ULTRASOUND SCANNING - a patient's guide
What is it?
Ultrasound uses high frequency sound waves to obtain a cross-sectional image of an organ or body part, in any desired plane. Sound waves are emitted by a hand-held transducer, and the reflections of these sound waves are detected in the same transducer and converted into black and white images on a TV screen. Selected images are frozen on the TV screen and filmed.
As ultrasound is a real-time examination, movement may be observed, for example fetal heartbeats and limb movements during obstetric scans. Doppler ultrasound measures an alteration of the reflected sound frequency caused by flowing blood, and colour or graphical images of blood flow may be obtained.
What is it used for?
Common scans include abdomen (including liver, gallbladder, kidneys and other organs), pelvis, obstetric, vascular (e.g. aorta, carotid arteries, leg veins), thyroid gland, and scrotum. Ultrasound is also used for scanning some tendons and joints, for example tendons of the knee or ankle, and the shoulder joint. It is also sometimes used for examination of the extremities, for example looking at lumps, and identifying small "foreign bodies", i.e. splinters in the hands or feet.
Who can have ultrasound?
Anyone may undergo an ultrasound scan. There are no known harmful effects from a diagnostic ultrasound scan.
Before the scan
Fasting is generally required for 4 hours prior to an abdominal or gallbladder ultrasound scan, and pelvic scans or early pregnancy scans require a full bladder. If you are having an obstetric scan and wish to have a video recording of the scan, please remember to bring along a blank videotape.
What happens during the scan?
The scan will be performed either by a sonographer or radiologist. A sonographer is a radiographer who has undergone speciality training in ultrasound scanning, and a radiologist is a specialist doctor with higher training in ultrasound. The radiologist may wish to have a second look at a scan performed by a sonographer; this additional check does not mean that something is wrong.
You will need to expose the skin of the body part being scanned. A clear gel is applied to the skin; this reduces friction and improves the transmission of sound waves into the body. The transducer is a small handheld device that is applied to the skin and moved into different positions to obtain the desired scan images. There is no pain or discomfort from the scan, other than having a full bladder.
In some gynaecological cases an internal or trans-vaginal scan will be performed. This will be discussed with you prior to the scan. The bladder is emptied prior to commencing the scan. A special transducer with a new protective covering is placed into the vagina for this scan, providing superior visualisation of pelvic organs.
After the scan
The films are examined by the radiologist, who then issues a report to the referring doctor. The report is usually available the same day, or immediately in urgent cases.