Biomedical subjects

Thomas Langø

Publications and source records attributed to Thomas Langø.

9 recordsLinked to original sources

PubMed2006

Are cold light sources really cold?

BACKGROUND: A fiber optic light source is the central part of endoscopic surgery. However, the light generation process causes heat transmission from a source to tip of a scope. In this study, we measured the amount of heating and pathologic effects of direct contact with the tip of scopes on the small bowel in an experimental set-up. MATERIALS AND METHODS: Temperature measurements were performed at the tip of 4 different scopes (Aesculap, Olympus, Karl Storz, and Richard Wolf), which were connected to either of 3 different xenon light sources (Olympus, Richard Wolf, Karl Storz). Temperatures at the outlet of light sources and the tip of fiber optic cables were measured as well. Tissue samples from the small bowel of a pig were obtained after exposing them to direct contact with the tip of the scopes or the fiber optic cable. RESULTS: The temperature measurements at the tip of the scopes varied between 60 degrees C and 100 degrees C (Celsius). The temperatures showed a wide variation according to the type of light source and fiber optic cable the scopes were connected to. The average temperature at the outlet of the light sources and the tip of fiber optic cables was 750 degrees C and 250 degrees C, respectively. The microscopic scores of the small bowel injury induced by exposition to the heat at the tip of the scopes were significantly high after 5 seconds of contact. Direct contact of the tip of the fiber optic cable caused total carbonization in the wall of the small bowel. CONCLUSION: Direct contact of the tip of the scope with small bowel may cause functional and cytologic injury even after short durations of exposure. Therefore, we do not recommend direct contact of scopes with the intra-abdominal organs to avoid heat injuries. In addition, this study also emphasizes the variation in heat generation at the tip of the scopes when used with a mismatching light source and fiber optic cable.

Animals↗

PubMed2005

A review of calibration techniques for freehand 3-D ultrasound systems.

Three-dimensional (3-D) ultrasound (US) is an emerging new technology with numerous clinical applications. Ultrasound probe calibration is an obligatory step to build 3-D volumes from 2-D images acquired in a freehand US system. The role of calibration is to find the mathematical transformation that converts the 2-D coordinates of pixels in the US image into 3-D coordinates in the frame of reference of a position sensor attached to the US probe. This article is a comprehensive review of what has been published in the field of US probe calibration for 3-D US. The article covers the topics of tracking technologies, US image acquisition, phantom design, speed of sound issues, feature extraction, least-squares minimization, temporal calibration, calibration evaluation techniques and phantom comparisons. The calibration phantoms and methods have also been classified in tables to give a better overview of the existing methods.

Algorithms↗

PubMed2005

A review of calibration techniques for freehand 3-D ultrasound systems.

Algorithms↗

PubMed2004

[3-D navigation in laparoscopic surgery].

BACKGROUND: The main drawback with the laparoscopic approach is that the surgeon lacks the possibility to palpate vessels, tumours and organs during surgery. Furthermore, the laparoscope only provides a surface view of organs. There is a need for more advanced visualization that enhances the view to include information below the surface of the organs when the procedure is planned and for control and guidance during treatment. MATERIAL AND METHODS: We propose 3-D navigation technology based on preoperatively acquired MR or CT data used in combination with a laparoscopic navigation pointer. The pointer has an attached position tracker which enables the surgeon to interactively control the display of images prior to and during surgery. RESULTS: We have used this technology during treatment of four patients with adrenal tumours. Preoperative registration of images of the patients was performed within two minutes with an average accuracy of 7.1 mm. 2-D and 3-D visualizations interactively controlled by the pointer were used both for planning and for guidance of the surgical procedures. INTERPRETATION: The pointer was a useful tool in image guidance of laparoscopic surgery in the reported cases both for planning the approach in detail and for guidance. We believe abdominal 3-D image guidance using a laparoscopic navigation pointer has a large potential for improving laparoscopic surgery, especially in cases where vessels and anatomical relations might be difficult to identify using only a laparoscope. Accordingly, this new technology will increase safety and facilitate successful laparoscopic surgery.

Adrenal Gland Neoplasms↗

PubMed2004

An experimental operating room project for advanced laparoscopic surgery.

With the challenges that the health sector now faces in accordance with readjustments and demands for increased efficiency, resource utilization, and innovation, we have initiated a project to develop the future operating room for advanced laparoscopic surgery. New hospitals are being built that contain numerous operating room theaters. To share experiences and avoid repeating the same mistakes as others, we find it suitable to build an "experimental" operating room theater where we can try out and study new equipment, logistics, and communications, and operating forms and new technology that both benefit the establishment of our hospital, as well as the establishment of other hospitals and their laparoscopic operating rooms nationally and internationally. The main goals in the project are, through research and development, to reveal information and develop technology and methods to establish more efficient and prospective patient treatment that is focused on quality. The project is deeply rooted in the established research environment in Trondheim, Norway. We will develop new integrated solutions in the laparoscopic operating unit to create a possibility to rapidly implement the results in the form of practical improvements, increased quality, and renovation in patient treatment. The goal is also that this will result in the establishment of new industry nationally.

Hospital Design and Construction↗

PubMed2003

A robust and automatic method for evaluating accuracy in 3-D ultrasound-based navigation.

We present a robust and automatic method for evaluating the 3-D navigation accuracy in ultrasound (US) based image-guided systems. The method is based on a precisely built and accurately measured phantom with several wire crosses and an automatic 3-D template matching by correlation algorithm. We investigated the accuracy and robustness of the algorithm and also addressed optimization of algorithm parameters. Finally, we applied the method to an extensive data set from an in-house US-based navigation system. To evaluate the algorithm, eight skilled observers identified the same wire crosses manually and the average over all observers constitutes our reference data set. We found no significant differences between the automatic and the manual procedures; the average distance between the point sets for one particular volume (27 point pairs) was 0.27 +/- 0.17 mm. Furthermore, the spread of the automatically determined points compared with the reference set was lower than the spread for any individual operator. This indicates that the automatic algorithm is more accurate than manual determination of the wire-cross locations, in addition to being faster and nonsubjective. In the application example, we used a set of 35 3-D US scans of the phantom under various acquisition configurations. The US frequency was 6.7 MHz and the average target depth was 6 cm. The accuracy, represented by the mean distance between automatically-determined wire-cross locations and physically measured locations, was found to be 1.34 +/- 0.62 mm.

Algorithms↗

PubMed2003

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.

Calibration↗

PubMed2003

Multimodal image fusion in ultrasound-based neuronavigation: improving overview and interpretation by integrating preoperative MRI with intraoperative 3D ultrasound.

OBJECTIVE: We have investigated alternative ways to integrate intraoperative 3D ultrasound images and preoperative MR images in the same 3D scene for visualizing brain shift and improving overview and interpretation in ultrasound-based neuronavigation. MATERIALS AND METHODS: A Multi-Modal Volume Visualizer (MMVV) was developed that can read data exported from the SonoWand neuronavigation system and reconstruct the spatial relationship between the volumes available at any given time during an operation, thus enabling the exploration of new ways to fuse pre- and intraoperative data for planning, guidance and therapy control. In addition, the mismatch between MRI volumes registered to the patient and intraoperative ultrasound acquired from the dura was qualified. RESULTS: The results show that image fusion of intraoperative ultrasound images in combination with preoperative MRI will make perception of available information easier by providing updated (real-time) image information and an extended overview of the operating field during surgery. This approach will assess the degree of anatomical changes during surgery and give the surgeon an understanding of how identical structures are imaged using the different imaging modalities. The present study showed that in 50% of the cases there were indications of brain shift even before the surgical procedure had started. CONCLUSIONS: We believe that image fusion between intraoperative 3D ultrasound and preoperative MRI might improve the quality of the surgical procedure and hence also improve the patient outcome.

Brain↗

PubMed2002

Accuracy evaluation of a 3D ultrasound-based neuronavigation system.

We have investigated the 3D navigation accuracy of a frameless ultrasound-based neuronavigation system (SonoWand) for surgical planning and intraoperative image guidance. In addition, we present a detailed description and review of the error sources associated with surgical neuronavigation based on preoperative MRI data and intraoperative ultrasound. A phantom with 27 precisely defined points was scanned with ultrasound by various translation and tilt movements of the ultrasound probe (180 3D scans in total), and the 27 image points in each volume were located using an automatic detection algorithm. These locations were compared to the physically measured locations of the same 27 points. The accuracy of the neuronavigation system and the effect of varying acquisition conditions were found through a thorough statistical analysis of the differences between the two point sets. The accuracy was found to be 1.40 +/- 0.45 mm (arithmetic mean) for the ultrasound-based neuronavigation system in our laboratory setting. Improper probe calibration was the major contributor to this figure. Based on our extensive data set and thorough evaluation, the accuracy found in the laboratory setting is expected to be close to the overall clinical accuracy for ultrasound-based neuronavigation. Our analysis indicates that the overall clinical accuracy may be as low as 2 mm when using intraoperative imaging to compensate for brain shift.

Humans↗