** Courtesy of KretzTechnik®, Zipf, Austria.
A short History of the Real-time ultrasound scanner
Dr. Joseph Woo
This is part of the full article A short History of the developments of
Ultrasound in Obstetrics and Gynecology, reproduced separately here.
Real-time scanners, the real revolution
The innovation which had soon completely changed the practice of ultrasound scanning was the advent of the Real-time scanners. The first real-time scanner, better known as fast B-scanners at that time, was developed by Walter Krause and Richard Soldner (with J Paetzold and and Otto Kresse) and manufactured as the Vidoson® by Siemens Medical Systems of Germany in 1965. D Hofmann, H Holländer and P Weiser published it's first use in Obstetrics and Gynecology in 1966 in the German language. Hofmann and Holländer's paper in 1968 on "Intrauterine diagnosis of hydrops fetus universalis using ultrasound" also in German, is probably the first paper in the medical literature describing formally the diagnosis of a fetal malformation using ultrasound.
The Vidoson used 3 rotating transducers housed in front of a parabolic mirror in a water coupling system and produced 15 images per second. The image was made up of 120 lines and basic gray-scaling was present. The use of fixed focus large face transducers produced a narrow beam to ensure good resolutions and image. Fetal life and motions could clearly be demonstrated.
The Vidoson*, its working mechanism and the resultant image of a fetal face and hand.
The transducer housing is mounted on a mobile gantry and rigidly connected to the main console.
The scanning frequency was 2.25 MHz. Scaling and caliper functions were not present.
Hans Holländer, in his paper in 1968 demonstrated the usefulness of a 'real-time' scanner in the diagnosis of ovarian tumors which were not spotted on pelvic examination. Malte Hinselmann, using the Vidoson, demonstrated in 1969 the universal visualization of fetal cardiac action from 12 weeks onwards. The Vidoson was popular in the ensuing 10 years or so and were used in many scientific work published from centers in Germany, France, Switzerland, Austria, Belgium, Italy and other European countries. The initial popularity was not based on its image resolution but rather its ability to allow the operator to display and study movements, such as fetal cardiac motion, gross body movements and fetal breathing movements (see also Part 3). In the International Symposium on Real-time ultrasound in Perinatal Medicine held in Charleroi, Belgium in 1978, most of the presentations were based on results from the Vidoson." ......... For almost ten years, real-time ultrasound has been used in many obstetrics departments. By means of an apparatus which has since become technologically outdated many doctors, technicians and expectant mothers had, at the time, the moving experience of being able to observe the living fetus. This seems to me to have been a psychological break-through. For the first time, the human eye pierced the 'black box' of the womb...... Those who were present in obstetrics departments when this technique was first used soon realized how indispensable it was proving to be in providing a valid means of observation of the fetus and its health, in ascertaining its age and studying its morphology and growth........ . Over the last three years, the appearance of the multitransducer scanner has brought about substantial technical progress. At the same time, but quite independently of this, numerous studies on fetal breathing movements, fetal behavior and neonatal cardiology were published ....... ."Read a history of the development of ultrasonography at Siemens, Germany.
--- R. Chef, Maternit?Reine-Astrid, Charleroi (Belgium), in the foreword to the Proceedings of the International Symposium on Real-time Ultrasound in Perinatal Medicine held in 1978 at Charleroi.
James Griffith and Walter Henry at the National Institute of Health produced a mechanical oscillating real-time scanning apparatus in 1973 which was capable of producing clear 30 degree sectoral real-time images of good resolution. The scanner was essentially a motor-driven oscillating transducer coupled with a commercially available one-dimensional echocardiograph (the SmithKline Eckoline 20). The 2-D scanning device was hailed as one of the most significant milestones in the development of echocardiography, and indeed in the development of sonography in general. Other mechanical systems published included an oscillating design with membrane-oil coupling from W N McDicken in Edinburgh (1974, produced commercially as the EMI® Emisonic 4260), a continuously rotating wheel with radially-mounted transducers from Hans Hendrik Holm and Allen Northeved in Denmark (1975), and a single transducer direct-contact design from Reginald Eggleton in Indiana (1975). The design, which was supposed to have been modified from the mechanisms of an "electric toothbrush", was a commercial success. Toshiba®, in Japan produced their first prototype real-time mechanical sector scanner in 1975, the SSL-51H. A number of others were available commercially soon afterwards and sold well such as the circular rotating system Combison 100 from Kretztechnik® of Austria (1977), produced under the ingenuity of Carl Kretz.
Although these have relatively heavy probes they produced outstanding real time resolution in the near and far field (because of highly focused beams resulting from the relatively large curvatured transducers and the lens apparatus) and with much less image-degrading electronic noise that was associated with electronic scanners that soon became available at around the same time.
The large hand-held circular rotating transducer (Combison 100) from KretzTechnik® and the resultant sector image.
The transducer is connected to the main console by a flexible cable.
The concept of the multi-element linear electronic arrays was first described by Werner Buschmann in an ophthalmologic application in 1964 in East Berlin. His probe, fabricated in collaboration with Kretztechnik AG consisted of 10 small transducers mounted on an arc-shaped appartus to fit over the eye. Buschmann's transducer however, never became very functional in a clinical setting and did not go into serial production. A number of similar designs followed on the same concept. Jean Perilhou and her group in France, working under the auspices of the Philips® Company, described a multi-element scanning array in 1967, although they do not produce images in a real-time fashion. The real-time array concept was further expanded by Nicolaas Bom at the Thoraxcenter, University Hospital, Erasmus University in Rotterdam, the Netherlands. His initial design in 1971, which was described in his application for a Dutch patent, consisted of only 20 crystals (each 4mm x 10mm). The probe face was 66 mm long and 10 mm wide and produced 20 scan lines. It operated at a frequency of 3.0 MHz sweeping at a frame rate of 150 frames/sec. The axial resolution was 1.25 mm while the beam width at 6 cm was 10 mm. This abeit simple and inadequate design at that time has evolved into the very sophisticated real-time scanners that are widely available today.
In collaboration with cardiologist Paul Hugenholtz and local Dutch company Organon Teknika, they produced in 1972 the "Multiscan system", notably the earliest commercial linear array scanner in the world, mainly aimed at cardiac investigations.
The transducers operated at either 2.25 or 4.5 MHz, again with 20 crystals producing 20 scan lines. The lateral resolution of this improved version at a dynamic range of 10dB was 3.7 mm at 6 cm and 6 mm at 10 cm depth. It did not sell very well though because of its relatively primitive resolution and its inability to image abdominal structures adequately.
In Japan, Rokuro Uchida at Aloka® (see also Part 1) had similar research on the array technology in the late 1960s predating their European counterpart. In 1971 they published in Japanese (and presented at the Japan Society of Ultrasonics in Medicine) a system based on 200 closely interspaced transducers. Electronic switching and use of overlapping groups of 20 small elements yielded 2-D images with a field depth of 20 cm at a rate of 17/frames per second. The company produced their first prototype linear array scanner in the same year. The model however, was not produced commercially or given a model number. The first commercial linear array scanner from Aloka® only debuted in 1976. Toshiba® produced their first commercial real-time linear array counterpart in the same year, the SSL-53H, aimed at abdominal applications. Like the Aloka® this was a huge machine considering present day fabrication standards.
Subsequent to Bom's work and the research in Rotterdam, Leandre Pourcelot and Therese Planiol in Tours, France was experimenting with more advanced segmented sequence transducer-array scanning possibilities in 1972, in order to enhance the lateral resolution of the devices. Donald L King at the Columbia University in New York described a 24-elements segmented sequence linear-array cardiac scanner in 1973, in collaboration with the Hoffrel Instruments Inc.®, at Norwalk, Connecticut. In his design 3 crystal elements were fired simultaneously to produce a single pulse of ultrasound. The echoes returned from the 3 reflections were written into a single line on the scan. The crystals were stepped in a "1,2,3,... 2,3,4,... 3,4,5... " manner. There was however no delay lines for the implementation of 'focusing' techniques.
Also concurrent to King's work was the work in from the Tony Whittingham group at Newcastle-upon-tyne in England, where crystal stepping techniques were also being investigated.
"...... I tried various ideas, but the one that worked was to make an array of very narrow rectangular elements and to use a group of these to form a square aperture. This group of elements defining a composite transducer would scan the line in front of itself. Then you drop one element off from one end, put another element on at the other end, infront of the group, and advance the active group along the array in this way. When I was doing this I was totally unaware that it would work. I hope it would work, but I was worried that there would be cross-coupling from the end elements of the group into what should have been passive elements, so that you might not be able to get a well-defined active aperture. But it did work, and that proved to be the way forward, because you could make finer and finer elements and get more lines into the array ........" -- Tony Whittingham, describing his work in real-time imaging in the mid 1970s. ^
Images of the earlier models were nevertheless hampered by the problems of small crystal size, lobe artifacts, unwanted specular reflections, low dynamic range, unsatisfactory lateral resolution and image noise from electronic processing. There was an overwhelming need for the refinement of beam characteristics. Fredrick (Fritz) Thurstone, Olaf von Ramm and H Melton Jr at the Duke University published some of the earliest and most important work on electronic focusing using annular arrays ('71-'74), both on transmit and receive. Similar techniques were subsequently employed in the design of linear arrays transducers. Basing on these designs, a number of centers and private laboratories were starting to embark on making machines geared to examination of the abdomen. Albert Macovski at the Standford University filed a patent in 1974 for a circular array where the elements generate dynamically focused beams that could also be swept through space by adjusting the delays to the array. This was one of the more advanced designs in dynamic focusing techniques. Another important design - "signal processor for ultrasonic imaging" was described by the William Beaver group of the Varian Associates® in Palo Alto in California in 1975 where selection of scan angles and focusing distances were effected. George Kossoff in Australia also filed a patent in 1973 on a linear array system incoporating phased-focusing electronics. A summary of the advances in design can be found with M Maginness's article (at Stanford) "State-of-the-art in two-dimensional ultrasonic transducer array technology" in 1976.
It was Martin H Wilcox, founder and engineer at the Advanced Diagnostic Research Corporation (ADR®, a company founded in 1972 in Tempe, Arizona), who designed and produced one of the earliest commercially available models of a linear-array real-time scanner in 1973 and very much set the standard for subsequent designs to follow. The array contained 64 crystals in a row (3 times the number in the earlier cardiac counterparts and 3 times as long and wide), fabricated with the best material available and in the best accoustic configurations and using 'stepping' crystals techniques. This was the first 'good-resolution' abdominal linear-array scanner that was in the commercial market.
Their second model the 2130 marketed in 1975 had brought the linear-array principle and the application of 'focusing techniques' to commercial fruition. It was a big hit in the United States and had sold over 5000 units worldwide, including Germany and other European countries. The machine was marketed in Europe under the Kranzbuehler label. In 1980 a new 3.0 MHz variable focus transducer was added on to the 2130. The new transducer contained 506 crystal elements, boasted both mechanical and phased focusing, improved gain and reduced noise, much quieter transducer operation, and switchable focal zones. The image had twice the number of data lines and probably the best real-time resolution in the industry at that time.
" ....... In Dallas, Texas, Ian was shown the first real-time scanning machine brought from Phoenix, Arizona, by some talented young men. Ian was of course, wildly excited. They wanted to carry him off to Phoenix to show him more, but sadly Ian couldn't change his next commitments. However, it wasn't too long before he had one of his own. ......."
--- Alix Donald, wife of the late Ian Donald, speaking in 1998 about their first encounter with the ADR real-time scanner in the early 1970s. ref.
ADR® merged with ATL® (Advanced Technology laboratories®, see below) in 1984. ADR® produced the 2150 in 1980 and the last model under the ADR label, the ADR 4000 in 1982.
Linear array and annular array technology had also been heavily investigated by the Japanese since the early 1970's. The country had been moving ahead very successfully with innovative electronic engineering in many domestic, commercial and professional sectors. Commercial linear array models from companies like Hitachi®, Toshiba®, and Aloka® soon began to dominate the world market. Hitachi® also produced their first linear array scanner the EUB-10 in 1976, followed by the EUB-20 in 1977 and the EUB-22 in 1979. The EUB-20Z produced in 1978 already incorporated the world's first digital scan converter.
The Toshiba® SAL-10A and the more portable SAL-20A (pictured on the left) and SAL-30A, which were marketed in 1977, 1978 and 1979 respectively, and the Aloka® SSD-202 (1979), SSD-203 (1980), SSD-240 (1981) and SSD-256 (1982) were popular and had found their way into notable Institutions outside of Japan such as the King's College Hospital in London (Campbell), the Herlev (Gentofte) Hospital in Copenhagen (Holm), the Hospital Universitaire Brugman in Belgium (Levi) and were employed in many important early studies. The SAL-10A which was designed by acclaimed Japanese engineer Kazuhiro Iinuma, received many commendations. Other popular early choices included the Axiscan 5 (1976) and Abdoscan 5 (1979) from Roche Kontron®, the Sono R from Philips® (1978), the RA-1 (1980) and the Imager 2300 (1981) from Siemens®, and the LS 1500 (1981) from Picker/ Hitachi®. Aloka® scanners were marketed in the United States under the brand Narco Air-Shield®. Diagnostic Sonar® Ltd, a company founded in 1975 in Edinburgh, Scotland produced the first electronic real-time scanner, the System 85 in the United Kingdom in 1976.
Many of the early models typically had very large probes housing an array of some 64 transducer (crystal) elements arranged in a linear row, and operating with sequential electronic switching or dynamic focusing. It was not until the early 1980s that probe size had gotten smaller and image resolution significantly improved.
Early scanner probe was bulky to fit on the abdomen ***
Images from early real-time scanners
had obstrusive scan lines, low dynamic range and resolution.
Read the short History of the development of Medical Ultrasonics in Japan for a chronology of Japanese contributions to the development of ultrasound scanners.
At around the same time, steered-beam phased array transducers and annular array transducers with more complicated electronic circuitry were described, and had found their way into echocardiographic examinations because of the relatively small contact surface.
The phased-array scanning mechanism was first described by Jan C Somer at the University of Limberg in the Netherlands and in use from 1968, way ahead of its time and several years before the appearance of linear-arrays systems. The principle of phased-arrays had probably been known much earlier where the technique was engaged in underwater submarine warfare and hence the technology was kept confidential. Fredrick (Fritz) Thurstone and Olaf von Ramm at the Duke University published one of the earliest and most significant phased-array designs in 1974, which was incorporated into a number of commercial sector-array scanners. Very sharp focusing over an extended range was obtained from annular arrays using focusing methods on both transmit and receive. Other early significant contributors to the beam-former techniques included Albert Macovski at Standford University and Samuel Maslak at Hewlett Packard®. Maslak later founded the Acuson Corporation (see also Part 3).
The Kossoff group in Australia had also made significant progress in the annular phased array transducer designs as early as 1973 and the technology was incoporated into their water-bath scanner, the UI Octoson. In England, EMI® produced the Emisonic 4500, a phased-array sector scanner which was nevertheless expensive, electronically noisy and had inferior resolution in the near fields. Early phased-arrays in the late 70s were all used in cardiac applications. Important manufacturers included Varian® and Irex®. In the first half of the 1980s, image quality in phased-arrays had continued to improve and some outstanding designs had come from Irex® and later on Elscint® (Dynex) and Hewlett Packard®. Despite the small probe size, phased-array sector scanners had never been popular with Obstetrical and Gynecological examinations.
Compound static scanners continued it's tradition of being very huge bulky machines, probably influenced by the design norms of other imaging modalities such as tomographic x-ray machines and the bulky digital electronics housed in the console (see above on scan converters) before the impact of the micro-processors. New static scanners which were in great demand and produced excellent images were still on the drawing board and production line in the early 1980s. It was believed that real-time scanners would play only a complimentary role to static scanners in the assessment of moving structures. These static machines however were starting to be replaced or phased out at a rate that was faster than expected. There was apparently little practical, economical or clinical advantage of these costly machines over the more mobile and flexible electronic real-time scanners.
There were initially many who were so used to and skillful at operating the static machines that they were unhappy to switch over entirely to the real-time counterparts. They were also anxious about the latter's limited field of view, poorer resolution and allegedly 'less accurate' on-screen measuring system that they have only started to get used to not too long ago. Static scanners were not completely out of the scene until about 1985-86. The switch-over had serious financial implications to some companies who had a large inventory of static scanners.
Read a commentary by Royal J Bartrum, Dartmouth Medical School, in the book "Real-time ultrasonography" in 1982, on the switch-over to the real-time scanner.
From Digital's PDP-11 to Intel's 8080 and beyond
The rapid reduction in the physical size of the machine console in the later half of the 1970s (See Aloka® and Toshiba®'s early products above) was the direct result of the invention of the microprocessor and the evolution of the minicomputer into the microcomputer.
By the late 1960's, computers built from discrete transistors and simple integrated circuits (IC) already existed. The first practical IC was fabricated in 1959 at Fairchild and Texas Instruments and Fairchild began its commercial manufacture in 1961. As manufacturing technology evolved, more and more transistors were put onto a single silicon chip with the maximum number of transistors per chip doubling every year between 1961 and 1971. They progressively became a device containing many circuits and was called a LSI (Large Scale Integration). The PDP-11 minicomputer from DEC® containing many ICs and LSIs, was used in many scanner consoles up to the late 1970s. The UNIBUS architecture used by the CPU in the PDP-11 was particularly suited to communicating with memory and peripherals.
Towards the end of 1969 the structure of the smaller programmable calculator had emerged. Intel®, under contract from Japanese company Busicom for the design of a small desktop programmable calculator, produced the world's first microprocessor chip the 4004 in 1971. In order to create a chip of such complexity, new semiconductor design technologies had to be developed. The 4004 is considered the first general-purpose programmable microprocessor, even though it was only a 4-bit device. The original 4004 measured 1/8th of an inch long by 1/16th of an inch wide and contained 2,300 transistors. It ran at 108 KHz and executing 60,000 operations in a single second. It had about the same amount of computing power as the original ENIAC which weighed 30 tons, occupied 3,000 cubic feet of space and used 18,000 vacuum tubes. Today's 64-bit microprocessors are still based on similar designs, with more than 8.5 million transistors performing hundreds of millions of calculations each second.
The 4004 was followed quickly by the 8-bit 8008 microprocessor. The 8008, which contained 3300 transistors, was originally intended for a CRT application and was developed concurrently with the 4004. By using some of the production techniques developed for the 4004, Intel® was able to manufacture the 8008 as early as March 1972. The 8-bit era between about 1975 and 1980 had a major impact on household computing and industry because the first few microprocessors were available at very affordable prices.
The 8008 microprocessor from Intel® was however relatively crude and unsophisticated. It had a poorly implemented interrupt mechanism and multiplexed address and data buses. The first really popular general-purpose 8-bit microprocessor was Intel's 8080, in production in early 1974. This had a separate 8-bit data bus and 16-bit address bus. It ran at 2 MHz with 6000 transistors. It has essentially ten times the performance of the 8008.
Shortly after the 8080 went into production, Motorola® created its own competitor, the 8-bit 6800, containing 4000 transistors and destined for use in automotive and industrial applications . Although the 8080 and 6800 were broadly similar in terms of performance, they had rather different architectures. The 6800 was, to some extent, modeled on the PDP-11 and had much a cleaner architecture than the 8080. Other newer processors followed and found their way into industrial operations including medical scanners and equipments.
Scanner engineering itself was soon in the hands of commercial companies rather than clinical personnel as advanced computer technologies were fiercely incoporated into each design to manipulate beam characteristics and signal processing to produce the best possible scan images. Apart from those mentioned above, other important early manufacturers of real-time equipments included Shimadsu® from Japan; EMI®, KretzTechnik AG, Bruel and Kjaer®, GEC® and Rohe® from Europe and Diasonics®, Dynex®, Ecoscan®, Elscint®, Hewlett-Packard®, Irex®, SKI®, Phosonic Searle®, Technicare® (acquired Unirad®) and Xonics® from the United States. The application of ultrasound in Obstetrics and Gynecology had since then undergone an explosive proliferation all over the world. By the early 1980s there were over 45 large and small ultrasonic scanner manufacturers worldwide.
Further Improvement in performance aside from focusing the ultrasound beam was acheived largely through an increase in the number of transducer crystals (or channels, from 64 to 128), improvements in transducer crystal technology (going into broad-band and high dynamic range), increasing array aperture (more crystals firing in a single time-frame), faster computational capabilities, improving technical agorithms for focusing on receive (increasing the number of focal zones along the beam), incoporating automatic time-gain controls and progressively replacing analog portions of the signal path to digital. It was perhaps regretable to see that British manufacturers have failed to keep up with developments made by other leaders in array technology, notably those from the United States and Japan. This was probably reflection of a similar trend in other arenas of electronic and micro-processor development in these countries. It is also of interest to note that the Siemens Vidoson® and the Octoson®from Australia both did not sell in North America at all. Both had the disadvantage of being cumbersome when scanners from other manufacturers were rapidly getting better in resolution and manuevability.
In the early 1980s (around 1980-1985), many agreed that mechanical sector scanners (be it rotating, oscillating or wobbling designs) which employed relatively large area transducers produced better and less noisy images than electronic linear-array scanners. Shown here are very good images from SKI® (left), Diasonics® (middle) and ATL® (right) taken in 1981. The market in Obstetrics and Gynecology was divided between the mechanical sector scanners and the linear-arrays until the second half of the 1980s where both were replaced by convex sector-arrays.
Because of its smaller convex contact surface, the curvilinear or convex sector-array fits much better on the abdomen and allows for a wider field of view than does the linear-array configuration. Work on the fabrication of an electronic convex array had started in the late 1970s in the larger Japanese companies such as Hitachi® (publishing their convex attachment to their EUB-10A scanner in 1978); Aloka® (filing their patent on the convex scanner in 1980), as well as in U. S. companies notably the North American Philips® and the Picker Corporation®, who had filed their patents for convex arrays and processors in 1979 and 1980 respectively. The first commercially available convex array transducer apparently only debuted in 1983 in a scanner from Kontron Instruments® in Europe, the Sigma 20, which was designed especially for use in Obstetrics and Gynecology. Hitachi® in Japan marketed their model EUB-40 with their new convex array later on in the same year.
Toshiba® introduced a similar array in 1985, in their new scanner model SAL-77A. Interestingly, the design actually replaced an earlier model (by only about 9 months) the SAL-90A which boasted a new "trapezoid" linear array in which the face of the transducer was flat but a trapezoid-shaped image was produced from the 128 transducer elements using phased electronics. American machines were apparently still using linear arrays by 1985, although very shortly they were quickly replaced by the new convex configuration. By about 1987, convex arrays are standard on every new scanner, whether or not it is configured for use in Obstetrics and Gynecology.
Model number of some of the scanners made after 1980 from important manufacturers are listed here with the year in which they were marketed. Also view pictures of some of the early scanners.
Skin Coupling material for ultrasonic transmission has also switched from oil to a water-soluble (non cloth-staining) gel medium. One of the more well-known manufacturers was the Parker Laboratories® at New Jersey. Images are commonly recorded on "peel-apart" Polaroid® films (the Type 611 was most commonly used). Multi-format radiographic films (6-9 images on one film) using dedicated video imagers soon became mainstream with institutional users and thermal paper printers in the private practice market.
Worthy of mention here was the attempt in the late 70s and early 80's to miniaturize scanners so that they could be portable and be used at the bedside. Four such examples were the all-in-one MiniVisor® from Organon Teknika® in the Netherlands, the Bion PSI-4000 from Bion Coporation® in Denver, the Shimasonic SDL-30 from Shimadzu Corporation®, Japan, and the 210DX from Aloka®.
The Minivisor® (available from 1979) was a spin-off from Bom's laboratory. It was battery operated, shaped like a mushroom, had no wires and used a 2-inches display with an on-screen caliper system and digital readout. The transducer is fused to the bottom of the device similar to a 'large' fetal pulse detector. Juiry Wladimiroff suggested in 1980 the device would be useful for routine BPD screening. Nevertheless the popularity of these machines were short-lived for several important reasons pertaining at that time: The resolution was unsatisfactory because of the available electronics. The images of the 'standard' and larger devices, as well as their overall 'portability' have seen rapid improvements round about the same time; and thirdly, real-time ultrasound has very rapidly established itself as a definitive diagnostic entity and the concern for good image information appeared to overide that of the extra portability.
The invention of the real-time scanner had enabled much more effective diagnosis of many fetal malformations and in particular cardiac anomalies which hitherto was impossible to diagnose accurately. (see Part 3). Fetal sonography and prenatal diagnosis (a term which was only coined in the 1970s) had emerged as the 'new' science in Obstetrics and fetal medicine.
John C. Hobbins at the Yale University, Connecticut and Stuart Campbell at the King's College Hospital in London were among others, the two most important forerunners on either side of the Atlantic. Their centers have also become two of the most important teaching centers in fetal sonography. Many of the research fellows and staff members that had come through Hobbins' department for example, have in time become celebrated names in the field of fetal sonography and prenatal diagnosis.
Other important early North American workers in fetal biometry included Peter Cooperberg, David Graham, Charles Hohler, Alfred Kurtz, Rudy Sabbagha and Roger Sanders. Their early work on the biparietal diameter was particularly notable, establishing charts for different populations, standardizing measuring methods and errors and comparing differences that may be present between measurements made on static and real-time equipments. (see also Part 3). The real-time scanner had soon enabled the accurate measurement of fetal limb bones that lead to the introduction of the important measurement of the fetal femur length by John Hobbins in 1979 for the evaluation of skeletal dysplasia followed by Gregory O'Brien and John Queenan who described it's use in fetal growth assessment. Phillipe Jeanty at Yale provided in 1984 measurement charts for all the fetal long bones.
Ultrasound guidance was started to be employed in procedures such as amniocentesis (Jens Bang and Allen Northeved 1972, Copenhagen), fetoscopy (John Hobbins and Maurice Mahoney, 1974) and transabdominal chorionic villus sampling (Steen Smidt-Jensen and N Hahnemann, 1984, Copenhagen).
Read here a short history of Amniocentesis, fetoscopy and chorionic villus sampling.
Doppler development in Obstetrics and GynecologyThe use of spectral flow analysis on the fetus and placenta was a remarkable late-comer. The detection of fetal pulsations using doppler ultrasound was first reported in 1964 by D A Callagan who was working with ultrasonic devices at the United States Naval medical Research Institute at Bethesda, Maryland. In the following year (1965), Gynecologist Wayne Johnson working with the Rushmer team at the University of Washington (see above) reported 100% accuracy in the detection of fetal life in 25 patients at 12 weeks (from LMP). Smith Kline Instruments® manufactured the first Doptone in the same year basing on their technology.
Edward Bishop at the University of Pennsylvania, using the SKI® Doptone, reported positive doppler signals from 11 weeks (LMP) pregnancies in 1966 and 65% success in locating the site of the placenta basing on audio doppler signals in the third trimester. The Callagan group in the same year reported doppler interrogation of the fetal heart and described "the sound of horse's hoofs when running' and oscilloscopic 'beats' of the cardiac doppler signals. John Barton at the Northwestern University in Chicago further reported in 1967 positive audio doppler signals at 10 weeks. In 1968, the Johnson group in Seattle expanded on the usefulness of the doppler flowmeter (audio signals) to the localization of the placenta, demonstrating the characteristic 'whirlwind' and 'rushing wind' sound of placental blood flow.
In 1967, the Rushmer group outlined the use of doppler ultrasound in Obstetrics in an article in JAMA, "Clinical applications of a Transcutaneous Ultrasonic Flow Detector", which was confined basicaly to the detection of fetal life, placental location, blood flow through the uterine vasculature and fetal movements. Aside from the SKI® Doptone, other similar devices marketed at that time included the Ames® Ultradop and the Magnaflux® MD 500. Other companies producing doppler fetal pulse detectors included Parks Medical Electronics, Imex, Medasonics, Sonicaid and Life Sciences. The Doptone was considered as one of the most important instruments that was ever invented in Obstetrics. Before that great difficulty was often encountered in detecting fetal life in both early and late gestations. This now seemingly trivial instrument has quite considerably changed the practice of Obstetrics since the 1960s.
While the use of vascular 'spectral flowmetry' was quite in place by the mid-1960s (see above), the use of doppler flowmetry in pregnancy assessment was not followed up in the American or European literature until about 1977 when 3 separate groups of investigators were making important pioneering contributions.
The study of flow velocity waveforms in fetal and placental blood vessels have nevertheless been reported by Japanese reseachers as early as 1968. In that year H Takemura and Y Ashitaka described umbilical arterial and placental doppler spectral velocity waveforms at the 14th meeting of the Japan Society of Ultrasonics and Medicine. Although the clinical significance of these signals were not quite known, their devices had allowed them to publish very clear and remarkable signal traces resembling those produced on recent equipment (see above right).
In 1977, J E Drumm, a gynecologist and D E FitzGerald, then director of the Angiology Research Group of the Irish Foundation for Human Development in Dublin, Ireland, reported in the British Medical Journal the combined use of continuous-wave doppler and 2-D static B-mode ultrasound in the study of flow velocity waveforms in the fetal umbilical artery, and described probably the first umbilical arterial velocity waveforms in the western literature. The shape and applications of these waveforms were not discussed, although they suggested that "... the shape of the blood-velocity waveforms will change with conditions affecting the efficiency of blood-supply, and the method should be useful in assessing conditons such as pre-eclampsia and intrauterine growth retardation .... ". The same group reported in 1980 in a much longer paper umbilical waveforms in relation to gestational age, their analysis in terms of systolic and diastolic components, and the use of various waveform ratios.
Another pioneering group consisting of researchers from Stanford University, the University of Washington and the Varian associates®, described in 1978 fetal flow velocity waveforms basing on pulsed-wave (range-gated) doppler instruments to overcome the short-coming of the continuous wave counterpart. William McCallum, a gynecologist at Stanford (who immigrated from Belfast, Ireland in 1975) together with his co-workers devised sophisticated computer-based techniques to process the doppler signals through a series of fast Fourier transformations instead of the older and more primitive method of 'time-interval histogram'. Although they commented that no general conclusions could be reached on the clinical significance of these waveforms from the small study, the group had firmly established the basic groundwork for further investigations.
Robert Gill, together with the Kossoff group in Sydney, Australia made quantitative measurements of human blood flow velocities since 1977 with the Octoson®. He determined that the flow in the fetal umbilical vein increased with gestational age but remains constant at around 103 ml per min per kg fetal weight. Accurate measurement of flow volumes and flow velocities in the fetal blood vessels was however affected by a diversity of factors such as operator skill, fetal position, blood vessel diameter and angle of insonation which made it an impractical investigation in the fetus. Sturla Eik-Nes, working with Karel Marsal in Norway, devised the first hand-held linear-array real-time apparatus coupled with range-gated doppler in 1980. The group in that year documented blood flow velocities in the fetal aorta and reported in 1983 volume flow through the umbilical vein using the new apparatus.
Early doppler work also came from the Pentti Jouppila and Pertti Kirkinen group at Oulu, Finland who also worked with quantitative blood flow velocities in the umbilical vein and found significant reduction in flow in growth-retarded fetuses. Their work importantly demonstrated (in 1981) that quantitative umbilical venous flow became unrecordable in fetuses with severe growth-retardation and (in 1984) a significant negative correlation existed between umbilical venous flow and the cord haemoglobin.
Although a relationship could be established between low flow volumes and fetal compromise, such measurements were difficult to be made accurately and thus had not become practical and popular as a fetal investigation. Measurement of volume and velocity flow in fetal blood vessels were not further pursued as a research and clinical tool after the mid-1980s.
Stuart Campbell and David Griffin at the King's College Hospital in London suggested in 1983 that the shape of the arterial flow velocity waveforms would be more useful in fetal assessment. In the same year Campbell also reported on the usefullness of uterine and placental arcuate arterial waveforms, particularly in conditions such as pre-eclampsia.
With the efforts of WB Giles and Brian J Trudinger, the Australian group made significant contributions to the study of velocity waveforms and had made popular the measurement of waveform ratios in the assessment of fetal well-being. Such ratios soon became standard in the assessment of fetal circulation in utero. The Trudinger group demonstrated in 1986 that abnormal doppler waveform tended to preceed abnormal fetal heart traces. The mid 1980s saw many other centers starting their investigations into doppler velocimetry, often on shared equipment with their cardiology collegues. The significance of a diminishing diastolic flow in the face of fetal compromise was most certainly established. It wasn't until the late 1980s that clinical applications of doppler arterial blood flow started to become an important and integral part in fetal assessment. (To continue in Part 3)
Further development led to 2D color flow imaging. Marco Brandestini and his team at the University of Washington in 1975 obtained blood-flow images using a 128-point multi-gated pulsed doppler system, where velocity waveforms and flow images were encoded in color and superimposed on M-mode and gray scale 2-D anatomical images. The team included physician Geoffrey Stevenson and engineers Mark Eyer and David Philips, who brought in new technology on scan-converters from the Thurstone group at Duke University. They were able to demonstrate the value of color flow imaging in the diagnosis of various cardiac defects. Leandre Pourcelot in Tours, France also described their first color-coded doppler images in 1977. 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.
It was not until the work of Chihiro Kasai, Koroku Namekawa, Ryozo Omoto and co-workers in Tokyo, Japan, which was published in the English language in 1985, that led to the widespread realization that real-time color flow imaging could be a practical possibility. The group had already reported on the technical details and clinical (cardiac) applications in the Japanese language in 1983. Namekawa and Kasai were bio-engineers working for Aloka® and Omoto was cardiologist at the Saitama Medical School in Tokyo which had a long history of collaboration with Aloka®. What is 'required' to produce a flow image of blood vessels is that the amplitude, phase and frequency contents of the returned echoes from a single linear array probe are captured and very rapidly analysed. The Japanese group used a phase detector based on an autocorrelation technique in which the changing phase of the received signal gave information about changing velocity along the ultrasonic beam. This provided a rapid means of frequency estimation to be performed in real-time. This approach to color flow mapping is still in use today.
Continuing advances in electronics have permitted the development of faster color Doppler instruments, which displayed two-dimensional blood velocity measurements at many frames per second. The successful introduction of color Doppler required fast and stable positioning of the ultrasound beam, which was provided by the development of the linear array and phased-array scanheads. A breakthrough filtering mechanism was also deployed in which the high amplitude/ low velocity clutter signals generated by the movements of tissue structures and vessel wall are removed. Such filters were described by Bjørn A. Angelsen and K Kristofferson at the Department of Physiology and Biomedical engineering at Trondheim, Norway in 1979 on the analysis of moving targets in radar systems. In the early 80's the Trondheim group published important work on annular array color flow imaging technology. Color flow mapping not only allowed elucidation of blood flow but had also helped in the determination of pathology in tissues.
The Company Vingmed Sound AS® which manufactured some of the earliest doppler applications was formed in 1974 with technology transfers from Angelsen's Department. The company's doppler equipments performed very well and had a sizeable market in the United States, teaming up with companies like Irex®, Ausonics® and Interspec® in cardiac applications. Vingmed® was later acquired by GE Medical Systems®.
Advertisements of the first machine with real-time Color flow mapping capabilities from Aloka® (the SSD-880CW) made it's debut in medical journals in the middle of 1985 (It was produced in Japan in 1984). Toshiba® followed up with their SSH-65A later on in the same year. Asim Kurjak in Croatia, using the Aloka® machine was the earliest pioneer to introduce the application of color flow doppler in fetal assessment, publishing his work in 1987. (See also Part 3).
Quantum Medical Systems®, Issaquah, Washington, a new company formed by a group of engineers who left ATL, had started introducing the concept of real-time color doppler imaging at the AIUM meeting in the fall of 1983. The first color images were shown at the RSNA (Radiological Society of North America) meeting in December 1984. The prototype machine was tried out at several centers and one of the first papers was reported in the October 1985 meeting of the RSNA by Christopher Merritt's group at Tulane University, New Orleans. Quantum® marketed their first machine, the QAD-1 in 1986 which produced some very impressive real-time color flow images of the carotid and other arteries basing on the newer array technology. They called it "AngioDynography" although the term had not subsequently become popular. The transducer design and signal processing were described by Alfred Persson and Raymond Powis, one of Quantum's founders in their article "Recent advances in imaging and evaluation of blood flow using ultrasound" in 1986.
Color flow imaging made it's real impact in the United States in 1987 and in Europe in the following year. ATL® after some re-organization, marketed its first color doppler machine, the UltraMark 9 in 1988. Irex® did not make its own color doppler but marketed Aloka®'s SSD-880 in the united States instead. Irex®, being acquired by the Johnson & Johnson Co®., and sold later to GE®, discontinued its line of duplex scanners. Quantum Medical Systems® was later acquired by Siemens® of Germany, who moved their main operations to Issaquah, Washington.
It was not until the early 1990's that the modality found it's way into the assessment of Gynecological and early pregnancy abnormalities.
"Power doppler" or "Color power imaging" continued to develop in the 1990s. "Tissue doppler imaging" developed further from a revived concept with the arrival of better computational electronics. These developments had important clinical impact on the diagnosis of malignant conditions where tissue vascularity is increased and on moving structures other then blood flow (see Part 3).
....... Image quality of real-time ultrasound scanners made steady improvements during the mid 1980's to early 90's secondary to the increasing versatility and affordability in microprocessor technology. Nev ertheless it was not until the early to mid 1990's that more substantial enhancements in image quality were seen (see Part 3) .......
....... The use of ultrasonography continued to boom into the 1980s. According to statistics from the Bureau of Radiological Health Surveys (FDA), in the United States, the percentage of hospitals using ultrasound for dating increased from 35% in 1976 to 97% in 1982 .......
....... The World Federation of Ultrasound in Medicine and Biology (WFUMB) 1988 Meeting in Washington was preceeded by a two day Symposium on the History of Ultrasound. This event was the culmination of the sustained efforts of the AIUM Archives Committee, chaired by Barry Goldberg. Of the 500 or so delegates about 200 were recognised as pioneers. During the awards ceremony a further 40 pioneers all over the world were recognised In Memorium. The British Medical Association (BMUS) held a similar parallel event in Glasgow in the same year. In both meetings there were exhibition of many historical ultrasound instruments .......
....... Stuart Campbell with his committee of international luminaries soon started the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) in 1990 and held it's first world congress in the following year. He also became the founding editor of the Society's official journal: Utrasound in Obstetrics and Gynecology .......
All original contents Copyright ?/SUP> 1998-2020 Joseph SK Woo. All Rights Reserved.
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