Frode Manstad-Hulaas

Three-dimensional endovascular navigation with electromagnetic tracking: ex vivo and in vivo accuracy.

Purpose To evaluate the accuracy of a 3-dimensional (3D) navigation system using electromagnetically tracked tools to explore its potential in patients. Methods The 3D navigation accuracy was quantified on a phantom and in a porcine model using the same setup and vascular interventional suite. A box-shaped phantom with 16 markers was scanned in 5 different positions using computed tomography (CT). The 3D navigation system registered each CT volume in the magnetic field. A tracked needle was pointed at the physical markers, and the spatial distances between the tracked needle positions and the markers were calculated. Contrast-enhanced CT images were acquired from 6 swine. The 3D navigation system registered each CT volume in the magnetic field. An electromagnetically tracked guidewire and catheter were visualized in the 3D image and navigated to 4 specified targets. At each target, the spatial distance between the tracked guidewire tip position and the actual position, verified by a CT control, was calculated. Results The mean accuracy on the phantom was 1.28±0.53 mm, and 90% of the measured distances were ≤1.90 mm. The mean accuracy in swine was 4.18±1.76 mm, and 90% of the measured distances were ≤5.73 mm. Conclusion This 3D navigation system demonstrates good ex vivo accuracy and is sufficiently accurate in vivo to explore its potential for improved endovascular navigation.

Side-branched AAA stent graft insertion using navigation technology: a phantom study.

Objective: To evaluate the feasibility of a side-branched stent graft inserted in an artificial abdominal aortic aneurysm (AAA), using navigation technology, and to compare procedure duration and dose of radiation with control trials. Methods: A custom-made stent graft was inserted into an artificial AAA using navigation technology in combination with fluoroscopy. The navigation technology was based on three-dimensional visualization of computed tomography data and electromagnetic tracking of microposition sensors. The stent graft had integrated position sensors in side branch and introducer and was guided into proper position with the aid of three-dimensional images. Control trials were performed with fluoroscopy alone. Results: It was feasible to insert a side-branched stent graft using three-dimensional navigation technology. The navigation-guided trials had a significantly lower X-ray load (p < 0.001), but showed no difference in the duration of the procedures (p = 0.34) as compared with controls. Conclusions: Inserting a side-branched stent graft in an artificial AAA using navigation technology is feasible. Side-branched stent grafts and navigation systems may become useful in the endovascular treatment of complicated aortic aneurysms.

Three-Dimensional Electromagnetic Navigation vs. Fluoroscopy for Endovascular Aneurysm Repair: A Prospective Feasibility Study in Patients:

Purpose To evaluate the in vivo feasibility of a 3-dimensional (3D) electromagnetic (EM) navigation system with electromagnetically-tracked catheters in endovascular aneurysm repair (EVAR). Methods The pilot study included 17 patients undergoing EVAR with a bifurcated stent-graft. Ten patients were assigned to the control group, in which a standard EVAR procedure was used. The remaining 7 patients (intervention group) underwent an EVAR procedure during which a cone-beam computed tomography image was acquired after implantation of the main stent-graft. The 3D image was presented on the navigation screen. From the contralateral side, the tip of an electromagnetically-tracked catheter was visualized in the 3D image and positioned in front of the contralateral cuff in the main stent-graft. A guidewire was inserted through the catheter and blindly placed into the stent-graft. The placement of the guidewire was verified by fluoroscopy before the catheter was pushed over the guidewire. If the guidewire was incorrectly placed outside the stent-graft, the procedure was repeated. Successful placement of the guidewire had to be achieved within a 15-minute time limit. Results With in 15 minutes, the guidewire was placed correctly inside the stent-graft in 6 of 7 patients in the intervention group and in 8 of 10 patients in the control group. In the intervention group, fewer attempts were needed to insert the guidewire correctly. Conclusion A 3D EM navigation system, used in conjunction with fluoroscopy and angiography, has the potential to provide more spatial information and reduce the use of radiation and contrast during endovascular interventions. This pilot study showed that 3D EM navigation is feasible in patients undergoing EVAR. However, a larger study must be performed to determine if 3D EM navigation is better than the existing practice for these patients.

Disocclusion-based 2D-3D registration for aortic interventions

Occlusions introduced by medical instruments affect the accuracy and robustness of existing intensity-based medical image registration algorithms. In this paper, we present disocclusion-based 2D-3D registration handling occlusion and dissimilarity during registration. Therefore, we introduce two disocclusion techniques, Spline Interpolation and Stent-editing, and two robust similarity measures, Huber and Tukey Gradient Correlation. Our techniques are validated on synthetic and real interventional data and compared with well-known approaches. Results prove that an integration of disocclusion into the registration procedure yield higher accuracy and robustness. It is also shown that the robust measures have different effects depending on the type of occluding structure.

A novel research platform for electromagnetic navigated bronchoscopy using cone beam CT imaging and an animal model

Abstract Electromagnetic guided bronchoscopy is a new field of research, essential for the development of advanced investigation of the airways and lung tissue. Consecutive problem-based solutions and refinements are urgent requisites to achieve improvements. For that purpose, our intention is to build a complete research platform for electromagnetic guided bronchoscopy. The experimental interventional electromagnetic field tracking system in conjunction with a C-arm cone beam CT unit is presented in this paper. The animal model and the navigation platform performed well and the aims were achieved; the 3D localization of foreign bodies and their navigated and tracked removal, assessment of tracking accuracy that showed a high level of precision, and assessment of image quality. The platform may prove to be a suitable platform for further research and development and a full-fledged electromagnetic guided bronchoscopy navigation system. The inclusion of the C-arm cone beam CT unit in the experimental setup adds a number of new possibilities for diagnostic procedures and accuracy measurements. Among other future challenges that need to be solved are the interaction between the C-arm and the electromagnetic navigation field, as we demonstrate in this feasibility study.

Quantification of abdominal aortic deformation after EVAR

Quantification of abdominal aortic deformation is an important requirement for the evaluation of endovascular stenting procedures and the further refinement of stent graft design. During endovascular aortic repair (EVAR) treatment, the aortic shape is subject to severe deformation that is imposed by medical instruments such as guide wires, catheters, and, the stent graft. This deformation can affect the flow characteristics and morphology of the aorta which have been shown to be elicitors for stent graft failures and be reason for reappearance of aneurysms. We present a method for quantifying the deformation of an aneurysmatic aorta imposed by an inserted stent graft device. The outline of the procedure includes initial rigid alignment of the two abdominal scans, segmentation of abdominal vessel trees, and automatic reduction of their centerline structures to one specified region of interest around the aorta. This is accomplished by preprocessing and remodeling of the pre- and postoperative aortic shapes before performing a non-rigid registration. We further narrow the resulting displacement fields to only include local non-rigid deformation and therefore, eliminate all remaining global rigid transformations. Finally, deformations for specified locations can be calculated from the resulting displacement fields. In order to evaluate our method, experiments for the extraction of aortic deformation fields are conducted on 15 patient datasets from endovascular aortic repair (EVAR) treatment. A visual assessment of the registration results and evaluation of the usage of deformation quantification were performed by two vascular surgeons and one interventional radiologist who are all experts in EVAR procedures.

Advanced 2D-3D Registration for Endovascular Aortic Interventions: Addressing Dissimilarity in Images

In the current clinical workflow of minimally invasive aortic procedures navigation tasks are performed under 2D or 3D angiographic imaging. Many solutions for navigation enhancement suggest an integration of the preoperatively acquired computed tomography angiography (CTA) in order to provide the physician with more image information and reduce contrast injection and radiation exposure. This requires exact registration algorithms that align the CTA volume to the intraoperative 2D or 3D images. Additional to the real-time constraint, the registration accuracy should be independent of image dissimilarities due to varying presence of medical instruments and contrast agent. In this paper, we propose efficient solutions for image-based 2D-3D and 3D-3D registration that reduce the dissimilarities by image preprocessing, e.g. implicit detection and segmentation, and adaptive weights introduced into the registration procedure. Experiments and evaluations are conducted on real patient data.

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

Abstract 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.

Interventional 2D-3D Registration in the Presence of Occlusion

It is crucial that 2D-3D medical image registration algorithms meet special requirements in terms of accuracy and robustness in order to be applied during clinical interventions. Existing algorithms may be affected by image dissimilarities introduced by medical instruments visible only in the interventional 2D image. Based on our previous results, we present a fully automatic framework for disocclusion-based 2D-3D registration technique that detects the occlusion and performs a matching on the reconstructed 2D image. Compared to earlier approaches, the proposed algorithm is fully automatic and therefore highly appropriate for clinical application. Our technique is validated on synthetic and real interventional data and compared with conventional methods. Results prove that disocclusion-based registration yield higher accuracy and robustness and outperforms existing approaches in terms of speed.

Manually Steerable Catheter With Improved Agility

Purpose: A prototype steerable catheter was designed for endovascular procedures. This technical pilot study reports the initial experience using the catheter for cannulation of visceral arteries. Technique: The 7F catheter was manually steerable with operator control handle for bending and rotation of the tip. The maximum bending angle was approximately 90° and full 360° rotation of the tip was supported. The study involved 1 pig with 4 designated target arteries: the left and right renal arteries, the superior mesenteric artery, and the celiac trunk. Fluoroscopy with 3-dimensional (3D) overlay showing the ostia from preoperative computed tomography angiography was used for image guidance. The cannulation was considered successful if the guidewire was placed well inside the target artery. In addition to evaluating cannulation success, procedure time and associated radiation doses were recorded. The procedure was performed twice with 2 different operators. Conclusions: Both operators successfully reached all 4 target arteries, demonstrating the feasibility of the steerable catheter for endovascular cannulation of visceral arteries. No contrast medium was used, and median radiation dose was 4.5 mGy per cannulation. An average of approximately 2 minutes was used per cannulation. This study motivates further testing in a more comprehensive study to evaluate reproducibility in several animals and with inclusion of more operators. Further development by integrating the new catheter tool in a navigation system is also an interesting next step, combining fine control of catheter tip movements and 3D image guidance without ionizing radiation.