Stereotaxic Technique
This method is indispensable for studying brain topography and targeted insertion of recording or stimulating electrodes into its deep structures. The fundamental working principle is determining the position of the target nucleus or pathway strictly along three spatial coordinates.
The reference points are anatomical landmarks on the cranial bones (in animal experiments) or internal landmarks of the brain itself (during neurosurgical operations in humans). The procedure is performed using a stereotaxic instrument, which includes two mandatory parts:
- Headholder — provides rigid and reliable fixation of the head.
- Positioning system — allows smooth movement of the instrument in a polar or rectangular coordinate system.
To calculate the exact insertion site, specialists use detailed brain atlases. They feature slice-by-slice frontal sections indicating the location of all structures relative to the sagittal and basal planes.
Depending on the objective, studies are conducted in two formats:
- Acute experiment — performed on anesthetized animals.
- Chronic experiment — involves surgery for electrode implantation under strict sterile conditions.
In addition to classical recording of bioelectrical activity, stimulation, or local tissue destruction, the stereotaxic technique is used for targeted placement of cannulas (for administering substances or taking samples) and devices for local cooling of brain structures.
Ultrasonic Echoencephalography (Echo-EG)
The physical basis of this diagnostic method is the ability of ultrasound waves to penetrate cranial bones and reflect from boundaries of anatomical zones with different densities. The main goal of Echo-EG is to determine whether there is any displacement of the brain midline structures.
During the examination, ultrasound emitters and receivers are placed exclusively in the temporal regions of the patient's head. The resulting curve (echoencephalogram) is traditionally divided into three components:
- Initial complex — the result of wave reflection from the skin and bones on the side of the active emitter.
- Midline complex (M-echo) — a crucial signal reflected from centrally located structures: the third ventricle, septum pellucidum, and pineal gland.
- Final complex — the signal returning from the skin and bone of the opposite side of the skull.
Normally, if the emitters are positioned on the left and right, the echoes are completely symmetrical. However, if pathology is present (e.g., intracranial hemorrhage), the distance to the M-echo becomes shorter on one side than on the other. The magnitude of this displacement is calculated from the difference in values.
The method has high sensitivity, detecting structural deviations as small as 1–2 millimeters. Due to equipment portability and ease of execution, the study can be performed on an emergency basis right at the patient's bedside. There is a strict clinical rule: if reliable signs of midline structure displacement are found, it is a direct indication for immediate advanced examination.
Neuroimaging Methods and CT
X-ray approaches are based on varying levels of X-ray absorption by different tissues. However, the natural ability of brain structures to transmit such rays differs very slightly. Because of this low contrast, additional techniques must be used for quality neurovascular visualization. Most commonly, special radiopaque agents are injected into the vascular bed or cerebrospinal fluid pathway, and special image analysis algorithms are applied.
The most informative method in this group is X-ray computed tomography (CT). Its operating principle is much more complex than standard radiography:
- The radiation source is not fixed; it moves continuously.
- A very narrow X-ray beam passes through the head at many different angles.
- The acquired data are processed using mathematical algorithms.
System models the layout of structures slice by slice, relying exclusively on their physical density (the ability to attenuate X-rays). As a result, the physician receives a detailed spatial reconstruction of multiple slices. The final result of the study is a high-precision in vivo 3D anatomical picture of the brain, allowing the detection of the slightest pathological changes.