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Déjà vue in the operating room—three-dimensional volumetric imaging
International Congress Series 1281 (2005) 788 – 792
www.ics-elsevier.com
De´ja` vue in the operating room—three-dimensional volumetric imaging S.K. Rosahla,T, U. Hubbea, S. Strahlb, S. Schersichb, A. Gharabaghic, G.C. Feiglc, R. Shahidid, M. Samiic a
Department of Neurosurgery, Albert-Ludwigs-University Freiburg, Germany b University of Hannover, Germany c International Neuroscience Institute Hannover, Germany d Image Guidance Laboratories, Stanford University, CA, USA
Abstract. The objectives for microsurgical image-guidance in intracranial procedures are different from the entry-trajectory-target paradigm for stereotactic purposes. From a neurosurgical series of 125 patients with various intracranial pathologies having received surgery that was aided by image guidance, we have derived three basic principles for the successful application of neuronavigation in daily routine: (1) Less is more. Redundant anatomical information-basically all information that is unrelated to surgical landmarks in a particular case-should be omitted from the guiding images. (2) The approach and the surgical target should be visible in a single 3D guiding image. To this end, gradual tuning of the opacity of outer tissue layers in images is the method of choice to outline the in relation to the anatomy that needs to be dissected by the surgeon in order to arrive at the target. (3) All available information on functional tissue properties should be added to the guiding image. Preservation of function has become the single most important demand for neurosurgical procedures. Results of fMRI, DTI and other validated functional studies can readily be added to the structural image. Adhering to these principles may truly enhance the capacities of the surgeon who not only experiences a de´ja` vue of the individual surgical anatomy when looking through the operating microscope but can also base his intra-operative decisions on invisible functional landmarks. D 2005 CARS & Elsevier B.V. All rights reserved. Keywords: Surgical image-guidance; Neuro-navigation; Volumetric image rendering; Three-dimensional (3D) imaging; Neurosurgery; Fractal extrapolation
T Corresponding author. E-mail address: [email protected] (S.K. Rosahl). 0531-5131/ D 2005 CARS & Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2005.03.295
S.K. Rosahl et al. / International Congress Series 1281 (2005) 788–792
789
1. Introduction Intracranial neurosurgery works on slightly different principles as compared to other surgical subjects. First, there is limited space in the surgical field. Second, objects in the field are small, in most cases requiring a microscope to be clearly outlined. Third, the surgical approach and target are often closely surrounded by vitally important tissue that cannot visually be discerned from less eloquent tissue. Fourth, the surgical target usually does not grossly move or change in the interval between imaging procedures and the surgical intervention. Relying on the latter, stereotaxy was created as a whole field within neurological surgery. In stereotaxy, the surgical task is to hit a target inside the intracranial space with needle-like instruments along a straight trajectory from a pre-defined entry point. Navigation, with or without a frame, just defines the coordinates of target and entry points in three-dimensional (3D) space. Tri-axial images are essentially sufficient for these procedures. In microneurosurgery, where the surgeon relies on direct 3D visual information in the surgical field, entirely different tasks should be assigned to image guidance. We set out to explore these tasks from a microsurgical view. 2. Methods MRI (1.5 T, 3 T), fMRI, diffusion tensor imaging (DTI), positron emission tomography (PET), computed tomography (CT), and CT angiography have been employed as the primary imaging modalities. Data taken from 125 patients with various intracranial pathologies (gliomas, meningiomas, cavernomas, sellar and parasellar tumors, lesions in the paranasal sinuses, in the petrous bone, in the brainstem, in the cerebello-pontine angle, and in the craniocervical junction) have been transferred to an image guidance system and processed with software that is capable of rendering high-resolution 3D images (Image Guidance Laboratories, Stanford University, CA, USA). For functional neurosurgery, image guidance was employed in cases of motor cortex stimulation for placement of electrodes and for epilepsy surgery. In selected cases, the surface of the cerebral cortex in the individual patient was extracted with an algorithm based on fractal extrapolation. After designing a surgical strategy, the segmentation and the creation of volumes of interest (VOI) from the imaging data, containing the landmark anatomical structures and functional detail, were done by the neurosurgical team. A virtual bfly throughQ 3D movie was generated that showed the major surgical steps in the planned procedure using the individual imaging data of the patient. The virtual bsurgical fieldQ was rotated to the assumed position of the real field in the OR. Surfaces were gradually rendered translucent in the image to allow a view on the lesion in relation to more superficial morphologic or functional landmarks. The surgical strategy was changed, whenever an improved surgical approach could be derived from these visualizations. With the objective to create a 3D image that contains all the anatomical landmarks that would also appear in the real field during surgery, the VOIs were selected and color-coded by the neurosurgical team. Bony landmarks and vessels were charted. Functional information for the tissue along the surgical route was added and the image was zoomed to the size of the field of the surgical microscope.
790
S.K. Rosahl et al. / International Congress Series 1281 (2005) 788–792
In the operating room, the patients head was registered as usual with 5 to 10 adhesive fiducials detected by a standard infrared-based camera, digital reference frame (DRF) and probe setup. Throughout the surgical procedure, macroscopic and microscopic pictures and videos have been taken and have been compared to the virtual 3D models of the patient’s anatomy. In addition, neurophysiological investigations employing somatosensory evoked potentials and electrical stimulation of cortical areas have been performed intraoperatively in order to validate data obtained in functional imaging studies. During surgery, the 3D views through the operating microscope were compared to the 3D images that had previously been generated. Intraoperative ultrasound was added to the navigation as required. After the procedures, bvirtualQ (off-line imaging data) and brealQ (intra-operative microscope view) 3D pictures were visually analyzed by radiologists and surgeons, and compared to common tri-axial 2D images. 3. Results The quality of 3D images, especially with respect to the cortical surface, largely depended on three factors: the quality of the primary data set, the anatomical location, and the breadth of the subdural cerebrospinal fluid space. The gyri and sulci were usually less accurately displayed in the temporal region than in other locations, except in patients with a larger amount of cortical atrophy. Fractal extrapolation can create smooth and potentially valid images of the cortical surface, also depending on the contrast and resolution in the primary data set (Fig. 1). Compared to tri-axial 2D images, orientation was significantly faster and more comprehensive with 3D images. In 3D, complex morphology (gyri, sulci, dural sinuses, Circle of Willis) with respect to an intracranial lesion can be readily understood by a surgeon well-trained in anatomy especially in cases where rotation of the operative field of view is necessary during the approach. Zooming in the virtual images in order to reduce them to the size of the surgical field once more reduces the amount of information presented at a time. These two factors–presenting the radiological data in a 3D view that is customized to the microsurgical field and reducing redundant information outside the current surgical
Fig. 1. Left: 3D image of a region of interest (ROI) in the left frontal cortex rendered by the software of the navigation system. Crosses are presumed entry points for a transsulcal approach. Middle: Fractal 3D extrapolation (Seymore, OpenGL) of the same data set. Left: Intraoperative microscope photograph of the ROI.
S.K. Rosahl et al. / International Congress Series 1281 (2005) 788–792
791
field is kept–significantly enhanced the attention that the surgeon paid to the navigation at hand. Image guidance became more valued the less time the surgeon had to spend by suppressing redundant information related to the virtual field on the images. In general, this was also true for the time spent on the technical requirements of the method itself. All morphological structures that were readily discerned in primary imaging data could also be visualized in virtual 3D models of the surgical situs. Conversely, anatomical details with a size of less than 2 mm (e.g. cranial nerves, smaller vessels) could hardly be shown. Gradual modulation of the opacity of surfaces allowed not only for visualization of hidden anatomical structures but also for relating them to more superficial landmarks that were already within the surgeon’s view. The addition of ultrasound proved helpful in updating the information in case of significant brainshift. Relevant functional information such as eloquent cortical areas or fiber tracts that cannot be accessed by any other technique during surgery was considered the most promising feature of image guidance. However, this information acquired during preoperative functional imaging is hard to validate (e.g. speech areas) and often requires invasive monitoring or additional intra-operative procedures. 4. Conclusion The objectives and prerequisites for microsurgical image-guidance in intracranial procedures differ significantly from those for stereotactic procedures and navigation in other parts of the body. Three key principles can turn intracranial image guidance from a nuisance into an instrument that is of real practical use for a neurosurgeon in daily routine. 4.1. Less is more 3D images zoomed to the size of the real surgical field containing relevant landmarks without redundant information that are delivered by a navigation rig that consumes minimal time in the OR form the basis for acceptance of image guidance by most neurosurgeons in a team. 4.2. Outline target and approach in a single 3D image Gradual tuning of the opacity of outer tissue layers in images is one method to show the structure and borders of the lesion in relation to the anatomy that needs to be dissected by the surgeon. In addition to intra-operative ultrasound, this technique reveals anatomic detail just hidden from direct sight along the surgical route. 4.3. Include functional information in the image During intracranial surgery, preservation of function has become the single most important demand. Data from fMRI or DTI studies can easily be added to the structural image. However, they should be carefully reviewed and–if possible–validated during surgery by monitoring techniques.
792
S.K. Rosahl et al. / International Congress Series 1281 (2005) 788–792
Because almost all intracranial neurosurgical procedures are carried out under microscope magnification, delivering an appropriate 3D image that virtually matches the surgical field calls for imaging procedures with very high image resolution. Anatomical knowledge and experience will remain the most crucial factors affecting the surgical result. Improved images, however, can truly expand the surgeon’s capacity by offering him a de´ja` vue on the individual anatomy and by delivering additional information on the operative field that is invisible through the operating microscope.
www.ics-elsevier.com
De´ja` vue in the operating room—three-dimensional volumetric imaging S.K. Rosahla,T, U. Hubbea, S. Strahlb, S. Schersichb, A. Gharabaghic, G.C. Feiglc, R. Shahidid, M. Samiic a
Department of Neurosurgery, Albert-Ludwigs-University Freiburg, Germany b University of Hannover, Germany c International Neuroscience Institute Hannover, Germany d Image Guidance Laboratories, Stanford University, CA, USA
Abstract. The objectives for microsurgical image-guidance in intracranial procedures are different from the entry-trajectory-target paradigm for stereotactic purposes. From a neurosurgical series of 125 patients with various intracranial pathologies having received surgery that was aided by image guidance, we have derived three basic principles for the successful application of neuronavigation in daily routine: (1) Less is more. Redundant anatomical information-basically all information that is unrelated to surgical landmarks in a particular case-should be omitted from the guiding images. (2) The approach and the surgical target should be visible in a single 3D guiding image. To this end, gradual tuning of the opacity of outer tissue layers in images is the method of choice to outline the in relation to the anatomy that needs to be dissected by the surgeon in order to arrive at the target. (3) All available information on functional tissue properties should be added to the guiding image. Preservation of function has become the single most important demand for neurosurgical procedures. Results of fMRI, DTI and other validated functional studies can readily be added to the structural image. Adhering to these principles may truly enhance the capacities of the surgeon who not only experiences a de´ja` vue of the individual surgical anatomy when looking through the operating microscope but can also base his intra-operative decisions on invisible functional landmarks. D 2005 CARS & Elsevier B.V. All rights reserved. Keywords: Surgical image-guidance; Neuro-navigation; Volumetric image rendering; Three-dimensional (3D) imaging; Neurosurgery; Fractal extrapolation
T Corresponding author. E-mail address: [email protected] (S.K. Rosahl). 0531-5131/ D 2005 CARS & Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2005.03.295
S.K. Rosahl et al. / International Congress Series 1281 (2005) 788–792
789
1. Introduction Intracranial neurosurgery works on slightly different principles as compared to other surgical subjects. First, there is limited space in the surgical field. Second, objects in the field are small, in most cases requiring a microscope to be clearly outlined. Third, the surgical approach and target are often closely surrounded by vitally important tissue that cannot visually be discerned from less eloquent tissue. Fourth, the surgical target usually does not grossly move or change in the interval between imaging procedures and the surgical intervention. Relying on the latter, stereotaxy was created as a whole field within neurological surgery. In stereotaxy, the surgical task is to hit a target inside the intracranial space with needle-like instruments along a straight trajectory from a pre-defined entry point. Navigation, with or without a frame, just defines the coordinates of target and entry points in three-dimensional (3D) space. Tri-axial images are essentially sufficient for these procedures. In microneurosurgery, where the surgeon relies on direct 3D visual information in the surgical field, entirely different tasks should be assigned to image guidance. We set out to explore these tasks from a microsurgical view. 2. Methods MRI (1.5 T, 3 T), fMRI, diffusion tensor imaging (DTI), positron emission tomography (PET), computed tomography (CT), and CT angiography have been employed as the primary imaging modalities. Data taken from 125 patients with various intracranial pathologies (gliomas, meningiomas, cavernomas, sellar and parasellar tumors, lesions in the paranasal sinuses, in the petrous bone, in the brainstem, in the cerebello-pontine angle, and in the craniocervical junction) have been transferred to an image guidance system and processed with software that is capable of rendering high-resolution 3D images (Image Guidance Laboratories, Stanford University, CA, USA). For functional neurosurgery, image guidance was employed in cases of motor cortex stimulation for placement of electrodes and for epilepsy surgery. In selected cases, the surface of the cerebral cortex in the individual patient was extracted with an algorithm based on fractal extrapolation. After designing a surgical strategy, the segmentation and the creation of volumes of interest (VOI) from the imaging data, containing the landmark anatomical structures and functional detail, were done by the neurosurgical team. A virtual bfly throughQ 3D movie was generated that showed the major surgical steps in the planned procedure using the individual imaging data of the patient. The virtual bsurgical fieldQ was rotated to the assumed position of the real field in the OR. Surfaces were gradually rendered translucent in the image to allow a view on the lesion in relation to more superficial morphologic or functional landmarks. The surgical strategy was changed, whenever an improved surgical approach could be derived from these visualizations. With the objective to create a 3D image that contains all the anatomical landmarks that would also appear in the real field during surgery, the VOIs were selected and color-coded by the neurosurgical team. Bony landmarks and vessels were charted. Functional information for the tissue along the surgical route was added and the image was zoomed to the size of the field of the surgical microscope.
790
S.K. Rosahl et al. / International Congress Series 1281 (2005) 788–792
In the operating room, the patients head was registered as usual with 5 to 10 adhesive fiducials detected by a standard infrared-based camera, digital reference frame (DRF) and probe setup. Throughout the surgical procedure, macroscopic and microscopic pictures and videos have been taken and have been compared to the virtual 3D models of the patient’s anatomy. In addition, neurophysiological investigations employing somatosensory evoked potentials and electrical stimulation of cortical areas have been performed intraoperatively in order to validate data obtained in functional imaging studies. During surgery, the 3D views through the operating microscope were compared to the 3D images that had previously been generated. Intraoperative ultrasound was added to the navigation as required. After the procedures, bvirtualQ (off-line imaging data) and brealQ (intra-operative microscope view) 3D pictures were visually analyzed by radiologists and surgeons, and compared to common tri-axial 2D images. 3. Results The quality of 3D images, especially with respect to the cortical surface, largely depended on three factors: the quality of the primary data set, the anatomical location, and the breadth of the subdural cerebrospinal fluid space. The gyri and sulci were usually less accurately displayed in the temporal region than in other locations, except in patients with a larger amount of cortical atrophy. Fractal extrapolation can create smooth and potentially valid images of the cortical surface, also depending on the contrast and resolution in the primary data set (Fig. 1). Compared to tri-axial 2D images, orientation was significantly faster and more comprehensive with 3D images. In 3D, complex morphology (gyri, sulci, dural sinuses, Circle of Willis) with respect to an intracranial lesion can be readily understood by a surgeon well-trained in anatomy especially in cases where rotation of the operative field of view is necessary during the approach. Zooming in the virtual images in order to reduce them to the size of the surgical field once more reduces the amount of information presented at a time. These two factors–presenting the radiological data in a 3D view that is customized to the microsurgical field and reducing redundant information outside the current surgical
Fig. 1. Left: 3D image of a region of interest (ROI) in the left frontal cortex rendered by the software of the navigation system. Crosses are presumed entry points for a transsulcal approach. Middle: Fractal 3D extrapolation (Seymore, OpenGL) of the same data set. Left: Intraoperative microscope photograph of the ROI.
S.K. Rosahl et al. / International Congress Series 1281 (2005) 788–792
791
field is kept–significantly enhanced the attention that the surgeon paid to the navigation at hand. Image guidance became more valued the less time the surgeon had to spend by suppressing redundant information related to the virtual field on the images. In general, this was also true for the time spent on the technical requirements of the method itself. All morphological structures that were readily discerned in primary imaging data could also be visualized in virtual 3D models of the surgical situs. Conversely, anatomical details with a size of less than 2 mm (e.g. cranial nerves, smaller vessels) could hardly be shown. Gradual modulation of the opacity of surfaces allowed not only for visualization of hidden anatomical structures but also for relating them to more superficial landmarks that were already within the surgeon’s view. The addition of ultrasound proved helpful in updating the information in case of significant brainshift. Relevant functional information such as eloquent cortical areas or fiber tracts that cannot be accessed by any other technique during surgery was considered the most promising feature of image guidance. However, this information acquired during preoperative functional imaging is hard to validate (e.g. speech areas) and often requires invasive monitoring or additional intra-operative procedures. 4. Conclusion The objectives and prerequisites for microsurgical image-guidance in intracranial procedures differ significantly from those for stereotactic procedures and navigation in other parts of the body. Three key principles can turn intracranial image guidance from a nuisance into an instrument that is of real practical use for a neurosurgeon in daily routine. 4.1. Less is more 3D images zoomed to the size of the real surgical field containing relevant landmarks without redundant information that are delivered by a navigation rig that consumes minimal time in the OR form the basis for acceptance of image guidance by most neurosurgeons in a team. 4.2. Outline target and approach in a single 3D image Gradual tuning of the opacity of outer tissue layers in images is one method to show the structure and borders of the lesion in relation to the anatomy that needs to be dissected by the surgeon. In addition to intra-operative ultrasound, this technique reveals anatomic detail just hidden from direct sight along the surgical route. 4.3. Include functional information in the image During intracranial surgery, preservation of function has become the single most important demand. Data from fMRI or DTI studies can easily be added to the structural image. However, they should be carefully reviewed and–if possible–validated during surgery by monitoring techniques.
792
S.K. Rosahl et al. / International Congress Series 1281 (2005) 788–792
Because almost all intracranial neurosurgical procedures are carried out under microscope magnification, delivering an appropriate 3D image that virtually matches the surgical field calls for imaging procedures with very high image resolution. Anatomical knowledge and experience will remain the most crucial factors affecting the surgical result. Improved images, however, can truly expand the surgeon’s capacity by offering him a de´ja` vue on the individual anatomy and by delivering additional information on the operative field that is invisible through the operating microscope.