Preoperative PET activation for assessment of motor cortex area in precentral chondroma.

BACKGROUND: A main problem in the preoperative planning for precentral tumors is the exact assessment of the spatial relationship between the tumor and the functionally relevant brain areas, which may be difficult using only morphologically oriented imaging (CT, MRI). Therefore, we applied motor activation PET and PET/MRI overlay in a patient with a precentral tumor. DESCRIPTION: We report the case of a 21-year-old woman suffering from progressive right-sided headache and intermittent dysesthesia of the left leg. MRI showed a hypointense tumor with inhomogenous contrast enhancement in the right precentral area. For preoperative assessment of the spatial relationship between the tumor and the motor cortex area, the patient underwent two F-18-fluorodeoxyglucose positron emission tomography (PET) scans (1. resting condition and 2. motor activation of the left leg) and subsequent calculation of subtraction images of activation minus rest. Fusion of PET and MRI data (PET/MRI overlay) was performed for bimodal function and morphology presentation. PET revealed an activation pattern behind and below the tumor, indicating that the motor cortex area was shifted to the back. PET findings were confirmed by intraoperative electrophysiology. Cortical stimulation combined with intraoperative neuronavigation localized the motor area of the left foot and leg exactly at the dorsal border, below and lateral to the lesion. After complete resection of the solid tumor, histopathological examination revealed a chondroma. The postoperative course was uneventful, and the patient was discharged without neurological deficits. CONCLUSIONS: This case shows that biomodal imaging (PET/MRI) provides a noninvasive exact assessment of functionally important cortex areas for preoperative planning in patients with cerebral lesions.     

Visualization of the eloquent motor system by integration of MEG,functional, and anisotropic diffusion-weighted MRI in functional neuronavigation

BACKGROUND: In this study, we visualized the eloquent motor system including the somatosensory-motor cortex and corticospinal tract on a neuronavigation system, integrating magnetoencephalography (MEG), functional magnetic resonance imaging (fMRI), and anisotropic diffusion-weighted MRI (ADWI). METHODS: Four patients with brain lesions adjacent to the eloquent motor system were studied. Motor-evoked responses (MER) by finger-tapping paradigm were acquired with a 1.5-Tesla MR scanner, and somatosensory-evoked magnetic fields (SEF) by median nerve stimulation were measured with a 204-channel MEG system. In the same fMRI examination, ADWI and anatomic three-dimensional T1-weighted imaging (3-D MRI) were obtained. Activated areas of MER, estimated SEF dipoles, and the corticospinal tract on ADWI were coregistered to 3-D MRI, and the combined MR data were transferred to a neuronavigation system (functional neuronavigation). Intraoperative recording of cortical somatosensory-evoked potentials was performed for confirmation of the central sulcus. RESULTS: Combination of fMRI and MEG enabled firm identification of the central sulcus. Functional neuronavigation facilitated extensive tumor resection, having the advantage of sparing the motor cortex and corticospinal tract in all cases. CONCLUSIONS: The proposed functional neuronavigation allows neurosurgeons to perform effective and maximal resection of brain lesions, identifying and sparing eloquent cortical components and their subcortical connections. Potential clinical application of this technique is discussed.     

Registration of functional and anatomical MRI: accuracy assessment and application in navigated neurosurgery.

OBJECTIVE: A procedure for acquisition, automated registration, and fusion of functional and anatomical magnetic resonance images is presented. Its accuracy is quantitatively assessed using a publicly available gold standard. A patient case is used to illustrate the technique's clinical usefulness in image-guided neurosurgery. MATERIALS AND METHODS: Before and after functional MRI (fMRI) acquisition, additional anatomical images were acquired at spatial locations identical to those of the functional images (5-10 slices) for the purpose of voxel-based image registration. Registration accuracy of the anatomical volumes and high-resolution 3D MRI volumes (MP-RAGE imaging) was quantified using adapted data (8 patients) originating from the Vanderbilt Retrospective Registration Evaluation Project (NIH project 1 R01 NS33926-02). Selecting three subsets of slices from that data (5 slices/6 mm slice distance, 10 slices/3 mm distance, and 10 slices/6 mm distance), the small number of images available from fMRI acquisition was taken into account. Accuracies in registering these sparse data sets were then compared to the accuracy achieved using complete data. For clinical patient data (16 patients), fMRI images were fused with MP-RAGE images, thereby integrating anatomical images with information about the locations of functional areas. The resulting images were used for planning and navigation during tumor resections using an operating microscope (MKM, Zeiss). RESULTS: Quantitative analysis showed no loss of registration accuracy due to a reduced number of slices, regardless of whether 5 or 10 slices were used. For small-volume coverage in the anatomical images (thickness 24 mm), registration of one patient failed, and this could easily be identified by visual inspection. No failures were experienced when 54 mm was covered. In the clinical environment, all 16 interventions using fused fMRI and MRI data were successful. CONCLUSIONS: Automatic registration of functional and high-resolution anatomical MRI was found to be sufficiently accurate and reliable for use in stereotactic neurosurgery.     

Functional neuronavigation combined with intra-operative 3D ultrasound: Initial experiences during surgical resections close to eloquent brain areas and future directions in automatic brain shift compensation of preoperative data

Summary Objective. The aims of this study were: 1) To develop protocols for, integration and assessment of the usefulness of high quality fMRI (functional magnetic resonance imaging) and DTI (diffusion tensor imaging) data in an ultrasound-based neuronavigation system. 2) To develop and demonstrate a co-registration method for automatic brain-shift correction of pre-operative MR data using intra-operative 3D ultrasound. Methods. Twelve patients undergoing brain surgery were scanned to obtain structural and fMRI data before the operation. In six of these patients, DTI data was also obtained. The preoperative data was imported into a commercial ultrasound-based navigation system and used for surgical planning and guidance. Intra-operative ultrasound volumes were acquired when needed during surgery and the multimodal data was used for guidance and resection control. The use of the available image information during planning and surgery was recorded. An automatic voxel-based registration method between preoperative MRA and intra-operative 3D ultrasound angiography (Power Doppler) was developed and tested postoperatively. Results. The study showed that it is possible to implement robust, high-quality protocols for fMRI and DTI and that the acquired data could be seamlessly integrated in an ultrasound-based neuronavigation system. Navigation based on fMRI data was found to be important for pre-operative planning in all twelve procedures. In five out of eleven cases the data was also found useful during the resection. DTI data was found to be useful for planning in all five cases where these data were imported into the navigation system. In two out of four cases DTI data was also considered important during the resection (in one case DTI data were acquired but not imported and in another case fMRI and DTI data could only be used for planning). Information regarding the location of important functional areas (fMRI) was more beneficial during the planning phase while DTI data was more helpful during the resection. Furthermore, the surgeon found it more user-friendly and efficient to interpret fMRI and DTI information when shown in a navigation system as compared to the traditional display on a light board or monitor. Updating MRI data for brain-shift using automatic co-registration of preoperative MRI with intra-operative ultrasound was feasible. Conclusion. In the present study we have demonstrated how both fMRI and DTI data can be acquired and integrated into a neuronavigation system for improved surgical planning and guidance. The surgeons reported that the integration of fMRI and DTI data in the navigation system represented valuable additional information presented in a user-friendly way and functional neuronavigation is now in routine use at our hospital. Furthermore, the present study showed that automatic ultrasound-based updates of important pre-operative MRI data are feasible and hence can be used to compensate for brain shift. Rasmussen and Lindseth have contributed equally to this paper.     

Cortical areas involved in virtual movement of phantom limbs: comparison with normal subjects

OBJECTIVE: To demonstrate that amputees performing "virtual" movements of their amputated limb activate cortical areas previously devoted to their missing limb, we studied amputees with functional magnetic resonance imaging (fMRI) and positron emission tomographic (PET) scans and compared the results with those of normal volunteers performing imaginary movements during fMRI acquisitions. METHODS: Ten amputees (age range, 33-92 yr; average age, 49 yr; six men and four women; eight upper-limb and two lower-limb amputations) able to move their phantom limb at will were studied by fMRI (all patients) and PET scan (seven patients). The time between amputation and fMRI and PET studies ranged from 1 to 27 years (average, 13 yr). Patients were asked to perform virtual movements of the amputated limb and normal movements of the contralateral normal limb according to the functional images acquisition procedure. Movements of the stump were also used to differentiate stump cortical areas from virtual movement-activated areas. Ten right-handed volunteers, age- and sex-matched to the amputees, were also studied by fMRI. All volunteers were asked to perform four tasks during their fMRI study: imaginary movements of their right arm (1 task) and foot (1 task) and real movements of their left arm (1 task) and foot (1 task). RESULTS: In amputees, virtual movements of the missing limbs produced contralateral primary sensorimotor cortex activation on both fMRI and PET scans. These activation areas, different from the stump activation areas, were similar in location to contralateral normal limb-activated areas. Quantitatively, in two amputees who claimed to be able to perform both slow and fast virtual movements, regional cerebral blood flow measured by PET scan in the precentral gyrus increased significantly during fast movements in comparison with slow virtual movements. In normal subjects, significant differences between real versus imaginary fMRI activations were found (for both foot and hand movements); imaginary right hand and foot tasks activated primarily the contralateral supplementary motor areas, with no significant activation detected in the contralateral precentral or postcentral gyri. CONCLUSION: Primary sensorimotor cortical areas can be activated by phantom-limb movements and thus can be considered functional for several years or decades after amputation. In this study, we found that the location of the activation of these areas is comparable to that of activations produced by normal movements in control subjects or in amputees.     

Enhanced accuracy in differential diagnosis of radiation necrosis by positron emission tomography-magnetic resonance imaging coregistration: technical case report

OBJECTIVE AND IMPORTANCE: To demonstrate the usefulness of positron emission tomography-magnetic resonance imaging (MRI) coregistration for differentiation of radiation necrosis and recurrent tumor in stereotactic planning. CLINICAL PRESENTATION: T1-weighted MRI scans of a 43-year-old woman revealed a contrast-enhancing lesion 4 years after open removal of a recurrent, right parieto-occipital Grade II oligodendroglioma and subsequent external radiation therapy. The suspected contrast-enhancing lesion revealed only moderate tracer uptake (1.3 times the uptake in the contralateral normal cortex) in a coregistered [11C]methionine positron emission tomographic scan. Approximately 15 mm posterior and mesial to the center of the contrast-enhancing lesion, however, an area of higher tracer uptake was found (1.8 times that of the contralateral normal cortex), which exhibited only very minor contrast enhancement on MRI. TECHNIQUE: The coregistered images were used for planning stereotactic serial biopsies, from the contrast-enhancing lesion as well as from the area with higher methionine uptake. Histological examination demonstrated that the contrast-enhancing lesion with low methionine uptake was necrotic tissue, and the nonenhancing area with high methionine uptake was recurrent tumor. CONCLUSION: High-resolution positron emission tomography and modern coregistration techniques allow differentiation of contrast enhancement and methionine uptake in irradiated brain tissue within small areas. High methionine uptake is typical for recurrent tumor tissue and can be differentiated from minor tracer accumulation resulting from disruption of the blood-brain barrier or macrophage activity within the necrotic area.     

Intraoperative magnetic resonance imaging combined with neuronavigation: a new concept

OBJECTIVE: Intraoperative image data may be used not only to evaluate the extent of a tumor resection but also to update neuronavigation, compensating for brain shift. To date, however, intraoperative magnetic resonance imaging (MRI) can be combined only with navigation microscopes that are separated from the magnetic field, thus requiring time-consuming intraoperative patient transport. To help solve this problem, we investigated whether a new navigation microscope can be used within the fringe field of the MRI scanner. METHODS: The navigation microscope was placed at the 5-G line of a 0.2 MRI device. Patients were positioned lying down directly on the table of the scanner, with their heads placed approximately 1.5 m from the center of the magnet, fixed in an MRI-compatible ceramic head holder. Standard operating instruments were used. For intraoperative imaging, we slid the table into the center of the magnet in less than 30 seconds. RESULTS: By use of this setup, we operated on 22 patients. In all patients, anatomic neuronavigation could be used in combination with intraoperative MRI. In addition, in 12 patients, functional data from magnetoencephalographic or functional MRI studies were integrated, resulting in functional neuronavigation. We did not encounter adverse effects of the low magnetic field during navigation. Moreover, intraoperative imaging was not disturbed by the navigation microscope and vice versa. CONCLUSION: Functional neuronavigation and intraoperative MRI can be used essentially simultaneously without the need for lengthy intraoperative patient transport. The combination of intraoperative imaging with functional neuronavigation offers the opportunity for more radical resections and fewer complications.     

Comparison of functional brain PET images and intraoperative brain-mapping data using image-guided surgery.

OBJECTIVE: Knowledge about the spatial localization of eloquent brain areas is essential for resecting lesions in the vicinity of these areas. The classical approach is to perform surgery on the awake patient under local anesthesia using brain-mapping techniques. As an alternative, the location of eloquent areas can be visualized by preoperative functional brain-imaging techniques, for example, positron emission tomography (PET), functional magnetic resonance imaging (fMRI), or magnetoencephalography (MEG). Using functional activation PET, both methods were combined by integration into a frameless navigation system (BrainLAB) and used to map speech-eloquent areas. PATIENTS AND METHODS: Speech-eloquent areas were localized preoperatively in seven patients with a left-sided glioma using 2-[(18)F]-2-desoxy-D-glucose PET. Patients were scanned under silence conditions (i.e., with the patient remaining silent in a sound-proof cabin), and speech was activated using a verb-generation paradigm. The PET data were transferred to the neuronavigation workstation and matched with a preoperative 3D-MRI using an automatic image-fusion algorithm. Intraoperative speech localization was performed using brain-mapping techniques under local anesthesia with bipolar cortical stimulation. The stimulator position was mapped into the MRI/PET data set by neuronavigational tracking of the instrument. RESULTS: Functional PET images were integrated into the MRI-based neuronavigational system and could be transferred exactly to the operative field. By the additional integration of cortical stimulation, intraoperative electrophysiological findings can be directly compared with preoperative functional images. Seven patients with left-sided glioma were operated on using this protocol, confirming the technical feasibility. In three of seven patients, preoperative PET findings were not supported by intraoperative mapping. CONCLUSIONS: This matching and mapping technique is suitable for monitoring eloquent speech areas during surgical resection of extensive left-sided low-grade gliomas, allowing a direct comparison between intraoperative electrophysiological brain mapping and preoperative functional brain-imaging findings. The sensitivity and specificity of functional imaging techniques can now be evaluated by reconciling the data with the intraoperative stimulation results.     

功能磁共振成像定位皮质运动区与术中电刺激运动诱发电位的前瞻对照研究

目的以术中电刺激运动诱发电位（MEP）监测为对照,评价中央区脑肿瘤术前运用血液氧饱和水平检测（BOLD）技术的功能磁共振成像（fMRI）定位皮质运动区的准确性。方法此项前瞻性研究选取了16例中央区脑肿瘤。开颅手术前分别执行手运动激发程式,运用BOLD技术的fMRI定位皮质运动区。将fMRI影像与磁共振导航序列影像融合。以术中MEP监测作为皮质运动区定位的标准技术。在神经导航下定位fMRI的各个激活区,单独或联合运用短串经颅电刺激（TCES）和直接皮质电刺激（DCES）,在前臂及手部记录复合肌肉动作电位。比较两种技术的吻合度,以评价fMRI定位的皮质运动区的准确性。结果fMRI与MEP的吻合率为92．3％,其中与TCES的吻合率为100．0％,与DCES的吻合率为66．7％。结论运用BOLD技术的fMRI敏感度高,可实现中央区脑肿瘤术前皮质运动区的准确定位。     

Preoperative assessment of motor cortex and pyramidal tracts in central cavernoma employing functional and diffusion-weighted magnetic resonance imaging

BACKGROUND: Functional MRI (fMRI) combines anatomic with functional information and has therefore been widely used for preoperative planning of patients with mass lesions affecting functionally important brain regions. However, the courses of functionally important fiber tracts are not visualized. We therefore propose to combine fMRI with diffusion-weighted MRI (DWI) that allows visualization of large fiber tracts and to implement this data in a neuronavigation system. METHODS: DWI was successfully performed at a field strength of 1.5 Tesla, employing a spin-echo sequence with gradient sensitivity in six noncollinear directions to visualize the course of the pyramidal tracts, and was combined with echo-planar T2* fMRI during a hand motor task in a patient with central cavernoma. RESULTS: Fusion of both data sets allowed visualization of the displacement of both the primary sensorimotor area (M1) and its large descending fiber tracts. Intraoperatively, these data were used to aid in neuronavigation. Confirmation was obtained by intraoperative electrical stimulation. Postoperative MRI revealed an undisrupted pyramidal tract in the neurologically intact patient. CONCLUSION: The combination of fMRI with DWI allows for assessment of functionally important cortical areas and additional visualization of large fiber tracts. Information about the orientation of fiber tracts in normal appearing white matter in patients with tumors within the cortical motor system cannot be obtained by other functional or conventional imaging methods and is vital for reducing operative morbidity as the information about functional cortex. This technique might, therefore, have the prospect of guiding neurosurgical interventions, especially when linked to a neuronavigation system.     

The relationship of imaging techniques to the accuracy of frameless stereotaxy

OBJECTIVE: We analyzed the accuracy of a frameless stereotactic system using computed tomographic (CT) and magnetic resonance imaging (MRI) scans of different slice thickness and T(1) versus T(2) weighting of MRI. METHODS: An open skull with graphite pegs fixed to its base was used for all scans. CT scans were done with slice thicknesses of 1, 2 and 3 mm. MRI-visible markers were placed on top of pegs for T(1)-weighted and T(2)-weighted MRI scans, which were acquired at thicknesses of 1.5, 3 and 5 mm. For each scan, 3 separate registrations of a probe were performed; the distance between the actual probe location and that displayed on the registered image was noted. Each measurements was repeated 3 times for each registration. RESULTS: Greatest accuracy was achieved with 3-mm-slice CT scans; this was not improved by using thinner slices. T(1)-weighted 1.5-mm MRI scans were 23% less accurate and T(2)-weighted 3-mm scans 37% less accurate. CONCLUSIONS: Frameless stereotaxy should be done using CT scans when the greatest possible accuracy is desired. There appears to be no advantage to using slice thicknesses less than 3 mm. For most craniotomy applications, T(1)-weighted MRI using 3-mm slices provides sufficient accuracy. Lesions imaged only on T(2)-weighted MRI also can be approached with adequate precision using 3-mm scans.     

Neuronavigation and functional MRI for surgery in patients with lesion in eloquent brain areas.

OBJECTIVE: Surgery in patients with lesions in eloquent areas is still a challenge for the neurosurgeon. The aim of surgical interventions should be the radical removal of the lesions with functional preservation. Functional brain imaging methods provide the preoperative demonstration of those brain areas and their relationship to pathologic structures. MATERIAL: Twenty-seven patients with pathologic lesions in or near eloquent regions were investigated with functional magnetic resonance imaging (fMRI). Nineteen patients were neurologically intact preoperatively, and presented only with headache and/or seizure. Eight patients had a minor neurological deficit. Twenty-five patients underwent surgery. Preoperatively a computed tomography (CT) scan or a magnetic resonance imaging procedure with five skin fiducials was performed. The data were transferred to the neuronavigation workstation. The tumour was lined out in colours, and reconstruction in a triplanar format as well as three-dimensionally was implemented. The information from the fMRI concerning the functional areas was transferred into the images manually to account for EPI distortions. Fifteen patients were operated on using the combination fMRI/neuronavigation. Diagnoses included eleven gliomas, two meningeomas, one metastasis and one cavernoma. RESULTS: In seven patients the tumour was removed completely, eight patients had residual tumour, demonstrated by early postoperative MRI. All patients with residual tumour had gliomas that involved functional areas. Postoperatively no patient had an additional neurological deficit. CONCLUSION: Functional MRI provides important additional information in patients with lesions in eloquent brain areas. In combination with neuronavigation this is a very helpful technique for surgical interventions on these patients to reduce morbidity. Nonetheless, there are still open questions concerning accuracy of display of the functional areas and integration into a neuronavigation system.     

Functional MR imaging and oligodendrogliomas

The localization of functional areas obtained from functional MRI (fMRI) is useful for patients suffering from tumors contiguous to eloquent brain areas. fRMI is an efficient tool in the strategy of treatment of low grade oligodendroglioamas in the rolandic area in intact or slightly impaired patients. It can be used preoperatively to assess motor functional areas. Indeed there is a good correlation for motor cortex lesions when using comparison between fMRI and intraoperative findings. Direct integration of fMRI data into neuronavigation enables to better visualize and preserve eloquent brain areas. One must be aware of fMRI limits. It is still often used with the control of direct cortical stimulations.     

Cranial neuronavigation with direct integration of (11)C methionine positron emission tomography (PET) data -- results of a pilot study in 32 surgical cases

BACKGROUND: MRI detects small intracranial lesions, but has difficulties in differentiating between tumour, gliosis and edema. (11)C methionine-PET may help to overcome this problem. For its appropriate intra-operative use, it must be integrated into neuronavigation. We present the results of our pilot study with this method. METHOD: 32 patients with 34 intracranial lesions detected by MRI underwent additional (11)C methionine-PET, because the pathophysiological behaviour or the tumour delineation was unclear. All lesions were treated surgically. In 25 patients PET data could be integrated directly into cranial neuronavigation. FINDINGS: (11)C methionine uptake was observed in 27/34 lesions, 26 of them were tumours: 14 malignant and 7 benign gliomas, 3 gliomas without further histological typing, one Ewing sarcoma and one non-Hodgkin lymphoma. Only one (11)C methionine positive lesion was non-tumourous: it was staged as post-irradiation necrosis in a patient operated on for a malignant glioma. 3/7 (11)C-methionine negative lesions were classified as gliosis (n=2) and M. Whipple (n=1), but 4/7 were tumours: 2 astrocytomas WHO(degrees)II, 1 DNT and one astrocytoma WHO(degrees)III. The sensitivity of (11)C methionine-PET was 87%, the specificity 75%, the positive predictive value 96% and the negative predictive value 43%. In all tumourous cases with positive tracer uptake the borderline area of the tumour was better defined by (11)C methionine-PET than by MRI. INTERPRETATION: A positive (11)C methionine-PET is highly suspicious of a tumour, a negative one does not exclude it. (11)C methionine-PET seems to be more sensitive than MRI for differentiating between tumour and edema or gliosis. Simultaneous integration MRI and (11)C methionine-PET into cranial neuronavigation can facilitate cross total tumour removal in glioma surgery.     

Supratentorial cavernomas in eloquent brain areas: application of neuronavigation and functional MRI in operative planning

AIM: Cavernomas located in eloquent areas of cerebral hemispheres represent a challenge for the neurosurgeon. An accurate surgical approach is essential to completely remove the lesion with function preservation. Aim of this study was to evaluate the usefulness of integration between standard magnetic resonance imaging (MRI) for neuronavigation and functional MRI (fMRI) in preoperative planning and intraoperative removal of cavernomas. METHODS: Between June 2000 and December 2002, 21 patients underwent surgery for supratentorial subcortical cavernomas. Eleven lesions were located adjacent to eloquent brain areas. All the patients in the series underwent MRI for neuronavigation and, since January 2002, in 6 cases of lesions located in eloquent areas, fMRI was also performed, with subsequent images fusion. The surgical approach was performed via the transgyral route under conventional and ultrasound-guided neuronavigation. RESULTS: All the lesions were totally removed. No morbidity was seen in patients harbouring lesions in non eloquent areas. Four patients with lesions in critical areas suffered transient focal deficits, but only one patient of this series was operated on by the auxilium of image fusion. In 7 patients operated on by conventional image-guided surgery and affected by preoperative seizures, no further seizures were observed after surgery. In 3 patients more hosting lesions neighbouring critical areas, the perilesional ring was not removed, observing persistence of seizures pharmacologically treated. In 4 of the 6 patients (all affected by seizures), operated on by fMRI auxilium, lesion removal was associated to the removal of the perilesional ring. No further epilepsy was seen in these patients. CONCLUSIONS: In all the cases the use of neuronavigation allowed minimally invasive approaches and radical excision of the lesions. Moreover, fMRI seemed to provide important additional information in patients with lesions in eloquent brain areas, allowing a more aggressive approach on the perilesional tissue to the aim of resolving seizures, in absence of an increase in the morbidity rate.     

Is the head position during preoperative image data acquisition essential for the accuracy of navigated brain tumor surgery?

OBJECTIVE: To analyze the influence of head positioning during preoperative image data acquisition on intraoperative accuracy of modern neuronavigation systems. MATERIAL AND METHODS: All measurements were performed preoperatively before opening the head. In 24 patients, preoperative MR image data acquisition was performed twice on a 0.5 T scanner using a contrast-enhanced T1-weighted sequence; first in the neutral head position, and thereafter in the surgical head position for pterional craniotomy. For both data sets, the Sylvian fissure, the central sulcus, and the superior and inferior temporal sulci were depicted on the patient's scalp using the frameless neuronavigation system EasyGuide Neurotrade mark. At the beginning of surgery, with the head fixed in a Mayfield clamp and an articulated instrument holder being used for fixation of the navigation system's pointer, the distances of 10 correlating points of the sulci for the two data sets were measured. To evaluate the accuracy of the navigation system in this experimental set-up, a phantom study was also performed. RESULTS: The phantom study revealed a mean inaccuracy of 1.6 mm (range 0.1-2.3 mm, standard deviation 0.6 mm). The patient study revealed a mean inaccuracy of 1.8 mm (range 0.4-2.8 mm, standard deviation 0.5 mm). CONCLUSIONS: The data suggest that the positioning of the patient's head during preoperative imaging plays no relevant role in intraoperative accuracy of neuronavigation. However, further studies and a larger number of patients with various pathologies in different regions of the brain are necessary to obtain a better understanding of the problem of brain shift in neuronavigation due to patient positioning alone, and to avoid procedure-related operative morbidity.     

Navigated transcranial magnetic stimulation for presurgical planning--correlation with functional MRI.

PURPOSE: This paper describes the potential of navigated transcranial magnetic stimulation to map the motor cortex in patients with mass lesions near the primary motor cortex by comparing the results of this technique to those of functional MRI. MATERIAL AND METHODS: Ten patients with mass lesions near the central sulcus were studied preoperatively using a figure-of-eight transcranial magnetic stimulator attached to a neuronavigation system to allow for direct visualization of the stimulated brain region. Subsequently, in all patients a blood oxygenation level dependent 2D multislice multishot T2*-weighted gradient echo EPI sequence on a 1.5 T Philips Gyroscan during motor activation was performed. Results of both methods were coregistered and compared. RESULTS: The distances between the peak parenchymal fMRI activation and the cortical area where TMS elicited the maximum MEPs ranged between 0 and 1.2 cm (mean 0.6 cm, SD 0.4 cm). CONCLUSION: We conclude that navigated TMS is a reliable alternative for localizing the motor-related areas in the human brain preoperatively and therefore may be a useful adjunct or, in selected patients, even a helpful alternative to functional MRI.     

Glioma surgery using a multimodal navigation system with integrated metabolic images

OBJECT: A multimodal neuronavigation system using metabolic images with PET and anatomical images from MR images is described here for glioma surgery. The efficacy of the multimodal neuronavigation system was evaluated by comparing the results with that of the conventional navigation system, which routinely uses anatomical images from MR and CT imaging as guides. METHODS: Thirty-three patients with cerebral glioma underwent 36 operations with the aid of either a multimodal or conventional navigation system. All of the patients were preliminarily examined using PET with l-methyl-[11C] methionine (MET) for surgical planning. Seventeen of the operations were performed with the multimodal navigation system by integrating the MET-PET images with anatomical MR images. The other 19 operations were performed using a conventional navigation system based solely on MR imaging. RESULTS: The multimodal navigation system proved to be more useful than the conventional navigation system in determining the area to be resected by providing a clearer tumor boundary, especially in cases of recurrent tumor that had lost a normal gyral pattern. The multimodal navigation system was therefore more effective than the conventional navigation system in decreasing the mass of the tumor remnant in the resectable portion. A multivariate regression analysis revealed that the multimodal navigation system-guided surgery benefited patient survival significantly more than the conventional navigation-guided surgery (p = 0.016, odds ratio 0.52 [95% confidence interval 0.29-0.88]). CONCLUSIONS: The authors' preliminary intrainstitutional comparison between the 2 navigation systems suggested the possible premise of multimodal navigation. The multimodal navigation system using MET-PET fusion imaging is an interesting technique that may prove to be valuable in the future.     

Factors influencing the application accuracy of neuronavigation systems

OBJECTIVE: The overall accuracy of neuronavigation systems may be influenced by (1) the technical accuracy, (2) the registration process, (3) voxel size and/or distortion of image data and (4) intraoperative events. The aim of this study was to test the influence of the registration and imaging modality on the accuracy. METHODS: A plexiglas phantom with 32 rods was taken for navigation targeting. Sixteen fiducials were attached to the surface of the phantom forming two different attachment patterns (clustered vs. diffusely scattered). This model was scanned by MRI and CT (1-mm slices). Registration was performed using different numbers and attachment patterns of the fiducials. Using CT or MRI, the localization error was measured in image space as the Euclidean distance between targets defined in image space and those detected in the physical space. Accuracy was measured with two commercial systems, the Zeiss MKM and the StealthStation. RESULTS: The mean localization error varied between 1.59 +/- 0.29 mm (MKM, 8 scattered fiducials, CT scanning) and 3.86 +/- 2.19 mm (MKM, 4 clustered fiducials, MRI). The worst localization error was 9.5 mm (MKM). In case of an optimal registration, the 95th percentile for the localization error was 2.2 (MKM) and 2.75 mm (StealthStation). The imaging modality has only minor influence on the localization error, with CT increasing accuracy minimally. Both the fiducial number and the attachment pattern critically influence the localization error: 8 fiducials and a generalized attachment pattern increase the accuracy significantly. No correlation between the calculated registration accuracy and the measured localization accuracy was found. CONCLUSION: The application accuracy of different neuronavigation systems critically depends on the registration. The calculated registration accuracy provided by the system does not correspond to the localization error found in reality. The accuracy of frameless neuronavigation systems is comparable to that of classical frame-based stereotactic devices.