Geir Arne Tangen

Probe calibration for freehand 3-D ultrasound

Ultrasound (US) probe calibration establishes the rigid body transformation between the US image and a tracking device attached to the probe. This is an important requirement for correct 3-D reconstruction of freehand US images and, thus, for accurate surgical navigation based on US. In this study, we evaluated three methods for probe calibration, based on a single-point phantom, a wire-cross phantom requiring 2-D alignment and a wire phantom for freehand scanning. The processing of acquired data is fairly common to these methods and, to a great extent, based on automated procedures. The evaluation is based on quality measures in 2-D and 3-D reconstructed data. With each of the three methods, we calibrated a linear-array probe, a phased-array sector probe and an intraoperative probe. The freehand method performed best, with a 3-D navigation accuracy of 0.6 mm for one of the probes. This indicates that clinical accuracy in the order of 1 mm may be achieved in US-based surgical navigation.

3D ultrasound-based navigation for radiofrequency thermal ablation in the treatment of liver malignancies

BACKGROUND The aim of the study was to compare three methods for ultrasound-based guidance of a radiofrequency probe into liver tumors in a model setup. METHODS The liver model tumors were placed inside excised calf livers, and the radiofrequency probe was guided into the center using either a new 3D navigation method or two conventional 2D methods-freehand scanning and a method based on a biopsy guide. We performed 54 experiments, measuring the physical distance (all methods) and image distance (3D method only) from the tip of the probe to the center of the tumors. RESULTS Based on the physical measurements alone, the biopsy-based guiding performed better than both the 2D freehand and the 3D navigation method. However, the 3D image measurements showed that the tip of the probe was better positioned in the center of the model tumors for the 3D navigation method as compared to the physical measurement results for the 2D methods. CONCLUSION Although it was easier to position the radiofrequency probe accurately using the 3D image display technique, movement of the model tumor during 3D navigation is a challenge.

Navigation in laparoscopy--prototype research platform for improved image-guided surgery.

The manipulation of the surgical field in laparoscopic surgery, through small incisions with rigid instruments, reduces free sight, dexterity, and tactile feedback. To help overcome some of these drawbacks, we present a prototype research and development platform, CustusX, for navigation in minimally invasive therapy. The system can also be used for planning and follow‐up studies. With this platform we can import and display a range of medical images, also real‐time data such as ultrasound and X‐ray, during surgery. Tracked surgical tools, such as pointers, video laparoscopes, graspers, and various probes, allow surgeons to interactively control the display of medical images during the procedure. This paper introduces navigation technologies and methods for laparoscopic therapy, and presents our software and hardware research platform. Furthermore, we illustrate the use of the system with examples from two pilots performed during laparoscopic therapy. We also present new developments that are currently being integrated into the system for future use in the operating room. Our initial results from pilot studies using this technology with preoperative images and guidance in the retroperitoneum during laparoscopy are promising. Finally, we shortly describe an ongoing multicenter study using this surgical navigation system platform.

Intrasellar ultrasound in transsphenoidal surgery: a novel technique.

OBJECTIVEResidual tumor masses are common after transsphenoidal surgery. The risk of a residual mass increases with tumor size and parasellar or suprasellar growth. Transsphenoidal surgery is usually performed without image guidance. We aimed to investigate a new technical solution developed for intraoperative ultrasound imaging during transsphenoidal surgery, with respect to potential clinical use and the ability to identify neuroanatomy and tumor. METHODSIn 9 patients with pituitary macroadenomas, intrasphenoidal and intrasellar ultrasound was assessed during transsphenoidal operations. Ultrasound B-mode, power-Doppler and color-Doppler images were acquired using a small prototype linear array, side-looking probe. The long probe tip measures only 3 × 4 mm. We present images and discuss the potential of intrasphenoidal and intrasellar and ultrasound in transsphenoidal surgery. RESULTSWe present 2-dimensional, high-resolution ultrasound images. A small side-looking, high-frequency ultrasound probe can be used to ensure orientation in the midline for the surgical approach to identify important neurovascular structures to be avoided during surgery and for resection control and identification of normal pituitary tissue. The image resolution is far better than what can be achieved with current clinical magnetic resonance imaging technology. CONCLUSIONWe believe that the concept of intrasellar ultrasound can be further developed to become a flexible and useful tool in transsphenoidal surgery.

Navigated Ultrasound in Laparoscopic Surgery

Laparoscopic surgery is performed through small incisions that limit free sight and possibility to palpate organs. Although endoscopes provide an overview of organs inside the body, information beyond the surface of the organs is missing. Ultrasound can provide real-time essential information of inside organs, which is valuable for increased safety and accuracy in guidance of procedures. We have tested the use of 2D and 3D ultrasound combined with 3D CT data in a prototype navigation system. In our laboratory, micro-positioning sensors were integrated into a flexible intraoperative ultrasound probe, making it possible to measure the position and orientation of the real-time 2D ultrasound image as well as to perform freehand 3D ultrasound acquisitions. Furthermore, we also present a setup with the probe optically tracked from the shaft with the flexible part locked in one position. We evaluated the accuracy of the 3D laparoscopic ultrasound solution and obtained average values ranging from 1.6% to 3.6% volume deviation from the phantom specifications. Furthermore, we investigated the use of an electromagnetic tracking in the operating room. The results showed that the operating room setup disturbs the electromagnetic tracking signal by increasing the root mean square (RMS) distance error from 0.3 mm to 2.3 mm in the center of the measurement volume, but the surgical instruments and the ultrasound probe added no further inaccuracies. Tracked surgical tools, such as endoscopes, pointers, and probes, allowed surgeons to interactively control the display of both registered preoperative medical images, as well as intraoperatively acquired 3D ultrasound data, and have potential to increase the safety of guidance of surgical procedures.

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.

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.

Blood flow imaging: an angle-independent ultrasound modality for intraoperative assessment of flow dynamics in neurovascular surgery.

OBJECTIVE The objective of this study was to investigate the clinical applicability of navigated blood flow imaging (BFI) in neurovascular applications. BFI is a new 2-dimensional ultrasound modality that offers angle-independent visualization of flow. When integrated with 3-dimensional (3D) navigation technology, BFI can be considered as a first step toward the ideal tool for surgical needs: a real-time, high-resolution, 3D visualization that properly portrays both vessel geometry and flow direction. METHODS A 3D model of the vascular tree was extracted from preoperative magnetic resonance angiographic data and used as a reference for intraoperative any-plane guided ultrasound acquisitions. A high-end ultrasound scanner was interconnected, and synchronized recordings of BFI and 3D navigation scenes were acquired. The potential of BFI as an intraoperative tool for flow visualization was evaluated in 3 cerebral aneurysms and 3 arteriovenous malformations. RESULTS The neurovascular flow direction was properly visualized in all cases using BFI. Navigation technology allowed for identification of the vessels of interest, despite the presence of brain shift. The surgeon found BFI to be very intuitive compared with conventional color Doppler methods. BFI allowed for quality control of sufficient flow in all distal arteries during aneurysm surgery and made it easier to discern between feeding arteries and draining veins during surgery for arteriovenous malformations. CONCLUSION BFI seems to be a promising modality for neurovascular flow visualization that may provide the neurosurgeon with a valuable tool for safer surgical interventions. However, further work is needed to establish the clinical usefulness of the proposed imaging setup.