The role of the Supplementary Motor Area (SMA) in the execution of primary motor activities in brain tumor patients: Functional MRI detection of time-resolved differences in the hemodynamic response
Interpreting volume of activation maps of brain tumor patients remains difficult using blood oxygenation-level dependent (BOLD) functional magnetic resonance imaging (fMRI) methods. A time-resolved fMRI may offer an informative strategy for investigating the possibility of functional reorganization by elucidating temporal variations in the activation of cortical structures . The aim of this study is to use time-resolved fMRI to investigate potential alterations in the spatially-varying and time-dependent hemodynamic response function within the supplementary motor area (SMA) and primary motor cortex (PMC) in the presence of an adjacent brain tumor, relative to normal control subjects.
Fifteen patients and eight healthy volunteers were recruited. By utilizing a brief motor paradigm that exerts a differential effect on the activation of these structures, latency differences in the hemodynamic responses of such areas may be sensitively investigated. The present study determines the utility of this approach in brain tumor patients by examining the time to peak of the BOLD hemodynamic response within the SMA and PMC.
In patients with glial tumors involving the PMC, the activation of the SMA was delayed and approached that of the PMC with time-to-peak difference between the PMC and SMA averaging 0.2 s. This delay in SMA activation was seen in all patients with glial tumors involving the PMC.
The results suggest that in patients with high-grade brain tumors invading the PMC , the SMA may assume a greater role in the execution of primary motor activities, in addition to its role in executive motor planning.
Available from: Bartosz Bryszewski
- "Its activation requires solely to imagine the movement. The results of the recently published studies suggest that the involvement of the SMAa area is greater in the case of HGG tumors, not only with regard to the principal role of this region, but also in supporting the M1a area in performing more complex motor tasks [18,19,20,21,22,23]. The accessory motor area seems to be the most stable motor area with regard to the frequency of activation. "
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ABSTRACT: The aim of this study was to analyze the reorganization of the centers of the motor cortex in patients with primary neuroepithelial tumors of the central nervous system (CNS) located in the region of the central sulcus in relation to the histopathological type and the size of tumor, as determined by means of functional magnetic resonance imaging (fMRI).
The fMRI was performed prior to the surgical treatment of patients with tumors located in the region of the central sulcus (WHO stage I and II, n=15; WHO stage III and IV, n=25). The analysis included a record of the activity in the areas of the primary motor cortex (M1) and the secondary motor cortex: the premotor cortex (PMA) and the accessory motor area (SMA). The results were correlated with the histopathological type of the tumor and its size expressed in cm(3).
The frequency of activation of the motor center was higher in the group of patients who had less aggressive tumors, such as low-grade glioma (LGG), as well as in tumors of lower volume, and this was true both for the hemisphere where the tumor was located and in the contralateral one. Mean values of t-statistics of activation intensity, mean numbers of activated clusters, and their ranges were lower in all analyzed motor areas of LGG tumors. The values of t-statistics and activation areas were higher in the case of small tumors located in ipsilateral centers, and in large tumors located in contralateral centers, aside from the SMA area where the values of t-statistics were equal for both groups. The contralateral SMA area was characterized by the highest stability of all examined centers of secondary motor cortex. No significant association (p>0.05) was observed between the absolute value of the mean registered activity (t-statistics) and the size of examined areas (number of clusters) when the groups were stratified with regards to the analyzed parameters.
The presence of a neoplastic lesion, its histopathological type and finally its size modulate the functional reorganization of the motor centers as suggested by the differences in the frequency of the neural center activation in the analyzed groups. Processes of functional rearrangement are more pronounced and more precisely defined in patients with less aggressive and/or smaller tumors. The contralateral accessory area is the most frequently activated center in all analyzed groups irrespective of the grade and size of the tumor.
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ABSTRACT: Data-driven methods for fMRI analysis are useful, for example, when an a priori model of signal variations is unavailable. However, activation sources are typically assumed to be linearly mixed, although non-linear properties of fMRI data, including resting-state data, have been observed. In this work, the non-linear locally linear embedding (LLE) algorithm is introduced for dimensionality reduction of fMRI time series data.
LLE performance was optimised and tested using simulated and volunteer data for task-evoked responses. LLE was compared with principal component analysis (PCA) as a preprocessing step to independent component analysis (ICA). Using an example data set with known non-linear properties, LLE-ICA was compared with PCA-ICA and non-linear PCA-ICA. A resting-state data set was analysed to compare LLE-ICA and PCA-ICA with respect to identifying resting-state networks.
LLE consistently found task-related components as well as known resting-state networks, and the algorithm compared well to PCA. The non-linear example data set demonstrated that LLE, unlike PCA, can separate non-linearly modulated sources in a low-dimensional subspace. Given the same target dimensionality, LLE also performed better than non-linear PCA.
LLE is promising for fMRI data analysis and has potential advantages compared with PCA in terms of its ability to find non-linear relationships.
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ABSTRACT: The aim of this study was to investigate the value and technical methods of 3D dynamic contrast-enhanced magnetic resonance lymphangiography (MRL) in the assessment of lymphatic anatomy and function in the presence of extremity lymphedema.
An improved experimental model of obstructive lymphedema was established in 1 hind limb of 6 New Zealand White rabbits. 3D contrast-enhanced MRL was performed with a 3.0-T MR unit after the intracutaneous injection of Gd-BOPTA into the interdigital webs of the dorsal paws. Maximum-intensity projection (MIP) was used to reconstruct the images of the lymphatic system. The dynamic nodal enhancement in the popliteal fossa and time-signal intensity curves between lymphedematous and contralateral limbs were compared. Morphologic abnormalities of the lymphatic system were also evaluated and compared with lymphoscintigraphy (LSG).
3D dynamic contrast-enhanced MRL images were obtained after the administration of Gd-BOPTA. In the normal limb, the popliteal fossa lymph nodes and their afferent and efferent lymph-collecting vessels were clearly visualized as the Gd tracer was rapidly cleared from the interstitial compartment. In contrast, the Gd tracer accumulated slowly at the prior surgical site in the lymphedematous limb. The nodal enhancement of lymphedematous limbs was significantly less than that of the contralateral limbs (P<0.01). Types of time-signal intensity curves were also significantly different between the 2 groups (P<0.001).
3D dynamic contrast-enhanced MRL can visualize the precise anatomy of lymphatic vessels and lymph nodes in extremity lymphedema, as well as objectively evaluate the functional status of lymph flow transport.
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