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Localization of human motor and somatosensory areas a functional MRI study
ABSTRACTS
L o c a l i z a t i o n o f h u m a n m o t o r and s o m a t o s e n s o r y a r e a s A functional M R I study 9 .1 9 l S. Martmkauppl, A. Korvenola , H. Pohjonen 2, M. Palva ~, E. Salli l, 9 ,3 R. J. Ilmomeml, H. J. Aronen 1
iDepartment of Radiology," 2Medical Engineering Center, 3BioMag Laboratory Helsinki University Central Hospital Helsinki, Finland introduction
Locating the central sulcus with fMRI for presurgical planning and for the purposes of functional brain mapping is ofWn based on activating the primary motor area (1). The patient usually performs a motor task (varying from a simple finger movement to complex movement patterns) while local blood oxygenation (BOLD) changes induced by cortical activation are measured. Even if the patient performing the requested motor tasks is co-operative and motivated, there is always a chance that patient's mistakes or undesirable movements during the measurement affect the data. The purpose of this study was to measure both motor task induced activation and cortical somatosensory activation elicited by electrical stimulation. Materials and Methods
Normal, healthy, right-handed subjects were tested with a three-state paradigm--Motor task, electrical stimulation of right median nerve and rest. The self-paced motor task was to touch the index finger and middle finger with the thumb. The median nerve was stimulated with a computer-triggered standard electric stimulator. The duration of one stimulation pulse was 10 ms with an inter-stimulus interval of 250 ms. The stimulating current was adjusted to the level causing a visible movement of the thumb. Images were acquired on a Siemens VISION 1.5-T Clinical Scanner equipped with EPI capability. A set of 2400 images with ten transaxial 4-mm slice levels were acquired using a gradient-echo EPI sequence with TR/TE/flip angle = 3 sec/66 msec/90 degrees, field of view 256 mm and matrix size of 128 x 128 pixels. The paradigm contained six conditions of motor tasks and six conditions of median nerve stimulation. All activation conditions were separated by resting state, giving a total of 60 measurements with the motor task, 60 measurements with median nerve stimulation and 120 measurements of the baseline. Subjects looked at a fixation point in all measurements to avoid artifacts from eye movements. Motor task start and stop points were presented visually with a computer and movements of hand muscles were monitored with EMG to control both the proper activation and the baseline phases. To avoid head movements we used a simple plastic-based bitebar system. The heart rate and arterial oxygenation level were monitored during measurements. In addition to collecting functional data, a whole-head-wide 3D MPRAGE measurement (TR/TE/flip angle = 9.7 msec/4msec/10 degrees, TI = 20 msec, FOV = 250 mm and matrix size = 256 • 256 pixels) was performed to obtain an anatomical brain map. Postprocessmg was done on an external work station using separate analysis software. Kolmogorov-Smirnov correlation maps were calculated for both activation paradigms using a common baseline. Finally, anatomical scans were rendered to a 3D cortical map; functional maps were added to them. Results and Discussion
We detected reliable activation (p-values ranging from 10-8 to 10-25) of primary motor (M1) and primary somatosensory (S1) areas. In 3D anatomical maps these fields of activation were situated on the pre- and postcentral gyri and in the central sulcus. These three main areas of activation can be used in identifying the central sulcus and the sensorimotor cortex. The objectivity of electrical nerve stimulation combined with a carefully monitored selfpaced motor task and proper head fixation improves confidence levels of activated areas and decrease the possibility of technical errors during an fMR1 measurement. The use of only one measurement with a common baseline for both activators ensures that the data from the two stimuli are fully comparable. The measurement time is reduced as well, thus increasing patient throughput.
References
1. Yousry, TA., Schmid, UD., Jassoy, AG., et al., Radiology. 1995, 195: 23-29.
$331
L o c a l i z a t i o n o f h u m a n m o t o r and s o m a t o s e n s o r y a r e a s A functional M R I study 9 .1 9 l S. Martmkauppl, A. Korvenola , H. Pohjonen 2, M. Palva ~, E. Salli l, 9 ,3 R. J. Ilmomeml, H. J. Aronen 1
iDepartment of Radiology," 2Medical Engineering Center, 3BioMag Laboratory Helsinki University Central Hospital Helsinki, Finland introduction
Locating the central sulcus with fMRI for presurgical planning and for the purposes of functional brain mapping is ofWn based on activating the primary motor area (1). The patient usually performs a motor task (varying from a simple finger movement to complex movement patterns) while local blood oxygenation (BOLD) changes induced by cortical activation are measured. Even if the patient performing the requested motor tasks is co-operative and motivated, there is always a chance that patient's mistakes or undesirable movements during the measurement affect the data. The purpose of this study was to measure both motor task induced activation and cortical somatosensory activation elicited by electrical stimulation. Materials and Methods
Normal, healthy, right-handed subjects were tested with a three-state paradigm--Motor task, electrical stimulation of right median nerve and rest. The self-paced motor task was to touch the index finger and middle finger with the thumb. The median nerve was stimulated with a computer-triggered standard electric stimulator. The duration of one stimulation pulse was 10 ms with an inter-stimulus interval of 250 ms. The stimulating current was adjusted to the level causing a visible movement of the thumb. Images were acquired on a Siemens VISION 1.5-T Clinical Scanner equipped with EPI capability. A set of 2400 images with ten transaxial 4-mm slice levels were acquired using a gradient-echo EPI sequence with TR/TE/flip angle = 3 sec/66 msec/90 degrees, field of view 256 mm and matrix size of 128 x 128 pixels. The paradigm contained six conditions of motor tasks and six conditions of median nerve stimulation. All activation conditions were separated by resting state, giving a total of 60 measurements with the motor task, 60 measurements with median nerve stimulation and 120 measurements of the baseline. Subjects looked at a fixation point in all measurements to avoid artifacts from eye movements. Motor task start and stop points were presented visually with a computer and movements of hand muscles were monitored with EMG to control both the proper activation and the baseline phases. To avoid head movements we used a simple plastic-based bitebar system. The heart rate and arterial oxygenation level were monitored during measurements. In addition to collecting functional data, a whole-head-wide 3D MPRAGE measurement (TR/TE/flip angle = 9.7 msec/4msec/10 degrees, TI = 20 msec, FOV = 250 mm and matrix size = 256 • 256 pixels) was performed to obtain an anatomical brain map. Postprocessmg was done on an external work station using separate analysis software. Kolmogorov-Smirnov correlation maps were calculated for both activation paradigms using a common baseline. Finally, anatomical scans were rendered to a 3D cortical map; functional maps were added to them. Results and Discussion
We detected reliable activation (p-values ranging from 10-8 to 10-25) of primary motor (M1) and primary somatosensory (S1) areas. In 3D anatomical maps these fields of activation were situated on the pre- and postcentral gyri and in the central sulcus. These three main areas of activation can be used in identifying the central sulcus and the sensorimotor cortex. The objectivity of electrical nerve stimulation combined with a carefully monitored selfpaced motor task and proper head fixation improves confidence levels of activated areas and decrease the possibility of technical errors during an fMR1 measurement. The use of only one measurement with a common baseline for both activators ensures that the data from the two stimuli are fully comparable. The measurement time is reduced as well, thus increasing patient throughput.
References
1. Yousry, TA., Schmid, UD., Jassoy, AG., et al., Radiology. 1995, 195: 23-29.
$331