BRAIN, GENERAL
| Preparatory steps: | |||
| - | Indications: traumatic lesions, and suspected or known focal or diffuse structural disease of the brain when MRI is contraindicated or not available | ||
| - | Advisable preliminary investigations: clinical neurological examination; MRI is often an alternative examination without exposure to ionizing radiation | ||
| - | Patient preparation: information about the procedure; restraint from food, but not fluid, is recommended, if intravenous contrast media are to be given | ||
| - | Scan projection radiograph: lateral from skull base to vertex; in patients with multiple injuries from cervical vertebra to vertex | ||
| 1. | DIAGNOSTIC REQUIREMENTS | ||
| Image criteria: | |||
| 1.1 | Visualization of | ||
| 1.1.1 | Whole cerebrum | ||
| 1.1.2 | Whole cerebellum | ||
| 1.1.3 | Whole skull base | ||
| 1.1.4 | Vessels after intravenous contrast media | ||
| 1.2 | Critical reproduction | ||
| 1.2.1 | Visually sharp reproduction of the border between white and grey matter | ||
| 1.2.2 | Visually sharp reproduction of the basal ganglia | ||
| 1.2.3 | Visually sharp reproduction of the ventricular system | ||
| 1.2.4 | Visually sharp reproduction of the cerebrospinal fluid space around the mesencephalon | ||
| 1.2.5 | Visually sharp reproduction of the cerebrospinal fluid space over the brain | ||
| 1.2.6 | Visually sharp reproduction of the great vessels and the choroid plexuses after intravenous contrast media | ||
| 2. | CRITERIA FOR RADIATION DOSE TO THE PATIENT | ||
| 2.1 | CTDIW | : | routine head: 60 mGy |
| 2.1 | DLP | : | routine head: 1050 mGy cm |
| 3. | EXAMPLES OF GOOD IMAGING TECHNIQUE | ||
| 3.1 | Patient position | : | supine |
| 3.2 | Volume of investigation | : | from foramen magnum to the skull vertex |
| 3.3 | Nominal slice thickness | : | 2-5 mm in posterior fossa; 5-10 mm in hemispheres |
| 3.4 | Inter-slice distance/pitch | : | contiguous or a pitch = 1.0 |
| 3.5 | FOV | : | head dimension (about 24 cm) |
| 3.6 | Gantry tilt | : | 10-12° above the orbito-meatal (OM) line to reduce exposure of the eye lenses |
| 3.7 | X-ray tube voltage (kV) | : | standard |
| 3.8 | Tube current and exposure time product (mAs) | : | should be as low as consistent with required image quality |
| 3.9 | Reconstruction algorithm | : | soft tissue |
| 3.10 | Window width | : | 0-90 HU (supratentorial brain) 140-160 HU (brain in posterior fossa) 2000-3000 HU (bones) |
| 3.11 | Window level | : | 40-45 HU (supratentorial brain) 30-40 HU (brain in posterior fossa) 200-400 HU (bones) |
| 4. | CLINICAL CONDITIONS WITH IMPACT ON GOOD IMAGING PERFORMANCE | ||
| 4.1 | Motion | - | movement artefact deteriorates image quality (prevented by head fixation or sedation of non-cooperative patients) |
| 4.2 | Intravenous contrast media | - | useful to identify vascular structures, enhancing lesions and alterations of blood-brain barrier |
| 4.3 | Problems and pitfalls | - | calcifications versus contrast enhancement |
| - | interpetrous beam hardening artefacts | ||
| 4.4 | Modification to technique | - | subtle irregularity can be checked with slices in the area of suspected pathology, before considering contrast administration |