Ultrasound (US) or sonography involves the sending of sound waves into the body. Those sound waves are reflected off the internal organs. The reflections are then recorded by special instruments that subsequently create an image of anatomic parts. No ionizing radiation (x-ray) is involved in ultrasound imaging.
For women, pelvic ultrasound is most often used to examine the uterus and ovaries and, during pregnancy, to monitor the health and development of the embryo or fetus. In males, a pelvic ultrasound usually focuses on the bladder and the prostate gland. Ultrasound images are captured in real-time, so they can show movement of internal tissues and organs, such as the flow of blood in arteries and veins.
What are some common uses of the procedure?
Millions of expectant parents have seen the first "picture" of their unborn child thanks to pelvic ultrasound examinations of the uterus and fetus (see Obstetric Ultrasound). However, monitoring of fetal development is not the only reason for a pelvic ultrasound exam.
For females, ultrasound examinations can help determine the causes of pelvic pain, abnormal bleeding, or other menstrual problems. Ultrasound images can also help to identify palpable masses such as ovarian cysts and uterine fibroid growths, as well as ovarian or uterine cancers. Sonohyserography (saline infusion sonography) is a relatively new procedure in which sterile saline is injected into the uterus while a transvaginal sonogram is performed. The purpose is to distend the uterine cavity (endometrial cavity) to look for polyps, fibroids, or cancer, especially in patients with abnormal uterine bleeding. Other indications include evaluation of the uterine cavity looking for uterine anomalies (abnormal formations since birth) or scars. The saline outlines the lesion and allows for easy visualization and measurement.
For males, pelvic ultrasound is a valuable tool for evaluating the prostate, as well as for evaluating the tubes that carry semen. In both sexes, a pelvic ultrasound exam can help to identify tumors and other disorders in the urinary bladder. Because ultrasound provides real time images, it can also be used to guide procedures, such as needle biopsies, in which a needle is used to sample cells from an abnormal area for laboratory testing.
How should I prepare for the procedure?
You should wear comfortable, loose-fitting clothing for your ultrasound exam. Other preparation depends on the type of examination you will have. For some scans, your doctor may instruct you not to eat or drink for as many as 12 hours before your appointment. You may be asked to drink up to six glasses of water two hours prior to your exam, so that your bladder is full when the scan begins. A full bladder helps with visualization of the uterus, ovaries and bladder wall.
What does the equipment look like?
The equipment consists of a transducer and a monitoring system. The transducer is a small, hand-held device that resembles a microphone. The radiologist or sonographer spreads a lubricating gel on the patient’s lower abdomen, where the uterus and ovaries are located, and then presses this device firmly against the skin.
Transvaginal ultrasound uses a wand like device that is lubricated and inserted into the vaginal canal. The ultrasound image is immediately visible on a nearby screen that looks much like a computer or television monitor. The radiologist or sonographer watches this screen during an examination and captures representative images for storage. Often, the patient is able to see it as well.
How does the procedure work?
Ultrasound imaging is based on the same principles as the sonar used by bats, ships at sea, and anglers with fish detectors. As a controlled sound wave bounces against objects, its echoing waves can be used to identify how far away the object is, how large it is, its shape and its internal consistency (fluid, solid or mixed).
The ultrasound transducer functions as both a loudspeaker (to transmit the sounds) and a microphone (to record them). When the transducer is pressed against the skin, it directs a stream of inaudible, high-frequency sound waves into the body. As the sound waves echo back from the body’s fluids and tissues, the sensitive microphone in the transducer records the strength and character of the reflected waves—with Doppler ultrasound the microphone captures and records tiny changes in the sound wave's pitch and direction. These signature waves are instantly measured and displayed by a computer, which in turn creates a real-time picture on the monitor.
The live images of the examination can be recorded on videotape or on a disc. In addition, still frames of the moving picture are usually "frozen" to capture a series of images.
How is the procedure performed?
There are three methods of performing pelvic ultrasound: abdominal (transabdominal), vaginal (transvaginal, endovaginal) in women, and rectal (transrectal) in men. The same principles of high-frequency sound apply in each technique.
For the transabdominal approach, the patient has a full urinary bladder and is positioned on an examination table. A clear gel is applied to the lower abdomen to help the transducer make secure contact with the skin. The sound waves produced by the transducer cannot penetrate air, so the gel helps to eliminate air pockets between the transducer and the skin. The sonographer then presses the transducer firmly against the skin and sweeps it back and forth to image the pelvic organs. Doppler sonography can be performed through the same transducer.
Transvaginal ultrasound involves the insertion of the transducer into the vagina after the patient empties her bladder and is performed very much like a gynecologic exam. The tip of the transducer is smaller than the standard speculum used when performing a Pap test. A protective cover is placed over the transducer, lubricated with a small amount of gel, and then inserted into the vagina. Only two to three inches of the transducer end are inserted into the vagina. The images are obtained from different orientations to get the best views of the uterus and ovaries. Doppler sonography can be performed through the transvaginal transducer, which is the same transducer used during sonohysterography. Below is an example of a transvaginal transducer (probe). Transvaginal ultrasound is usually performed with the patitent lying on her back. In some cases she may bring her knees toward her chest with her legs spread—stirrups may be used as is common during a Pap smear or internal exam.
The prostate gland is located directly in front of the rectum, so the ultrasound exam is performed transrectally. A protective cover is placed over the transducer, lubricated, and then placed into the rectum so the sound need only travel a short distance. The images are obtained from different orientations to get the best view of the prostate gland. Ultrasound of the prostate is most often performed with the patient lying with his left side down on the table and with his knees bent up slightly.
Each method has its advantages. The transabdominal approach offers an expanded view of the entire pelvis, showing where one internal structure is in relation to another. Since the transducer is brought closer to the area being examined in the transvaginal and transrectal approaches, improved visualization may be achieved. Thus, it can be helpful in locating the embryonic heartbeat in an early pregnancy, evaluating the uterine texture, or measuring a cyst in an ovary. Your physician or radiologist will decide whether one or a combination of approaches is best for your particular case.
When the examination is complete, the patient may be asked to dress and wait while the ultrasound images are reviewed, either on film or on a monitor. Often, though, the sonographer or radiologist is able to review the ultrasound images in real time as they are acquired, and the patient can be released immediately.