Donald W. Baker was born in Skagway, Alaska in 1932. From 1951, he served for 4 years in the United States Air Force in the Korean War. He spent 2 years working at the Air Force Cambridge Research Center investigating the detection of low-flying aircrafts and airborne bombers basing on returned radar signals. During his Service he was able to acquire knowledge on various electronic applications and in particular those concerning the different types of radar devices. Discharged from the Air force in 1955, Baker entered the University of Washington, Seattle and graduated BScE from the Electrical Engineering Department in 1960.
Since 1958 and as a student he has started working under Robert Rushmer in a Cardiovascular Instrumentation development program. He was first introduced to Rushmer by his classmate Wayne Quinton, who subsequently became bio-medical engineer and "instrument creator" at the University of Washington, and founder of the Quinton Instruments Company.
Rushmer was a trained Paediatrician and physiologist who was determined to elucidate and document cardiovascular functions and parameters in animals. At that time experiments were all conducted on open-chest anesthetised specimens. These were impractical and time-consuming. Rushmer felt that new instruments and methodologies are needed to look into such functions in the intact un-anesthetised subjects. Having set his heart to pursuing this Rushmer established facilities, secured funding and recruited staff to embark on an instrumentation development program to design the necessary 'hardware' and methodologies. Their aim was to look at cardiovascular dimensions, pressures and flow. Rushmer was able to recruit Dean Franklin, Dick Ellis and Baker, along with a number of other students and technicians. Franklin was the pioneering engineer who was behind the projects at the start. Ellis was knowlegeable in sonar techniques which he had also acquired from the Navy.
Franklin, Ellis and Baker started with the design of a multichannel transit-time flowmeter (which measured the velocity of blood flow in a blood vessel by determining the time interval between two electric pulses along the vessel). This was a device that was attached to the wall of the animal's blood vessel. What were available as electronic components at that time were basic analog components such as analog differentiators and multipliers. Baker's next project was on an ultrasonic measuring device for sensing the diameter of the left ventricle in experimental animals. The group described "A pulsed ultrasonic flowmeter" in the IRE Transections in Medical Electronics in 1959. These was an invasive device being implanted and attached to the the blood vessel wall of an unanaesthetised animal. Rushmer published their early findings in the book "Cardiovascular Dynamics" in 1961. Because of the invention of new instruments and the advent of better barium-titanate transducers, the department at Washington attracted many new and budding post-doctoral Fellows in their ultrasonic cardiovascular research programs.
Franklin left the University of Washington in the early 1960s to take up a NASA grant project on implanted doppler radio control systems in animals. In 1964 Franklin, Watson and Van Citters published in "Nature" their telemeter system where the implanted doppler device transmitted the flow signals to a receiver nearby. Baker went on to become the chief of the technical team. Continuous wave applications were further refined and applied to humans and made to work transcutaneously. At that time instruments were all based on vaccum tube designs, often cumbersome, operating at high voltages and with heavy electronic hum. Subsequent developments led to the use of the newly available FairChild 2484 silicon transistor circuitory which allowed for much greater portablility in the instruments and lower electronic noise generated. The shift in focus also had gone from animal experiments to diagnostic human applications. Eugene Strandness, a cardiovascular surgeon (became associate Professor in 1966), took on many of the clinical projects to look into the use of transcutaneous doppler applications. Many of the earlier portable devices are now on exhibit at the Smithsonian Museum in Washington DC.
By about 1963, Baker and his colleagues had developed spectral analysis from the continuous wave doppler basing on the time-interval histogram method. Working with HF Stegall, Baker published "a sonic transcutaneous flow-meter" in 1964. Apart from cardiovascular applications, other clinicians such as Wayne Johnson worked with Rushmer and reported on the detection of fetal cardiac pulsations with continuous wave doppler in 1964. The technology was transferred to Smith Kline Instruments® and the first fetal pulse detector, the Doptone was marketed in 1965. With the instrument it was generally possible to detect cardiac pulsations in the audio format in 100% of live fetuses after 12 weeks of gestation. In 1967, Rushmer, baker, Johnson and Strandness published in the JAMA: "Clinical applications of a Transcutaneous Ultrasonic Flow Detector", which described the detection of fetal life, blood flow through the uterine vasculature, fetal movements and placental location using continuous wave doppler in an Obstetric situation.
The continuous wave doppler method however did not provide explicit information about the distance between the ultrasonic transducer and the moving target. Baker saw an article on the study of the motion of snow and raindrops in the clouds using a pulsed-doppler radar which inspired him to start working on pulsed-doppler instrumentations. The initial device was of a phased-coherent pulsed-doppler design with a reference frequency transmitting a sample of the doppler signal into the target tissue and comparing the relative phase to give a phased-modulated signal at a particular depth of the vessel that can be range-gated to obtain flow and positional information at that particular sample volume. Baker published the landmark articles: "A phase coherent pulse Doppler system for cardiovascular measurement" in 1967 followed by "Pulsed Ultrasonic Blood Flow Sensing" in 1969.
The group recruited John (Jack) Reid (one of the very earliest pioneers who worked with John J Wild) from the University of Pennsylvania who brought along with him technology for grayscale 2D and M-mode imaging. They went on to implement "flow maping". The first 2D and M-mode cardiac echographic machine were developed in 1970. By 1972, they were able to publish 2D doppler images of femoral and carotid arteries. The probe was moved manually by hand over the area of the underlying blood vessel. Only where doppler signals are detected does the instrument cause registrations to appear on the display. Their doppler shift information was displyed as white dots overlaid on the B-mode image - the display method used by modern color doppler instruments. This early instrument had the disadvantage that it required many cardiac cycles to acquire an image and was therefore difficult to operate.
Reid and George Tome (an MSc student from Beirut) helped to develop their first "rotor-mechanical" duplex scanner where 2D imaging and pulsed-doppler interrogation can be performed together although not simultaneously. Frank Barber, another graduate student doing his Ph.D., developed with the team a new rotor-transducer duplex device which commanded better resolution of tissue and spectral flow although it was still incapable of displaying both at the same time. The moving parts of the mechanical (rotor) scanner cannot be stopped and started instantaneously and so only a stored image can be available during doppler signal acquisition. Only through the advent of the phased and linear arrays that finally allowed simultaneous duplex operation.
Frank Barber described the refined version of the Duplex scanner in 1974. A good digital scan-convertor was also a prerequisite to dispense with the oscilloscope displays and strip chart recorders, and to have a good overlay of the flow image over 2D images. The technology was acquired through Fritz Thurstone at Duke University whose group was heavily researching on linear and phased array focusing electronics and scan convertors. David Philips was recruited from the Thurstone group. In 1975, velocity waveform and flow images were encoded in color and superimposed on M-mode and gray scale 2-D anatomical images. Marco Brandestini from Zurich who designed new and efficient Multi-gate circuitory made the project come together. The team also included physician Geoffrey Stevenson and engineer Mark Eyer. They had demonstrated quite clearly the value of color flow imaging in the diagnosis of various cardiac defects. Color doppler systems in the late 1970s and early 80s were however limited by the processing power of the equipment, the lack of good duplex arrays (as contrasted to the mechanical rotor systems) and the agorithm and technique with which doppler frequency estimation was performed.
Between 1973 and 1974 Baker effected a technology transfer of the doppler instruments to a newly-founded (1969) Seattle company ATL (Advanced Technology Laboratories, Bellevue, WA). Howard Suskin, founder of the United Control Corporation was the entrepreneur behind the business venture, the technology being introduced to him and his engineering partner Ralph Astengo by Baker and his wife Joan, who was a sonographer. "Technology transfer", rather then simple transfer or licensing of 'patents' included a range of formal and informal co-operations between the technology developer and commercial enterprise. In addition, technology transfer involved the transfer of knowledge and technical know-how as well as physical devices and equipment. By agreement, the University of Washington also received from ATL® a sum of money each year for a number of years, basing on sales revenue.
ATL® started with 3 engineers and the first ATL pulsed doppler scanner appeared in the fall of 1974. The Mark I was soon commercially available in 1975. The 400B pulsed-doppler unit (pictured above) developed slightly later became part of the well-known ATL Mark V duplex scanner which debuted in 1978. Duplex doppler was in fact way ahead of its time and most physicians did not know what to do with it. A lot of ground data would need to be built. Baker realized that in order to sell the duplex doppler to the cardiovascular physicians they would need a better M-mode in their instruments. This was done after bringing in new engineers in applied physics and ATL soon boasted in their machines some of the best M-mode functions and traces (incorporating grayscale) that was available at that time.
Baker travelled extensively around the world in 1980 to hold seminars and to promote the duplex devices. ATL produced the Mk 300 and 500 in '80 and '81 respectively (followed by the MK 600 in '82 and the MK 100 in '83). The Mk 500 and 600 had probably the best real time duplex doppler at that time.
" ....... The program was instrument and hardware orientated, because in those days, medical research was carried out in little the same way as wars are fought. Wars are fought according to the weapons you have, and the rules of the game will be according to the weapons you have. I think a lot of researches are in the same way. If you have the tools that nobody else has you can create a new game that nobody else can play........ People saw this as an opportunity. ...... They saw an opportunity to get ahead of their colleagues and publish ....... ." --- Baker speaking on his early work in doppler instrumentations and his efforts in popularising them at ATL.
In 1970, Donald Baker was married to Joan Baker, who was founder & first president of the Society of Diagnostic Medical Sonographers ( SDMS) in the same year and first chair of the American Registry of Diagnostic Medical Sonographers (ARDMS). Donald Baker retired from the University of Washington in 1979 and subsequently was out of the Ultrasound field in 1984. Prior to that, he was a full-time consultant to Squibb Medical Systems®, the International division of ATL and had taught in numerus seminars on the application of doppler ultrasound. Among other accolaides he was given the Pioneer award from the AIUM in 1987 and the Pioneer Award from the Society of Vascular Technology in 2000. Baker holds a number of important patents and has authored over 30 articles and book chapters on Ultrasonic Instrumentations. A few of his original continuous wave doppler and the pulsed-doppler devices are now exhibited in the Smithsonian Museum of American Medical History.
The University of Washington Center for Bioengineering, of which Robert Rushmer was the founding director in 1967, became a department in 1997 and was jointly administered by the schools of Medicine and Engineering. Rushmer became Professor Emeritus of Bioengineering. Since 1989 a Robert F. Rushmer lecture was given annually at the university in honor of him. Dr. Rushmer passed away in July 2001at the age of 86. Donald Baker is retired. In 2002 he received the Alumnus Summa Laude Dignatus award from the University of Washington for "an outstanding alumnus, distinguished for service and achievement over a period of years since graduation". Eugene Strandness retired from the Head of Vascular Surgery in 1995. He passed away in January 2002 at the age of 73. John Reid is Emeritus and Research Professor at Drexel University, and Affiliate Professor of Bioengineering at the University of Washington. Other engineers who took part in the early development of doppler ultrasound at the University in the 1970s such as Barber, Eyer, Brandestini and others, also had very promising careers in various fields of advanced engineering and inventive technology.