FACE AND SINUSES
Preparatory steps: | |||
- | Indications: trauma, malformations, malignancies and inflammation | ||
- | Advisable preliminary investigations: appropriate x-ray examination of the face except for isolated evaluation of the sinuses; MRI may be an alternative examination, especially in malignancies | ||
- | 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 jaw to vertex | ||
1. | DIAGNOSTIC REQUIREMENTS | ||
Image criteria | |||
1.1 | Visualization of | ||
1.1.1 | Entire face from palate to the top of the frontal sinus | ||
1.1.2 | Vessels after intravenous contrast media | ||
1.2 | Critical reproduction | ||
1.2.1 | Visually sharp reproduction of the cortical and trabecular bone structures | ||
1.2.2 | Visually sharp reproduction of the frontal sinuses | ||
1.2.3 | Visually sharp reproduction of the sphenoid sinuses | ||
1.2.4 | Visually sharp reproduction of the orbitae | ||
1.2.5 | Reproduction of the globe, optic nerve and orbital muscles | ||
1.2.6 | Visually sharp reproduction of the ethmoid | ||
1.2.7 | Visually sharp reproduction of the maxilla and its sinuses | ||
1.2.8 | Visually sharp reproduction of the nasal cavity | ||
1.2.9 | Visually sharp reproduction of the rhinopharynx | ||
2. | CRITERIA FOR RADIATION DOSE TO THE PATIENT | ||
2.1 | CTDIW | : | 35 mGy (pilot study (17)) |
2.1 | DLP | : | 360 mGy cm (pilot study) |
3. | EXAMPLES OF GOOD IMAGING TECHNIQUE | ||
3.1 | Patient position | : | supine for axial scans; supine or prone for coronal scans |
3.2 | Volume of investigation | : | from palate to the top of the frontal sinus |
3.3 | Nominal slice thickness | : | 3-5 mm. Helical CT is preferable for evaluation of the face |
3.4 | Inter-slice distance/pitch | : | contiguous or a pitch = 1.0; 1-2 mm or a pitch up to 1.2 - 1.5 may be used in screening examinations of the sinuses |
3.5 | FOV | : | head dimension (about 24 cm) |
3.6 | Gantry tilt | : | 0 to -10° from OM for axial scanning of the face; according to the patient position for coronal scanning |
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 | : | high resolution or standard |
3.10 | Window width | : | 1500-3000 HU (bones) 140-1000 HU (soft tissue) |
3.11 | Window level | : | 200-400 HU (bones) 30-100 HU (soft tissue) |
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 and enhancing lesions |
4.3 | Problems and pitfalls | - | artefacts from teeth or dental prothesis/fillings |
4.4 | Modification to technique | - | change of gantry angulation or patient position to avoid artefact |
- | examination of the sinuses in a prone position to keep inflammatory secretion away from the osteomeatal complex | ||
- | examination of the sinuses preliminary to functional endoscopic sinus surgery is best performed directly in the coronal plane |