Sound is an oscillating pressure wave that for human hearing covers a frequency range from about 20 Hz to 20 kHz. Ultrasound devices operate from 20 kHz to gigahertz frequencies. Other than being inaudible to humans, ultrasonic sound waves follow the same physical – acoustic – principles. Just like audible sound, ultrasound can echo off surfaces, pass through water and vibrate solids. Today, ultrasonic devices use the frequencies to detect objects, measure distances, detect invisible material flaws, clean, mix and promote chemical reactions. However, the most exciting applications of ultrasound are in medical imaging, diagnostics and treatment.
How It All Began…..
Of course, the history of ultrasound begins with the first investigations into audible sound and acoustics centuries ago. Italian biologist Lazzaro Spallanzani developed the first scientific high-frequency ultrasound theories during his work on the navigational ability of bats. In the 1800s, many physicists around the world helped develop an understanding of sound and ultrasound.
In 1826, Swiss physicist Jean-Daniel Colladon discovered sonography using a church bell and rear trumpet to show that sound traveled faster through water than air. In 1881, Pierre Curie discovered that pressure on some types of crystals produced an electrical voltage. Piezo-electric crystals serve as the basis for the modern ultrasound transducer that transforms sound pressure into a measurable voltage.
In 1914, after the sinking of the Titanic, Paul Langevin invented a method to detect icebergs. His “hydrophone” first emitted sound waves and then became a receiver to detect echoes from submerged objects. Later used to detect submarines in World War I, his hydrophone was the first sound transducer and a forerunner of ultrasound transducers.
In the late 1940s, Dr. George Luwig developed the use of ultrasound while working at the Bethesda Naval Medical Research Institute. Dr. Ludwig recorded and studied the change in sound waves as they traveled through animal tissues: organs, muscles and gallstones. In 1953, at Lund University, Swedish cardiologist Inge Edler first used medical ultrasonography. Working with a nuclear physics graduate student, Edler measured heart activity ultrasonically using a device borrowed from a ship builder.
Meanwhile, at Glasgow Royal Maternity Hospital, Professor Ian Donald developed the first diagnostic applications of ultrasound. Using industrial ultrasound detectors from boilermakers, Donald used morbid anatomical specimens to observe the effects of ultrasound on how human tissues. Working with medical and scientific colleagues, Donald developed equipment that could detect pathology in human volunteers. Publication of their findings, in 1958, was a milestone in diagnostic ultrasonography.
Donald also invented the B-mode scanner to measure signal intensities. B-mode is also called brightness mode, sonography and 2-D mode ultrasound. Displayed as a 2D map, B-mode provides an actual ultrasound image of a fetus, organ or tumor. Known as the father of obstetric ultrasound, he was able to detect twins in one case and differentiate between an ovarian cyst and cancer in another.
The 50s and 60s saw many improvements in the B-mode scanner. Douglas Howry and Joseph Holmes invented a contact scanner on an articulated arm that allowed the transducer to touch the patient. Until their work, a patient was immersed in water to make a 2D image. The ability to position the transducer by hand and moving it to various angles changed ultrasound procedures dramatically. The maneuverable transducer allowed ultrasound pictures, as we know them today.
Dr. John Wild and John Reid developed a hand held B-mode instrument by modifying standard imaging equipment. They used the hand held instrument to detect breast tumors by swinging it side to side for cross sectional views from several angles. Producing the first breast ultrasound, their instrument was the forerunner of today’s modern machines.
By improving the gain (sensitivity) of the apparatus, an accurate reading could be obtained of thicker or thinner tissues. This advance allowed visualization of tumors and made detection of breast cancer possible. Wild and Reid developed the use of transvaginal and transrectal transducers useful in the detection of ovarian and other cancerous tumors. These efforts were the start of ultrasound endoscopies.
For at least 50 years, radiologists and sonographers have used medical sonography (ultrasonography) as a diagnostic tool to image the human body. It can visualize muscles, tendons and internal organs. Obstetric, transvaginal, gynecological, abdominal, breast and cardiac ultrasound procedures are now routine. Abdominal sonography now includes renal, gallbladder, liver, spleen and prostate scans.
What Lies Ahead for Sonography
The most recent developments in ultrasound is like 3D/4D, Doppler effect and holographic techniques have not yet reached their full potential. Additionally, clinical ultrasound techniques are providing visual guidance for biopsies, aspirations, intravenous line placements and more.