SALIVARY GLANDS (PAROTID AND SUBMANDIBULAR)
Preparatory steps: | |||
- | Indications: lateral facial mass; recurrent parotid or submandibular swelling; T/N staging of salivary gland neoplasms | ||
- | Advisable preliminary investigations: radiography if calculus is suspected; ultrasonography or MRI 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: frontal from orbital region to glottis | ||
1. | DIAGNOSTIC REQUIREMENTS | ||
Image criteria: | |||
1.1 | Visualization of | ||
1.1.1 | Entire parotid gland | ||
1.1.2 | Entire submandibular gland | ||
1.1.3 | Overlaying subcutaneous fat and skin | ||
1.1.4 | Regional lymph node territories (in cases of neoplasm) | ||
1.1.5 | Vessels after intravenous contrast media | ||
1.2 | Critical reproduction | ||
1.2.1 | Visually sharp reproduction of the glandular tissue | ||
1.2.2 | Visually sharp reproduction of the margins of normal glands | ||
1.2.3 | Visually sharp reproduction of the paraglandular fat spaces | ||
1.2.4 | Visually sharp reproduction of regional lymph node areas | ||
1.2.5 | Reproduction of the mandible and associated muscles | ||
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 | : | parotid: from external ear to angle of jaw; submandibular gland: from dorsum of tongue to hyoid bone; from external ear to glottis if detection of lymphadenopathy is required |
3.3 | Nominal slice thickness | : | 3-5 mm |
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 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 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 (prevented 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 and blood vessels |
- | for better definition of lesions | ||
- | for demonstrating involvement of cranium by neoplasms | ||
4.3 | Problems and pitfalls | - | artefact from dental prothesis/fillings |
- | movement artefact due to swallowing | ||
- | submandibular lymphadenopathy may mimic enlarged submandibular glands | ||
4.4 | Modification to technique | - | extension of the examination to the cranium to demonstrate relationship of disease to the base of the skull and the parapharyngeal space |
- | change of gantry angulation or patient position to avoid artefact |