Ultrasound
Ultrasound is a technique for visualising internal structures in the body using sound waves. The sound waves are of a much higher frequency than audible sound. The sound waves are produced by a small hand held device known as a transducer or ultrasound probe. The probe consists of a piezoelectric crystal that vibrates when a voltage is applied. These vibrations are transmitted from the probe into the body and travel through the soft tissues until they hit an interface between two different structures. At a tissue interface some echoes are reflected back to the transducer and some are transmitted deeper into the body. The reflected sound waves travel back to the probe and set up small vibrations in the transducer crystal that produced the sound in the first place. The vibrations produce a small voltage across the crystal. The voltage is read and digitised for subsequent computer analysis. By measuring the time taken for the sound to return to the transducer it is possible to calculate the exact depth the echo came from. A bright dot is placed on a monitor at an appropriate position corresponding to the depth of the echo and of a brightness determined by the strength of the echo. By analysing thousands of echoes returning from multiple positions in the body, a composite picture is built up. The result is a two dimensional image of the region of interest.
The Procedure Transvaginal probes are designed to be inserted into the vagina to enable more detailed images of the pelvic structures. Transvaginal imaging is only performed after full explanation of the procedure and with consent of the patient. A hysterosonogram is a transvaginal scan obtained after the introduction of saline into the uterine cavity via a small catheter. This technique enables definition of small lesions growing into the uterine cavity that cannot be adequately delineated with conventional ultrasound imaging.
Ultrasound has a wide range of clinical applications including imaging of the abdomen, pelvis, breast, small parts such as the thyroid gland, salivary glands, scrotum, musculoskeletal system including muscles and tendons, lumps and bumps etc. Specialised fields of ultrasound imaging include echocardiography and vascular ultrasound. The ultrasound examination is performed by a specially trained radiographer known as an 'ultrasonographer'. The radiologist may also perform part or all of the examination. A gown may be required depending on the region being examined. A gel is applied to the skin surface. This gel allows the probe to glide freely across the skin and also acts as a coupling medium which greatly improves transmission of the sound waves into the body. The procedure is painless and harmless and takes from ten minutes up to half an hour or more to perform. Interested observers can be allowed in the room particularly with obstetric scanning. Usually, however, a preliminary scan is performed prior to admission of interested parties to ensure a thorough examination without distraction. A series of representative pictures is obtained and recorded on hard copy laser film. The images are reviewed by a radiologist who issues a report for the referring doctor. The gel is wiped off the skin at the end of the procedure.
