Movement artefacts and MR BOLD signal increase during different paradigms for mapping the sensorimotor cortex

Pneumatic artificial muscle-based stimulator for passive functional magnetic resonance imaging sensorimotor mapping in patients with brain tumours

BACKGROUND

Two concerns with respect to pre-operative task-based motor functional magnetic resonance imaging (fMRI) in patients with brain tumours are inadequate performance due to patients' impaired motor function and head motion artefacts.

NEW METHOD

In the present study we validate the use of a stimulator based on a pneumatic artificial muscle (PAM) for fMRI mapping of the primary sensorimotor (SM1) cortex in twenty patients with rolandic or perirolandic brain tumours. All patients underwent both active and passive motor block-design fMRI paradigms, performing comparable active and passive PAM-induced flexion-extensions of the icontralesional index finger.

RESULTS

PAM-induced movements resulted in a significant BOLD signal increase in contralateral primary motor (M1) and somatosensory (S1) cortices in 18/20 and 19/20 (p<.05 FWE corrected in 16/18 and 18/19) patients, versus 18/20 and 16/20 (p<.05 FWE corrected) during active movements. The two patients in whom the PAM-based stimulator failed to induce any significant BOLD signal change in the contralateral M1 cortex differed from the two in whom active motion was conversely ineffective. At the group level, no significant difference in contrast magnitude was observed within the contralateral SM1 cortex when comparing active with passive movements. During passive movements, head motion was significantly reduced. Comparison with existing method(s) As compared to the several robotic devices for passive motion that were introduced in the past decades, our PAM-based stimulator appears smaller, handier, and easier to use.

CONCLUSION

The use of PAM-based stimulators should be included in routine pre-operative fMRI protocols along with active paradigms in such patients' population.

Optimizing fMRI preprocessing pipelines for block-design tasks as a function of age

Functional Magnetic Resonance Imaging (fMRI) is a powerful neuroimaging tool, which is often hampered by significant noise confounds. There is evidence that our ability to detect activations in task fMRI is highly dependent on the preprocessing steps used to control noise and artifact. However, the vast majority of studies examining preprocessing pipelines in fMRI have focused on young adults. Given the widespread use of fMRI for characterizing the neurobiology of aging, it is critical to examine how the impact of preprocessing choices varies as a function of age. In this study, we employ the NPAIRS cross-validation framework, which optimizes pipelines based on metrics of prediction accuracy (P) and spatial reproducibility (R), to compare the effects of pipeline optimization between young (21-33 years) and older (61-82 years) cohorts, for three different block-design contrasts. Motion is shown to be a greater issue in the older cohort, and we introduce new statistical approaches to control for potential biases due to head motion during pipeline optimization. In comparison, data-driven methods of physiological noise correction show comparable benefits for both young and old cohorts. Using our optimization framework, we demonstrate that the optimal pipelines tend to be highly similar across age cohorts. In addition, there is a comparable, significant benefit of pipeline optimization across age cohorts, for (P, R) metrics and independent validation measures of activation overlap (both between-subject, within-session and within-subject, between-session). The choice of task contrast consistently shows a greater impact than the age cohort, for (P, R) metrics and activation overlap. Finally, adaptive pipeline optimization per task run shows improved sensitivity to age-related changes in brain activity, particularly for weaker, more complex cognitive contrasts. The current study provides the first detailed examination of preprocessing pipelines across age cohorts, demonstrating a significant benefit of adaptive pipeline optimization across age groups.

Pediatric applications of functional magnetic resonance imaging

Pediatric functional MRI has been used for the last 2 decades but is now gaining wide acceptance in the preoperative workup of children with brain tumors and medically refractory epilepsy. This review covers pediatrics-specific difficulties such as sedation and task paradigm selection according to the child's age and cognitive level. We also illustrate the increasing uses of functional MRI in the depiction of cognitive function, neuropsychiatric disorders and response to pharmacological agents. Finally, we review the uses of resting-state fMRI in the evaluation of children and in the detection of epileptogenic regions.

Clinical applications of functional MR imaging

Functional magnetic resonance (fMR) imaging for neurosurgical planning has become the standard of care in centers where it is available. Although paradigms to measure eloquent cortices are not yet standardized, simple tasks elicit reliable maps for planning neurosurgical procedures. A patient-specific paradigm design will refine the usability of fMR imaging for prognostication and recovery of function. Certain pathologic conditions and technical issues limit the interpretation of fMR imaging maps in clinical use and should be considered carefully. However, fMR imaging for neurosurgical planning continues to provide insights into how the brain works and how it responds to pathologic insults.

Diagnostic benefits of presurgical fMRI in patients with brain tumours in the primary sensorimotor cortex

Objectives

Reliable imaging of eloquent tumour-adjacent brain areas is necessary for planning function-preserving neurosurgery. This study evaluates the potential diagnostic benefits of presurgical functional magnetic resonance imaging (fMRI) in comparison to a detailed analysis of morphological MRI data.

Methods

Standardised preoperative functional and structural neuroimaging was performed on 77 patients with rolandic mass lesions at 1.5 Tesla. The central region of both hemispheres was allocated using six morphological and three functional landmarks.

Results

fMRI enabled localisation of the motor hand area in 76/77 patients, which was significantly superior to analysis of structural MRI (confident localisation of motor hand area in 66/77 patients; p < 0.002). FMRI provided additional diagnostic information in 96% (tongue representation) and 97% (foot representation) of patients. FMRI-based presurgical risk assessment correlated in 88% with a positive postoperative clinical outcome.

Conclusion

Routine presurgical FMRI allows for superior assessment of the spatial relationship between brain tumour and motor cortex compared with a very detailed analysis of structural 3D MRI, thus significantly facilitating the preoperative risk-benefit assessment and function-preserving surgery. The additional imaging time seems justified. FMRI has the potential to reduce postoperative morbidity and therefore hospitalisation time.

INFLUENCE OF MOTOR FUNCTIONAL MAGNETIC RESONANCE IMAGING ON THE SURGICAL MANAGEMENT OF CHILDREN AND ADOLESCENTS WITH SYMPTOMATIC FOCAL EPILEPSY

OBJECTIVE

To determine the clinical value of motor functional magnetic resonance imaging (fMRI) in the presurgical evaluation of a large group of children and adolescents with epilepsy caused by lesions close to the central sulcus.

METHODS

Forty-three patients (19 males; mean age, 13 years) with lesional focal epilepsy underwent motor fMRI as part of a multidisciplinary standardized presurgical evaluation between 2000 and 2006. fMRI data were analyzed using statistical parametric mapping (SPM2) and screened for the presence of movement-related artifacts. The ways in which the results of motor fMRI influenced the decision-making process were reviewed.

RESULTS

The success rate of motor fMRI was 93% and data were of high quality in 67.5% of the patients. Together with other clinical considerations, motor fMRI results contributed to the surgical management of 32 patients (74%). They helped 1) to determine the type of surgery in 23 patients (72%; 12 cases with and 11 cases without invasive functional mapping), 2) to indicate a reduced benefit-risk ratio with the consequence that surgery was not further considered in 5 patients (16%), and 3) to indicate that surgery was not an appropriate option because of the high risk of motor function deficit in 4 patients (12%).

CONCLUSION

Motor fMRI can be performed with a high degree of success and good data quality in this population of patients. It has an important additive role in the discussion of the feasibility of resective surgery contributing to the decision-making process for children with epilepsy caused by brain lesions close to the central sulcus.

Functional magnetic resonance mapping of motor cortex in patients with mass lesions near primary motor and sensory cortices

PURPOSE

To study motor cortex mapping in patients with mass lesions near primary motor and sensory cortices with BOLD-fMRI.

MATERIAL AND METHODS

18 patients with mass lesions near primary motor and sensory cortices, and 8 healthy volunteers were investigated with fMRI using a 1.5 T GE Signa scanner. The specific task was repetitive selfpaced index finger to thumb opposition with a frequency of approximately 2 Hz. Each task paradigm consisted of twelve 20-second blocks alternating between rest and activation. All functional data was sent to SUN GE Advanced Workstation 4.0 for post processing.

RESULTS

14 patients showed functional activation near mass lesion, 4 patients failed to show, and one patient with meningeoma was excluded because of heavy head movement. Of 14 patients, the functional activation of eloquent cortex was different between the group with declination of muscle force and the group with normal muscle force, generally the activated areas of the former were more scattered, dislocated, relative smaller than that of the latter.

CONCLUSION

fMRI is a valuable method for pre-operative evaluation of neurosurgical patients and probably can evaluate the muscle force pre- and post-operation approximately.

Reorganisation of the somatosensory system after early brain damage

OBJECTIVE

To examine the reorganisation of the somatosensory system after early brain lesions.

METHODS

We studied 12 young patients with congenital hemiplegia. Causative lesions were brain malformations, periventricular injuries and cortico-subcortical lesions. We explored the somatosensory system using evoked potentials, fMRI during sensory stimulation and clinical assessment of sensory function. To correlate sensory and motor function, we also performed transcranial magnetic stimulation, fMRI of hand movement and assessment of motor function by means of Melbourne test.

RESULTS

Eleven patients showed a perilesional reorganisation of primary somatosensory function, as expressed by short latency potentials following stimulation of the paretic hand; in a remaining patient, delayed latency responses (N27.1) were only elicited over the ipsilateral undamaged hemisphere. Five of the eleven patients with perilesional somatosensory representation of the affected hand showed contralesional shifting of motor function, thus exhibiting sensory-motor dissociation. Significant correlation was found between sensory deficit and fMRI activation during sensory stimulation.

CONCLUSIONS

In subjects with early brain lesions, somato-sensory function is generally reorganised within the affected hemisphere. A contralesional shifting is uncommon and poorly efficient in function restoration.

SIGNIFICANCE

This study confirms and further explores the difference in reorganisation capabilities of the motor and sensory system following early brain injury of different etiologies and timing.

Imaging speech production using fMRI

Human speech is a well-learned, sensorimotor, and ecological behavior ideal for the study of neural processes and brain-behavior relations. With the advent of modern neuroimaging techniques such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), the potential for investigating neural mechanisms of speech motor control, speech motor disorders, and speech motor development has increased. However, a practical issue has limited the application of fMRI to issues in spoken language production and other related behaviors (singing, swallowing). Producing these behaviors during volume acquisition introduces motion-induced signal changes that confound the activation signals of interest. A number of approaches, ranging from signal processing to using silent or covert speech, have attempted to remove or prevent the effects of motion-induced artefact. However, these approaches are flawed for a variety of reasons. An alternative approach, that has only recently been applied to study single-word production, uses pauses in volume acquisition during the production of natural speech motion. Here we present some representative data illustrating the problems associated with motion artefacts and some qualitative results acquired from subjects producing short sentences and orofacial nonspeech movements in the scanner. Using pauses or silent intervals in volume acquisition and block designs, results from individual subjects result in robust activation without motion-induced signal artefact. This approach is an efficient method for studying the neural basis of spoken language production and the effects of speech and language disorders using fMRI.