Elisabet O. Orville
Ultrasound imaging has become part of our lives in the last decade. We are now all familiar with the blurry black and white sonograms (ultrasound pictures) that show the unborn baby inside the mother’s uterus. Although it may take a little imagination on our part to understand that a round circle is the baby’s head, that does not prevent a proud mother-to-be from showing off her first baby picture. See sonogram below.
Thirty four week fetus
(figure available in print form)
Reprinted by permission of Dr. K.J.W. Taylor, from “
Atlas of
Gray Scale Ultrasonography
”, (c) 1978 by Churchill Livingstone.
This unit emphasizes the medical applications of ultrasound. An important part of the unit is a collection of slides depicting ultrasound scans of various organs, showing both the normal condition as well as various pathological states. There are drawings that accompany and clarify many of these sonograms, because ultrasound pictures can be very difficult to understand without explanations. These slides are available by calling me at Polly T. McCabe Center (787-8758).
This unit is designed primarily for biology, ninth-grade physical science, health and human physiology classes in high school, but could be easily adapted as well for the middle school level.
It is strongly advised that this unit emphasizing the medical aspects of ultrasound be used in conjunction with Beverly Stern’s unit in the same volume called “
The Basic Concepts of Ultrasound
”. Explained in her unit is the physical basis of ultrasound including:the nature of sound waves;equipment such as the transducer crystal which both emits sound waves and then receives the returning echoes; acoustic impedance and reflectivity; as well as an explanation of B-mode scanning, real-time and gray-scale.
Perhaps only a teacher of ninth-grade physical science or technology would wish to put equal emphasis on both our units, but we feel that since all our lives are becoming increasingly dependent on technology and that is where the jobs will be, students should be exposed to both the biological and technical aspects of ultrasound.
It has been exciting for us to learn about this dynamic , new method of imaging the human body. We participated in Dr. Ronald Ablow’s seminar on Medical Imaging during the spring and summer of 1983 and as well as learning about ultrasound, we explored other modalities of imaging such as CT scanning, Nuclear Magnetic Resonance, and Nuclear Medicine. To supplement our theoretical knowledge we visited the Ultrasound Lab at Yale-New Haven Hospital where Paula Jacobsen and staff demonstrated the actual procedures and cheerfully offered themselves as guinea pigs to allow us to get some sonograms.
I am also grateful to Dr. Kenneth J.W. Taylor, Professor of Diagnostic Imaging at Yale, who allowed me to reproduce many of the sonograms from his book, “
Atlas of Gray-Scale Ultrasonography
”, 1978; as well as to Dr. John Hobbins, Professor of Obstetrics and Gynecology at Yale, who discussed recent uses of ultrasound in obstetrics with me. Many of the slides are reproduced with permission from his book,”
Ultrasonography in Obstetrics and Gynecology
”, 1983.
I especially want to thank our seminar leader, Dr. Ronald Ablow, Professor of Diagnostic Radiology and Pediatrics, who initiated us into the mysteries of medical imaging, and patiently and with good humor helped us to learn the concepts and language of a field that was new to most of us.
Introduction to Ultrasound and Echolocation
:.
The use of soundwaves in order to “see” is a new and strange concept for students. It might help your classes to get a proper perspective on the subject if they can first understand the phenomenon of echolocation in animals.
Before I continue, I need to define some terms that are used
in the study of sound. HERTZ is the number of sound waves per second. KILOHERTZ is 1000 waves/second and is abbreviated KHz. MEGAHERTZ (MHz) is one million waves/second. ULTRASOUND is sound with a frequency too high for the human ear to hear (over 20 KHz). ECHOLOCATION is the ability of certain animals to produce pulses of sound (either audible or ultrasonic) and then to receive the returning echoes which are processed by the brain to give information about prey or obstacles.
Many animals are adapted to niches where vision is not a particularly useful sense. Some of these animals live in the depths of the ocean or in dark caves, whereas others are nocturnal. Many of these species have evolved the ability to echolocate. For instance, dolphins and all the other species of toothed whales, such as the sperm whale and narwhale,use ultrasound to locate schools of fish at depths where little light penetrates. Oil birds of tropical South America give off audible clicks of sound to avoid flying into the walls of the caves where they live, and shrews echolocate when they are exploring for food.
The best known animal echolocator is of course the bat. There are more than 600 species of bats who use ultrasound in order to catch flying insects at night and to avoid obstacles. By rapidly vibrating their vocal cords they can emit short pulses of ultrasound at a frequency of up to 120KHz. These beams of ultrasound are beamed directionally into the darkness by means of the lips or noseflaps. If a moth happens to be cruising by, the sound waves are reflected from its body and return to the bat’s ears as echoes. When his brain has processed this information, he knows the size of the insect and its speed and direction and thus can swoop in on his prey in the darkness with great accuracy. (An interesting side note is that certain moths have evolved the ability to detect the ultrasound pulses of the bat, and to emit their own soundwaves with the same frequency as those of the bat. This confuses the bat who abruptly stops his attack.)
Just as a bat “sees” in the dark by emitting pulses of soundwaves, so the sonographer (ultrasound technologist) can “see” our insides by aiming high-frequency soundwaves, produced by a crystal with very special properties. There are a few differences of course. The frequencies used in medical ultrasound are much higher (from 1 to 5 MHz) whereas the maximum frequency for bats is 120 KHz.Another major difference is that the bat uses one organ to send sound (the vocal cords) and another to receive the echoes (the ears). In diagnostic ultrasonography the same crystal in the transducer both emits soundwaves
and
receives the returning echoes as well. See Beverly Stern’s unit for a fuller explanation.
