PHARYNX
| Preparatory steps: | |||
| - | Indications: diagnosis of parapharyngeal masses; T/N staging of pharyngeal neoplasms | ||
| - | Advisable preliminary investigations: endoscopy may be performed; MRI and ultrasonography may be alternative examinations without exposure to ionising radiation, ultrasonography especially with regard to surrounding structures | ||
| - | 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 orbital roof to root of neck | ||
| 1. | DIAGNOSTIC REQUIREMENTS | ||
| Image criteria: | |||
| 1.1 | Visualization of | ||
| 1.1.1 | Entire pharynx | ||
| 1.1.2 | Regional lymph node areas and associated muscles | ||
| 1.1.3 | Base of the skull | ||
| 1.1.4 | Oesophagopharyngeal junction | ||
| 1.1.5 | Vessels after intravenous contrast media | ||
| 1.2 | Critical reproduction | ||
| 1.2.1 | Reproduction of the wall of pharynx throughout the area of examination | ||
| 1.2.2 | Visually sharp reproduction of the mucosal margin | ||
| 1.2.3 | Visually sharp reproduction of the parapharyngeal fat spaces | ||
| 1.2.4 | Visually sharp reproduction of the parapharyngeal muscles | ||
| 1.2.5 | 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 | : | nasopharynx: from sphenoid bone to hyoid bone and continue to root of the neck for N-staging of neoplasms; oropharynx/hypopharynx: from palate to root of the neck |
| 3.3 | Nominal slice thickness | : | 3-5 mm serial or preferably helical |
| 3.4 | Inter-slice distance/pitch | : | contiguous, but for large lesions distances of <3-5 mm or a pitch up to 1.5 - 2 may be used |
| 3.5 | FOV | : | adjusted to the minimum required to demonstrate complete cross section of the face. Reduction of FOV may be necessary for the evaluation of subtle pathologies |
| 3.6 | Gantry tilt | : | none |
| 3.7 | X-ray tube voltage (kV) | : | standard |
| 3.8 | Tube current and exposure time product (mAs) | : | should be as low as consistent with image quality |
| 3.9 | Reconstruction algorithm | : | soft tissue/standard or if necessary high resolution |
| 3.10 | Window width | : | 300-500 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 (swallowing should be suspended during exposure but encouraged between exposures to avoid salivary pooling) |
| 4.2 | Intravenous contrast media | - | may be required to improve contrast between normal and abnormal tissues or characterize some parapharyngeal lesions |
| - | routinely required if invasion of the base of the skull is suspected | ||
| 4.3 | Problems and pitfalls | - | artefact from dental prothesis/fillings |
| - | apposition of the pharyngeal mucosal folds may obscure pathology | ||
| - | pooling of saliva may mimic pathology | ||
| - | superficial mucosal extent of neoplasms may not be identified | ||
| - | secretion from oropharyngeal neoplasms | ||
| 4.4 | Modification to technique | - | coronal sections for demonstrating the relation ship of disease to the skull base |
| - | exposure with open mouth or with oral Valsava to open nasopharyngeal folds | ||
| - | change of gantry angulation or patient position to avoid artefact | ||