The Trail of Invisible Light: A Century of Medical Imaging
Ultrasound
Ultrasound imaging enables us to make pictures of the organs beneath the skin in the same way sonar allows fishermen to locate fish under water -- by sending a pulse of sound and waiting for its echo. The echoes are sent and received by a small "microphone" or transducer which the doctor or technologist slides over the skin. The transducer sends sound waves with a frequency of over 20,000 vibrations per second--inaudible to the human ear. Each echo appears as a bright dot on the ultrasound monitor. The depth and location of the echo (represented by the dot) can be determined by measuring the time it takes to return to the transducer. |
22. Submandibular technique. From Principles
and Practice of X-ray Technic for Diagnosis, John
A. Metzger, St. Louis, The C.V. Mosby Company. 1922. |
| When sound waves are sent at high frequency, an image consisting of many dots is formed on the monitor. This is an image of the organs beneath the skin. As soon as one image of the organs below the transducer is formed, a new image is formed and stored, and so on. These successive images are rapidly stored in the memory of a computer in the ultrasound machine. Because these images are continually and rapidly updated by the computer, they allow us to see not only the shape but the real-time motion of what is occurring within the body, without discomfort or risk to the patient. |
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| 23. Ultrasound image of a fetal hand. Courtesy of the Department of Radiology, UIHC. |
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