Steinar Ommedal

Neuronavigation by Intraoperative Three-dimensional Ultrasound: Initial Experience during Brain Tumor Resection

OBJECTIVE Three-dimensional (3-D) ultrasound is an intraoperative imaging modality used in neuronavigation as an alternative to magnetic resonance imaging (MRI). This article summarizes 4 years of clinical experience in the use of intraoperative 3-D ultrasound integrated into neuronavigation for guidance in brain tumor resection. METHODS Patients were selected for inclusion in the study on the basis of the size and location of their lesion. Preoperative 3-D MRI data were registered and used for planning as in other conventional neuronavigation systems. Intraoperative 3-D ultrasound images were acquired three to six times, and tumor resection was guided on the basis of these updated 3-D images. RESULTS Intraoperative 3-D ultrasound represents a good solution to the problem of brain shift in neuronavigation because it easily provides an updated, and hence more accurate, map of the patient’s true anatomy in all phases of the operation. Ultrasound makes it possible to follow the progression of the operation, and it improves the radicality of tumor resection by detecting tumor tissue that would remain if the imaging technology had not been used (in 53% of the cases). Integration of 3-D ultrasound with navigation technology solves the orientation problem experienced previously with two-dimensional ultrasound in neurosurgery. The technology makes it possible to directly compare intraoperative ultrasound and MRI data regarding visualization of the lesion. Ultrasound image quality is useful for guiding surgical procedures. CONCLUSION Intraoperative 3-D ultrasound seems to provide a time- and cost-effective way to update high-quality 3-D maps used in neuronavigation.

Brain operations guided by real-time two-dimensional ultrasound: new possibilities as a result of improved image quality.

OBJECTIVE In 1995, a project was initiated in Trondheim, Norway, to investigate various possibilities for more frequent use of ultrasound in brain surgery. Since that time, the quality of ultrasonic images has improved considerably through technological adjustment of parameters. The objective of the present study was to explore essential clinical parameters required for the successful use of ultrasonic guidance in brain surgery. METHODS During the study period, several surgical setups designed to optimize the use of intraoperative real-time two-dimensional ultrasonic imaging were explored. These included various positions of the ultrasound probe in relation to both the operation cavity and the lesion, as well as the position of the operation channel in relation to the gravity line. RESULTS All lesions from the latest period (1997–2001; n = 114) were depicted well by ultrasound imaging, with the exception of two cases. High image quality and direct image guidance of the tool were maintained best throughout the operation by imaging through an intact dura and at an angle relative to a vertical operation channel. All tumor operations were performed without complications, and ultrasound imaging was found to be an important factor in the detection of remaining tumor tissue at the conclusion of surgery. For 14 low vascular tumors, the operation was guided only by ultrasound imaging. No bleeding complications occurred. A method of minimally invasive ultrasound-guided evacuation of hematomas was developed. In 19 patients, the method was found to be efficient (i.e., >90% of the hematoma was evacuated) and without complications, except for one patient who experienced rebleeding. CONCLUSION With proper planning and surgical setup, ultrasound imaging may provide acceptable image quality for use in image-guided brain operations.

Ability of navigated 3D ultrasound to delineate gliomas and metastases – comparison of image interpretations with histopathology

SummaryBackground. The objective of the study was to test the ability of a 3D ultrasound (US) based intraoperative imaging and navigation system to delineate gliomas and metastases in a clinical setting. The 3D US data is displayed as reformatted 2D image slices. The quality of the displayed 3D data is affected both by the resolution of the acquired data and the reformatting process. In order to investigate whether or not 3D US could be used for reliable guidance in tumour surgery, a study was initiated to compare interpretations of imaged biopsy sites with histopathology. The system also enabled concomitant comparison of navigated preoperative MR with histopathology.Method. Eighty-five biopsies were sampled between 2–7 mm from the tumour border visible in the ultrasound images. Biopsies were collected from 28 operations (7 low-grade astrocytomas, 8 anaplastic astrocytomas, 7 glioblastomas and 6 metastases). Corresponding cross-sections of preoperative MR T1, MR T2 and intraoperative US were concomitantly displayed, steered by the biopsy forceps equipped with a positioning sensor. The surgeons’ interpretation of the images at the electronically indicated biopsy sites were compared with the histopathology of the samples.Findings. The ultrasound findings were in agreement with histopathology in 74% (n = 31) for low-grade astrocytomas, 83% (n = 18) for anaplastic astrocytomas, 77% (n = 26) for glioblastomas and 100% (n = 10) for metastases. Excluding irradiated patients, the results for glioblastomas improved to 80% concurrence (n = 20). As expected tumour cells were found in biopsies outside the US visible tumour border, especially in low-grade gliomas. Navigated 3D US have a significantly better agreement with histopathology than navigated MR T1 for low-grade astrocytomas.Conclusion. Reformatted images from 3D US volumes give a good delineation of metastases and the solid part of gliomas before starting the resection. Navigated 3D US is at least as reliable as navigated 3D MR to delineate gliomas and metastases.

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 (MMW) 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.

Operation of arteriovenous malformations assisted by stereoscopic navigation-controlled display of preoperative magnetic resonance angiography and intraoperative ultrasound angiography.

OBJECTIVE To study the application of navigated stereoscopic display of preoperative three-dimensional (3-D) magnetic resonance angiography and intraoperative 3-D ultrasound angiography in a clinical setting. METHODS Preoperative magnetic resonance angiography and intraoperative ultrasound angiography are presented as stereoscopic images on the monitor during the operation by a simple red/blue technique. Two projections are generated, one for each eye, according to a simple ray casting method. Because of integration with a navigation system, it is possible to identify vessels with a pointer. The system has been applied during operations on nine patients with arteriovenous malformations (AVMs). Seven of the patients had AVMs in an eloquent area. RESULTS The technology makes it easier to understand the vascular architecture during the operation, and it offers a possibility to identify and clip AVM feeders both on the surface and deep in the tissue at the beginning of the operation. All 28 feeders identified on the preoperative angiograms were identified by intraoperative navigated stereoscopy. Twenty-five were clipped at the beginning of the operation. The other three were clipped at a later phase of the operation. 3-D ultrasound angiography was useful to map the size of the nidus, to detect the degree of brain shift, and to identify residual AVM. CONCLUSION Stereoscopic visualization enhances the surgeons perception of the vascular architecture, and integrated with navigation technology, this offers a reliable system for identification and clipping of AVM feeders in the initial phase of the operation.

Image fusion of ultrasound and MRI as an aid for assessing anatomical shifts and improving overview and interpretation in ultrasound-guided neurosurgery

Abstract We have developed an image fusion module for combined 3D ultrasound and MRI/CT visualization in image-guided neuronavigation. The module demonstrates alternative image visualization possibilities, which might be integrated in future ultrasound-based neuronavigation systems. The image fusion visualization module reads 3D ultrasound, MRI/CT image data sets and patient registration information which are saved during the operation using the SonoWand ultrasound-based neuronavigation system earlier presented by our group [1] . The images are visualized simultaneously in the same scene by overlay, compositing or splitting visualization techniques which makes perception of information easier as compared to visualizing images in different scenes. Quantitation of brain shift between similar structures recognized in both preoperative MRI and intraoperative ultrasound images was done using both a manual and an automatic image processing algorithm. The results show that alternative image visualizations may be useful in order to get immediate feedback regarding brain shift in the early beginning of the operation. The present paper summarizes the experiences gained using this visualization module on patient image data acquired in our clinic during the last year using the SonoWand ultrasound-based neuronavigation system.

Ultrasound-guided neurosurgery: a feasibility study in the 3-30 MHz frequency range

This study, which includes seven patients, illustrates some potential values of the interactive use of ultrasound technology prior to, during and after brain tumour resection. Ultrasound B-scan and colour flow imaging were applied during open surgery using a cardiac scanner in the 3.25-7.5 MHz frequency range and an intravascular scanner with catheters at 10, 20 and 30 MHz. The tumour and vital blood vessels were localized prior to resection using low frequency imaging from the brain surface. High frequency, high resolution close-up imaging was applied during and after resection in order to identify remaining tumour tissue, as well as to detect blood vessels in the vicinity of the resection wall. The study also demonstrates that the tumour and surgical tools such as, for example, bipolar diathermy, acoustic aspirator or biopsy forceps,can be visualized simultaneously. This simplifies the localization of remaining tumour tissue.

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.

Ultrasound imaging during endovascular abdominal aortic aneurysm repair using the Stentor bifurcated endograft.

Purpose: To evaluate different ultrasound modalities during implantation and follow-up of endovascular grafts for abdominal aortic aneurysm (AAA) exclusion. Methods: Between February 1995 and May 1996, 18 patients (14 men; aged 49 to 80 years, mean 67) were treated with endovascular intervention for infrarenal AAA. Seventeen patients received Mialhe Stentor bifurcated grafts, while one patient was treated with a straight graft for pseudoaneurysm. During and after the implantation, 3.25- and 5-MHz annular array ultrasound probes were used for transabdominal visualization of the endograft. Intravascular ultrasound was applied in combination with angiography for postoperative control. Results: Intraprocedurally, transabdominal two-dimensional (2D) ultrasound successfully monitored guidewire passage from the groin into the main part of the bifurcated endograft for implantation of the second limb. All implantation procedures were technically successful, but four endoleaks were identified intraprocedurally by 2D ultrasound and angiography. One healed spontaneously, two were treated with endovascular techniques at 1 and 4 months, and the last leak was scheduled for repair when the patient died of probable myocardial infarction at 2 months. During follow-up, 2D ultrasound successfully visualized all the endografts; no endoleaks were found in up to 18 months of surveillance. Conclusions: Transabdominal ultrasound imaging could be valuable in bifurcated endograft deployment both for guiding guidewire insertion and for controlling wire position before the second graft limb is connected to the main graft. Provided that satisfactory visualization of the entire endograft can be obtained, ultrasound examination may possibly replace arteriography and computed tomographic scanning as a follow-up investigation.

Neurosurgical biopsies guided by 3D ultrasound - comparison of image evaluations and histopathological results

The imaging of gliomas and metastases by 3D ultrasound has been evaluated by comparing image findings and histopathological results. Biopsies have been taken prior to resection and close to the tumour border as shown in the ultrasound images. The tumour border shown in the ultrasound images was verified by an edge detection algorithm using the Sobel method. Ultrasound images, with the biopsy position indicated, have been evaluated and compared to the histhopathology of the corresponding biopsy. The degree of match between image evaluations and histopathology should reflect the ability of 3D ultrasound to image size and location of tumours correctly. The image slices of intraoperative 3D ultrasound are also compared to corresponding image slices of preoperative MR data (Tl and T2). The preliminary results show that intraoperative 3D ultrasound provides accurate information about tumour border and location and may accordingly be used for guiding surgical procedures. For gliomas the histopathologic match for the intraoperative 3D ultrasound is better than the corresponding match for the preoperative MR data.