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Methodology of head computed tomography
Last reviewed: 06.07.2025
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Preparing for a CT scan of the brain
Before contrast computed tomography, the patient must refrain from eating for 4 hours before the examination.
Before the examination, the patient is informed about the procedure method; if a contrast computed tomography is planned, the patient should be warned that after the introduction of the contrast agent, a feeling of heat and flushing, headache, metallic taste in the mouth, nausea or vomiting may occur.
The patient should be dressed in comfortable light clothing, all metal objects located in the field of the CT scanner should be removed. In case of emotional arousal and motor restlessness, sedatives are prescribed.
The doctor is obliged to find out and record in the patient's medical history the presence of iodine intolerance (seafood), contrast agents. In case of iodine intolerance, it is necessary to prescribe antiallergic drugs prophylactically or refuse contrast agents.
How is a CT scan of the brain performed?
The patient is placed on his back on the X-ray table, the head is fixed with straps if necessary and the patient is asked not to move.
Tomography is performed with the scanner rotating around the patient's head in 1 cm increments along a 180° arc, producing a series of sections, or scans. Then, if necessary, a contrast agent is injected intravenously and another series of scans is made. Information about the sections is stored digitally in a computer, displayed on a monitor, and issued as a photograph.
First, a sagittal projection section (topogram) is made, on which the marking of the upcoming sections, located parallel to the orbitomeatal line, is made. This line is drawn from the superciliary arch to the external auditory canal, and then, repeating many times, the marking is applied upwards throughout the entire scanning zone. The standard technique of section planning when performing computed tomography of the head allows reliable comparison of data from several CT studies. To reduce artifacts due to the distribution of X-ray radiation hardness when visualizing the posterior cranial fossa, thin sections (2-3 mm) are used, whereas for supratentorial structures of the brain located above the pyramids of the temporal bones, it is desirable to set a larger section width (5 mm).
The images produced by a CT scan of the head are a bottom (caudal) view of a cross-section of the head, so the sides are inverted. For example, the left lateral ventricle is visualized on the right side of the image, and the right on the left. An exception to this rule are CT scans for planning neurosurgical operations. Then they are a top (cranial) view, where right = right, which corresponds to the usual view of the neurosurgeon of the patient's head during trephination.