A diagnostic technique in which very high frequency sound waves (inaudible to the human ear) are passes in to the body,and the reflected echoes are detected and analyzed to build a picture of the internal organs or of a fetus in the uterus.The procedure is painless and considered safe.
Also called sonography ,ultrasound scanning was originally a spin-off from naval sonar (used to detect submarines in World War II) and was first used medically in the 1950s.The original ultrasound scanners produced still images;most modern scanners produced moving pictures,which are easier to interpret.
How ultrasound scanners works and how they are operatedUltrasound waves are emitted by a device called a transducer ,which is placed on the skin over the part of the body to be viewed.The transducer contains a cristal that converts an electric current into sound waves.The waves used have frequencies in the range of 1-15 million hertz.At these high frequencies ,the waves can be focus into a fine parallel beam,which pass through a "slice" of the body if the transducer crystal is made to oscillate back and forth.Some of the waves are reflected at tissue boundaries ,so a series of echoes is returned.The transducer also acts as a reciever,converting these echoes into electrical signals,which are processed and displayed diamentional image of the scaned boady slice By moving the transducer across the outer wall of the abdomen, views of the growing fetus are obtain from various angles,so it is possible to screen for abnormalities.
Ultrasound waves pass readily through soft tissues and fluids,making this procedure particularly useful for examining fluid-filled organs (such as the uterus in pregnancy ,and the gallbladder)and soft organs (such as liver).Ultrasound waves cannot ,however, pass through bone or gas.They
are thus of limited use for examining regions that are surrounded by bone(such as adult brain) or that contain gas (such as the lunger or intestines).
Uses for pregnancy One of the most common uses of ultrasound is to view the uterus and fetus in pregnancy.
ultrasound scanning is often performed about 16 to 18 weeks in to the pregnancy,but may be performed at any stage.If the date of conception is known,the scan shows whether the fetus is of the expected size;conversely,fetal size can help establish the accurate date of conception and therefore predict the expected date delivery.The scan also reveals whether there is a multiple pregnancy .It is also possible to identify certain gross abnormalities ,such as
anencephaly or
spina bifida.Congenital Heart diseses can some times be detect,enabling the baby to be delivered in hospital that specializes in correcting such defects soon after birth.The scanne also shows the position of the placenta.If the
placenta in a position that could be obstruct normal childbirth(a condition known as a
placenta previa),delivery by
caesarean section may be necessary.
Scans earlier in pregnancy may be perfomed if the doctor suspects an
ectopic regnancy(presence of an embryo outside the uterus),
hydatidiform mole (abnormal tumer in uterus),
impending (miscarriage,or early death of the fetus.
Ultrasound is also vital for the procedure of
amniocentesis (removal of amniocentic fluid via needle for analysis).A scans shows the position of the fetus and placenta before eather of these procedures and also helps in guiding the needle in to the uterus.
Later in pregnancy,the scan may be carried out if the growth of the fetus seems slow,if fetal movements cases or or are excessive, or if the mother experiences viginal bleeding.For high-risk or overdue pregnancies,a scane may be carried out before delevery to check on an fetal size,development and position in the uterus,the amount of amniotic fluid,and to recheck the position of the placenta.
How It Is PerformedIf the scan is being performed on a woman who is in the early stages of pregnancy, she will be asked to drink several glasses of water about an hour before the scan. She also will be asked to refrain from urinating because a full urinary bladder allows for clearer visualization of the uterus and fetus by displacing nearby loops of intestine.
For all ultrasound scanning, the person lies on an examining table, clothing over the reagion to be scanned is removed and a special water-soluble gel is applied to the skin area to be examined. The gel may feel cool to the skin. The transducer is placed on the skin, positioned over the internal organ or structure that will be scanned, and gently pressed against the area that has been lubricated with gel. For certain examinations, a wandlike transducer may be inserted into the vagina or rectum. For example, in early pregnancy, insertion of the transducer into the vagina allows a closer view of the uterus and fetus. A rectal probe is helpful for assessing a man's prostate gland. Ultrasound scanning is generally considered painless and does not require special care after the procedure.
