7/11/2023 0 Comments Speed of sound formulaFrequency, period, amplitude and intensity are determined by the sound source. All waves have the following characteristics: frequency, period, wavelength, propagation speed, amplitude and intensity. Along with conventional radiography (X-ray), nuclear magnetic resonance (NMR), and computed tomography (CT or CAT scan), ultrasound is one of modern medicines most powerful diagnostic tools.įigure 4 THE BASIC METHOD USED IN ULTRASOUND IMAGING. Ultrasound medical imaging produces readable images of inner body structures and motion without surgical entry into the body or radiation. The operator reads the information that appears on the screen. Depending on a) the time it takes an electrical pulse to make the round trip into the body and back and b) its intensity, a computer determines where on the display screen to make a dot and what shade of gray, from light to dark, it should be. The electric pulse is then sent to the computer/display. The part that is reflected back, the echo, is picked up by the transducer and changed into an electric pulse. Because of this interface, some of the sound wave will be reflected back and some will continue to travel through the next tissue. The sound wave will travel through the first body tissue until it hits an interface, where two different tissues are contiguous. An electric current can be produced in a continuous current form or a “pulsed” form where the current is on and then off in a periodic way. The transducer, or probe, changes the electrical pulse into a sound pulse and sends it into the body.ġ. The operator, usually a sonographer or radiologist, signals the generator which produces an electrical pulse and sends it to the transducer. The basic ultrasound process goes as follows. Ultrasound Medical Imaging-The Basic Process Briefly StatedĪn ultrasound study in progress is illustrated in Figure 4. If it took 3 seconds to return, how deep would it be? If the water were 15 feet deep, how long would it take for the sound wave to return? These questions will be answered in the section on math.ī. Since the sound wave had to travel 19,200 ft round trip, one way, the depth of the water at that point, would be half that or 9,600 ft. ![]() Your ultrasound instrument sends out sound waves that hit the bottom and return in 4 seconds. You are on a sailing vessel out at sea and you want to know the depth of the water. During this unit when reference is made to body tissue it means soft body tissue like liver or kidney rather than hard tissue like bone. Meanwhile, if you are going to try it, remember that 5280 feet = 1 mile.ġ. We’ll get back to this problem in the section on math. Using the same information, if you see lightning flash 15 seconds before you heard the rumble of thunder, how far away would the lightning be? Answer should be to the nearest mile. Since the sound had to travel 110 ft across the canyon and back, one way, the distance across the canyon, would be half that or 55 ft. If you stand in the canyon and yell, “HELLO!”, and in 0.1 seconds an echo comes back to you, how far is it across the canyon? Using the data in the above table and the distance formula you can solve that. ![]() How is an echo produced? It is produced from the sound of your voice going forth and bumping into the side of the canyon wall then being reflected back to you. Now what would happen? Sure, you’d hear an echo. Next suppose you were in a canyon and yell, “HELLO!”. What would happen? Your voice would go forth and disappear. First, suppose you are standing on an open plane and shout, “HELLO!”. Why do you think that is so? The reason is that body tissue contains such a large proportion of water that sound travels through it at approximately the same rate it travels through water.īefore beginning to study the ultrasound medical imaging process, there are two situations I’d like to consider. Also notice that the approximate speed of sound in water and soft body tissue is the same. Notice that the table uses both the metric unit meter and the English unit feet. Hz is the symbol for “hertz”, the internationally accepted unit for measuring cycles. Section I: Diagnostic Ultrasound and Section II: A Little Math Here and There have been put before the unit purpose, level and objectives in Section III so that they may more easily be copied for classroom sets of text materials.Ģ. ![]() The rate will differ with different media. In any homogeneous material, sound Will travel at a constant rate. ![]() Sound waves cannot travel in a vacuum like light waves they must have a medium to travel through. Ultrasound refers to waves that have a frequency higher than 20,000 Hz and are therefore outside our hearing range. The human ear can hear sound waves that have a frequency of 20-20,000 hertz.
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