- 1.What is a Ultrasound?Ultrasound examinations use a beam of sound waves to create an image. The sound waves are of “ultra” high frequency, higher than the range of human hearing. Audible sound is in the range of frequencies from 16 Hertz to 20 Kilohertz (16 cycles per second to 20,000 cycles per second). Obstetric and gynaecological ultrasound uses frequencies in the 1 to 8 Megahertz (1 to 8 million cycles per second) range -way above the audible range.The examination, which may sometimes be called a ‘scan’, allows the doctor performing the scan to examine many tissues and organs of the body, and to see normal and abnormal anatomy. It is particularly suitable for the examination of pregnancies, and especially fetal structure.
Ultrasound waves are sent out from small piezo-electric crystals within a plastic case, the ultrasound probe. The crystals convert electric energy into soundwaves, and convert soundwaves back into electrical energy.
Gel is first spread on the skin to allow the ultrasound waves to pass from the probe into the body. The probe is then moved over the skin. There is no pain or other sensation from the ultrasound waves.
The probe sends short pulses of sound waves into the tissue, similar to radar. The sound waves are reflected as they move through different issue types. The probe ”listens” for returning reflected sound waves and changes them into electrical energy that is converted into an image on a screen by the ultrasound machine. The probe can determine where a point is, and how dense it is by how long it takes for the sound waves to return to the probe, and the strength of the signal.
The probe uses a very narrow beam, creating an image of a thin ‘slice’ or section of tissue. When the doctor moves the probe, multiple slices can be seen in sequence.
- 2. Is Ultrasound safe?Diagnostic Ultrasound has been used commonly on large populations from the 1960s. Safety has been the subject of ongoing scrutiny. The Australasian Society for Ultrasound in Medicine Statement (ASUM) concludes: There is no convincing evidence that diagnostic ultrasound causes adverse health effects in human patients. ASUM however acknowledges that epidemiology data has several limitations. Ongoing research may reveal factors now not known. More research is always needed.Good practice, therefore, limits ultrasound exposure to situations where benefit is anticipated. The ASUM safety recommendation is that care be taken to “ensure that examinations are performed prudently using the ALARA ( as low as reasonably achievable) principle of applying lowest acoustic output and dwell time consistent with that required to obtain the necessary diagnostic information”.
Doppler Imaging (pulse and colour) usually involves higher energy outputs; so particular care is taken to minimise exposure, especially in early pregnancy.
- 3. How is an Ultrasound performed? Abdominal and Vaginal scansYou will be asked to lie down on an examination couch. For an abdominal scan, the lower abdomen is examined. Clothing is lowered to the pubic bone and covered by a paper towel. Gel is spread on the skin to allow the ultrasound waves to pass from the probe into the body. There is no pain or other sensation from the ultrasound waves. The doctor moves the probe over the skin. To obtain good views, at times some pressure has to be applied to the probe which may be uncomfortable.A vaginal scan may also be performed by placing a small probe into the vagina. The probe is narrow and usually causes minimal discomfort. Vaginal scans are used particularly in the early weeks of pregnancy, or gynaecological scans to examine the pelvic organs. It generally provides the best pelvic imaging. In pregnancy, this examination cannot harm the fetus. The transducer does not go into the uterus. Between patients, the probe is cleaned and disinfected. A new protective cover is applied for each examination. The cover is latex free. The probe is inserted by the examiner, or you may prefer to insert it yourself. If you wish to have another person in the room for a vaginal scan, please let us know.
You will be offered a gown if you need a vaginal ultrasound.
- 4. Are there any special preparations before a scan? Is a full bladder needed?There are no preparations before a scan. You may eat normally before the examination.You do not need to remove your jewellery, although in pregnancy scans you may be asked to remove a belly ring.
For a vaginal scan, the bladder can be empty. A very full bladder is only required if a vaginal scan is not suitable for you. Please let our staff know you need an abdominal scan.