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