Metabolic and electrophysiological validation of functional MRI

Intraoperative Use of Functional MRI for Surgical Decision Making after Limited or Infeasible Electrocortical Stimulation Mapping

BACKGROUND AND PURPOSE

Functional magnetic resonance imaging (fMRI) is becoming widely recognized as a key component of preoperative neurosurgical planning, although intraoperative electrocortical stimulation (ECS) is considered the gold standard surgical brain mapping method. However, acquiring and interpreting ECS results can sometimes be challenging. This retrospective study assesses whether intraoperative availability of fMRI impacted surgical decision-making when ECS was problematic or unobtainable.

METHODS

Records were reviewed for 191 patients who underwent presurgical fMRI with fMRI loaded into the neuronavigation system. Four patients were excluded as a bur-hole biopsy was performed. Imaging was acquired at 3 Tesla and analyzed using the general linear model with significantly activated pixels determined via individually determined thresholds. fMRI maps were displayed intraoperatively via commercial neuronavigation systems.

RESULTS

Seventy-one cases were planned ECS; however, 18 (25.35%) of these procedures were either not attempted or aborted/limited due to: seizure (10), patient difficulty cooperating with the ECS mapping (4), scarring/limited dural opening (3), or dural bleeding (1). In all aborted/limited ECS cases, the surgeon continued surgery using fMRI to guide surgical decision-making. There was no significant difference in the incidence of postoperative deficits between cases with completed ECS and those with limited/aborted ECS.

CONCLUSIONS

Preoperative fMRI allowed for continuation of surgery in over one-fourth of patients in which planned ECS was incomplete or impossible, without a significantly different incidence of postoperative deficits compared to the patients with completed ECS. This demonstrates additional value of fMRI beyond presurgical planning, as fMRI data served as a backup method to ECS.

Regional neuronal activity in patients with relapsing remitting multiple sclerosis

OBJECTIVES

Although interferon-beta is an established drug for relapsing remitting multiple sclerosis (RRMS), its impact on neuronal activity is not well understood.

METHODS

We investigated 15 patients with RRMS by [¹⁸ F]fluorodeoxyglucose positron emission tomography (FDG-PET) to assess cerebral metabolic rate of glucose (CMR_glc ) before interferon-beta therapy. Further, we performed clinical and neuropsychological investigations. In nine patients, these investigations were repeated after 6 months of therapy. Ten healthy controls were also studied.

RESULTS

We found no significant differences in absolute CMR_glc between patients and controls, or in patients before and during treatment. However, during treatment, relative regional glucose metabolism (rCMRl_glc ) was decreased in cerebellum and increased in parts of left inferior parietal, temporo-occipital, frontal cortical areas, left striatum and right insula. In untreated patients, higher fatigue was associated with lower rCMRl_glc in portions of left posterior cingulate cortex, and higher depression was associated with lower rCMRl_glc within the left superior temporal sulcus. In the pooled sample, higher depression was associated with higher rCMRl_glc in parts of the right precuneus.

CONCLUSIONS

Our results indicate effects of IFN-beta treatment on cerebellar, cortical and subcortical neuronal function. Moreover, more severe fatigue and depression in untreated patients seem to be associated with reduced neuronal activity in left posterior cingulate cortex and left superior temporal cortex, respectively.

Intraoperative Functional Ultrasound Imaging of Human Brain Activity

The functional mapping of brain activity is essential to perform optimal glioma surgery and to minimize the risk of postoperative deficits. We introduce a new, portable neuroimaging modality of the human brain based on functional ultrasound (fUS) for deep functional cortical mapping. Using plane-wave transmissions at an ultrafast frame rate (1 kHz), fUS is performed during surgery to measure transient changes in cerebral blood volume with a high spatiotemporal resolution (250 µm, 1 ms). fUS identifies, maps and differentiates regions of brain activation during task-evoked cortical responses within the depth of a sulcus in both awake and anaesthetized patients.

Radiomic Texture Analysis Mapping Predicts Areas of True Functional MRI Activity

Individual analysis of functional Magnetic Resonance Imaging (fMRI) scans requires user-adjustment of the statistical threshold in order to maximize true functional activity and eliminate false positives. In this study, we propose a novel technique that uses radiomic texture analysis (TA) features associated with heterogeneity to predict areas of true functional activity. Scans of 15 right-handed healthy volunteers were analyzed using SPM8. The resulting functional maps were thresholded to optimize visualization of language areas, resulting in 116 regions of interests (ROIs). A board-certified neuroradiologist classified different ROIs into Expected (E) and Non-Expected (NE) based on their anatomical locations. TA was performed using the mean Echo-Planner Imaging (EPI) volume, and 20 rotation-invariant texture features were obtained for each ROI. Using forward stepwise logistic regression, we built a predictive model that discriminated between E and NE areas of functional activity, with a cross-validation AUC and success rate of 79.84% and 80.19% respectively (specificity/sensitivity of 78.34%/82.61%). This study found that radiomic TA of fMRI scans may allow for determination of areas of true functional activity, and thus eliminate clinician bias.

Functional imaging of cerebral perfusion

The functional imaging of perfusion enables the study of its properties such as the vasoreactivity to circulating gases, the autoregulation and the neurovascular coupling. Downstream from arterial stenosis, this imaging can estimate the vascular reserve and the risk of ischemia in order to adapt the therapeutic strategy. This method reveals the hemodynamic disorders in patients suffering from Alzheimer's disease or with arteriovenous malformations revealed by epilepsy. Functional MRI of the vasoreactivity also helps to better interpret the functional MRI activation in practice and in clinical research.

Effect of disease and recovery on functional anatomy in brain tumor patients: insights from functional MRI and diffusion tensor imaging

Patients with brain tumors provide a unique opportunity to understand functional brain plasticity. Using advanced imaging techniques, such as functional MRI and diffusion tensor imaging, we have gained tremendous knowledge of brain tumor behavior, transformation, infiltration and destruction of nearby structures. Using these advanced techniques as an adjunct with more proven techniques, such as direct cortical stimulation, intraoperative navigation and advanced microsurgical techniques, we now are able to better formulate safer resection trajectories, perform larger resections at reduced risk and better counsel patients and their families about possible complications. Brain mapping in patients with brain tumors and other lesions has shown us that the old idea of fixed function of the adult cerebral cortex is not entirely true. Improving care for patients with brain lesions in the future will depend on better understanding of the functional organization and plasticity of the adult brain. Advanced noninvasive brain imaging will undoubtedly play a role in advancing this understanding.

Acoustically presented semantic decision-making tasks provide a robust depiction of the temporo-parietal speech areas

Functional MRI (fMRI) is routinely used to depict language areas, for example in the preoperative diagnostic work-up of patients with a brain tumour. The objective of this study was to test whether semantic decision making can activate the temporo-parietal language areas better than phonological generation stimuli. Five fMRI language stimuli were tested in 20 healthy volunteers: (i) word generation to a given letter (WG); (ii) verb generation to a given noun (VG); (iii) generation of groups of words (GW); (iv) detection of a semantic violation in sentences (SV); and (v) detection of pseudowords (PW). The stimuli were presented both visually and acoustically. We used a block design and evaluated the data with SPM5 with predefined regions of interest in the frontal and temporo-parietal language areas. A lateralisation index (LI) was also calculated. We found that WG and VG achieved the best results in frontal language areas; VG, SV and PW presented acoustically achieved the best results in the temporo-parietal language areas; and that LI was most reliably calculated in the frontal language areas. An acoustically presented semantic decision making stimulus should be implemented in the preoperative diagnostic work-up to robustly depict the temporo-parietal language areas. The stimulus is easy to understand and perform, and it achieves robust results.

[Clinical application of functional MRI for chronic epilepsy]

Functional magnetic resonance imaging (fMRI) is frequently used in the presurgical diagnostic procedure of epilepsy patients, in particular for lateralization of speech and memory and for localization of the primary motor cortex to delineate the epileptogenic lesion from eloquent brain areas. fMRI is one of the non-invasive procedures in the presurgical diagnostic process, together with medical history, seizure semiology, neurological examination, interictal and ictal EEG, structural MRI, video EEG monitoring and neuropsychology. This diagnostic sequence leads either to the decision for or against elective epilepsy surgery or to the decision to proceed with invasive diagnostic techniques (Wada test, intra-operative or extra-operative cortical stimulation). It is difficult to evaluate the contribution of the fMRI test in isolation to the validity of the entire diagnostic sequence. Complications such as memory loss and aphasia in temporal lobe resections or paresis after frontal lobe resections are rare and rarely of disastrous extent. This further complicates the evaluation of the clinical relevance of fMRI as a predictive tool. In this article studies which investigated the concordance between fMRI and other diagnostic gold standards will be presented as well as the association between presurgical fMRI and postsurgical morbidity.

Is preoperative functional magnetic resonance imaging reliable for language areas mapping in brain tumor surgery? Review of language functional magnetic resonance imaging and direct cortical stimulation correlation studies

OBJECTIVE

Language functional magnetic resonance imaging (fMRI) has been used extensively in the past decade for both clinical and research purposes. Its integration in the preoperative imaging assessment of brain lesions involving eloquent areas is progressively more diffused in neurosurgical practice. Nevertheless, the reliability of language fMRI is unclear. To understand the reliability of preoperative language fMRI in patients operated on for brain tumors, the surgical studies that compared language fMRI with direct cortical stimulation (DCS) were reviewed.

METHODS

Articles comparing language fMRI with DCS of language areas were reviewed with attention to the lesion pathology, the magnetic field, the language tasks used pre- and intraoperatively, and the validation modalities adopted to establish the reliability of language fMRI. We tried to explore the effectiveness of language fMRI in gliomas.

RESULTS

Nine language brain mapping studies compared the findings of fMRI with those of DCS. The studies are not homogeneous for tumor types, magnetic fields, pre- and intraoperative language tasks, intraoperative matching criteria, and results. Sensitivity and specificity were calculated in 5 studies (respectively ranging from 59% to 100% and from 0% to 97%).

CONCLUSION

The contradictory results of these studies do not allow consideration of language fMRI as an alternative tool to DCS in brain lesions located in language areas, especially in gliomas because of the pattern of growth of these tumors. However, language fMRI conducted with high magnet fields is a promising brain mapping tool that must be validated by DCS in methodological robust studies.

Quantitative imaging biomarkers in neuro-oncology

Conventional structural imaging provides limited information on tumor characterization and prognosis. Advances in neurosurgical techniques, radiotherapy planning and novel drug treatments for brain tumors have generated increasing need for reproducible, noninvasive, quantitative imaging biomarkers. This Review considers the role of physiological MRI and PET molecular imaging in understanding metabolic processes associated with tumor growth, blood flow and ultrastructure. We address the utility of various techniques in distinguishing between tumors and non-neoplastic processes, in tumor grading, in defining anatomical relationships between tumor and eloquent brain regions and in determining the biological substrates of treatment response. Much of the evidence is derived from limited case series in individual centers. Despite their 'added value', the effect of these techniques as an adjunct to structural imaging in clinical research and practice remains limited.

[Functional magnetic resonance imaging in brain tumour neurosurgical resection risk assessment]

To establish the possibilities of functional magnetic resonance (fMRI) in the assesment of preservation of the motor and speech brain functions in the primary brain tumour patients planed for neurosurgery.

METHODS AND MATERIAL

fMRI of motor and/or speech areas was performed on 3T MRI unit in 17 patients with primary brain tumours and dominant focal epileptic symptomatology.

RESULTS

None of the patients demonstrated motor neurologic deficit before the operation, while in one patient a moderate speech disorder was noted. Operative treatment has been performed in 11/17 patients, and in 6/11 patients total tumour resection has been performed. Motor deficit has not been noted in any of the patients. Transitory speech deficit was noted in 3/11 patients, while 1/11 patients demonstrated a permanent but mild speech deficit.

CONCLUSION

fMRI may be of significant help in the assessment of potential postoperative neurological deficit risks, enabling the optimization of neurosurgical resection procedure in the brain tumour patients.

Quantitative comparison of functional MRI and direct electrocortical stimulation for functional mapping

BACKGROUND

Mapping functional areas of the brain is important for planning tumour resections. With the increased use of functional magnetic resonance imaging (fMRI) for presurgical planning, there is a need to validate that fMRI activation mapping is consistent with the mapping obtained during surgery using direct electrocortical stimulation (DECS).

METHODS

A quantitative comparison of DECS and fMRI mapping techniques was performed, using a patient-specific conductivity model to find the current distribution resulting from each stimulation site. The resulting DECS stimulation map was compared to the fMRI activation map, using the maximal Dice similarity coefficient (MDSC).

RESULTS

Our results show some agreement between these two mapping techniques--the stimulation site with the largest MOSC was the only site that demonstrated intra-operative effect.

CONCLUSIONS

There is a substantial effort to improve the techniques used to map functional areas, particularly using fMRI. It seems likely that fMRI will eventually provide a valid non-invasive means for functional mapping.

Movement-dependent stroke recovery: a systematic review and meta-analysis of TMS and fMRI evidence

Evidence indicates that experience-dependent cortical plasticity underlies post-stroke motor recovery of the impaired upper extremity. Motor skill learning in neurologically intact individuals is thought to involve the primary motor cortex, and the majority of studies in the animal literature have studied changes in the primary sensorimotor cortex with motor rehabilitation. Whether changes in engagement in the sensorimotor cortex occur in humans after stroke currently is an area of much interest. The present study conducted a meta-analysis on stroke studies examining changes in neural representations following therapy specifically targeting the upper extremity to determine if rehabilitation-related motor recovery is associated with neural plasticity in the sensorimotor cortex of the lesioned hemisphere. Twenty-eight studies investigating upper extremity neural representations (e.g., TMS, fMRI, PET, or SPECT) were identified, and 13 met inclusion criteria as upper extremity intervention training studies. Common outcome variables representing changes in the primary motor and sensorimotor cortices were used in calculating standardized effect sizes for each study. The primary fixed effects model meta-analysis revealed a large overall effect size (ES=0.84, S.D.=0.15, 95% CI=0.76-0.93). Moreover, a fail-safe analysis indicated that 42 null effect studies would be necessary to lower the overall effect size to an insignificant level. These results indicate that neural changes in the sensorimotor cortex of the lesioned hemisphere accompany functional paretic upper extremity motor gains achieved with targeted rehabilitation interventions.

Integrated image- and function-guided surgery in eloquent cortex: a technique report

The ability to effectively identify eloquent cortex in close proximity to brain tumours is a critical component of surgical planning prior to resection. The use of electrocortical stimulation testing (ECS) during awake neurosurgical procedures remains the gold standard for mapping functional areas, yet the preoperative use of non-invasive brain imaging techniques such as fMRI are gaining popularity as supplemental surgical planning tools. In addition, the intraoperative three-dimensional display of fMRI findings co-registered to structural imaging data maximizes the utility of the preoperative mapping for the surgeon. Advances in these techniques have the potential to limit the size and duration of craniotomies as well as the strain placed on the patient, but more research accurately demonstrating their efficacy is required. In this paper, we demonstrate the integration of preoperative fMRI within a neuronavigation system to aid in surgical planning, as well as the integration of these fMRI data with intraoperative ECS mapping results into a three-dimensional dataset for the purpose of cross-validation.

Functional brain mapping and its applications to neurosurgery

Functional brain mapping may be useful for both preoperative planning and intraoperative neurosurgical decision making. "Gold standard" functional studies such as direct electrical stimulation and recording are complemented by newer, less invasive techniques such as functional magnetic resonance imaging. Less invasive techniques allow more areas of the brain to be mapped in more subjects (including healthy subjects) more often (including pre- and postoperatively). Expansion of the armamentarium of tools allows convergent evidence from multiple brain mapping techniques to bear on pre- and intraoperative decision making. Functional imaging techniques are used to map motor, sensory, language, and memory areas in neurosurgical patients with conditions as diverse as brain tumors, vascular lesions, and epilepsy. In the future, coregistration of high resolution anatomic and physiological data from multiple complementary sources will be used to plan more neurosurgical procedures, including minimally invasive procedures. Along the way, new insights on fundamental processes such as the biology of tumors and brain plasticity are likely to be revealed.

Rater-dependent accuracy in predicting the spatial location of functional centers on anatomical MR images

OBJECTIVES

The determination of eloquent cortex is essential when planning neurosurgical approaches to brain lesions. This study examined the abilities of medical personnel of various backgrounds to predict the location of functional cortex using anatomical information provided by MR imaging.

PATIENTS AND METHODS

Neurosurgeons, neuroscientists, neuroradiologists, medical students and MR technologists viewed anatomical MR images acquired from patients with brain tumors and healthy controls. These five groups of raters were then asked to locate the primary motor hand, supplementary motor and primary auditory areas and their predictions were compared to fMRI data acquired from the same subjects.

RESULTS

The overall mean distance from the center of the fMRI activation was 2.38 cm. The neuroscientists performed the best and MR technologists performed the worst (mean distance from center of 1.83 and 3.04 cm, respectively, p<0.05). The difference between patients and controls was not significant. The mean distance by ROI was primary motor hand 2.03 cm, auditory area 2.06 cm and supplementary motor area 3.18 cm (p<0.05). Raters also performed best in the medial-lateral direction, compared to superior-inferior and anterior-posterior directions (mean distances from center 0.42, 1.04 and 1.81 cm, respectively). Finally, the approximate minimum fields of view necessary to capture the entire fMRI activations using the raters' predictions ranged from 5 to 15 cm, or 3 to 12 cm larger than the fMRI activations.

CONCLUSION

Medical personnel of various training perform poorly when using only anatomical information to predict the location of functional areas of cortex.

IRM fonctionnelle cérébrale : bases physiologiques, techniques et applications cliniques

Brain functional MRI (fMRI) provides an indirect mapping of cerebral activity, based on the detection of local changes in blood flow and oxygenation levels that are associated with neuronal activity (BOLD contrast). fMRI allows noninvasive studies of normal and pathological aspects of the brain's functional organization. It is based on the comparison of two or more cognitive states. Echoplanar imaging is the technique of choice, providing the quickest study of the entire brain. Activation maps are calculated from a statistical analysis of the local signal changes. fMRI has become one of the most widely used functional imaging techniques in neuroscience. In clinical practice, fMRI can identify eloquent areas involved in motor and language functions in surgical patients and can evaluate the risk of postoperative neurological deficit.

Sensorimotor Cortex Localization: Comparison of Magnetoencephalography, Functional MR Imaging, and Intraoperative Cortical Mapping

PURPOSE

To prospectively evaluate magnetoencephalography (MEG) and functional magnetic resonance (MR) imaging, as compared with intraoperative cortical mapping, for identification of the central sulcus.

MATERIALS AND METHODS

Fifteen patients (six men, nine women; age range, 25-58 years) with a lesion near the primary sensorimotor cortex (13 gliomas, one cavernous hemangioma, and one meningioma) were examined after institutional review board approval and written informed consent from each patient were obtained. At MEG, evoked magnetic fields to median nerve stimulation were recorded; at functional MR imaging, hemodynamic responses to self-paced palmar flexion of the wrist were imaged. General linear model analysis with contextual clustering (P < .01) was used to analyze functional MR imaging data, and dipole modeling was used to analyze MEG data. MEG and functional MR localizations were compared with intraoperative cortical mappings. The distance from the area of functional MR imaging activation to the tumor margin was compared between the patients with discordant and those with concordant intraoperative mapping findings by using unpaired t testing.

RESULTS

MEG depicted the central sulcus correctly in all 15 patients, as verified at intraoperative mapping. The functional MR imaging localization results agreed with the intraoperative mappings in 11 patients. In all four patients with a false localization, the primary activation was in the postcentral sulcus region, but it did not differ significantly from the primary activation in the patients with correct localization with respect to proximity to the tumor (P = .38). Furthermore, at functional MR imaging, multiple nonprimary areas were activated, with considerable interindividual variation.

CONCLUSION

Although both MEG and functional MR imaging can provide useful information for neurosurgical planning, in the present study, MEG proved to be superior for locating the central sulcus. Activation of multiple nonprimary cerebral areas may confound the interpretation of functional MR imaging results.

Preoperative functional MR imaging localization of language and motor areas: effect on therapeutic decision making in patients with potentially resectable brain tumors

PURPOSE

To prospectively evaluate the effect of preoperative functional magnetic resonance (MR) imaging localization of language and motor areas on therapeutic decision making in patients with potentially resectable brain tumors.

MATERIALS AND METHODS

The Institutional Review Board approved this HIPAA-compliant study, and each patient gave written informed consent. Thirty-nine consecutive patients (19 male, 20 female; mean age, 42.2 years) referred for functional MR imaging for possible tumor resection were prospectively evaluated. A preoperative diagnosis of brain tumor was made in all patients. Sentence completion and bilateral hand squeeze tasks were used to map language and sensory motor areas. Neurosurgeons completed questionnaires regarding the proposed treatment plan before and after functional MR imaging and after surgery. They also gave confidence ratings for functional MR imaging results and estimated the effect on surgical time, extent of resection, and surgical approach. The effect of functional MR imaging on changes in treatment plan was assessed with the Wilcoxon signed rank test. Differences in confidence ratings between altered and unaltered treatment plans were assessed with the Mann-Whitney U test. The estimated influence of functional MR imaging on surgical time, extent of resection, and surgical approach was denoted with summary statistics.

RESULTS

Treatment plans before and after functional MR imaging differed in 19 patients (P < .05), with a more aggressive approach recommended after imaging in 18 patients. There were no significant differences in confidence ratings for functional MR imaging between altered and unaltered plans. Functional MR imaging resulted in reduced surgical time (estimated reduction, 15-60 minutes) in 22 patients who underwent surgery, a more aggressive resection in six, and a smaller craniotomy in two.

CONCLUSION

Functional MR imaging enables the selection of a more aggressive therapeutic approach than might otherwise be considered because of functional risk. In certain patients, surgical time may be shortened, the extent of resection increased, and craniotomy size decreased.

L’imagerie par résonance magnétique cérébrale fonctionnelle en pratique clinique

In the last decade, functional MRI (fMRI) has become one of the most widely used functional imaging technique in neurosciences. However, its clinical applications remain limited. Despite methodological and practical issues, fMRI data has been validated by different techniques (magnetoencephalography, Wada test, electrical and magnetic stimulations, and surgical resections). In neurosurgical practice, fMRI can identify eloquent areas involved in motor and language functions, and may evaluate characteristics of postoperative neurological deficit including its occurrence, clinical presentation and duration. This may help to inform patients and to prepare postoperative care. fMRI may also identify epileptic foci. In neurological practice, fMRI may help to determine prognosis of recovery after stroke, appropriate medication, and rehabilitation. fMRI may help to identify patients at risk of developing Alzheimer disease. Finally, cerebrovascular reactivity imaging is an interesting approach that might provide new radiological insights of vascular function.

Correspondence between EEG-fMRI and EEG dipole localisation of interictal discharges in focal epilepsy

EEG-fMRI and EEG dipole source localisation are two non-invasive imaging methods that can be applied to the study of the haemodynamic and electrical consequences of epileptic discharges. Using them in combination has the potential to allow imaging with the spatial resolution of fMRI and the temporal resolution of EEG. However, although considerable data are available concerning their concordance in studies involving event-related potentials (ERPs), less is known about how well they agree in epilepsy. To this end, 17 patients were selected from a database of 57 who had undergone an EEG-fMRI scanning session followed by a separate EEG session outside of the scanner. Spatiotemporal dipole modelling was compared with the peak and closest EEG-fMRI activations and deactivations. On average, the dipoles were 58.5 mm from the voxel with the highest positive t value and 32.5 mm from the nearest activated voxel. For deactivations, the corresponding values were 60.8 and 34.0 mm. These values are considerably higher than is generally observed with ERPs, probably as a result of the relatively widespread field, which can lead to artificially deep dipoles, and the occurrence of EEG-fMRI responses remote from the presumed focus of the epileptic activity. The results suggest that EEG and MEG inverse solutions for equivalent current dipole approaches should not be strongly constrained by EEG-fMRI results in epilepsy, and that the use of distributed source modelling will be a more appropriate way of combining EEG-fMRI results with source localisation techniques.

Functional Magnetic Resonance Imaging-integrated Neuronavigation: Correlation between Lesion-to-Motor Cortex Distance and Outcome

OBJECTIVE:

The integration of functional magnetic resonance imaging (fMRI) data into neuronavigation is a new concept for surgery adjacent to the motor cortex. However, the clinical value remains to be defined. In this study, we investigated the correlation between the lesion-to-fMRI activation distance and the occurrence of a new postoperative deficit.

METHODS:

fMRI-integrated “functional” neuronavigation was used for surgery around the motor strip in 54 patients. During standardized paradigms for hand, foot, and tongue movements, echo-planar imaging T2* blood oxygen level-dependent sequences were acquired and processed with BrainVoyager 2000 software (Brain Innovation, Maastricht, The Netherlands). Neuronavigation was performed with the VectorVision2 system (BrainLAB, Heimstetten, Germany). For outcome analysis, patient age, histological findings, size of lesion, distance to the fMRI areas, preoperative and postoperative Karnofsky index, postoperative motor deficit, and type of resection were analyzed.

RESULTS:

In 45 patients, a gross total resection (&gt;95%) was performed, and for 9 lesions (low-grade glioma, 4; glioblastoma, 5), a subtotal resection (80–95%) was achieved. The neurological outcome improved in 16 patients (29.6%), was unchanged in 29 patients (53.7%), and deteriorated in 9 patients (16.7%). Significant predictors of a new neurological deficit were a lesion-to-activation distance of less than 5 mm (P &lt; 0.01) and incomplete resection (P &lt; 0.05).

CONCLUSION:

fMRI-integrated neuronavigation is a useful concept to assess the risk of a new motor deficit after surgery. Our data suggest that a lesion-to-activation distance of less than 5 mm is associated with a higher risk of neurological deterioration. Within a 10-mm range, cortical stimulation should be performed. For a lesion-to-activation distance of more than 10 mm, a complete resection can be achieved safely. The visualization of fiber tracks is desirable to complete the representation of the motor system.

Preoperative blood oxygen level-dependent functional magnetic resonance imaging in patients with primary brain tumors: clinical application and outcome

OBJECTIVE

This study sought to evaluate the ability of blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to successfully identify functional cortical areas in patients with primary brain tumors, to evaluate the use of the fMRI results in presurgical planning, and to assess the functional outcome of the patients with respect to the functional maps obtained with fMRI.

METHODS

The study included 25 consecutive preoperative fMRI sessions in patients with primary brain tumors in or near sensorimotor and/or language cortices. All fMRI paradigms were analyzed and rated according to the degree of success. Several distances between tumor and functional cortex as delineated with BOLD fMRI were measured to assess the topographic relationship between these two structures. Pre- and postoperative neurological statuses were obtained from the patients' journals.

RESULTS

Acquisition of BOLD fMRI images was successful in 80% of the cases. The primary cause of unsuccessful fMRI was echo-planar imaging signal voids that were the result of previous craniotomy; the secondary cause was excessive motion. The neurosurgeons used the fMRI results for preoperative planning in 75% of the cases in which fMRI was successful. The risk of postoperative loss of function tested with fMRI was significantly lower when the distance between tumor periphery and BOLD activity was 10 mm or more.

CONCLUSION

The majority of patients with primary brain tumors were capable of satisfactorily performing the fMRI paradigms, and the information obtained was used in the preoperative planning. A distance of 10 mm or more between the functional cortex, as delineated with fMRI, and the tumor significantly reduced the risk of postoperative loss of function.

Motor Evoked Potential Monitoring with Supratentorial Surgery

OBJECTIVE:

To assess feasibility and clinical value of motor evoked potential (MEP) monitoring with surgery close to supratentorial motor areas and pathways.

METHODS:

Functional mapping by somatosensory evoked potential phase reversal and continuous MEP recording after high-frequency repetitive electrical cortex stimulation was performed during 182 operations in 177 patients. Significant MEP changes were reported to trigger surgical reaction. Intraoperative surgical and electrophysiological findings were documented prospectively. Patient files were reviewed for clinical data. MEP monitoring results were correlated with motor outcome.

RESULTS:

MEP recording was successful in 167 cases (91.8%). Inadequate electrode placement was an important reason for failed recording in the remaining patients, whereas preoperative paresis and anesthesia had no significant effect. Permanently disabling new motor deficit occurred in 8 cases (4.9%), whereas transient and non-disabling weakness was frequent (27.4%). Significant MEP changes occurred during 64 operations (39%). Irreversible MEP loss always predicted new, usually permanent, paresis. Unaltered MEP recordings indicated unimpaired motor function in the monitored muscle groups, except for rare transient deficit because of late edema and rebleeding. Irreversible MEP deterioration without loss and reversible changes could be associated with new paresis, which was transient in most patients. No major complications were observed, except for intraoperative generalized seizure in one epilepsy patient under insufficient anticonvulsant therapy.

CONCLUSION:

MEP monitoring with supratentorial surgery is feasible and safe. It may help to maximize resection within the limits of preserved motor function. Further evidence is needed to confirm these results.

Functional MR imaging: paradigms for clinical preoperative mapping

Clinical applications of functional MR imaging include mapping of brain functions in relationship to intracranial tumors, seizure foci, or vascular malformations to determine the risk for performing surgical excision, the need for intraoperative mapping during excision, and selecting the optimal surgical approach to a lesion. A variety of paradigms are used to produce a blood-oxygen-level-dependent response in various brain regions, which can be identified with functional MR imaging. The paradigms used include active motor, language, or cognitive tasks, and passive tactile, auditory, or visual stimuli. Activation usually indicates the location of eloquent cortex. Lack of function in a region cannot be assumed when functional MR imaging shows absence of activation within the region.

Evaluating requirements for spatial resolution of fMRI for neurosurgical planning

The unambiguous localization of eloquent functional areas is necessary to decrease the neurological morbidity of neurosurgical procedures. We explored the minimum spatial resolution requirements for functional magnetic resonance imaging (fMRI) data acquisition when brain mapping is used in neurosurgical planning and navigation. Using a 1.5 Tesla clinical MRI scanner, eight patients with brain tumors underwent fMRI scans using spatial resolution of approximately 4 x 4 x 4 mm(3) to map the eloquent motor and language areas during the performance of cognitive/sensorimotor tasks. The fMRI results were then used intra-operatively in an open MRI system to delineate eloquent areas. Retrospectively, activation patterns were visually inspected by a neurosurgeon to determine qualitatively whether ambiguity with respect to the activation boundaries, due to low spatial resolution, could be of potential significance for surgical guidance. A significant degree of ambiguity in both the extent and shape of activation was judged to be present in data from six of the eight patients. Analysis of fMRI data at multiple resolutions from a normal volunteer showed that at 3 mm isotropic resolution, eloquent areas were better localized within the gray matter although there was still some potential for ambiguity caused by activations appearing to cross a sulcus. The data acquired with 2-mm isotropic voxels significantly enhanced the spatial localization of activation to within the gray matter. Thus, isotropic spatial resolution on the order of 2 x 2 x 2 mm(3), which is much higher than the resolutions used in typical fMRI examinations, may be needed for the unambiguous identification of cortical activation with respect to tumors and important anatomical landmarks.

Motor Evoked Potential Monitoring for the Surgery of Brain Tumours and Vascular Malformations

Brain surgery incurs a significant risk of a new motor deficit in lesions within or adjacent to the motor areas and pathways which, for the patient, presents one of the most disabling complications of such operations. It is a major concern of intracranial procedures to delineate and monitor motor regions in order to preserve their structural and functional integrity, while still achieving maximal cytoreduction. The technique of motor evoked potential recording has had to be adapted to intraoperative recording conditions under general anaesthesia, but has been available for clinical use now for almost ten years. This contribution summarizes the current technique and related methods, as well as our clinical experience in some 400 cases of MEP monitoring in supratentorial tumors, lesions in and around the brainstem, and aneurysm surgery. Intraoperative MEP recordings have been shown to reliably reflect an impending new motor deficit. Irreversible MEP deterioration heralds new paresis, and unaltered recordings predict preserved motor function. This is also true in aneurysm surgery where conventional SEP monitoring may yield false-negative results with regard to development of a new motor deficit. Moreover, if MEP deterioration can be reversed, or halted by early surgical intervention, the presence of only a transient motor deficit, or even the lack of a new postoperative deficit, indicates the success of the MEP monitoring method in the prevention of a significant motor impairment. Certain complicated lesions can only be operated on at all because MEP monitoring is available. In conclusion, intraoperative MEP monitoring is a useful aid in brain surgery with which to avoid a new motor deficit without compromise to the surgical result. Controlled prospective studies will be required to verify the clinical value of the method.

[Physiological and technical limitations of functional magnetic resonance imaging (fMRI)--consequences for clinical use]

Functional magnetic resonance imaging (fMRI) is the most common noninvasive technique in functional neuroanatomy. The capabilities and limitations of the method will be discussed based on a short review of the current knowledge about the neurovascular relationship. The focus of this article is on current methodical and technical problems regarding fMRI-based detection and localization of neuronal activity. Main error sources and their influence on the reliability and validity of fMRI-methods are presented. Appropriate solution strategies will be proposed and evaluated. Finally, the clinical relevance of MR-based diagnostic methods are discussed.

Four facets of a single brain: behaviour, cerebral blood flow/metabolism, neuronal activity and neurotransmitter dynamics

Is functional neuroimaging a royal way to understand brain function or is it a new phrenology without an exact understanding what we measure? After two decades of imaging revolution, more and more authors ask this question. Brain functions are multidimensional, which can be approached from the point of (1) behavioural measures, (2) brain activation as reflected by blood flow and metabolic changes, (3) electrical activity of cells and cell-populations, and (4) neurotransmitter dynamics (release, receptor binding and reuptake). Using imaging techniques, we must take into consideration that even during the simplest task all of these processes operate in a closely interacting manner. Therefore, before drawing final conclusions about brain functions on the basis of a single aspect of these mechanisms, we must clarify the exact relationship among them. In this paper, we address this issue in order to draw attention to a number of uncertainties and controversies in the relationship of the four facets of brain functions.

Reproducibility of functional MR imaging results using two different MR systems

BACKGROUND AND PURPOSE

In the application of functional MR imaging for presurgical planning, high reproducibility is required. We investigated whether the reproducibility of functional MR imaging results in healthy volunteers depended on the MR system used.

METHODS

Visual functional MR imaging reproducibility experiments were performed with 12 subjects, by using two comparable 1.5-T MR systems from different manufacturers. Each session consisted of two runs, and each subject underwent three sessions, two on one system and one on the other. Reproducibility measures D (distance in millimeters) and R(size) and R(overlap) (ratios) were calculated under three conditions: same session, which compared runs from one session; intersession, which compared runs from different sessions but from the same system; and intermachine, which compared runs from the two different systems. The data were averaged per condition and per system, and were compared.

RESULTS

The average same-session values of the reproducibility measures did not differ significantly between the two systems. The average intersession values did not differ significantly as to the volume of activation (R(size)), but did differ significantly as to the location of this volume (D and R(overlap)). The average intermachine reproducibility did not differ significantly from the average intersession reproducibility of the MR system with the worst reproducibility.

CONCLUSION

The location of activated voxels from visual functional MR imaging experiments varied more between sessions on one MR system than on other MR system. The amount of the activated voxels is independent of the MR system used. We suggest that sites performing functional MR imaging for presurgical planning measure the intersession reproducibility to determine an accurate surgical safety margin.

Usefulness of intraoperative electrical subcortical mapping during surgery for low-grade gliomas located within eloquent brain regions: functional results in a consecutive series of 103 patients

OBJECT

Although a growing number of authors currently advocate surgery to treat low-grade gliomas, controversy still persists, especially because of the risk of inducing neurological sequelae when the tumor is located within eloquent brain areas. Many researchers performing preoperative neurofunctional imaging and intraoperative electrophysiological methods have recently reported on the usefulness of cortical functional mapping. Despite the frequent involvement of subcortical structures by these gliomas, very few investigators have specifically raised the subject of fiber tracking. The authors in this report describe the importance of mapping cortical and subcortical functional regions by using intraoperative real-time direct electrical stimulations during resection of low-grade gliomas.

METHODS

Between 1996 and 2001, 103 patients harboring a corticosubcortical low-grade glioma in an eloquent area, with no or only mild deficit, had undergone surgery during which intraoperative electrical mapping of functional cortical sites and subcortical pathways was performed throughout the procedure. Both eloquent cortical areas and corresponding white fibers were systematically detected and preserved, thus defining the resection boundaries. Despite an 80% rate of immediate postoperative neurological worsening, 94% of patients recovered their preoperative status within 3 months--10% even improved--and then returned to a normal socioprofessional life. Eighty percent of resections were classified as total or subtotal based on control magnetic resonance images.

CONCLUSIONS

The use of functional mapping of the white matter together with cortical mapping allowed the authors to optimize the benefit/risk ratio of surgery of low-grade glioma invading eloquent regions. Given that preoperative fiber tracking with the aid of neuroimaging is not yet validated, we used intraoperative real-time cortical and subcortical stimulations as a valuable adjunct to the other mapping methods.

Motor functional MRI for pre-operative and intraoperative neurosurgical guidance

Functional MRI (fMRI) may provide a means of locating areas of eloquent cortex that can be used to guide neurosurgeons in their quest to maximize intracerebral tumour resection whilst minimizing post-procedural neurological deficits. This work aimed to develop and provide an initial assessment of such a technique. 19 patients with mass lesions close to the primary motor cortex underwent fMRI at 1.5T. A single shot echo planar technique was used to acquire data corresponding to right and left hand movement. Resultant activation maps were used to aid pre-surgical planning. Data was used in conjunction with an intraoperative navigation system in 13 cases. Activation was attributed to primary motor, primary somatosensory or supplementary motor cortex in 17 of 19 subjects. No permanent changes in motor deficit were detected post surgery. The additional information provided by fMRI, particularly when incorporated into a neuronavigation guided craniotomy, was deemed highly valuable to the neurosurgeon as it enabled safe resection of tumour in anatomical locations previously deemed to be too high risk for safe resection using conventional (non-fMRI-guided) technique. This observation is reinforced by the fact that no patients suffered permanent neurological deficit after radical tumour debulking (surgical estimates >90% tumour resection).