Navigated retrograde endoscopic myotomy (REM) for the treatment of therapy-resistant achalasia.

BACKGROUND: In achalasia, muscle spasm may involve the proximal esophagus. When the muscle spasm is located in the proximal esophagus, conventional per oral endoscopic myotomy (POEM) may not be sufficient to relieve symptoms. In this paper, we describe retrograde endoscopic myotomy (REM) as a novel approach to perform myotomy of the proximal esophagus, with the application of a navigation tool for anatomical guidance during REM. We aim to evaluate the feasibility and safety of REM and usefulness of the navigation during REM. METHOD: A 42-year-old male with type III achalasia who was treated with laparoscopic myotomy with fundoplication, multiple pneumatic balloon dilations, Botox injections and anterior POEM of the middle and distal esophagus without symptomatic effect. Repeated high-resolution- manometry (HRM) revealed occluding contractions of high amplitude around and above the aortic arch. A probe-based real-time electromagnetic navigation platform was used to facilitate real-time anatomical orientation and to evaluate myotomy position and length during REM. RESULTS: The navigation system aided in identifying the major structures of the mediastinum, and position and length of the myotomy. Twelve weeks after REM, the Eckardt score fell from seven at baseline seven to two. We also observed improvement with reduction of the pressure at the level of previous spasms in the proximal esophagus from 124 mmHg to 8 mmHg on HRM. CONCLUSION: REM makes the proximal esophagus accessible for endoscopic myotomy. Potential indication for REM is motility disorders in the proximal esophagus and therapy failure after POEM.

A novel in vivo method for lung segment movement tracking.

Knowledge about lung movement in health and disease is sparse. Current evaluation methods, such as CT, MRI and external view have significant limitations. To study respiratory movement for image guided tumour diagnostics and respiratory physiology, we needed a method that overcomes these limitations.We fitted balloon catheters with electromagnetic sensors, and placed them in lung lobes of ventilated pigs. The sensors sensed their position at 40 Hz in an electromagnetic tracking field with a precision of ∼0.5 mm. The method was evaluated by recording sensor movement in different body positions and at different tidal volumes. No 'gold standard' exists for lung segment tracking, so our results were compared to 'common knowledge'. The sensors were easily placed, showed no clinically relevant position drift and yielded sub-millimetre accuracy. Our measurements fit 'common knowledge', as increased ventilation volume increased respiratory movement, and the right lung moved significantly less in the right than the left lateral position. The novel method for tracking lung segment movements during respiration was easy to implement and yielded high spatial and temporal resolution, and the equipment parts are reusable. It is easy to implement as a research tool for lung physiology, navigated bronchoscopy and radiation therapy.

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.

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.

Ergonomic design criteria for a novel laparoscopic tool handle with tactile feedback.

Laparoscopic surgery has many ergonomic disadvantages often not considered in the design of instruments. The poorly designed surgical tools produce inconveniences in both functional and cognitive aspects; including tactile sensation and visual-motor space coordination. The aim of this article is to find out how laparoscopic handle design can be improved by combining classical ergonomic guidelines with tactile feedback related to handle design. The article briefly discusses how the human hand and hand-held tools are used to perform tasks. An ergonomic handle for laparoscopic grasping, with a built-in tactile sensation display, is presented. Our review of laparoscopic instruments reveals important aspects for handle design. It is concluded that there is a need for greater awareness of ergonomic guidelines for users' sensory requirements when designing and manufacturing laparoscopic instruments.

Image-guided laparoscopic surgery. Review and current status.

The main drawback with laparoscopic surgery is that the surgeon is unable to palpate vessels, tumours and organs during surgery. Further-more, the laparoscope only provides a surface view of organs. There is a need for more advanced visualizations techniques that can enhance the display presented to the surgeon so that important information below the surface of the organs is included when planning the procedure as well as for guidance and control during treatment. In this paper, we present a review of the literature and the state of art within image-guided laparoscopic surgery. We describe our own experience using a prototype navigation system for advanced visualizations and guidance during laparoscopic procedures in the retroperitoneum. Furthermore, we show sample images from the Future Operating Room for laparoscopic surgery in Trondheim, where this technology is being further developed and tested in clinical studies. Our system is based on three-dimensional navigation technology, i.e. preoperatively acquired magnetic resonance or computed tomography data used in combination with tracked instruments, allowing the surgeon to interactively control the display of images prior to and during surgery with normal use of the instruments. In summary, we believe that abdominal image navigation using tracked instruments and advanced visualizations has a large potential for improving future laparoscopic surgery, especially in cases where vessels and anatomical relations beyond surfaces is difficult to identify using only a laparoscope. The technology helps the surgeon to better understand the anatomy and locate blood vessels. Accordingly, we believe that this new technology could increase safety and make it easier for the surgeon to perform successful laparoscopic surgery.

Laparoscopic navigation pointer for three-dimensional image-guided surgery.

BACKGROUND: The main drawback with the laparoscopic approach is that the surgeon is unable to palpate vessels, tumors, and organs during surgery. Furthermore, the laparoscope provides only surface view of organs. There is a need for more advanced visualizations that can enhance the view to include information below the surface of the organs for planning of the procedure and for control and guidance during treatment. METHODS: We propose three-dimensional (3D) navigation technology based on preoperatively acquired magnetic resonance or computed tomography data used in combination with a laparoscopic navigation pointer (LNP). The LNP has an attached position tracker that allows the surgeon to control the display of images interactively before and during surgery. This study evaluated the patient registration accuracy, the feasibility of image-based navigation and, qualitatively, the navigation precision in the retroperitoneum during laparoscopic surgery. RESULTS: This technology was used during the treatment of six patients (involving adrenalectomies and a neuroma protruding into the pelvis). An average patient registration accuracy of 6.90 mm was achieved. The precision during navigation in the retroperitoneum was, in some cases, better than the patient registration accuracy suggested. The technology helped the surgeons to understand better the anatomy and to locate blood vessels. CONCLUSIONS: In the reported cases, the LNP was a useful tool for image guidance in laparoscopic surgery, both for planning the surgical approach in detail and for guidance. The authors believe that adominal 3D image guidance using an LNP has a large potential for improving laparoscopic surgery, especially when vessels and anatomic relations may be difficult to identify using only a laparoscope. Accordingly, they believe this new technology could increase safety and make it easier for the surgeon to perform successful laparoscopic surgery.

Stereoscopic navigation-controlled display of preoperative MRI and intraoperative 3D ultrasound in planning and guidance of neurosurgery: new technology for minimally invasive image-guided surgery approaches.

OBJECTIVE: This paper demonstrates a method that brings together three essential technologies for surgery planning and guidance: neuronavigation systems, 3D visualization techniques and intraoperative 3D imaging technologies. We demonstrate the practical use of an in-house interactive stereoscopic visualization module that is integrated with a 3D ultrasound based neuronavigation system. MATERIALS AND METHODS: A stereoscopy volume visualization module has been integrated with a 3D ultrasound based neuronavigation system, which also can read preoperative MR and CT data. The various stereoscopic display modalities, such as "cut plane visualization" and "interactive stereoscopic tool guidance" are controlled by a pointer, a surgical tool or an ultrasound probe. Interactive stereoscopy was tested in clinical feasibility case studies for planning and guidance of surgery procedures. RESULTS: By orientating the stereoscopic projections in accordance to the position of the patient on the operating table, it is easier to interpret complex 3D anatomy and to directly take advantage of this 3D information for planning and surgical guidance. In the clinical case studies, we experienced that the probe-controlled cut plane visualization was promising during tumor resection. By combining 2D and 3D display, interpretation of both detailed and geometric information may be achieved simultaneously. The possibilities of interactively guiding tools in a stereoscopic scene seemed to be a promising functionality for use during vascular surgery, due to specific location of certain vessels. CONCLUSION: Interactive stereoscopic visualization improves perception and enhances the ability to understand complex 3D anatomy. The practical benefit of 3D display is increased considerably when integrated with surgical navigation systems, since the orientation of the stereoscopic projection corresponds to the orientation of the patient on the operating table. Stereoscopic visualizations work well on MR and CT images, although volume rendering techniques are especially suitable for intraoperative 3D ultrasound image data.

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.

Bayesian 2-D deconvolution: a model for diffuse ultrasound scattering.

Observed medical ultrasound images are degraded representations of the true acoustic tissue reflectance. The degradation is due to blur and speckle and significantly reduces the diagnostic value of the images. To remove both blur and speckle, we have developed a new statistical model for diffuse scattering in 2-D ultrasound radio frequency images, incorporating both spatial smoothness constraints and a physical model for diffuse scattering. The modeling approach is Bayesian in nature, and we use Markov chain Monte Carlo methods to obtain the restorations. The results from restorations of some real and simulated radio frequency ultrasound images are presented and compared with results produced by Wiener filtering.

Bayesian 2-D deconvolution: effect of using spatially invariant ultrasound point spread functions.

Observed ultrasound images are degraded representations of the-true tissue reflectance. The specular reflections at boundaries between regions of different tissue types are blurred, and the diffuse scattering within homogenous regions causes speckle because of the oscillating nature of the transmitted pulse. To reduce both blur and speckle, we have developed algorithms for the restoration of simulated and real ultrasound images based on Markov random field models and Bayesian statistical methods. The algorithm is summarized here, although a more detailed description can be found in our companion paper [1]. Because the point spread function (psf) is unknown, we investigate the effects of using incorrect frequencies and sizes for the model psf during the restoration process. First, we degrade the images either with a known simulated psf or a measured psf. Then, we use different psf shapes during restoration to study the robustness of the method. We found that small variations in the parameters characterizing the psf, less than +/- 25% change in frequency, width, or length, still yielded satisfactory results. When altering the psf more than this, the restorations were not acceptable. The restorations were particularly sensitive to large increases in the restoring psf frequency. Thus, 2-D Bayesian restoration using a fixed psf may yield acceptable results as long as the true variant psfs have not varied too much during imaging.

Wavelet-based edge detection in ultrasound images.

We introduce a new wavelet-based method for edge detection in ultrasound (US) images. Each beam that is analyzed is first transformed into the wavelet domain using the continuous wavelet transform (CWT). Because the CWT preserves both scale and time information, it is possible to separate the signal into a number of scales. The edge is localized by first determining the scale at which the power spectrum, based on the wavelet transform, has its maximum value. Next, at this scale we find the position of the peak for the squared CWT. This method does not depend on any threshold, after the range of scales have been determined. We suggest a range of scales for US images in general. Sample edge detections are demonstrated in US images of straight and jagged edges of simple structures submerged in water bath, and of an abdominal aorta aneurysm phantom.

SonoWand, an ultrasound-based neuronavigation system.

OBJECTIVE: We have integrated a neuronavigation system into an ultrasound scanner and developed a single-rack system that enables the surgeon to perform frameless and armless stereotactic neuronavigation using intraoperative three-dimensional ultrasound data as well as preoperative magnetic resonance or computed tomographic images. The purpose of this article is to describe our two-rack prototype and present the results of our work on image quality enhancement. DESCRIPTION OF INSTRUMENTATION: The system consists of a high-end ultrasound scanner, a modest-cost computer, and an optical positioning/digitizer system. Special technical and clinical efforts have been made to achieve high image quality. A special interface between the ultrasound instrument and the navigation computer ensures rapid transfer of digital three-dimensional data with no loss of image quality. OPERATIVE TECHNIQUE: The positioning system tracks the position and orientation of the patient, the ultrasound probe, the pointer, and various surgical instruments. This makes it possible to update the three-dimensional map during surgery and navigate by ultrasound data in a similar manner as with magnetic resonance data. METHODS: The two-rack prototype has been used for clinical testing since November 1997 at the University Hospital in Trondheim. EXPERIENCE AND RESULTS: The image quality improvements have enabled us, in most cases, to extract information from ultrasound with clinical value similar to that of preoperative magnetic resonance imaging. The overall clinical accuracy of the ultrasound-based navigation system is expected to be comparable to or better than that of a magnetic resonance imaging-based system. CONCLUSION: The SonoWand system enables neuronavigation through direct use of intraoperative three-dimensional ultrasound. Further research will be necessary to explore the potential clinical value and the limitations of this technology.

Initial experience with stereoscopic visualization of three-dimensional ultrasound data in surgery.

Initial in vivo and in vitro experiments were performed to evaluate the feasibility of stereoscopically displaying three-dimensional (3D) ultrasound data from neurosurgery, laparoscopic surgery, and vascular surgery. Stereoscopic visualization was illustrated by four video sequences, which can be downloaded from http://www.us.unimed. sintef.no/. These sequences show a brain tumor, hepatic arteries in relation to the gallbladder, a model that mimics a neuroendoscope in a cyst, and a "flight" into model of an artery with an intima flap. The experiments indicate that stereoscopic display of ultrasound data is feasible when there is sufficient contrast between the objects of interest and the surrounding tissue. True 3D vision improves perception, thus enhancing the ability to understand complex anatomic structures such as irregular lesions and tortuous vessels.

Diffusion coefficients and solubility coefficients for gases in biological fluids and tissues: a review.

Based on a review of 166 references for diffusion and solubility coefficients in biological fluids and tissues, we have tabulated experimental values for the gases Ar, CO2, H2, He, N2, Ne, N2O, O2, and SF6. Two major conclusions can be drawn: a) for tissues, there is a scarcity of available data; and b) in general, there are significant differences between values determined by different investigators, the discrepancies being most prominent for diffusion coefficients. For water, we give numeric values of the temperature coefficients and preferred diffusion and solubility coefficients at 25 degrees and 37 degrees C. Further, we describe several methods for estimation of coefficients where experimental data are lacking. For tissues, none of the formulas described give precise predictions for all gases, but rough estimates sufficient for most qualitative work can almost always be found. In particular, the data material indicates that for all tissues other than fatty tissues consisting of mainly triacylglycerols, the solubility coefficients for water may be used as a good approximation. Except for SF6, the error in this approximation probably does not exceed 20%. In contrast, diffusion coefficients for most tissues are from 25 to 50% lower than the respective coefficients in water, generally increasing with the water content of the tissue.