LARYNX
| Preparatory steps: | |||
| - | Indications: T/N staging of neoplasm; evaluation of congenital or post-traumatic abnormalities of airway | ||
| - | Advisable preliminary investigations: MRI and ultrasonography may be alternative examinations without exposure to ionising 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 floor of mouth to thoracic inlet | ||
| 1. | DIAGNOSTIC REQUIREMENTS | ||
| Image criteria: | |||
| 1.1 | Visualization of | ||
| 1.1.1 | Entire larynx | ||
| 1.1.2 | Paralaryngeal tissues, including muscles, blood vessels and the thyroid gland | ||
| 1.1.3 | Regional lymph node areas | ||
| 1.1.4 | Spine and paravertebral muscles. | ||
| 1.1.5 | Vessels after intravenous contrast media | ||
| 1.2 | Critical reproduction | ||
| 1.2.1 | Reproduction of the wall of the larynx throughout the area of examination | ||
| 1.2.2 | Visually sharp reproduction of the mucosal folds | ||
| 1.2.3 | Visually sharp reproduction of the perimucosal fat spaces | ||
| 1.2.4 | Visually sharp reproduction of the intrinsic pharyngeal muscles | ||
| 1.2.5 | Visually sharp reproduction of the paralaryngeal muscles | ||
| 1.2.6 | Visually sharp reproduction of regional lymph node areas | ||
| 2. | CRITERIA FOR RADIATION DOSE TO THE PATIENT | ||
| 2.1 | CTDIW | : | no specific value as yet available (for information: routine head: 60 mGy) |
| 2.1 | DLP | : | no specific value as yet available (for information: routine head: 1050 mGy cm) |
| 3. | EXAMPLES OF GOOD IMAGING TECHNIQUE | ||
| 3.1 | Patient position | : | supine |
| 3.2 | Volume of investigation | : | from base of tongue to root of neck |
| 3.3 | Nominal slice thickness | : | 3-5 mm serial or preferably helical CT, especially in patients having difficulties with salivary pooling |
| 3.4 | Inter-slice distance/pitch | : | contiguous, but for large lesions distances of <3-5 mm or a pitch up to 1.5 - 2.0 may be used |
| 3.5 | FOV | : | adjusted to the minimum required to demonstrate complete cross section of the neck. Reduction of FOV may be necessary for the evaluation of subtle pathologies |
| 3.6 | Gantry tilt | : | none or modified parallel to the line of vocal folds on scan projection radiograph |
| 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/standard or if necessary high resolution |
| 3.10 | Window width | : | 250-500 HU |
| 3.11 | Window level | : | 0-30 HU (unenhanced examination) 30-60 HU (enhanced examination) |
| 4. | CLINICAL CONDITIONS WITH IMPACT ON GOOD IMAGING PERFORMANCE | ||
| 4.1 | Motion | - | movement artefact deteriorates the image quality (avoided by quiet respiration; swallowing should be suspended during exposure but encouraged between exposures to avoid salivary pooling) |
| 4.2 | Intravenous contrast media | - | may be required to distinguish lymphadenopathy |
| - | improves delineation of neoplasm | ||
| 4.3 | Problems and pitfalls | - | movement artefact due to respiration |
| - | staging errors due to poor discrimination between normal and abnormal tissues | ||
| - | salivary pooling may mimic pathology | ||
| - | displacement of vocal fold by adjacent mass may mimic glottal involvement | ||
| 4.4 | Modification to technique | - | reformatted images may require thin serial slices if helical CT is not available |
| - | sections through glottis may be obtained during phonation | ||