Magnetic Levitation: Neurosurgery Evaluation

Magnetic levitation: Neurosurgery evaluation

Introduction

The concept of cerebral cortical topological specialization is the result of the contribution of many scientists. To mention some, Descartes described the visual system in 1662;Rolando used galvanic currents to stimulate the cortex, in 1809;Broca studied the cerebral cortex and identified the center of expressive language, in 1861;Wernicke described the receptive language area, in 1874, and William James speculated, in 1890, that the blood flowed more to the most active brain regions. 

By the middle of the twentieth century, the concept of cortical specialization had matured and the cerebral topological distribution looked like what is known today. Brodmann, in 1909, classified different regions of the brain in a numerical way, based on the cytoarchitecture. While Brodmann did not study brain function, his hypothesis was that the different brain regions defined by his cytoarchitecture could have different functions. In fact, it was found that the areas originally defined by Brodmann also approximately demarcated some specific function areas determined by electrocorticographic measurements and by studies of focal brain injuries.

Developing

These validations erroneously consolidated the Atlas de Brodmann as the standard of cerebral functional location for many applications, even if this ATLAS is purely descriptive of the neuronal microscopic organization and not of the function. Since the majority of brain activation studies by RMF refers the Brodmann areas, this Atlas will continue to enjoy the success of tradition, until more specific maps of brain function are developed.

Many RMF studies have been carried out in healthy volunteers confirming the findings derived from the different brain mapping methods. In this little Atlas we include some representative cases of normal cortical activations carried out at the Antioquia Medical Institute of Medical Technology (IATM)

Clinical protocols

• The tasks that a person performs in the resonance apparatus is called the protocol. Each of the protocols is related to the identification of a function.

Motor and sensory protocols

• These protocols will be applied to injuries in the frontal or parietal lobe. The regions of interest that we intend to identify are the pre -Romanesque area and the post -Romantic area, that is, the location of the central groove or rlando fissure.
• Among the clinical motors protocols, the most commonly applied are the open and closing protocol. In the first the activation task consists in opening and closing the palm of the hand. The patient performs this movement with the contralateral hand to the hemisphere in which the lesion is located. The control task can be to move the ipsilateral hand to the injury or rest, that is, not move anything.
• In the tapping protocol, the activation task is to play with each of the fingers the thumb of the same. For this protocol, the control task can be, as in the previous case, the resting or the iPsilateral hand movement.

Language protocols

• Language functions are divided into productive and receptive. The productive functions are located at the front level and the receptive at the temporal-partal level, forming both functions a continuum in its connection by the arched fascicle.
• The most commonly used protocols are the rhyme protocol and the task of judging lines. In the rhyme protocol the activation task is to judge whether two words presented visually rhyme or not, in this protocol, the control task consists of judgments of physical similarity. The task of judgment of lines is that the patient judges whether a series of lines arranged in two parallel rows are equal or not.
• Among the productive language protocols, the most useful in its application for the lateralization and location of language are, generation of verbs and verbal creep. The task of generating verbs is that for a certain name the patient says a verb. As a control task, the look at a blade was carried out. This task allows minimizing eye movements that produce artifacts in the image.

Memory protocols

• The application of memory protocols focuses on determining the functional integrity of the hippocampus and the hippocympic circumvolution. The two protocols that have shown an involvement of both hippocampos are, the image of images and the walk through your city. 
• In the first protocol to the patient before starting it is instructed to try to memorize the images of the activation task, but not the images of the control task. 
• The patient indicates whether the image appears or not squeezing one button or another of a device.

Relevant variables in the pre -surgical application of the RMF

The biggest advantage of RMF is to be a non -invasive technique, with a good temporary resolution and a very good spatial resolution. But we must know certain factors that can lead us to error.

Corregistro of the functional image in the structural image

The applied RMF sequence is Coplanar, which is characterized by its low anatomical resolution. Therefore, the functional image must overlap a structural image. In this overlap there is the possibility of error, given the distortion that the coplanar technique produces in the anatomical data. As a solution, it is proposed to reduce the distance between the cuts, thus the error in the overlap of images is reduced. Not all activation areas are functionally eloquent:

Therefore, RMF results must be complemented with the data provided by other metabolic, pre -surgical, electromagnetic or neuropsychologies methods. Studies conducted in this regard must apply tests, electromagnetic or other validation procedures for pre -surgical or post -surgical evaluation, which allow to see the validity of the application of each of the protocols.

Univoted areas could be functionally eloquent

After an exploration it could happen that an area of interest for the function we study is not activated. This result can be attributed to pathological conditions, effects of certain drugs, alterations in blood vessels, or mass effects of the surrounding edema to a tumor. The appearance of these conditions is uncommon, but they must be taken into account. The best solution is the validation of the RMF results with other procedures.

Variables in the change of signal

In general terms, there is a greater signal change for motor and sensory protocols than for cognitive tasks. For example, for a motor protocol there is a signal change close to 5%, while for more complex cognitive tasks the signal change is between 0.5% and 1.5%. Given this low percentage in the change of signal, the measures made must be maintained for a long period of time to obtain a solid statistical interpretation.

Significance thresholds applied to images analysis

Variations in thresholds produce changes in the number, shape and extension of activation areas. We will observe these variations along the tests for the same analysis threshold. These differences do not allow the determination of levels of significance that admit identifying a precision functional area. For this point there is no agreement in the clinical application beyond setting a threshold that allows us to identify the activated areas for each patient according to a clinical criterion.

Movement devices

Various factors can produce the movement of the head while the 6-12 minutes of registration of an RMF protocol are carried out. These slight displacements are an important problem when averaging the various activations of the same activation and control task. However, some programs already include a corrector for movement. Despite this, the possibility of movements should be minimized by fixing the head with clamps.

conclusion

Prior to any RMF session, the patient will be described what is going to be done. Explain the objective of the pre -surgical evaluation to the patient seeks its collaboration that is decisive to complete a reliable evaluation. The purpose is double, avoid errors in the resonance session and ensure that the patient is able to perform the task. The explanation of the task must include the realization of a practice on the same. It is recommended to ensure the compression of the tasks at the time the person, already lying in the device, will start the session.