Toril A. Nagelhus Hernes

Comparison of navigated 3D ultrasound findings with histopathology in subsequent phases of glioblastoma resection

ObjectiveThe purpose of the study was to compare the ability of navigated 3D ultrasound to distinguish tumour and normal brain tissue at the tumour border zone in subsequent phases of resection.Materials and methodsBiopsies were sampled in the tumour border zone as seen in the US images before and during surgery. After resection, biopsies were sampled in the resection cavity wall. Histopathology was compared with the surgeon’s image findings.ResultsBefore resection, the tumour border was delineated by ultrasound with high specificity and sensitivity (both 95%). During resection, ultrasound had acceptable sensitivity (87%), but poor specificity (42%), due to biopsies falsely classified as tumour by the surgeon. After resection, sensitivity was poor (26%), due to tumour or infiltrated tissue in several biopsies deemed normal by ultrasound, but the specificity was acceptable (88%).ConclusionsOur study shows that although glioblastomas are well delineated prior to resection, there seem to be overestimation of tumour tissue during resection. After resection tumour remnants and infiltrated brain tissue in the resection cavity wall may be undetected. We believe that the benefits of intraoperative ultrasound outweigh the shortcomings, but users of intraoperative ultrasound should keep the limitations shown in our study in mind.

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.

Laparoscopic ultrasound: a survey of its current and future use, requirements, and integration with navigation technology

AbstractBackgroundLaparoscopic ultrasound (LUS) increases surgical safety by allowing the surgeon to see beyond the organ surface, by visualizing vascular structures and by improving surgical precision of tumor resection. A questionnaire-based survey was used to investigate the current use and future expectations of LUS technology.MethodsA questionnaire consisting of 26 questions was distributed manually at four different conferences (60% at the European Association for Endoscopic Surgery (EAES) conference, Stockholm 2008). The answers were summarized with descriptive statistics and nonparametric tests at a significance level of 0.05.ResultsThe questionnaire was answered by 177 surgeons from 40 different countries (85% from Europe). Of these surgeons, 43% use ultrasound during laparoscopic procedures. Generally, more LUS users are found at university hospitals than at general community hospitals. Surgeons use LUS primarily in procedures related to the liver (67% of the surgeons who use LUS), but LUS also is used in other procedures related to the pancreas, biliary tract, and colon. In a 5-year perspective, 82% of surgeons believe in an increased use of LUS, and 79% of surgeons also think that the use of LUS combined with navigation technology will increase and that the most important requirements for such a system are good image quality, easy interpretation, and a high degree of precision.ConclusionsAlthough the surgeons believe LUS has advantages, only 43% of the respondents reported using it. The surveyed surgeons were largely positive toward an increased use of LUS in a 5-year perspective and believe that LUS combined with navigation technology will contribute to improving the surgical precision of tumor resection.

Navigated bronchoscopy: a technical review.

Background:Navigated bronchoscopy uses virtual 3-dimensional lung model visualizations created from preoperative computed tomography images often in synchronization with the video bronchoscope to guide a tool to peripheral lesions. Navigated bronchoscopy has developed fast since the introduction of virtual bronchoscopy with integrated electromagnetic sensors in the late 1990s. The purposes of the review are to give an overview and update of the technological components of navigated bronchoscopy, an assessment of its clinical usefulness, and a brief assessment of the commercial platforms for navigated bronchoscopy. Methods:We performed a literature search with relevant keywords to navigation and bronchoscopy and iterated on the reference lists of relevant papers, with emphasis on the last 5 years. Results:The paper presents an overview of the components necessary for performing navigated bronchoscopy, assessment of the diagnostic accuracy of different approaches, and an analysis of the commercial systems. We were able to identify 4 commercial platforms and 9 research and development groups with considerable activity in the field. Finally, on the basis of our findings and our own experience, we provide a discussion on navigated bronchoscopy with focus on the next steps of development. Conclusions:The literature review showed that the peripheral diagnostic accuracy has improved using navigated bronchoscopy compared with traditional bronchoscopy. We believe that there is room for improvement in the diagnostic success rate by further refinement of methods, approaches, and tools used in navigated bronchoscopy.

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.

Tissue Motion and Strain in the Human Brain Assessed by Intraoperative Ultrasound in Glioma Patients

The objective of the study was to investigate tissue motion and strain imposed by cardiovascular pulsation in pathologic and normal brain parenchyma, as quantified from in vivo ultrasound data. Ultrasound acquired during surgery of 16 patients with glial tumors was retrospectively processed and analyzed. The tissue velocity was quantified at depths of 1cm, 2cm and 3cm from brain cortex to investigate spatial dependency with depth. Comparison of strain and velocity in tumor and adjacent normal parenchyma was performed by selecting two regions-of-interest in the hyperechoic tumor and two regions in the low-echogenic areas interpreted as mainly normal tissue with some degree of tumor cell infiltration. The absolute maximum tissue velocity is seen to increase with increasing depths in 14 of 16 cases (87.5%). The maximum tissue velocities in the four regions close to the ultrasound visible tumor border are not statistically different (p=0.163 to p=0.975). The strain magnitudes are significantly higher in the regions with expected normal brain parenchyma than in regions with expected glial tumor tissue, both for the two regions being closest to the tumor border (p=0.0004) and for the two regions further away from the tumor border (p=0.0009). We conclude that the velocity of the brain parenchyma imposed by arterial pulsation during a cardiac cycle is generally increasing with increasing depth from cortex. The maximum velocity appears to be similar in regions with expected normal brain and tumor tissue, thus, does not seem to be affected by pathology. Strain magnitude is, however, a suitable parameter for discrimination of glial tumor and normal brain parenchyma. (E-mail: Tormod.Selbekk@sintef.no).

Versatile robotic probe calibration for position tracking in ultrasound imaging

Within the field of ultrasound-guided procedures, there are a number of methods for ultrasound probe calibration. While these methods are usually developed for a specific probe, they are in principle easily adapted to other probes. In practice, however, the adaptation often proves tedious and this is impractical in a research setting, where new probes are tested regularly. Therefore, we developed a method which can be applied to a large variety of probes without adaptation. The method used a robot arm to move a plastic sphere submerged in water through the ultrasound image plane, providing a slow and precise movement. The sphere was then segmented from the recorded ultrasound images using a MATLAB programme and the calibration matrix was computed based on this segmentation in combination with tracking information. The method was tested on three very different probes demonstrating both great versatility and high accuracy.