Structural Tomography: CT, MRI, and Myelography
For a detailed assessment of the anatomical structure of the brain and spinal cord, tomography methods are used to create cross-sectional tissue slices.
- Computed Tomography (CT): Based on the differential absorption of X-rays by skull structures. Spiral CT takes little time and is widely used for emergency patients. It reliably visualizes hemorrhages, bone fractures, edema, and tumors. Limitations: CT has poor visualization of the posterior cranial fossa due to bone artifacts and cannot detect ischemic softening of the brain in the first hours of a stroke.
- Magnetic Resonance Imaging (MRI): Based on the nuclear magnetic resonance phenomenon. Scanners of 1.5 T (Tesla) and above provide the highest resolution without ionizing radiation. Depending on the sequence, different images are obtained: on T1, anatomy looks maximally realistic, on T2, fluid (CSF) appears bright white, and in the FLAIR sequence, the fluid signal is suppressed, making the ventricles dark and highlighting pathological lesions (demyelination, edema). The procedure lasts 20–30 minutes.
- CT Myelography: A symbiosis of tomography and contrast examination. Through a lumbar puncture, 5–25 ml of contrast is injected into the subarachnoid space, followed by CT. The method helps visualize nerve roots and spinal canal stenosis when conventional MRI is insufficient.
Study of the Vascular Bed
To visualize precerebral and cerebral vessels, variants of angiography are used:
- Digital Subtraction Angiography: A classic invasive method. A catheter is inserted into an artery (femoral or brachial), from where the contrast flows into the basin of the target arteries. Due to the risk of complications (1–3%), it is used less and less in diagnostics, giving way to interventional surgery (e.g., for local thrombolysis or aneurysm coiling with a platinum coil).
- CT Angiography: A fast outpatient examination. Contrast is administered safely—intravenously. It allows the creation of detailed 3D models and the detection of stenosis or pathological tortuosity (kinking) of arteries.
- MR Angiography: The method can show the vascular network without using contrast agents at all. For maximum image quality, gadolinium-based contrast is used.
Electrophysiology and Functional Neuroimaging
Anatomical integrity does not always mean tissue health. To assess metabolism and electrophysiology, other approaches are used:
- Positron Emission Tomography (PET): The examination is performed strictly on an empty stomach. The patient is administered a radiopharmaceutical (glucose or oxygen isotopes), which accumulates in the brain. The method assesses cellular metabolism and allows the detection of areas of hyper- or hypometabolism at the earliest stages.
- Electroencephalography (EEG): Recording of brain biopotentials. The main method for epilepsy. Pathological activity manifests as spikes (spikes with a duration of < 70 ms and amplitude of > 50 µV) and sharp waves. EEG is also a mandatory criterion for diagnosing brain death (flat line).
- Evoked Potentials (EP): Computer summation of brain responses to external stimuli (visual, auditory). It evaluates the response latency period, making it possible to detect slowed nerve impulses even at a subclinical stage.
Classic Radiography
Cranial radiography and spondylography in modern neurology have been practically supplanted by CT and MRI, as they cannot visualize nerve fibers. Nevertheless, the methods retain importance for diagnosing bone structure injuries:
- vault of skull fractures;
- wedge compression fractures of the vertebrae;
- spine infections (spondylitis);
- Schmorl's nodes (when a disc herniates into the body of the underlying vertebra).
Briefly: answers to topical questions
What specific radiopharmaceuticals are used for brain PET?
The sources do not provide specific names of radiopharmaceuticals for brain PET. It is indicated that tumorotropic radiopharmaceuticals can be used for brain PET/CT, and PET uses biomedical compounds labeled with fluorine-18, carbon-11, or oxygen-15. Fluorodeoxyglucose (FDG) is used in oncology for diagnostics, staging, assessing treatment response, and detecting recurrences.
What types of evoked potentials (EP) are used in neurology besides visual and auditory?
In addition to visual and auditory (brainstem auditory) evoked potentials, somatosensory and cognitive potentials are used in neurological practice.
Additional types of evoked potentials:
- Somatosensory evoked potentials (EP) are used to assess the state of sensory pathways, the propagation velocity of excitation, and receptive structures of the brain.
- Cognitive evoked potentials (EP) are used during EEG monitoring with functional tests to detect disorders of the functional activity of cortical areas.
Class and exam questions
Why is CT performed first when a stroke is suspected, even though it does not visualize fresh ischemia?
CT is performed rapidly (about a minute) and reliably detects intracerebral hemorrhage. This is critically important for the immediate selection of the correct treatment strategy and saving the patient's life.
Does a normal EEG rule out the diagnosis of epilepsy?
No. The absence of interictal epileptiform activity is not a reason to exclude the diagnosis. To clarify in such cases, prolonged multi-hour monitoring is used.
Why is the FLAIR sequence needed on brain MRI?
In the FLAIR sequence, the signal from free cerebrospinal fluid (CSF) is suppressed, making it appear dark. This allows the clinician to easily distinguish the ventricles from bright pathological lesions (e.g., edema).
Is contrast necessary for MR angiography?
MR angiography is unique in that it allows visualization of cerebral arteries without the use of contrast. Contrast (gadolinium agents) is added only in complex diagnostic cases to enhance detail.
What else to study on this topic
- Pathological patterns on EEG: spikes, sharp waves, and their complexes
- Features of radiological anatomy on T1- and T2-weighted images
- The role of digital subtraction angiography in interventional neurosurgery
- Differences between X-ray and computed myelography
- Principles of positron emission tomography (PET) interpretation
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