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ULTRASONOGRAPHY
It uses a very high frequency (3.5-10 MHz) pulsed ultrasound beam which is directed in to the body from a transducer placed directly in contact with the skin. It produces echoes, which are converted in to signals and then in to black,white and grey visual echo picture image ,which is displayed on the television.screen. It represents a topograohical map of the depth of the tissue interfaces.
COLOUR DOPPLER
This is a recent advance which utilizes a change in the frequency of sound reflected from a moving source to detect arterial and venous blood flow.The computer then adds the appropriate colour ,to the vascular structures in the visual echo picture image, making differentiation between structures easy.
ADVANTAGES
• Uses nonionising radiation,so there is decreased radiation dose.
• Non invasive ,easily available and inexpensive
• Images show good differentiation between soft tissues and are very sensitive for evaluation of salivary gland disease.
DISADVANTAGES
• It has limited use in the head and neck region as the sound waves are not absorbed by the bone.Its use is restricted to yhe superficiakl structures.
• Technique is opereator dependent
• Images can be difficult to interpret for inexperienced operators as the image resolution is poor.


APPLICATIONS
• Evaluation of the swelling of the head and neck-lymph nodes,thyroid and salivary gland.
• It is used as a diagnostic modality for salivary gland ultrasonography in children to avoid the radiation effects of CT and in adults with allergy to contrast agents.
• It is the investigation of choice to diffrenciate between solid and cystic lesions.
• Determination of the relationship of vascular structures to masses with the addition of COLOR DOPPLER imaging.
• Detection of salivary gland and duct calculi.

RADIONUCLEIDE IMAGING
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