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.

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 surgeon's 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.

Intraoperative navigated 3-dimensional ultrasound angiography in tumor surgery.

BACKGROUND: Avoiding damage to blood vessels is often the concern of the neurosurgeon during tumor surgery. Using angiographic image data in neuronavigation may be useful in cases where vascular anatomy is of special interest. Since 2003, we have routinely used 3D ultrasound angiography in tumor surgery, and between January 2003 and May 2005, 62 patients with different tumors have been operated using intraoperative 3D ultrasound angiography in neuronavigation. METHODS: An ultrasound-based neuronavigation system was used. In addition to 3D ultrasound tissue image data, 3D ultrasound angiography (power Doppler) image data were acquired at different stages of the operation. The value and role of navigated 3D ultrasound angiography as judged by the surgeon were recorded. RESULTS: We found that intraoperative ultrasound angiography was easy to acquire and interpret, and that image quality was sufficient for neuronavigation. In 26 of 62 cases, ultrasound angiography was found to be helpful by visualizing hidden vessels adjacent to and inside the tumor, facilitating tailored approaches and safe biopsy sampling. CONCLUSIONS: Intraoperative 3D ultrasound angiography is straightforward to use, image quality is sufficient for image guidance, and it adds valuable information about hidden vessels, increasing safety and facilitating tailored approaches. Furthermore, with updated 3D ultrasound angiography imaging, accuracy of neuronavigation may be maintained in cases of brain shift.

Three-dimensional ultrasonography navigation in spinal cord tumor surgery. Technical note.

The authors describe the technical application of three-dimensional (3D) ultrasonography navigation in spinal cord tumor surgery. The spinal cord is a complex neurological structure in which there is the potential for causing neurological morbidity during tumor resection. Standard neuronavigation systems based on computed tomography or C-arm images are not adapted to tumor surgery in the spinal cord. Since 2004 the authors have been using a 3D ultrasonography-based neuronavigation system. During surgery, two-dimensional ultrasound images were acquired and reconstructed into 3D image data to assist in tumor resection. The navigation cameras read the position of a patient reference frame attached to a spinous process, the ultrasonography probe, and surgical instruments. Five- and 10-MHz phased-array ultrasonography probes equipped with optical tracking frames were used for image data acquisition. Spinal cord tumors were visualized using ultrasonography, and 3D ultrasonography-guided tumor biopsy sampling and resection were performed. The practice of attaching the reference frame to a spinous process adjacent to the spinal cord tumor, as well as performing image acquisition just before starting the resection, reduced the possible sources of inaccuracy. The technical application of a navigation system based on intraoperative 3D ultrasound image reconstruction seems feasible and may have the potential of improving functional outcome in association with spinal cord tumor surgery.

Computer-assisted 3D ultrasound-guided neurosurgery: technological contributions, including multimodal registration and advanced display, demonstrating future perspectives.

BACKGROUND: Navigation systems are now frequently being used for guiding surgical procedures. Existing neuronavigation systems suffer from the lack of updated images when tissue changes during surgery as well as from user-friendly displays of all essential images for accurate and safe surgery guidance. METHODS: We have developed various new technologies for improved neuronavigation. Using intraoperative 3D ultrasound (US) imaging, we have developed various registration algorithms for using and updating a complete multimodal and multivolume 3D map for navigation. RESULTS: We experienced that advanced multimodal visualization makes it easy to interpret information from several image volumes and modalities simultaneously. Using high quality intraoperative 3D ultrasound, essential preoperative information could be corrected due to brain shift. fMRI and other important preoperative data could then be used together with intraoperative ultrasound imaging for more accurate, safer and improved guidance of therapy. CONCLUSIONS: We claim that new features, as demonstrated in the present paper, using intraoperative 3D ultrasound in combination with advanced registration and display algorithms will represent important contributions towards more accurate, safer and more optimized future patient treatment.

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 surgeon's 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.