Elisabet O. Orville
The following section will explore ultrasound imaging of organs such as the liver, gallbladder and kidneys.
The science of ultrasound is constantly improving. Before the early 1970’s ultrasound machines were able to record only the strong echoes arising from the outlines of an organ, and not any low-level echoes from the internal structure. Therefore liver scans, for instance, did not show possible carcinomas or other pathological states.
In 1972 a refined imaging mode was introduced called gray-scale display. This was a huge step forward because the internal texture of many organs became visible. In gray-scale display, low-level echoes are amplified and recorded as well as the higher-level ones, giving many degrees of brightness. Because of this, ultrasound (along with radionuclide scans) are now the most useful method of imaging the liver.
The following picture is a longitudinal sonogram through a normal liver with its characteristic homogeneous texture. The echoes represent the fibrous structure (collagen) of the liver. The diaphragm shows up clearly on the left (towards the patient’s head) and the gallbladder is the dark structure on the right. Remember that this is a two-dimensional section through three-dimensional organs.
Longitudinal section through the liver
(figure available in print form)
Reprinted by permission of Dr. K.J. W. Taylor , from “
Atlas
of Gray-Scale Ultrasonography
”, © 1978 by Churchill Livingstone.
Cirrhosis of the liver produces very different echoes from those of the normal liver. Excessive alcohol intake causes destruction of normal parenchyma cells which are then replaced by fibrous tissues. These scarred areas produce many distinct echoes and also keep soundwaves from traveling deeper. Characteristically this attenuation (weakening) of sound means that the lower part of the cirrhotic liver does not show up on sonograms.
Ultrasound is also very useful in diagnosing gallstones. The patient is asked to fast before the exam so that the lumen of the bladder will be filled with bile, and hence be more easily visualized. If gallstones are present and the scan happens to traverse them, a very interesting phenomenon can be observed. Gallstones are sonoopaque; that is, they reflect almost all soundwaves so that in a sonogram there will be a dark shadow below each stone. See picture below.
Longitudinal section through two gallstones
(figure available in print form)
Reprinted by permission of Dr. K.J.W. Taylor, from “Atlas of Gray-Scale Ultrasonography”, © 1978 by Churchill Livingstone.
The kidneys have a very characteristic appearance in sonograms. They look like doughnuts in cross-section and are oval with a light interior and dark exterior in a longitudinal view. The light interior represents the renal collecting system and the dark exterior is the renal cortex and medulla. Ultrasound can determine the size and location of the kidneys. In addition, masses or tumors in the kidneys can be imaged. See sonogram below.
Longitudinal section through liver and kidney
(figure available in print form)
Sonogram courtesy of the Yale-New Haven Hospital Ultrasound Lab.
Imaging the female reproductive system by ultrasound
The female reproductive system becomes visible in its entirety when the filled urinary bladder is used as an acoustic window to push aside the air-filled bowels. Vagina, cervix, uterus and ovaries show up clearly. See sonogram below.
Transverse section through the female reproductive system
(figure available in print form)
Reprinted by permission of Dr. K.J.W. Taylor, from “Atlas of Gray-Scale Ultrasonography”, © 1978 by Churchill Livingstone
It is even possible sometimes to see the uterine endometrial layer developing during the menstrual cycle; this layer returns especially strong echoes when it reaches its greatest thickness just before menstruation. According to Dr. John Hobbins, Professor of Obstetrics and Gynecology at Yale, in the future we may be able to use ultrasound to detect precancerous or cancerous changes of the endometrium. Not much work is being done on this aspect of ultrasound presently however.
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Ultrasound is useful for showing various abnormalities in non-pregnant women For instance, fibroids(benign tumors of the uterus) are clearly visualized. Occasionally an IUD gets lost, which is, of course, a cause of great concern. The material in an IUD, whether plastic or metal, is opaque to sound, so that these devices return strong echoes on sonograms. By the location of these echoes the gynecologist will be able to tell whether the IUD is in its proper place (but without the string) or whether it has imbedded itself in the uterine wall. See sonogram below.
Lippes loop—courtesy Dr. K.J.W. Taylor
(figure available in print form)
During the last few years ultrasound has been used to study the development of normal ovarian follicles. This application has great promise in the treatment of infertility.
By constant ultrasonic monitoring, ovarian follicles have been observed to grow in diameter at the rate of approximately 3 mm per day during a normal woman’s cycle, until they reach an average diameter of 2.0 to 2.5 cm at the time of ovulation. At the same time the follicle is developing,the woman’s estradiol (hormone) levels also rise. Then 28 to 35 hours before ovulation there is a sudden spurt of Luteinizing Hormone (LH) as well.
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Using all these indications a doctor would know fairly exactly when the woman was about to ovulate. This knowledge would be crucial for the timing of artificial insemination if a couple were infertile.
In
vitro
fertilization (commonly known as test tube babies) is a procedure that is done at Yale-New Haven Hospital as well as at many other medical centers around the world. A woman who is a candidate for this procedure usually produces normal ovarian follicles with eggs but because her fallopian tubes are blocked or missing, the egg is unable to descend to the uterus.
She is first given hormone treatments to stimulate the development of several follicles at once. These follicles are carefully monitored by ultrasound until they reach their maximal size just before ovulation. Previously the woman would be admitted to the hospital at this point and a procedure called laparoscopy would be performed. That is, two small incisions would be made in her abdomen and the eggs would be gently sucked out of all the large follicles.
Now at Yale the procedure has advanced to the point that the woman can be admitted on an out-patient basis and goes home the same day. Instead of making incisions in her abdomen, doctors can insert the aspirating needle through the urethra and bladder, watching continuously on real-time ultrasound ( ultrasound that shows motion). When the follicles are located, the needle is pushed directly through the bladder wall into the ovary. As many eggs as possible are aspirated and placed in a petri dish with the husband’s sperm to be fertilized. (“Test tube babies” are not started in test tubes.) When the fertilized eggs reach the 8-cell stage they are placed in the woman’s uterus where, hopefully, one of them will develop to maturity.
