Diagnostic Imaging: Ultrasound technology

Mar 6, 202313 min read

Updated: Aug 26, 2023

What do an 18th century scientist analyzing the flight of cave-dwelling bats, piezoelectric quartz crystals generating high frequency sound, and the echolocation of warships, submarines, and icebergs all have in common?

In this article, we continue our discussion on the evolution of medical products, with focus on diagnostic imaging and ultrasound technology. We will explore the history and advancements of this area of medical technology, current status, implications within our global society, and future outlook. Let’s look into the past for a closer look at four great scientists, the thousands of hours of their lives dedicated to research, and their discoveries and their contributions to reach the ultrasound diagnosis we know today. Together let’s delve in to the evolution of ultrasonography.

"You can't connect the dots by looking in to the future; you can only connect them by looking in to the past" - Steve Jobs.

Today, we often take it for granted when the doctor tells us to have an ultrasound, because we will simply make an appointment with the ultrasound imaging specialist, fast or drink water in some cases, and go on the day of the appointment. Our family doctor can obtain the report in just a couple of days, or even at the same time to obtain a diagnosis and treatment for our condition. But in history it was not so simple, and it took a little less than 300 years to arrive where we are today.

But what is an ultrasound?

Ultrasound is the obtaining of diagnostic images from the echoes obtained by the emission of ultrasound waves. A transducer that can be easily held in the hand is used, and the device emits ultrasound waves that are transmitted to that area of the body under study. In turn, it collects the echo of the waves and a computer transforms it into an image that appears on the screen.

We will explain some theoretical and scientific concepts later on. However, first, remembering Steve Jobs' phrase, and looking backwards in time, we will cover some of the most important points:

The Myth Buster: Point 1

Courage to contradict

We will travel to Scandiano, Italy in the year 1729, where the controversial and controversial scientist Lazzaro Spallanzini was born, destined by "paternal inheritance" to study law and religion, but who was finally able to study biology, specializing in Botany and Zoology. He set out to demolish false concepts and myths, deeply rooted for hundreds of years until then, demonstrating empirically the functioning of some organs. Interested in reproduction, he was one of the greatest opponents and detractors of the theory of spontaneous generation. Refuting one of the most controversial topics of the 18th century (already refuted earlier by Francesco Redi, known as the founder of experimental biology), it is now taken as a transcendental fact since it was the starting point of the concept that every living being comes from another living being, including microscopic ones. Pasteur would later successfully apply this principle to microorganisms. He was a pioneer in performing successful artificial inseminations. He debunked the myth of the aura seminalis, demonstrating the need for contact between the seminal fluid and the oocyte for fertilization and not a kind of "vapor" emanated by the oocyte itself.

Spallanzini also performed tests that proved the action of the digestive juices, as well as of the gaseous exchange in the lungs, of the action of the heart in the blood vessels and in the movement of the blood, and in its changing speed according to the different calibers of blood vessels.

Eco-location

Spallanzini realized that, unlike most living beings, even those animals that hunt at night like owls, bats had a very high precision to move with their eyes covered, to orient themselves perfectly and to find shelters up to about 5 cm in diameter. They were even able to fly through subway tunnels. He also observed that their orientation was not by hearing, but he could see that it came from their hearing.

For these reasons Spallanzini concluded that bats could navigate in total darkness being blind, and using inaudible sounds. At a time when the only sounds known were the audible to the human ear, and knowing that the bat's flight was silent, it was very controversial and questioned. The knowledge of ultrasound and being able to identify it as a sound not audible to humans, will only be known in 1938 by biologists Donald Griffin and Robert Galambos, almost 200 years later!

From a family of scientists: Point 2

130 years later, in 1859, Pierre Curie was born in France. His father decided that he would have an unusual education: it would be with private tutors, rather than going to an institution, given his "temperament" and keen intellect. She showed early talent in mathematics, and at 16 entered the Sorbonne, and at 18 earned the equivalent of a master's degree. At 20, together with his brother Jacques, he began experimenting with crystals and their pyroelectric effect (a change in the temperature of crystals generates an electric potential). Armed with the most rudimentary materials: aluminum foil, wire, glue, magnets and a jeweler's saw. They experimented with various crystals such as quartz, topaz, cane sugar, Rochelle salt. The brothers noticed that when some materials were subjected to compression, this mechanical stress resulted in an electrical potential.

They immediately used their discovery to invent the piezoelectric quartz electrometer.

There was an unexpected twist the following year, when mathematician Gabriel Lippman theorized that there would also be an inverse effect, and that, when an electric field was applied to a crystal, it would deform in response.

The Curie brothers demonstrated that this theory was also true and that piezoelectricity worked in both directions producing high frequency sounds.

Piezoelectricity fell into oblivion for almost 40 years, until in 1917 by Paul Langevin was developed the first transducer with quartz crystals, for use in a submarine, similar to those used today in automobiles to measure and alert the proximity to obstacles.

Between 1912 and 1938 there are several events where Maxium and Richarson begin to use ultrasound to detect icebergs, after the sinking of the Titanic. Langevin invents the ultrasonic generator to detect submarines. As already mentioned, in 1938 Griffin and Galambos demonstrate the ultrasound emission of the bat, and the concept of the existence of sounds that we do not hear is finally understood.

Who came up with the idea? The father of ultrasound: Point number 3

To join the third most important point in this story, we will travel to Vienna, Austria, in 1908, where Karl Theodore Dussik was born, the son of an immigrant dentist from Czechoslovakia. He studied medicine, and later specialized in psychiatry and neurology. In 1937 he began research on how to use ultrasound for medical diagnosis and to find brain tumors, knowing that it had been used to find schools of fish in the sea.

His idea was to visualize intracranial structures, and take measurements with ultrasound waves. This procedure was based on a two-dimensional representation of the intensity of the attenuation that ultrasound waves have when passing through the fluids and tissues of the human body. With this application, he became the first physician to apply ultrasound as a diagnostic method in humans. This procedure he would refer to as Hyperphonography.

In 1941 he presented a paper explaining all his theory, as well as explaining and describing the quartz ultrasound generator, with transmitter and receiver. After World War II ended in 1945, he began to develop the prototype and in 1947 the first ultrasound image in history, which he produced, was published. In 1948 he presented his work at the world's first congress on "Ultrasound in Medicine" in Erlangen, Germany. There were only two papers presented that spoke of the use of such a methodology in diagnosis, since the rest used it as a treatment.

After Dussik moved to the US with his family, he presented his work at MIT, where research was done, but they closed the project in 1954 concluding that they are too sharply "noised" and are of “unqualified clinical value"

For many years, ultrasound continued to be used only as a treatment method for arthritis, multiple sclerosis and other conditions, and not as a diagnostic method.

Called the father of ultrasound, according to many of the pioneers who followed him and who even wrote books mentioning it in that way.

Later in the late 1950s and 1960s the concept of ultrasound as a diagnostic method evolved. Water immersion techniques were used with all kinds of containers: a laundry tub, a cattle trough, and a machine gun turret of a B-29 aircraft. They were able to produce images with less "noise", and successfully detected digestive and mammary tumors. It began to be used in B-mode (explained below).

In 1951 Composite Ultrasound appeared, in which a mobile transducer produced several shots of ultrasonic beams from different positions, and towards a fixed area.

In the 1970s the gray scale was introduced.

In 1972 Leopold and McDonald made the first B-mode image of a joint.

In 1981 it was used to perform a joint aspiration.

We will digress from this timeline to recall the Austrian physicist Christian Andreas Doppler, born in 1842. He studied the change in the properties of ultrasound when the object emitting it is in motion. Doppler initially studied the change in color of starlight, referring to distance as the main cause of this phenomenon. As he did not have elements to measure the speed of light, he designed an experiment in which he could apply his theory of sound waves. Collaterally this allowed him to find the mathematical expressions that describe the phenomenon that occurs when an object approaches us, the sound it emits becomes more acute, while the same object moving away makes the sound becomes more serious.

Going out of parenthesis and following the time line , in 1982 Aloka developed color Doppler in two-dimensional imaging and introduced it to the market. The emitted echoes were recorded and integrated into a single image.

In this same decade transesophageal echocardiography was born. In the 1990s omniplanar and biplanar transducers with Doppler capability and color flow were introduced. Cardiac intravascular ultrasound (IVUS) was also introduced.

Some scientific concepts:

If we were to summarize this analogically, it would be as if the ultrasounds and their echoes, noticed by Spallanzinni, and produced by bats, could be emitted, captured and transformed by the piezoelectric effect of the Curie brothers. And in turn put into a single device to study the human body by Dussik.

What is sound? According to the RAE (Real Academia Española): It is a sensation produced in the organ of hearing by the vibratory movement of bodies, transmitted by an elastic medium such as air. The human ear can hear up to 20,000 cycles/sec (20 KHz).

What is ultrasound? Sound whose vibration frequency is higher than that perceptible by the human ear. Frequencies higher than 20,000 cycles/sec are considered ultrasound. And in medicine they are used from 1 to 20,000,000 cycles/sec, i.e. 1 to 20 MHz.

Both sound and ultrasound are events in nature, discovered at some point in history by humans. Some animals that also use it, besides bats, include: mice and whales, grasshoppers, moths, dolphins and some birds. For echolocation (or echolocation), mating, peer-to-peer communication, detecting prey or predators, and even "sensing" the ultrasound that other animals emit to know when to escape.

On the other hand, after its discovery, people have used it not only for images, but also in a wide variety of fields, for echolocation of all types of vessels: warships, submarines, fishing boats; location of schools of fish and icebergs; in our cars that tell us when we are approaching an obstacle, in physiotherapy, detection of cracks in industrial equipment, among others.

Ultrasound: As we have already covered, it is an image produced by the rebound of the ultrasound echoes emitted by a transducer, when it passes through the tissues of an organism. And it is when these echoes return to the transducer that it is possible to reconstruct a two-dimensional or three-dimensional map, in grayscale, in color, static or moving and in real time, of the tissues. In short, it is acoustic energy transformed into another type of energy.

Ultrasound is used in three different modes:

Mode A: Echoes are reflected in peaks and is mainly used in measurement of different structures, encephalography and ophthalmology for example.
Mode B: It is mainly used to study abdominal structures. It provides two-dimensional images.
M-mode: Shows movement as a function of time, used in echocardiography.

An important concept is that of the propagation velocity of a wave: it is defined as a value given by the distance the sound travels in a unit of time. It is not affected by the nature of the sound or by the operator. But it does vary according to the medium in which it travels. This makes that in the denser organs travel faster, for example, in the bone 4080 m/s. And on the other hand are the organs that generate more resistance to the passage of ultrasound waves (therefore, they produce a large amount of echo and the resulting image can not be used). At the opposite pole the tissues that contain very little density becomes very slow 330 m/s, and generate very little resistance to ultrasound as the lungs, which contain a large amount of air in its interstitium and this causes the wave to pass directly along and not bounce the echoes, so the transducer will not receive something that causes an image.

And in the middle of these extremes are most of the rest of the soft tissues of the body that have an average resistance and where the ultrasound velocity is 1400 m/s to 1600 m/s, is where the echoes returning to the transducer generate the ideal image that can be interpreted for diagnosis. And that is the reason why soft tissues are the ideal ones to study by this method.

The greater the difference in impedance (the resistance of the tissue to the passage of the ultrasound beam) of each of the media, the greater the amplitude of echoes that are reflected and the lower the ability of the ultrasound to pass through the tissues. To avoid this effect produced by the interface (with a great difference in impedance) produced by the air between the transducer and the skin, a gel is used.

What is Doppler? It reflects the change in sound frequency reflected by the mobile structure explored, and is combined with ultrasound. It is used to evaluate the blood flow, and to determine if there is any reduction or obstruction in it, its speed, diameter of the vessels, atheroma plaques, inflammatory lesions, stenosis, etc. It is also used in cardiology, obstetrics, phlebology, among other specialties.

IVUS: Cardiac Intravascular Ultrasound: This ultrasound is used in cardiology to evaluate the coronary arteries and cardiac muscle exclusively.

Through an outpatient process

using a tiny ultrasound transducer attached to a catheter, which is introduced into an artery in the groin area and carried to the heart.

What do the United Nations, World Health Organization, and ICRP at the Genoa Convention have to say about ultrasound?

Ultrasound is one of the safest and one of the most widely used diagnostic imaging methods known to date, and it has been constantly evolving. According to a report written in 1982 about ultrasound in all its aspects (Environmental health criterion 22), at the Genoa convention, and with the sponsorship of the United Nations Environmental Program, the World Health Organization, International Association for Radiation Protection, it is mentioned that there is no evidence of adverse health effects in humans exposed to ultrasound diagnosis. However, its rapid increase in use as the preferred method during pregnancy is still a concern because of the susceptibility of the fetus to other chemical and physical elements, although it is still the safest and most preferred method during pregnancy.

The report evaluates and provides information for the use of ultrasound as a diagnostic method, aimed at health authorities and regulatory agencies, about the possible effects of its use, and to provide guidance for risk management in physicians, occupational use, and in the general population. As well as characteristics, techniques, resources and applications, exposure levels, among other data.

Latest advances in ultrasound

Bone and metal: In the last decade, a new technique was developed that allows the use of ultrasound as a diagnostic method and in therapeutic applications. As we have mentioned, metal or bone distort ultrasound waves due to the impedance of each material and the interface they produce. Anisotropic structures have been designed with Acoustic Complementary Metamaterials (CMM) composed of membrane cell units in different directions, with different densities and thicknesses. The focus of ultrasound waves has been found to be improved from 28% to 88%. And the potential applications of this are anti-reflection layers, which are used for ultrasound, camouflage, detection and others.

A new technique has also been developed to use an ultrasound drill in which nanodroplets are burst around blood clots. As they burst, they become microbubbles that oscillate thanks to the ultrasound, piercing the physical structure of the clot.

Another method, combining SC-CO2 Super Critical CO2 and HP-US high-power ultrasound, produces enzyme inactivation in extremely hazardous microorganisms such as E coli and S Cerevisiae, in liquid and solid media in just a few minutes (approximately 1 to 5). This would reduce costs and changes in the organoleptic properties of products in food industries.

A hydrogel that can be modulated using ultrasound has also been developed. The changes that ultrasound produces non-invasively to the mechanical and morphological properties of the hydrogel can be used to control cell behavior. The ultrasound allows them to reach the gel, which was previously implanted in a noninvasive way very deep into the body, and with a precision of less than a millimeter. This gel would be used in the near future to heal chronic wounds and to model fibrosis.

Conclusion

Dussik said: "However, complicated the problems may be the importance of these possibilities seems so great as to justify any and all efforts to overcome the technical difficulties.... ". Although he encountered a great many financial, political, historical, and other difficulties, he firmly believed that diagnostic ultrasound would have a promising future, and that it would be well worth the effort to achieve his goal. And without hesitation, it has been worth the journey from Lazzaro's bats, the special character and curiosity of Jacques Curie and his brother, and Dussik's tireless race to realize the idea of his Hyperphonography, to today's most sophisticated intra-cardiac Doppler echocardiography.

I frequently read the biographies of great discoverers or inventors, each one in such different disciplines and fields. I have come to realize that it is not only their intelligence, knowledge and curiosity, but also the fortitude to pursue their idea in spite of great and various adversities.

As we have seen in this journey through history "connecting the dots backwards", ultrasound has been continuously evolving and improving, and extending its use as a diagnostic method in a growing field in medicine.

How far would we achieve in science, or in our lives, if we could all get up every time we fall, to pursue our ideas to fruition? Even against resounding or deafening "NO's." And what points will be forming now for new generations?

"You can't connect the dots by looking into the future; you can only connect them by looking into the past. Therefore, they have to trust that the dots will somehow connect in their future. You have to trust something - your gut, your destiny, your life, your karma, whatever. This perspective has never let me down, and it has made all the difference in my life."

- Steve Jobs 2005

Sobre la autora:

María Soledad Gómez tiene más de 10 años de experiencia en la industria trabajando en una variedad de funciones dentro de la industria regulada, la asistencia sanitaria y la medicina, incluyendo alimentos / bebidas, hospitales y medicina veterinaria. Maria Sole escribe artículos técnicos sobre una amplia variedad de temas del ámbito médico.

Sobre el editor:

Brian Hoy tiene más de 20 años de experiencia en el sector de los dispositivos medicos y la creación de empresas, apoyando el ciclo de vida completo con alcance mundial. Brian es consultor de la industria y ofrece asesoramiento general y apoyo fuera del horario laboral.