Exploring the History and Evolution of Ultrasound: From Bats to Medical Imaging

  Ultrasound, a form of energy created by high-frequency acoustic waves traveling through solid or liquid materials, has wide-ranging applications. From serving medical purposes to facilitating industrial processes known as "high-power applications" (within the frequency range of 20 to 100 kHz), like ultrasonic welding, ultrasound's significance is vast. 

Unraveling the Origins of Ultrasound

Lazzaro Spallanzani, the Italian physiologist and priest, was the pioneer of ultrasound studies. His experiments aimed at deciphering how bats managed nocturnal flights gave birth to the concept of ultrasound. Spallanzani deduced that bats relied more on sound than sight for navigation.

Echolocation and Bats

Bats and ultrasound share a unique relationship. From being a source of inspiration for Leonardo Da Vinci for his early model of a wing to laying the foundation for ultrasound technology, bats have been integral to the process. 

Ultrasound for Bats Orientation

Technological advancements in receiving ultrasound – acoustic waves with a frequency too high to be audible by humans – revealed that bats exploit high-frequency emissions. Bats can produce sounds through their larynx to navigate and hunt. 

Their auditory function enables them to analyze the reflections of obstacles encountered during flight, primarily in darkness. For hunting, bats emit ultrasounds in varying frequency bands, and through their auditory system and brain processing, they can identify and discriminate the interesting targets (like an insect) from uninteresting ones (an obstacle). 

Sonar: The First Practical Application of Ultrasound

Paul Langevin, the inventor of Sonar (SOund Navigation And Ranging) in 1917, used ultrasound for the detection of submarines during World War I. Sonar, which uses the propagation of sound underwater for navigation, communication, or detecting submarines or underwater objects, marks the first practical application of ultrasound.

Ultrasound in the Medical Field: B-Mode Imaging

The 1940s witnessed the introduction of ultrasound in the medical field for therapeutic (like neurosurgery) and diagnostic purposes. However, it was only in the 1950s that ultrasound found practical diagnostic applications, first in obstetrics and then in other medical fields like abdomen, pelvis, cardiology, ophthalmology, orthopedics, etc. 

Ultrasound, with no dependence on ionizing radiation, proves to be a powerful tool, making it safe for fragile patients, including pregnant women. The widespread availability of commercial systems has increased the dissemination of this technology. The medical field has seen a shift from the simplest "A-mode" technique to the more familiar "B-mode" applications.

Exploring the Role of an Ultrasound Probe during a Pregnancy Examination

In the medical world, a probe, also known as a transducer, is utilized to generate and capture ultrasound waves. This device comprises one or more ceramic elements, known for their electromagnetic attributes. These elements adeptly convert electrical energy into mechanical energy to produce ultrasound, and vice versa for detection.

The centerpiece of the transducer's functionality is the piezoelectric material. The piezoelectric effect encompasses the ability to generate pressure waves by altering the material's volume when exposed to fluctuating voltage, and the reverse process.

The Science Behind Therapeutic Ultrasound

The main attenuation property of ultrasound leads to a rise in tissue temperature due to absorption. While the local temperature increase in diagnostic imaging is typically minimal, in therapeutic imaging, absorption is strategically used for hyperthermia treatment of tumors, such as those in prostate cancer. The tissue temperature can reach between 50°-100°, causing irreversible tissue damage, also known as coagulative necrosis.

Expanding the Scope of Ultrasound Applications

Ultrasound technology made significant strides into the realms of welding and printing plastics and metals in the 1960s. Today, the power applications of ultrasound encompass:

Ultrasonic Welding of Plastics: This method harnesses vibrations within the 20 to 40 kHz range, proving to be quick, clean, efficient, repeatable, and energy-efficient.

Ultrasonic Cutting of Plastics and Food Products: Here, the vibrations are directed onto a blade without altering or damaging the material intended for cutting. There's no need for pre-heating or pre-cooling the material before cutting. Plus, it's highly efficient for large scale projects.