History of Ultrasound
Categories of Sound
Sound is categorized based on its frequency:
Infrasound: Frequencies below 20Hz.
Audible Sound: Frequencies ranging from 20Hzto 20,000{ Hertz (20 kHz)} .
Ultrasound: Frequencies above 20,000{ Hertz (20 kHz)}.
Medical Applications of Ultrasound
Diagnostic Medical Uses: Utilizes frequencies typically between 1 { Megahertz (MHz)} and 30{ Megahertz}. (A Megahertz is 1 million Hertz).
Therapeutic Medical Uses: Utilizes lower frequencies compared to diagnostic ultrasound, generally between 1{ Megahertz} and 3{ Megahertz}. These higher energies cause therapeutic effects in tissue.
Summary of Frequency Ranges and Categories
Frequency Range | Category of Sound |
|---|---|
1 \text{ MHz} – 30 \text{ MHz} | Diagnostic Ultrasound |
1 \text{ MHz} – 3 \text{ MHz} | Therapeutic Ultrasound |
20 \text{ Hz} – 20 \text{ kHz} | Audible Sound |
0 \text{ Hz} – 20 \text{ Hz} | Infrasound |
History of Ultrasound
The Beginning: Observations of Bats (1793)
Lazzaro Spallanzani, an Italian priest and scientist, conducted experiments on bats.
He observed that blinded bats could still navigate and function effectively.
However, deafened bats were unable to function, indicating that hearing was crucial for their navigation.
At the time, the phenomenon of echolocation (using high-frequency sound to perceive environments) was not understood.
Discovery of the Piezoelectric Effect (1880)
The Curie Brothers (Jacques and Pierre Curie) discovered the piezoelectric effect.
They demonstrated that applying mechanical pressure (pressure waves) to a quartz crystal caused it to generate an electrical voltage.
Conversely, they also discovered the reverse piezoelectric effect.
Applying an electrical pulse to a quartz crystal caused it to vibrate and produce mechanical pressure waves (sound).
Military and Industrial Applications
Sonar Invention (1906): Sonar (Sound Navigation and Ranging) technology was initially invented to detect icebergs, especially after incidents like the Titanic.
Submarine Detection (1916): During World War I, sonar technology was adapted for the detection of submarines, becoming a critical military tool.
Metal Flaw Detectors (1928): Ultrasound began to be used in industrial settings to check the integrity of metal components for ships and aircraft, identifying structural weaknesses.
First Medical Applications
Karl Dussik (1942): An Austrian neurologist and psychiatrist, conducted the first recorded medical application of ultrasound at the University of Vienna.
He utilized A-mode scanning (Amplitude mode) to visualize a brain tumor.
George Ludwig (1947): Used A-mode ultrasound to successfully diagnose the presence of gallstones.
Development of Cardiac and Obstetrical Ultrasound
Hertz and Edler (1954): Pioneered the use of A-mode ultrasound to demonstrate heart motion.
Their work was foundational, leading directly to the development of M-mode ultrasound (Motion mode), specifically designed to visualize the movement of structures like the heart.
Ian Donald: Known as the "father of obstetrical ultrasound" for his significant contributions to its development and clinical application.