implanted stent can be used to adjust the fusion. However, detecting the stent automatically without the use of contrast is challenging as only thin stent wires are visible. METHOD: We propose a fast, learning-based method to segment aortic stents in single uncontrasted X-ray images. To this end, we employ a fully convolutional network with residual units. Additionally, we investigate whether incorporation of prior knowledge improves the segmentation. RESULTS: We use 36 X-ray images acquired during EVAR for training and evaluate the segmentation on 27 additional images. We achieve a Dice coefficient of 0.933 (AUC 0.996) when using X-ray alone, and 0.918 (AUC 0.993) and 0.888 (AUC 0.99) when adding the preoperative model, and information about the expected wire width, respectively. CONCLUSION: The proposed method is fully automatic, fast and segments aortic stent grafts in fluoroscopic images with high accuracy. The quality and performance of the segmentation will allow for an intraoperative comparison with the preoperative information to assess the accuracy of the fusion.

Automatic detection of selective arterial devices for advanced visualization during abdominal aortic aneurysm endovascular repair.

Here we address the automatic segmentation of endovascular devices used in the endovascular repair (EVAR) of abdominal aortic aneurysms (AAA) that deform vascular tissues. Using this approach, the vascular structure is automatically reshaped solving the issue of misregistration observed on 2D/3D image fusion for EVAR guidance. The endovascular devices we considered are the graduated pigtail catheter (PC) used for contrast injection and the stent-graft delivery device (DD). The segmentation of the DD was enhanced using an asymmetric Frangi filter. The segmented geometries were then analysed using their specific features to remove artefacts. The radiopaque markers of the PC were enhanced using a fusion of Hessian and newly introduced gradient norm shift filters. Extensive experiments were performed using a database of images taken during 28 AAA-EVAR interventions. This dataset was divided into two parts: the first half was used to optimize parameters and the second to compile performances using optimal values obtained. The radiopaque markers of the PC were detected with a sensitivity of 88.3% and a positive predictive value (PPV) of 96%. The PC can therefore be positioned with a majority of its markers localized while the artefacts were all located inside the vessel lumen. The major parts of the DD, the dilatator tip and the pusher surfaces, were detected accurately with a sensitivity of 85.9% and a PPV of 88.7%. The less visible part of the DD, the stent enclosed within the sheath, was segmented with a sensitivity of 63.4% because the radiopacity of this region is low and uneven. The centreline of the DD in this stent region was alternatively traced within a 0.74 mm mean error. The automatic segmentation of endovascular devices during EVAR is feasible and accurate; it could be useful to perform elastic registration of the vascular lumen during endovascular repair.

Source of errors and accuracy of a two-dimensional/three-dimensional fusion road map for endovascular aneurysm repair of abdominal aortic aneurysm.

PURPOSE: To evaluate the accuracy and source of errors using a two-dimensional (2D)/three-dimensional (3D) fusion road map for endovascular aneurysm repair (EVAR) of abdominal aortic aneurysm. MATERIALS AND METHODS: A rigid 2D/3D road map was tested in 16 patients undergoing EVAR. After 3D/3D manual registration of preoperative multidetector computed tomography (CT) and cone beam CT, abdominal aortic aneurysm outlines were overlaid on live fluoroscopy/digital subtraction angiography (DSA). Patient motion was evaluated using bone landmarks. The misregistration of renal and internal iliac arteries were estimated by 3 readers along head-feet and right-left coordinates (z-axis and x-axis, respectively) before and after bone and DSA corrections centered on the lowest renal artery. Iliac deformation was evaluated by comparing centerlines before and during intervention. A score of clinical added value was estimated as high (z-axis < 3 mm), good (3 mm ≤ z-axis ≤ 5 mm), and low (z-axis > 5 mm). Interobserver reproducibility was calculated by the intraclass correlation coefficient. RESULTS: The lowest renal artery misregistration was estimated at x-axis = 10.6 mm ± 11.1 and z-axis = 7.4 mm ± 5.3 before correction and at x-axis = 3.5 mm ± 2.5 and z-axis = 4.6 mm ± 3.7 after bone correction (P = .08), and at 0 after DSA correction (P < .001). After DSA correction, residual misregistration on the contralateral renal artery was estimated at x-axis = 2.4 mm ± 2.0 and z-axis = 2.2 mm ± 2.0. Score of clinical added value was low (n = 11), good (n= 0), and high (n= 5) before correction and low (n = 5), good (n = 4), and high (n = 7) after bone correction. Interobserver intraclass correlation coefficient for misregistration measurements was estimated at 0.99. Patient motion before stent graft delivery was estimated at x-axis = 8 mm ± 5.8 and z-axis = 3.0 mm ± 2.7. The internal iliac artery misregistration measurements were estimated at x-axis = 6.1 mm ± 3.5 and z-axis = 5.6 mm ± 4.0, and iliac centerline deformation was estimated at 38.3 mm ± 15.6. CONCLUSIONS: Rigid registration is feasible and fairly accurate. Only a partial reduction of vascular misregistration was observed after bone correction; minimal DSA acquisition is still required.

Optimized viewing angles for cardiac electrophysiology ablation procedures.

PURPOSE: Catheter ablation is a common treatment option for atrial fibrillation (AF). Interventional C-arm X-ray systems are used for guiding AF procedures, employing standard view positions. Since the projection angles are not adapted to the individual patient anatomy, standard projections do not necessarily offer the best views of important anatomical structures. Using a pre-procedural 3D data set acquired with MRI or CT, suitable ablation sites (lines) can be identified in advance so an ablation plan can be superimposed on fluoroscopic images to guide the procedure. METHODS: A method was developed to estimate optimized projection views for biplane X-ray C-arm systems based on planning data for AF ablation procedures. The estimated viewing angles were compared to standard angulations using an objective quality metric, the length of the planned ablation line as seen under X-ray. This method was tested using 35 clinical datasets annotated with planned ablation lines for ipsilateral pulmonary vein isolation. RESULTS: The optimized views computed using the new method yielded 28 % less foreshortening of pre-planned ablation lines on average. In one case, anatomy-based view calculation lead to a 69 % reduction in foreshortening. CONCLUSION: The commonly used standard views provide reasonable a priori choices, and some improvement is possible by switching among common angulations depending on the treatment region. Further gains are possible by using anatomy-optimized biplane C-arm angulations.

Interventional tool tracking using discrete optimization.

This work presents a novel scheme for tracking of motion and deformation of interventional tools such as guide-wires and catheters in fluoroscopic X-ray sequences. Being able to track and thus to estimate the correct positions of these tools is crucial in order to offer guidance enhancement during interventions. The task of estimating the apparent motion is particularly challenging due to the low signal-to-noise ratio (SNR) of fluoroscopic images and due to combined motion components originating from patient breathing and tool interactions performed by the physician. The presented approach is based on modeling interventional tools with B-splines whose optimal configuration of control points is determined through efficient discrete optimization. Each control point corresponds to a discrete random variable in a Markov random field (MRF) formulation where a set of labels represents the deformation space. In this context, the optimal curve corresponds to the maximum a posteriori (MAP) estimate of the MRF energy. The main motivation for employing a discrete approach is the possibility to incorporate a multi-directional search space which is robust to local minima. This is of particular interest for curve tracking under large deformation. This work analyzes feasibility of employing efficient first-order MRFs for tracking. In particular it shows how to achieve a good compromise between energy approximations and computational efficiency. Experimental results suggest to define both the external and internal energy in terms of pairwise potential functions. The method was successfully applied to the tracking of guide-wires in fluoroscopic X-ray sequences of several hundred frames which requires extremely robust techniques. Comparisons with state-of-the-art guide-wire tracking algorithms confirm the effectiveness of the proposed method.

System and method for 3-D/3-D registration between non-contrast-enhanced CBCT and contrast-enhanced CT for abdominal aortic aneurysm stenting.

In this paper, we present an image guidance system for abdominal aortic aneurysm stenting, which brings pre-operative 3-D computed tomography (CT) into the operating room by registering it against intra-operative non-contrast-enhanced cone-beam CT (CBCT). Registration between CT and CBCT volumes is a challenging task due to two factors: the relatively low signal-to-noise ratio of the abdominal aorta in CBCT without contrast enhancement, and the drastically different field of view between the two image modalities. The proposed automatic registration method handles the first issue through a fast quasi-global search utilizing surrogate 2-D images, and solves the second problem by relying on neighboring dominant structures of the abdominal aorta (i.e. the spine) for initial coarse alignment, and using a confined and image-processed volume of interest around the abdominal aorta for fine registration. The proposed method is validated offline using 17 clinical datasets, and achieves 1.48 mm target registration error and 100% success rate in 2.83 s. The prototype system has been installed in hospitals for clinical trial and applied in around 30 clinical cases, with 100% success rate reported qualitatively.

Endovascular image-guided navigation: validation of two volume-volume registration algorithms.

The limited volume covered by intraoperatively acquired CT scans makes the use of navigation systems difficult. Preoperative images cover a larger volume of interest. Hence, reliable registration of high quality preoperative to intraoperative CT will provide the necessary image information required for navigation. This study evaluates two algorithms (Siemens, CAMP) for volume-volume registration for usage during endovascular navigation. Twenty patients treated for abdominal aortic aneurysm were scanned with pre-, intra- and postoperative CT. Six data sets were excluded due to variations in image acquisition parameters and severe artifacts. Fourteen intra- and postoperative datasets were registered ten times with both algorithms, altogether 140 registrations for each program. In all data sets five specified landmarks placed by two radiologists were used to evaluate registration accuracy. The distance between the paired landmarks in the registered intra- and postoperative volumes was measured and the root mean square value calculated. Reference registrations were based on rigid body registration of the five landmarks in the intra- and postoperative volumes. Registration accuracy (mean ± SD) was for Siemens 5.05 ± 4.74 mm, for CAMP 4.02 ± 1.52 mm and for the reference registrations 2.72 ± 1.18 mm. The registration algorithms differed significantly, p < 0.001.

C-arm cone beam computed tomography needle path overlay for fluoroscopic guided vertebroplasty.

STUDY DESIGN: Retrospective review. OBJECTIVE: To report our early clinical experience using C-arm cone beam computed tomography (C-arm CBCT) with fluoroscopic overlay for needle guidance during vertebroplasty. SUMMARY OF BACKGROUND DATA: C-arm CBCT is advanced three-dimensional (3-D) imaging technology that is currently available on state-of-the-art flat panel based angiography systems. The imaging information provided by C-arm CBCT allows for the acquisition and reconstruction of "CT-like" images in flat panel based angiography/interventional suites. As part of the evolution of this technology, enhancements allowing the overlay of cross-sectional imaging information can now be integrated with real time fluoroscopy. We report our early clinical experience with C-arm CBCT with fluoroscopic overlay for needle guidance during vertebroplasty. METHODS: This is a retrospective review of 10 consecutive oncology patients who underwent vertebroplasty of 13 vertebral levels using C-arm CBCT with fluoroscopic overlay for needle guidance from November 2007 to December 2008. Procedural data including vertebral level, approach (transpedicular vs. extrapedicular), access (bilateral vs. unilateral) and complications were recorded. Technical success with the overlay technology was assessed based on accuracy which consisted of 4 measured parameters: distance from target to needle tip, distance from planned path to needle tip, distance from midline to needle tip, and distance from the anterior 1/3 of the vertebral body to needle tip. Success within each parameter required that the distance between the needle tip and parameter being evaluated be no more than 5 mm on multiplanar CBCT or fluoroscopy. RESULTS: Imaging data for 12 vertebral levels was available for review. All vertebral levels were treated using unilateral access and 9 levels were treated with an extrapedicular approach. Technical success rates were 92% for both distance from planned path and distance from midline to final needle tip, 100% when distance from needle tip to the anterior 1/3 border of the vertebral body was measured, and 75% when distance from target to needle tip was measured. There were no major complications. Minor complications consisted of 3 cases (25%) of cement extravasation. CONCLUSION: C-arm CBCT with needle path overlay for fluoroscopic guided vertebroplasty is feasible and allows for reliable unilateral therapy of both lumbar and thoracic vertebral bodies. Extrapedicular approaches were performed safely and with good accuracy of reaching the targets.

Technical feasibility of 2D-3D coregistration for visualization of self-expandable microstents to facilitate coil embolization of broad-based intracranial aneurysms: an in vitro study.

INTRODUCTION: The use of self-expandable microstents for treatment of broad-based intracranial aneurysms is widely spread. However, poor fluoroscopic visibility of the stents remains disadvantageous during the coiling procedure. Flat detector angiographic computed tomography (ACT) provides high resolution imaging of microstents even though integration of this imaging modality in the neurointerventional workflow has not been widely reported. METHODS: An acrylic glass model was used to simulate the situation of a broad-based sidewall aneurysm. After insertion of a self-expandable microstent, ACT was performed. The resulting 3D dataset of the Microstent was subsequently projected into a conventional 2D fluoroscopic roadmap. This 3D visualization of the stent supported the coil embolization procedure of the in vitro aneurysm. RESULTS: In vitro 2D-3D coregistration with integration of 3D ACT data of a self-expandable microstent in a conventional 2D roadmap is feasible. CONCLUSIONS: Unsatisfying stent visibility constrains clinical cases with complex parent vessel anatomy and challenging aneurysm geometry; hence, this technique potentially may be useful in such cases. In our opinion, the clinical feasibility and utility of this new technique should be verified in a clinical aneurysm embolization study series using 2D-3D coregistration.

Enhancing transjugular intrahepatic portosystemic shunt puncture by using three-dimensional path planning based on the back projection of two two-dimensional portographs.

The purpose of this study was to prevent transjugular intrahepatic portosystemic shunt (TIPS) puncture failure by using three-dimensional (3D) path planning. This study was approved by the institutional review board; informed consent was obtained for the TIPS procedure. In four patients, a 3D path was planned from two two-dimensional (2D) CO2 portograms obtained at projections of 0 degrees and right anterior oblique 30 degrees . This path was overlaid onto the live fluoroscopy to guide the puncture image. In three of four patients, the target vessel was entered in the first attempt. In one patient with portal vein (PV) stenosis, the PV was entered with the third pass. This method has high potential to improve safety of the procedure and to reduce intervention time.

C-arm cone beam computed tomographic needle path overlay for fluoroscopic-guided placement of translumbar central venous catheters.

C-arm cone beam computed tomography is an advanced 3D imaging technology that is currently available on state-of-the-art flat-panel-based angiography systems. The overlay of cross-sectional imaging information can now be integrated with real-time fluoroscopy. This overlay technology was used to guide the placement of three percutaneous translumbar inferior vena cava catheters.

Localization of fluorescence spots with space-space MUSIC for mammographylike measurement systems.

Breast cancer diagnosis may be improved by optical fluorescence imaging techniques in the near-infrared wavelength range. We have shown that the recently proposed space-space MUSIC (multiple signal classification) algorithm allows the 3-D localization of focal fluorophore-tagged lesions in a turbid medium from 2-D fluorescence data obtained from laser excitations at different positions. The data are assumed to be measured with two parallel planar sensor arrays on the top and bottom of the medium. The laser sources are integrated at different positions in one of the planes. The space-space data are arranged into an MxN matrix (M, number of sensors; N, number of excitation sources). A singular-value decomposition (SVD) of this matrix yields the detectable number of spot regions with linearly independent behavior with respect to the laser excitation positions and thus allows definition of a signal subspace. Matches between this signal subspace and data from model spots are tested at scanned points in a model medium viewed as the breast region under study. The locations of best matches are then considered the centers of gravity of focal lesions. The optical model used was unbounded and optically homogeneous. Nevertheless, simulated spots in bounded, inhomogeneous media modeling the breast could be localized accurately.