Functional MRI and 18F FDG-positron emission tomography for presurgical planning: comparison with electrical cortical stimulation

Comparative study of preoperative functional imaging combined with tractography for prediction of iatrogenic motor deficits

OBJECTIVE

Robust preoperative imaging can improve the extent of resection in patients with brain tumors while minimizing postoperative neurological morbidity. Both structural and functional imaging techniques can provide helpful preoperative information. A recent study found that transcranial magnetic stimulation (TMS) tractography has significant predictive value for permanent deficits. The present study directly compares the predictive value of TMS tractography and task-based functional MRI (fMRI) tractography in the same cohort of glioma patients.

METHODS

Clinical outcome data were collected from charts of patients with motor eloquent glioma and preoperative fMRI and TMS studies. The primary outcome was a new or worsened motor deficit present at the 3-month postoperative follow-up, which was termed a "permanent deficit." Postoperative MR images were overlaid onto preoperative plans to determine which imaging features were resected. Multiple fractional anisotropic thresholds (FATs) were screened for both TMS and fMRI tractography. The predictive value of the various thresholds was modeled using receiver operating characteristic curve analysis.

RESULTS

Forty patients were included in this study. Six patients (15%) sustained permanent postoperative motor deficits. A significantly greater predictive value was found for TMS tractography than for fMRI tractography regardless of the FAT. Despite 35% of patients showing clinically relevant neuroplasticity captured by TMS, only 2.5% of patients showed a blood oxygen level–dependent signal displaced from the precentral gyrus. Comparing the best-performing FAT for both modalities, TMS seeded tractography showed superior predictive value across all metrics: sensitivity, specificity, positive predictive value, and negative predictive value.

CONCLUSIONS

The results from this study indicate that the prediction of permanent deficits with TMS tractography is superior to that with fMRI tractography, possibly because TMS tractography captures clinically relevant neuroplasticity. However, future large-scale prospective studies are needed to fully illuminate the proper role of each modality in comprehensive presurgical workups for patients with motor-eloquent tumors.

Surgical Treatment of Glioblastoma: State-of-the-Art and Future Trends

Glioblastoma (GBM) is a highly aggressive disease and is associated with poor prognosis despite treatment advances in recent years. Surgical resection of tumor remains the main therapeutic option when approaching these patients, especially when combined with adjuvant radiochemotherapy. In the present study, we conducted a comprehensive literature review on the state-of-the-art and future trends of the surgical treatment of GBM, emphasizing topics that have been the object of recent study.

Correlation of Preoperative Functional Magnetic Resonance Imaging (fMRI) with Intraoperative Cortical Stimulation in Surgeries of Eloquent Brain Lesions

Background

Direct Cortical Stimulation (DCS) represents the gold standard for mapping of eloquent brain cortex. However, DCS is an invasive and time-consuming procedure. fMRI has become a useful tool to delineate motor and sensory eloquent cortex from the areas of planned neurosurgical resection. In our study, we will be studying the reliability of preoperative imaging when compared with the intraoperative DCS.

Objectives

The aim of this study was to assess the reliability of fMRI by comparing it with DCS.

Methods and Materials

Thirty patients with eloquent cortex lesions were admitted. Preoperative fMRI sequences were loaded into a neuro-navigational system. Intraoperative motor mapping was done by DCS. The location of all cortical stimulated points was correlated with the cortical functional structures. Based on it, specificity, sensitivity, positive predictive value, negative predictive value of fMRI was calculated. Preoperative and postoperative Karnofsky score and MRC grading was then noted.

Results

Concordance between fMRI and DCS was noted in 26 cases. Overall mean sensitivity, specificity, positive and negative predictive value of fMRI as compared to DCS was 95%, 92.48%, 85.56%, and 96.08%, respectively. Preoperative and Postoperative Karnofsky score stayed same in most of the cases [25/30].

Conclusions

DCS remains the gold standard for mapping eloquent cortex in-spite of its invasiveness, side effects such as seizures and cost concerns. Although fMRI cannot replace DCS, it can guide and increase the efficacy in resection, select high-risk patients for intraoperative monitoring, help in preoperative stratification of risk counseling and preservation of neurological status in eloquent brain lesions.

Advanced Imaging Techniques for Newly Diagnosed and Recurrent Gliomas

Management of gliomas following initial diagnosis requires thoughtful presurgical planning followed by regular imaging to monitor treatment response and survey for new tumor growth. Traditional MR imaging modalities such as T1 post-contrast and T2-weighted sequences have long been a staple of tumor diagnosis, surgical planning, and post-treatment surveillance. While these sequences remain integral in the management of gliomas, advances in imaging techniques have allowed for a more detailed characterization of tumor characteristics. Advanced MR sequences such as perfusion, diffusion, and susceptibility weighted imaging, as well as PET scans have emerged as valuable tools to inform clinical decision making and provide a non-invasive way to help distinguish between tumor recurrence and pseudoprogression. Furthermore, these advances in imaging have extended to the operating room and assist in making surgical resections safer. Nevertheless, surgery, chemotherapy, and radiation treatment continue to make the interpretation of MR changes difficult for glioma patients. As analytics and machine learning techniques improve, radiomics offers the potential to be more quantitative and personalized in the interpretation of imaging data for gliomas. In this review, we describe the role of these newer imaging modalities during the different stages of management for patients with gliomas, focusing on the pre-operative, post-operative, and surveillance periods. Finally, we discuss radiomics as a means of promoting personalized patient care in the future.

[Functional magnetic resonance imaging in neurosurgery]

The study is a short review of articles concerning functional magnetic resonance imaging (fMRI) and its practical application in neurosurgery. Advantages and disadvantages of the methods are considered, the results of surgical treatment of patients using functional navigation are presented. Separate attention is paid to fMRI precision, a new resting-state method of visualization. Practical advices of fMRI application in neurooncology and surgery of arteriovenous malformations are given.

Role of MRI-Based Functional Imaging in Improving the Therapeutic Index of Radiotherapy in Cancer Treatment

Advances in radiation technology, such as intensity-modulated radiation therapy (IMRT), have largely enabled a biological dose escalation of the target volume (TV) and reduce the dose to adjacent tissues or organs at risk (OARs). However, the risk of radiation-induced injury increases as more radiation dose utilized during radiation therapy (RT), which predominantly limits further increases in TV dose distribution and reduces the local control rate. Thus, the accurate target delineation is crucial. Recently, technological improvements for precise target delineation have obtained more attention in the field of RT. The addition of functional imaging to RT can provide a more accurate anatomy of the tumor and normal tissues (such as location and size), along with biological information that aids to optimize the therapeutic index (TI) of RT. In this review, we discuss the application of some common MRI-based functional imaging techniques in clinical practice. In addition, we summarize the main challenges and prospects of these imaging technologies, expecting more inspiring developments and more productive research paths in the near future.

[Functional magnetic resonance imaging in neurosurgery]

The review of publications on functional magnetic resonance imaging (fMRI) and its practical application in neurosurgery is presented. Advantages and disadvantages are selected taking pathogenesis into account. Results of surgical treatment with use of functional navigation are described. Separate attention is paid to fMRI precision by its comparing with direct cortical stimulation. New resting-state method of visualization is observed. Practical advices are given of fMRI application in neurooncology and surgery of arteriovenous malformations.

Functional Mapping for Glioma Surgery, Part 1: Preoperative Mapping Tools

Although intraoperative mapping of brain areas was shown to promote greater extent of resection and reduce functional deficits, this was shown only recently for some noninvasive techniques. Yet, proper surgical planning, indication, and patient consultation require reliable noninvasive techniques. Because functional magnetic resonance imaging, tractography, and neurophysiologic methods like navigated transcranial magnetic stimulation and magnetoencephalography allow identifying eloquent areas prior to resective surgery and tailor the surgical approach, this article provides an overview on the individual strengths and limitations of each modality.

State-of-the-art imaging for glioma surgery

Diffuse gliomas are infiltrative primary brain tumors with a poor prognosis despite multimodal treatment. Maximum safe resection is recommended whenever feasible. The extent of resection (EOR) is positively correlated with survival. Identification of glioma tissue during surgery is difficult due to its diffuse nature. Therefore, glioma resection is imaging-guided, making the choice for imaging technique an important aspect of glioma surgery. The current standard for resection guidance in non-enhancing gliomas is T2 weighted or T2w-fluid attenuation inversion recovery magnetic resonance imaging (MRI), and in enhancing gliomas T1-weighted MRI with a gadolinium-based contrast agent. Other MRI sequences, like magnetic resonance spectroscopy, imaging modalities, such as positron emission tomography, as well as intraoperative imaging techniques, including the use of fluorescence, are also available for the guidance of glioma resection. The neurosurgeon’s goal is to find the balance between maximizing the EOR and preserving brain functions since surgery-induced neurological deficits result in lower quality of life and shortened survival. This requires localization of important brain functions and white matter tracts to aid the pre-operative planning and surgical decision-making. Visualization of brain functions and white matter tracts is possible with functional MRI, diffusion tensor imaging, magnetoencephalography, and navigated transcranial magnetic stimulation. In this review, we discuss the current available imaging techniques for the guidance of glioma resection and the localization of brain functions and white matter tracts.

Management of Glioblastoma, Present and Future

Glioblastomas are the most common malignant brain tumor and despite extensive research have a dismal prognosis. This review focuses on the current treatment paradigms of glioblastoma and highlights current advances in surgical approaches, imaging techniques, molecular diagnostics, and translational efforts. Several promising clinical trials in immunotherapy and personalized medicine are discussed and the importance of quality of life in the patients and their caregivers both during active treatment and survivorship is also commented on.

Neuroanatomical Considerations in Preoperative Functional Brain Mapping

Task-based functional magnetic resonance imaging (fMRI) for the presurgical assessment of eloquent cortex is increasingly relied upon by surgeons, neurologists, and radiologists. The utility of fMRI stems from the lack of correlation between topographic anatomy and functional anatomy. fMRI can noninvasively reveal the functional anatomy of a given individual thereby allowing the surgeon to choose the most appropriate surgical trajectory, attain the most complete resection, and offer the best chance of preserving function. This dissociation between function and topography is even more critical to understand when disease distorts normal anatomic relations and when chronic evolution of pathology leads to reorganization of cortical function as can be seen with seizures or slow growing tumors. fMRI can demonstrate the functional anatomy of language, motor, vision, and memory systems. Accurate interpretation not only requires knowledge of the expected patterns of activations in the regions of interest but also demands an understanding of the many adjacent "bystander" activations that represent participatory neural activity but not the eloquent region in question. In addition, fMRI interpretation requires an understanding of the limitations of this technique when expected activity is either missing or seemingly displaced in location.

Clinical Long-Term Follow-Up Evaluation of Functional Neuronavigation in Adult Cerebral Gliomas

OBJECTIVE

To assess the application of functional neuronavigation in surgeries of adult cerebral gliomas.

METHODS

We performed a retrospective analysis of 375 cases of adult cerebral glioma patients who underwent microsurgical treatment between 2011 and 2017 in our department. Among them, 142 patients underwent surgery using functional neuronavigation (group A), and the other 233 patients were operated on without the help of functional neuronavigation (group B). For both groups, we categorized them into several subgroups according to the lesion locations.

RESULTS

A significant difference in the gross total resection rate was observed between group A and group B (P = 0.001 for overall; P = 0.036 for EO area; and P = 0.004 for BBT area). The postoperative complication rate of group A was much lower than that of group B (P = 0.003 for overall; and P = 0.016 for BBT area). The postoperative 6-month Karnofsky Performance Scale score of all patients in group A was significantly higher than that of group B. Kaplan-Meier survival analyses showed significant increases in the median survival time of group A compared with that of group B (P < 0.001 for overall; P = 0.012 for EO area; P = 0.006 for BBT area), and the Cox proportional regression analysis estimated the hazard ratio of the functional neuronavigation to be 0.533, helping reduce the risk of death by 46.7%.

CONCLUSIONS

This study confirmed that the application of neuronavigation in adult glioma surgery can improve postoperative quality of life and lengthen the survival time of patients, especially in cases involving the brainstem and the eloquent area.

Combining Functional Studies with Intraoperative MRI in Glioma Surgery

Maximal safe resection is the cornerstone of treatment for low-grade and high-grade gliomas. In addition to high-resolution anatomic MRI studies that highlight tumor architecture, it is important to determine the relationship of the tumor to the eloquent cortical and subcortical areas to avoid introducing or exacerbating a neurologic deficit. The goal of this review was to highlight imaging modalities that provide functional information and can be integrated with intraoperative MRI navigation to maximize the extent of resection while preserving a patient's neurologic function.

Current and future strategies for treatment of glioma

Gliomas are one of the most common types of primary brain tumors and have remained particularly challenging to treat. This review illustrates a multidisciplinary approach to the treatment of glioma and glioblastoma. We will review current advances in surgical approaches, novel imaging techniques, advanced molecular characterization of tumors and translational efforts for treatment. We will focus on current clinical trials as well as the pursuit of personalized or precision therapy. We will also comment on the importance of both quality of life of our patients and their care givers.

Functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) maps the spatiotemporal distribution of neural activity in the brain under varying cognitive conditions. Since its inception in 1991, blood oxygen level-dependent (BOLD) fMRI has rapidly become a vital methodology in basic and applied neuroscience research. In the clinical realm, it has become an established tool for presurgical functional brain mapping. This chapter has three principal aims. First, we review key physiologic, biophysical, and methodologic principles that underlie BOLD fMRI, regardless of its particular area of application. These principles inform a nuanced interpretation of the BOLD fMRI signal, along with its neurophysiologic significance and pitfalls. Second, we illustrate the clinical application of task-based fMRI to presurgical motor, language, and memory mapping in patients with lesions near eloquent brain areas. Integration of BOLD fMRI and diffusion tensor white-matter tractography provides a road map for presurgical planning and intraoperative navigation that helps to maximize the extent of lesion resection while minimizing the risk of postoperative neurologic deficits. Finally, we highlight several basic principles of resting-state fMRI and its emerging translational clinical applications. Resting-state fMRI represents an important paradigm shift, focusing attention on functional connectivity within intrinsic cognitive networks.

Functional preoperative and intraoperative mapping and monitoring: increasing safety and efficacy in glioma surgery

Greater extent of resection (EOR) of low-grade gliomas is associated with improved survival. Proximity to eloquent cortical regions often limits resectability and elevates the risk of surgery-related deficits. Therefore, functional localization of eloquent cortex or subcortical fiber tracts can enhance the EOR and functional outcome. Imaging techniques such as functional MRI and diffusion tensor imaging fiber tracking, and neurophysiological methods like navigated transcranial magnetic stimulation and magnetoencephalography, make it possible to identify eloquent areas prior to resective surgery and to tailor indication and surgical approach but also to assess the surgical risk. Intraoperative monitoring with direct cortical stimulation and subcortical stimulation enables surgeons to preserve essential functional tissue during surgery. Through tailored pre- and intraoperative mapping and monitoring the EOR can be maximized, with reduced rates of surgery-related deficits.

Cortical Activation Through Passive-Motion Functional MRI

BACKGROUND AND PURPOSE

Functional brain mapping is an important technique for neurosurgical planning, particularly for patients with tumors or epilepsy; however, mapping has traditionally involved invasive techniques. Existing noninvasive techniques require patient compliance and may not be suitable for young children. We performed a retrospective review of our experience with passive-motion functional MR imaging in anesthetized patients to determine the diagnostic yield of this technique.

MATERIALS AND METHODS

A retrospective review of patients undergoing passive-motion fMRI under general anesthesia at a single institution over a 2.5-year period was performed. Clinical records were evaluated to determine the indication for fMRI, the ability to detect cortical activation, and, if present, the location of cortical activation.

RESULTS

We identified 62 studies in 56 patients in this time period. The most common indication for fMRI was epilepsy/seizures. Passive-motion fMRI identified upper-extremity cortical activation in 105 of 119 (88%) limbs evaluated, of which 90 (86%) activations were in an orthotopic location. Lower-extremity cortical activation was identified in 86 of 118 (73%) limbs evaluated, of which 73 (85%) activations were in an orthotopic location.

CONCLUSIONS

Passive-motion fMRI was successful in identifying cortical activation in most of the patients. This tool can be implemented easily and can aid in surgical planning for children with tumors or candidates for epilepsy surgery, particularly those who may be too young to comply with existing noninvasive functional measures.

Preoperative functional MRI localization of language areas in Chinese patients with brain tumors: Validation with intraoperative electrocortical mapping

Ten Chinese patients with brain tumors involving language regions were selected. Preoperative functional MRI was performed to locate Broca's or Wernicke's area, and the cortex that was essential for language function was determined by electrocortical mapping. A site-by-site comparison between functional MRI and electrocortical mapping was performed with the aid of a neuronavigation device. Results showed that the sensitivity and specificity of preoperative functional MRI were 80.0% and 85.0% in Broca's area and 66.6% and 85.2% in Wernicke's area, respectively. These experimental findings indicate that functional MRI is an accurate, reliable technique with which to identify the location of Wernicke's area or Broca's area in patients with brain tumors.

Frequency-dependent neural activity in Parkinson's disease

The brainstem and basal ganglia are important in the pathophysiology of Parkinson's disease (PD). Reliable and sensitive detection of neural activity changes in these regions should be helpful in scientific and clinical research on PD. In this study, we used resting state functional MRI and amplitude of low frequency fluctuation (ALFF) methods to examine spontaneous neural activity in 109 patients with PD. We examined activity in two frequency bands, slow-4 (between 0.027 and 0.073 Hz) and slow-5 (0.010-0.027 Hz). Patients had decreased ALFF in the striatum and increased ALFF in the midbrain, and changes were more significant in slow-4. Additionally, changes in slow-4 in both basal ganglia and midbrain correlated with the severity of the parkinsonism. The ALFF in the caudate nucleus positively correlated with the dose of levodopa, while the ALFF in the putamen negatively correlated with the disease duration in both slow-4 and slow-5 bands. In addition, the ALFF in the rostral supplementary motor area negatively correlated with bradykinesia subscale scores. Our findings show that with a large cohort of patients and distinguishing frequency bands, neural modulations in the brainstem and striatum in PD can be detected and may have clinical relevance. The physiological interpretation of these changes needs to be determined.

Validation of functional motor and language MRI with direct cortical stimulation

BACKGROUND

Functional magnetic resonance imaging (fMRI) is a widely available method and is therefore progressively utilized in neurosurgical practice. This study was carried out to determine fMRI sensitivity and specificity and to emphasize the threshold dependence of fMRI data.

METHODS

A total of 17 consecutive patients, scheduled for surgery on intracerebral lesions near eloquent brain areas, underwent preoperative motor (N = 12) and language (N = 5) fMRI. Functional data were analyzed with SPM software and displayed on a neuronavigation system for intraoperative guidance. High-risk maps for motor and language deficits obtained from direct electric cortical stimulation (DECS) were used for validation of functional activated areas. In a first analysis step, sensitivity and specificity were calculated in terms of a side-by-side correlation. The next step, the threshold dependence of fMRI data sensitivity and specificity, was estimated according to four statistical thresholds (p1 < 0.05, p2 < 0.0005, p3 < 0.00001, p4 < 0.0000001).

RESULTS

Both functional imaging and DECS revealed definite results for the investigated areas in all patients. Calculation of sensitivity and specificity resulted in 100 % and 68 % for the motor group and a sensitivity of 75 % and specificity of 68 % for the language group at the fixed threshold analysis. Threshold-dependent analysis of the obtained data revealed a sensitivity/specificity relationship from 100 %/0 % at threshold (p1), 100 %/5 % at (p2), 74 %/9 % at (p3), and 37 %/36 % at (p4) for the motor group. Evaluation of threshold-dependent sensitivity and specificity for the language group resulted in 78 %/51 % at threshold (p1), 67 %/75 % at (p2), 50 %/78 % at (p3), and 33 %/89 % at (p4).

CONCLUSIONS

The present findings on the threshold dependence of fMRI data demonstrate why individualized thresholds should be obtained in case of fMRI evaluation. Although the results are satisfying in most cases, fMRI is apparently not sufficient for critical intraoperative decision-making.

Cerebrovascular reactivity mapping for brain tumor presurgical planning

This article provides a review of Blood Oxygen Level Dependent functional magnetic resonance imaging (BOLD fMRI) applications for presurgical mapping in patients with brain tumors who are being considered for lesion resection. Initially, the physical principle of the BOLD effect is discussed, followed by a general overview of the aims of presurgical planning. Subsequently, a review of sensorimotor, language and visual paradigms that are typically utilized in clinical fMRI is provided, followed by a brief description of studies demonstrating the clinical impact of preoperative BOLD fMRI. After this thorough introduction to presurgical fMRI, a detailed explanation of the phenomenon of neurovascular uncoupling (NVU), a major limitation of fMRI, is provided, followed by a discussion of the different approaches taken for BOLD cerebrovascular reactivity (CVR) mapping, which is an effective method of detecting NVU. We then include one clinical case which demonstrates the value of CVR mapping in clinical preoperative fMRI interpretation. The paper then concludes with a brief review of applications of CVR mapping other than for presurgical mapping.

Clinical impact of integrated physiologic brain tumor imaging

The development of new MRI techniques in the last two decades has provided neuroradiologists and neurosurgeons with additional noninvasive imaging tools for management and treatment of brain tumors. When coupled with standard structural MR sequences in imaging brain tumors, Blood Oxygenation Level Dependent (BOLD) functional MRI (fMRI), Perfusion Weighted Imaging (PWI) and Diffusion Tensor Imaging (DTI) provide additional physiologic information that is very useful for differential diagnosis, presurgical planning and prognosis. In this review after a brief technical description of BOLD fMRI, PWI and DTI, studies are described from the literature that have extensively validated these imaging techniques in comparison with invasive "gold standard" techniques such as intraoperative electrical cortical and subcortical stimulation mapping or biopsy. Additional studies are mentioned that demonstrate the positive impact of BOLD fMRI, PWI and DTI on brain tumor treatment and clinical outcome. In the final section an interesting clinical case treated at our institution is presented that highlights the clinical utility of this integrated physiologic brain tumor imaging approach.

The evolution of clinical functional imaging during the past 2 decades and its current impact on neurosurgical planning

BOLD fMRI has, during the past decade, made a major transition from a purely research imaging technique to a viable clinical technique used primarily for presurgical planning in patients with brain tumors and other resectable brain lesions. This review article briefly examines the history and evolution of clinical functional imaging, with particular emphasis on how the use of BOLD fMRI for neurosurgical planning has changed during the past 2 decades. Even more important, this article describes the many published studies during that same period that have examined the overall clinical impact that BOLD and DTI have made on surgical planning.

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.

Formulation of current density weighted indices for correspondence between functional MRI and electrocortical stimulation maps

OBJECTIVE

Accurate localization of functionally significant brain regions reduces risks of post-operative neurological deficits. The gold standard for presurgical brain mapping is subdural electrocortical stimulation (ECS), which is an open-cranium surgical procedure. Functional MRI (fMRI) may be a noninvasive alternative if it can be shown that fMRI and ECS maps are spatially consistent. We formulate new 3D current density weighted ECS-fMRI correspondence indices and illustrate their use on human data.

METHODS

Current density maps were computed for simulated and human datasets by solving the electrostatic Laplace equation. The proposed indices were characterized and compared with fixed radii and Euclidean distance indices.

RESULTS

Results from simulated datasets showed that the proposed indices quantify correspondence between fMRI and the ECS truth predictably, and provide conspicuous sensitivity increase from fixed radii indices, whereas Euclidean distances may not be suitable measures of the correspondence.

CONCLUSIONS

The proposed indices reflect contextual information from surrounding electrodes and may be physiologically more meaningful in evaluating ECS-fMRI correspondence.

SIGNIFICANCE

To identify safe limits of resection, an ECS map requires placement of electrodes on a patient's brain. Our proposed indices accurately quantify ECS-fMRI correspondence and may be used to evaluate fMRI as a noninvasive alternative for defining resection limits.

Individual Variability in Brain Activity: A Nuisance or an Opportunity?

Functional imaging research has been heavily influenced by results based on population-level inference. However, group average results may belie the unique patterns of activity present in the individual that ordinarily are considered random noise. Recent advances in the evolution of MRI hardware have led to significant improvements in the stability and reproducibility of blood oxygen level dependent (BOLD) measurements. These enhancements provide a unique opportunity for closer examination of individual patterns of brain activity. Three objectives can be accomplished by considering brain scans at the individual level; (1) Mapping functional anatomy at a fine grained analysis; (2) Determining if an individual scan is normative with respect to a reference population; and (3) Understanding the sources of intersubject variability in brain activity. In this review, we detail these objectives, briefly discuss their histories and present recent trends in the analyses of individual variability. Finally, we emphasize the unique opportunities and challenges for understanding individual differences through international collaboration among Pacific Rim investigators.

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 of actual car-driving using [18F]FDG-PET

AIMS

This study aims at identifying the brain activation during actual car-driving on the road, and at comparing the results to those of previous studies on simulated car-driving.

METHODS

Thirty normal volunteers, aged 20 to 56 years, were divided into three subgroups, active driving, passive driving and control groups, for examination by positron emission tomography (PET) and [18F]2-deoxy-2-fluoro-D-glucose (FDG). The active driving subjects (n = 10) drove for 30 minutes on quiet normal roads with a few traffic signals. The passive driving subjects (n = 10) participated as passengers on the front seat. The control subjects (n = 10) remained seated in a lit room with their eyes open. Voxel-based t-statistics were applied using SPM2 to search brain activation among the subgroups mentioned above.

RESULTS

Significant brain activation was detected during active driving in the primary and secondary visual cortices, primary sensorimotor areas, premotor area, parietal association area, cingulate gyrus, the parahippocampal gyrus as well as in thalamus and cerebellum. The passive driving manifested a similar-looking activation pattern, lacking activations in the premotor area, cingulate and parahippocampal gyri and thalamus. Direct comparison of the active and passive driving conditions revealed activation in the cerebellum.

CONCLUSION

The result of actual driving looked similar to that of simulated driving, suggesting that visual perception and visuomotor coordination were the main brain functions while driving. In terms of attention and autonomic arousal, however, it seems there was a significant difference between simulated and actual driving possibly due to risk of accidents. Autonomic and emotional aspects of driving should be studied using an actual driving study-design.

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.

Effect of brain surgery on auditory and motor cortex activation: a preliminary functional magnetic resonance imaging study

OBJECTIVE

The effect of glioma removal on blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) activation has not been widely documented. The aim of this preliminary study was to observe the effect of tumor resection on BOLD fMRI of the auditory and motor cortices.

METHODS

Seven patients with gliomas underwent preoperative and early postoperative BOLD fMRI, and five of them underwent additional late postoperative BOLD fMRI. The auditory and motor cortices were localized with activation studies. A hemispheric activation index was used to quantify the relative extent of BOLD activation.

RESULTS

The resection of a glioma with preoperative edema resulted in an increase from the preoperative to the early postoperative fMRI on auditory BOLD activation on the side of the tumor compared with the contralateral side. The same phenomenon was observed in one patient with motor BOLD activation. However, when no preoperative edema was present, a transient decrease in relative auditory BOLD activation was found.

CONCLUSION

The results of this study suggest that the resection of a glioma with preoperative edema affecting the auditory and/or motor cortex may cause a transient increase in the BOLD response ipsilateral to the tumor. It seems that when the tumor is resected, the pressure on the brain, specifically on the affected auditory and/or motor cortex, decreases and the functional cortex becomes more easily detectable in BOLD fMRI.

Neuroimaging of Metastatic Brain Disease

This review discusses imaging techniques for the diagnosis, treatment, and monitoring of brain metastases. It assesses the various modalities on the basis of their respective advantages and limitations. Recent advances in imaging technologies provide evaluation that is more accurate for tumor localization, morphology, physiology, and biology. When used in combination, these technologies provide clinicians with a powerful diagnostic and prognostic tool for managing metastatic brain disease.

Preoperative mapping of cortical motor function: prospective comparison of functional magnetic resonance imaging and [15O]-H2O-positron emission tomography in the same co-ordinate system

BACKGROUND

Two of the most widely accepted approaches to map eloquent cortical areas preoperatively are positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). As yet, no study has compared these two modalities within the same frame of reference in tumour patients.

AIM

We employed [15O]-H2O-PET and fMRI in patients undergoing presurgical evaluation and compared the results with those obtained by direct electrical cortical stimulation (DECS).

METHODS

Twenty-five patients with tumours of different aetiology near the central region were investigated. fMRI and PET were processed using the same methods, i.e. statistical parametric mapping (SPM) without anatomical normalization, and transformed into the same frame of reference.

RESULTS

fMRI activity was found in more cranial and lateral sections, i.e. closer to the brain surface, in comparison with PET, which demonstrated parenchymal activation. The mean localization difference between fMRI and PET was 8.1 +/- 4.6 mm (range, 2-18 mm). fMRI and [15O]-H2O-PET could reliably identify the central sulcus, as demonstrated by DECS.

CONCLUSIONS

fMRI and [15O]-H2O-PET demonstrate comparable results and are sensitive and reliable tools to map the central region, especially in cases of infiltrating brain tumours. However, fMRI is more prone to artefacts, such as the visualization of draining veins, which may explain the more cranial and lateral activation visualized by fMRI, whereas PET depicts capillary perfusion changes and therefore shows activation closer to the parenchyma.