Ultrasound (US), also called ultrasound scanning or sonography, is a method of imaging the inside of the human body with the use of high-frequency sound waves. The sound waves are recorded and displayed as a real-time visual image. No radiation is involved in ultrasound imaging.
Ultrasound is a useful way of examining many of the body’s internal organs, including the heart, liver, gallbladder, spleen, pancreas, kidneys and bladder. Because ultrasound images are seen in real-time, they can show movement of internal tissues and organs, and blood flow and heart valve functions. It can also be used to guide procedures such as needle biopsies, in which a needle is used to sample cells from an organ or tissue for laboratory testing.
Doppler ultrasound is a special technique used to examine blood flow. It is useful in evaluating blockages to blood flow, such as clots; build-up of plaque inside the vessel; and congenital malformations.
You should wear comfortable, loose-fitting clothing. Other preparation depends on the type of examination you will have, and you will be advised of this at the time of making your appointment. For some scans you will be instructed not to eat for as many as six hours beforehand, for others you will need to drink fluid and not empty your bladder prior to the examination.
Ultrasound scanners consist of a console containing a computer and electronics, a video display screen, and a transducer that is used to scan the body. The transducer is a small hand-held device attached to the scanner by a cord. The Sonographer or Radiologist spreads a lubricating gel on the skin in the area to be examined, then presses the transducer firmly against the skin to obtain images.
The ultrasound image is immediately visible on a screen that looks much like a computer monitor. The sonographer watches this screen during the examination and if wished, the patient is able to see it as well.
As sound passes through the body, echoes are produced that can be used to identify how far away an object is, how large it is, and how uniform it is.
When the transducer is pressed against the skin, it directs, inaudible, high-frequency sound waves into the body. As the sound echoes from the body’s fluids and tissues the transducer records tiny changes in the pitch and direction of the sound. These echoes are instantly measured and displayed on the monitor. The live images may be recorded and frames can be frozen to capture a series of still images.
The patient is positioned on an examination table. A gel is applied to the body in the area to be examined, to help the transducer make secure contact with the skin. The sound waves produced by the transducer cannot penetrate air, and the gel helps eliminate air pockets between the transducer and the skin. The sonographer or radiologist presses the transducer firmly against the skin and sweeps it back and forth to image the area of interest.
Ultrasound imaging is painless. There may be varying degrees of discomfort as the transducer is guided firmly over your abdomen, especially if you are required to have a full bladder. If scanning is performed over an area of tenderness, there may be minor discomfort associated with the procedure. The examination usually takes about 15-20 minutes.
Ultrasound waves do not reflect clearly from bone or air. Ultrasound can see only the outer surface of bones and not what lies within them. For visualisation of bone or the internal structure of joints, other imaging modalities, such as MRI, should be used.
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