Remembering the life of ultrasound pioneer Floyd Dunn


Floyd Dunn, a groundbreaking pioneer in the science of ultrasound and bioacoustics, died January 24, 2015.

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Floyd Dunn, a groundbreaking pioneer in the science of ultrasound and bioacoustics, died January 24, 2015. A veteran of the World War II Battle of the Ardennes, he was 90 years old. His death came 30 days after that of his wife, Elsa, who died on December 26, 2014. Dunn was introduced to Elsa shortly after his service in WWII, and they were married for more than 64 years.

Floyd Dunn in Belgium around Thanksgiving 1944 during World War II.
Floyd Dunn in Belgium around Thanksgiving 1944 during World War II.

An event on campus scheduled for Aug. 21-22, 2015, will celebrate his life. In addition, the Elsa and Floyd Dunn Endowed Fund has been established in the ECE Department at Illinois to honor the memory of Floyd and Elsa. Contributions of any size are welcome.

Dunn attended the University of Illinois at Urbana-Champaign in the Department of Electrical Engineering (which became the Department of Electrical and Computer Engineering in 1984), arriving in 1946 as an undergraduate student and earning three degrees, including his PhD in 1956. He remained at the U of I for 50 years and retired in 1995.

“In an era that often shunned basic research, he shepherded, almost single-handedly at times, a discipline that made way for the safe, commercial development of a stunning array of today’s ubiquitous devices,” said Professor William D O'Brien, Jr., the director of Illinois’ Bioacoustics Research Laboratory. “Dunn had an extraordinarily creative science and engineering career at the interface between diagnostic and therapeutic ultrasound and living systems for which he conducted influential research that significantly promoted diagnostic and therapeutic ultrasound.” 

These scientific questions bridged life science and engineering. Their medically significant answers directly affected the developments of diagnostic and therapeutic ultrasound. 

“Dunn’s fundamental engineering and bioengineering accomplishments and their applications toward the promotion of diagnostic and therapeutic ultrasound directly benefited and continues to benefit the welfare of mankind,” O’Brien said.

For more than 20 years, Dunn directed the U of I's Bioacoustics Research Laboratory, the laboratory that his research adviser William J. Fry started with his brother Frances J. Fry in 1946.

From a converted, 19th-century power plant deep within the engineering campus, Dunn mentored generations of students, some of whom preceded him into retirement. His recognized contributions afforded him decades of opportunities to teach and lead research in the U.S., the former USSR, the United Kingdom, and for more than 40 years, in Japan.

Floyd Dunn, wearing his NAE tie.
Floyd Dunn, wearing his NAE tie.

Dunn was a member of both the National Academy of Sciences and the National Academy of Engineering. He was also the past president of the Acoustical Society of America. He was a recipient of the IEEE Edison Medal, the ASA Gold and Silver Medals as well as the American Institute of Ultrasound in Medicine William J. Fry Memorial Lecture Award in 1984 and the AIUM Joseph P. Holmes Basic Science Pioneer Award in 1990. He served on several FDA and NIH committees and was a member of Committee 66 of the National Council on Radiation Protection.

Additionally, he served the scientific community by preparing compilations of published ultrasonic propagation properties of mammalian tissues. He collaborated with investigators in the former USSR, the UK, and Japan, and helped establish certain ultrasonic biophysical measuring procedures in the People's Republic of China. 

In retirement, Dunn continued to contribute to the work of his colleagues, and he carried an appointment at the University of Arizona-Tucson. He edited peer-reviewed scientific articles and, until 2013, consulted with private companies interested in using ultrasound. Dunn was an avid reader and scholar of the works of James Joyce. Over the course of many years, he amassed a sizable collection of his works, including a rare photo reproduction of Joyce's handwritten manuscript of Ulysses.

“As a sustained leader in biomedical ultrasound, Floyd Dunn stood alone,” O’Brien said. “For nearly six decades, his full efforts had been devoted to the subject; he maintained a steady flow of productive research; he built one of the largest organizations devoted to the field; he encouraged the development of the field nationally and internationally, behind the scenes and through leadership and participation in many different organizations.”

What was so remarkable about Dunn’s life-long research career is the element of completeness with which he approached difficult scientific questions. He was especially accomplished in half a dozen areas.

He was the first to quantify in vivo — within living tissues — the temperature-dependent ultrasonic absorption coefficient, showing it to exhibit behavior considerably different than in vitro — or outside normal biological context — preparations.

“This finding had a seminal influence on therapeutic ultrasound, and is particularly important now, when ultrasonic hyperthermia is being exploited for treatment of cancer,” O’Brien said.

Dunn was the first to show that diagnostic ultrasonic images of tissue structures, and their pathologies, resulted from structural protein constituents. This seminal finding initiated the worldwide spread of research activity in ultrasonic tissue characterization (now being recognized for its quantitative ultrasound capabilities) and its application in diagnostic ultrasound.

He was also the first to recognize the need for quantitative measurements of the nonlinearity parameter in biological materials. He was the first to show the dependence of this nonlinearity parameter on the structure of tissues. This work demonstrated how the nonlinearity parameter provided information related to more effective therapeutic treatments. It also opened up an entirely new imaging area in diagnostic ultrasound. 

Dunn developed innovative experimental preparations to show that physical interactions of ultrasound in living systems occur under conditions where thermal and cavitation events can be innocuous, thus demonstrating the control achievable in producing reversible and irreversible changes in living systems.

“A medically significant aspect of these studies has been the determination of ultrasonic thresholds for irreversible structural changes,” O’Brien said.

Early in the development of diagnostic ultrasound, these thresholds become de facto worldwide diagnostic ultrasonic standards for separating bioeffects from lack of bioeffects, from which government and standards setting bodies established diagnostic ultrasound safety criteria.

“The widespread and beneficial use of diagnostic ultrasound (virtually every pregnant woman’s fetus in the world is evaluated ultrasonically) could not have occurred without such safety assurances in the 1950s and 1960s,” O’Brien said.

Dunn’s study of ultrasonic toxicity dealt largely with mammalian reproductive organs, as these organ systems had ample opportunity to be exposed during routine therapeutic and diagnostic procedures.

“The response of the mammalian testis to ultrasound exposure was shown to be considerably different from its response to ionizing radiation,” O’Brien said. “Also, studies with the mammalian ovary demonstrated that the different ovarian phases manifested different ultrasonic responses. Both organ systems had been evaluated extensively clinically, and these research findings were reassuring as to the safety of diagnostic ultrasound.”

Dunn’s work on reproductive tissues was doubly important because of the concern with genetic effects in the early days of diagnostic ultrasound. 

Another significant contribution was Dunn’s development of measurement methods.

“A continuing problem in this field was the ability to specify and quantify the values of the ultrasonic parameters in ultrasound fields noninvasively,” O’Brien said. “He was instrumental in developing measurement methods that were adopted worldwide, both by research laboratories and in government safety standards.

And finally, Dunn was perhaps the first to contribute in the field of ultrasonic microscopy by an early suggestion for using thermal detectors. He also contributed significantly with some of the earliest applications to living systems.

“He was involved in the first major blossoming of biomedical ultrasound in the ‘50s,” O’Brien said. “In the ‘60s, there were a few years when he almost single-handedly managed to keep the field alive.  Now, of course, biomedical ultrasound is a major industry and basic research in the field receives a significant fraction from the NIH budget. No single scientist is more responsible for this success than Floyd Dunn.”

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This story was published March 31, 2015.