medical science
Award winner.
A little boy in Liverpool who dropped out of school because of acute abdomen hospitalization delayed his studies eventually led to the invention of CT. On the occasion of 50 years of clinical application of CT, let’s review this wonderful and tortuous story together.
Richard
One day, 6-year-old Richard began to complain about abdominal pain.
At first, his mother thought that his discomfort would pass, but the situation gradually deteriorated. In the evening, when she finally took him to the hospital, Richard soon fell ill.
The first doctor was not sure about his diagnosis, and his condition continued to deteriorate. A few hours later, he was sent to the operating room for exploratory laparotomy. The operation found that Richard’s appendix had ruptured.
Richard stucky in infancy Richard Starkey (image from the Internet)
After the operation, Richard suffered from septicemia and lingered in a coma for several days. The doctor told his mother to prepare for the worst.
Fortunately, Richard finally woke up after three days of painful torture. However, his illness was so serious that it took him several months to recover, during which more operations were performed.
Shortly after he woke up, he tried to give a toy bus to another boy in the bed next door, and unfortunately fell down, causing a concussion.
A few months in hospital made him miss a whole year of school.
When Richard returned to the classroom again, he found himself far behind the other children.
Finally, he gave up his studies at the age of 13. At the same time, he turned his attention to a new hobby, which he found in the hospital cheerleading association: music.
Richard stucky Richard Starkey and his mother Elsie (image from the Internet).
At first glance, Richard’s story is unremarkable and has nothing to do with the invention and development of CT. But it is noteworthy for three reasons.
First, these events happened not today, but in 1947. At that time, the main means of evaluating acute abdomen like today, such as CT scanner, had not yet come out. Doctors have almost nothing to rely on except medical history, physical examination, laboratory results and their own clinical experience. This diagnostic approach may delay the definite treatment and lead to Richard’s appendix rupture.
Secondly, the damage to Richard’s academic career was compensated by his development as a musician to some extent. Later Richard became one of the most famous musicians in the 20th century and is still active on the stage.
Thirdly, Richard’s fame and fortune as a musician made it possible to develop CT scanner, one of the most important diagnostic tools in medical history. The extensive use of CT scanning enables doctors to diagnose acute appendicitis and other diseases more quickly and accurately than in the past, and saves other sick children in the world from suffering like Richie.
Richard stucky grew up in a working-class community in Liverpool, England. Richard Starkey is not his widely known name. He changed his name to Ringo Starr when he was young. In 1962, he became the drummer of the Beatles, one of the most successful and influential music groups in history.
Ringo Starr, Ringo Starr, in 1968. (Image from the Internet)
This provided enough profit for EMI, the recording company of the band, so that an electronic engineer named Godfrey Houns?eld could realize his dream.
Huntsfield believes that X-rays can pass through a solid object from different angles and measure the attenuation of the beam, thus creating a two-dimensional image of the interior of the object.
The result was the world’s first CT scanner, and Godfrey Huntsfield won the Nobel Prize in Physiology or Medicine with Allan Cormack in 1979. (See: Looking Back: Fifty Years of CT (1968-2018))
1979 Nobel Prize in Physiology or Medicine (Image from the Internet)
EMI: established
Let’s start with the story of EMI.
The predecessor of EMI’s company is The Gramophone Company in London, which was founded in 1897. As a new upstart in the recording industry, the phonograph company was one of the few enterprises that saw the potential market of record music at that time. In the 10 years after its establishment, the international market expanded rapidly, and more than 60% of its income came from outside the UK.
Angel logo of the phonograph company, 1898 (image from the Internet)
Unfortunately, for the phonograph company, the world quickly became more unstable as World War I destroyed the business in Germany and Russia. With the expansion of World War I, even the domestic recording business was forced to close.
The new logo of the phonograph company, 1910 (image from the internet)
Fortunately, after the war, the business rebounded rapidly, and the phonograph company had its first million sales in 1926: O for the Wings of a Dove in Felix Mendelssohn’s Hear My Prayer. If you know that the phonograph company sold only 4 million records in 1914, this feat of selling 1 million records is quite rare.
Click play to enjoy "O for the Wings of a Dove".
Mendelssohn (German: Jakob Ludwig Felix Mendelssohn Bartholdy, 1809-1847) is a German Jewish composer and one of the most representative figures of German romantic music school. (Image from the Internet)
Unfortunately, the good times did not last long. During the Great Depression, record sales suffered more serious damage, falling by more than 80%.
In 1931, the phonograph company and one of its main competitors, British Columbia Phonograph, merged to form Electric and Musical Industries Ltd, or EMI for short.
EMI company logo, 1931-1967 (image from the network)
From the beginning, EMI was known as an innovator.
Alan Blumlein, a former Columbia engineer, is the leader of his business. Bloom Rheinland holds 128 patents. He developed stereo recording technology and created the first electronic television. Even for the later history of ultrasound, Bloom Rheinland and EMI made contributions.
During World War II, EMI turned its attention to war, and Bloom Rhein’s work on radar helped Britain and its allies finally win.
Unfortunately, Bloom Rhein himself died in a plane crash when he was testing an experimental radar system in 1942, at the age of 38.
Alan Bloom Rheinland Alan Blumlein(1903-1942) (Image from the Internet)
Godfrey Huntsfield, a young man from Nottinghamshire, was a young radar operator in the war.
Godfrey
Another protagonist, Godfrey, appeared.
Growing up on a farm bought by Huntsfield’s father after World War I, the farm made him interested in engineering.
Huntsfield later recalled, "When I was very young, I became interested in all mechanical and electrical equipment, which could even be found on the farm at that time: threshers, balers, generators. But in my memory, the period from the age of 11 to the age of 18 is the most vivid, because this is the time when I first tried the experiment … I am free to follow the footsteps of any interesting ideas. I built an electronic tape recorder; I made a dangerous study on the flight principle and launched it from the top of the haystack with a homemade glider. I almost blew myself up in an exciting experiment using tar barrels filled with water and acetylene. "
Godfrey Huntsfield (1919-2004), taken in 1939. (Image from the Internet)
When World War II broke out, Hoorns Field became interested in aviation, joined the Royal Air Force, became a radar teacher, and participated in improving radar design.
During this period, Huntsfield’s work was appreciated by Deputy Air Force Marshal John Reginald Cassidy (1892-1974), who helped Hausfield get a grant after the war. This grant enabled him to study mechanical and electrical design at Faraday House in London, where he obtained a diploma.
Huntsfield joined EMI in 1949 and became an engineer, working in radar and guided weapons.
John Reginald Cassidy (1892-1974) (Image from the Internet)
After the war, EMI was in an enviable position because of its developed electronic technology strength, but it encountered difficulties in converting research and engineering expertise into market capitalization.
One of its high-level symbols was the creation of the first all-transistor computer in Britain in 1958, namely EMIDEC1100. The project is led by Huntsfield.
However, due to the lack of experience in this market, EMI failed to make use of its innovative achievements to achieve economic success.
EMIDEC1100 computer (picture from network)
Fortunately, at about the same time, the recorded music business really started to take off.
EMI has invested heavily in its domestic market, and by the end of 1950s, its artists accounted for 40% of uk charts.
EMI also receives a lot of support from its American subsidiaries Columbia and RCA Victor. With the vigorous development of American music industry, Elvis Presley and other stars have just appeared, and EMI has increased its investment in this emerging market.
In 1955, EMI acquired Capitol, one of the largest record companies in the United States, which is the hometown of artists such as Frank Sinatra (1915-1998).
Click Play to enjoy Love Me Tender.
Elvis Presley, Elvis Presley(1935-1977), is an American rock singer and actor.
(Image from the Internet)
The Beatles
The recording industry made amazing progress in the 1950s, but it was dwarfed in the next decade.
In 1962, a wealthy Liverpool businessman, Brian Epstein, decided to manage a popular local band, the Beatles.
Brian Epstein Brian Epstein(1934-1967), Beatles manager.
(Image from the Internet)
Beatles 1
Founded in Liverpool in 956, it was originally called The Quarrymen, and was briefly renamed the Silver Beetles in the summer of 1960, after 8
Renamed The Beatles in June. The main members at that time included John Lennon (1940-1980), rhythm guitar, keyboard music and lead singer; Paul mccartney Paul McCartney (1942-), bass guitar, keyboard music and lead singer; And george harrison George Harrison (1943-2001), lead guitar, sitar, piano and harmony.
Ringo Starr, who was self-taught after dropping out of school, formed a band with his friends in 1957, when he was called Ritchie. Later, he moved to several bands and changed his name to Ringo Starr when he was in Rory Storm & The Hurricanes. In a club in Liverpool, I often perform with the Beatles.
The logo of Decca Records Company, founded in 1914. (Image from the Internet)
Epstein paid for the Beatles to record Demo in the studio of Decca, one of the largest record companies in Britain at that time.
Unfortunately, they failed in the interview, in part because the executives of Dika Group thought that guitar music was "on the way out".
Members of the Beatles, from left to right: John Lennon(1940-1980), George Harrison of George Harrison(1943-2001), Paul McCartney of Paul McCartney(1942-) and Ringo Starr of Ringo Starr(1940-) (Image from the Internet).
Persevering Epstein took the band to EMI, Dika’s main competitor in Britain, and persuaded George Martin, a talented young music producer, to audition the band’s works.
At first, Martin listened to Decca’s recordings, which he thought were "hopeless". However, he really enjoyed the singing of John Lennon and paul mccartney.
The main entrance of Abbey Road Studios (image from the Internet)
On June 6th, 1962, the Beatles passed Martin’s audition at Abbey Road Studios (then called EMI Studio, but later changed its name because The Beatles were too popular), except for the drummer Pete Best (1941-). George martin suggested a new drummer, and finally Ringo Starr.
After the original drummer Best was fired, he joined the band Lee Curtis & the All Stars. After Lee Curtis left, the band was renamed Pete Best & the All Stars. They signed a contract with Decca Records, and the response was mediocre. Later, Best quit the show business, but that was another story.
Martin saw the great potential of the Beatles, and finally EMI signed a contract with the Beatles. This signing is considered to be one of the best business decisions in the history of performing arts.
George martin George Martin(1926-2016) (second from the right) was with the Beatles. (Image from the Internet)
George martin later said that Epstein finally signed the Beatles because of his persistent enthusiasm and his assurance that the band would become famous internationally one day.
Four months later, george martin did the trick, and the Beatles released their first single "Love Me Do" in the UK, which ranked 17th in the UK singles chart and topped the US singles chart. In November 1962, their second single "Please Please Me" was recorded, and once published in January 1963, it quickly reached the top of NME magazine charts.
Click Play to Please Please Me.
Author: Lennon-McCartney Recording time: September 11th, 1962, November 26th Producer: George Martin.
John Lennon: lead singer, rhythm guitar, harmonica
Paul McCartney: harmony, bass
George Harrison: Harmony, lead guitar
Ringo Starr: Drum
Beatlemania. Sandy Gardiner, a reporter from Ottawa Daily, wrote on November 9, 1963: A new disease is sweeping across Britain, Europe and the Far East … Doctors are powerless to stop it. The name of this new disease is-Beatlemania. (Image from the Internet.
)
Soon, the Beatlemania officially began.
The cover photo of the album Abbey Road, taken on August 8, 1969. In March 2021, the street sign on Abbey Road was sold at auction for 37,200 pounds. (Image from the Internet)
The Beatles are the driving force to push the whole music industry from single to album release.
Their first two British albums "Please Please Me" and "With the Beatles" ranked first in the UK charts for 51 weeks in a row, and the new album format greatly increased the profits of record companies.
In the first year when the Beatles joined the company, EMI’s profits increased by 80%.
The album With the Beatles cover, 1963. (Image from the Internet)
Fortunately, the creative output of EMI Group has not slowed down. Before the Beatles broke up in 1970, 13 albums and 24 singles were released.
In addition to the Beatles, EMI also owns the international distribution rights of Motown (Motown Records, founded in 1959, signed by mainly black musicians, and cultivated international superstars such as Michael Jackson Michael Jackson) and The Beach Boys (founded in 1962 in beach boys).
The Beach Boys, a classic representative band of American surf rock music in the 1960s. The Beatles set off the "Beatlemania" craze in idolize, and a group of British bands and musicians led by them landed in the United States one after another, conquering American charts and American fans, and were called "British Invariance". At that time, the main force of American music "resistance" was The Beach Boys. (Image from the Internet)
CT
Let’s go back to Godfrey’s story.
A few years later, as the head of EMI medical research department, Huntsfield came up with the idea of CT when considering the potential of automatic pattern recognition in medical practice. However, due to EMI’s unwillingness to fund his project, Huntsfield approached the British Ministry of Health and Social Security (DHSS). They were happy to finance the 2,500 pounds that Huntsfield needed at that time.
Huntsfield tried to get the support of a neuroradiologist. When he visited Atkinson Morley Hospital in Wimbledon, London, he met Dr. Jamie Ambrose, a neuroradiologist. Ambrose immediately realized the potential of Huntsfield’s vision and began one of the most fruitful cooperation in medical history.
James Ambrose (1923-2006) (Image from the Internet)
Ambrose is a former fighter pilot and an excellent neuroradiologist. Before meeting Huntsfield, Ambrose had been experimenting with transcranial ultrasound and linear radioisotope scanning.
Huntsfield provides expertise in engineering and physics, while Ambrose is committed to clinical technology.
Hounsfield’s CT machine prototype (picture from the network)
Huntsfield initially experimented with a weak gamma-ray source, but the scanning took 9 days to complete.
Huntsfield realized that his work would not be of practical clinical use unless there was a way to shorten the time for obtaining the scan, so he obtained 12,000 pounds from EMI and DHSS to finance the work of replacing gamma rays with stronger X-ray sources. The first scan took 9 hours.
While Huntsfield was busy perfecting the prototype of CT, Ambrose used his knowledge of neuroanatomy to explain the first brain scans.
EMI CT scanner installed in Atkinson-Murray hospital (image from network)
Ambrose’s many early observations, such as calcification can be identified by its high density, and synovial cyst is deeper than water due to fat content, which is the basis of neuroradiology teaching today.
Unfortunately, Ambrose’s contribution is rarely recognized and his work is rarely publicized, but he undoubtedly paved the way for most knowledge of modern CT neuroanatomy.
After a series of preparations, on October 1, 1971, the first human patient, a woman suspected of having a tumor, was scanned at Atkinson-Murray Hospital. To Huntsfield’s and Ambrose’s surprise, the picture clearly shows a dark circular cyst in the brain and indicates a new era of neurosurgery.
From this moment on, as more and more patients are scanned, it is obvious that this machine is sensitive enough to diagnose brain lesions.
The first CT image of human brain (image from network)
EMI is convinced that Huntsfield’s innovation can provide the company with the first-Mover advantage in diagnostic imaging.
However, this poses a challenge to EMI because it lacks experience and expertise in this field: the production and sale of medical equipment.
Shortly after the success of the trial in Atkinson-Murray Hospital, EMI was faced with the decision of how to promote the new scanner. The inherent advantages of Huntsfield’s innovation are enough to promote the success of this product.
Hounsfield and Ambrose on RSNA in 1972 (Image from the Internet)
In the summer of 1972, EMI launched Huntsfield and Ambrose’s lecture tour in Britain and the United States to give speeches to radiologists and other medical practitioners. Their reaction was amazing. Five scanners were pre-ordered and are expected to be delivered in 1973. EMI recognizes that it must establish a sales force in the United States.
Huntsfield’s research results shocked the world and quickly triggered a "CT fever". More than 15 companies joined EMI in developing CT scanners.
In 1972, Siemens established its own CT R&D department, led by physicist Friedrich Gudden. When Gooden visited EMI’s laboratory in London, Huntsfield left a deep impression on him. "He is calm and humble, and he is a real English gentleman."
In 1974, Siemens developed its own head CT scanner. Became the first manufacturer with CT products among traditional medical equipment manufacturers.
Siemens’ first CT, SIRETOM, 1974
06
EMI: later stage
During 1973 and 1974, EMI enjoyed a monopoly position in the new CT technology and generated considerable profits. By June 1974, EMI had sold 35 scanners in the United States alone. Although it only accounts for 1.26% of the company’s total sales, this business enjoys a profit margin of 24.5%.
A magazine signed by Hounsfield, published around 1976. (Image from the Internet)
Unfortunately, EMI’s monopoly on this industry did not last long. By the beginning of 1975, EMI’s monopoly on CT market had ended. Two competitors entered the American market.
This is the Acta (Automatic Computerized Transverse Axial) scanner developed by Georgetown University and manufactured by DISCO Company and the Delta scanner of Ohio Nuclear Company.
Both are head and body scanners, contrary to EMI’s pure head products. In addition, both scanners are cheaper than EMI’s. In fact, the price of ACTA scanner is nearly $100,000 lower than that of EMI.
More important than price or full-body function is the technology behind Delta scanner. This is a second-generation scanner, which can reduce the scanning time by 50% to 2.5 minutes and improve the image resolution.
The first whole-body CT and the inventor Robert Ridley (1926-2012), doctor of dentistry, physicist. His teacher IsidorIsaac Rabi (1898-1988, inventor of magnetic resonance apparatus; He won the Nobel Prize in Physics in 1944) joked that he was the only physicist who could pull out a tooth. (Image from the Internet)
EMI did not expect that this technology could be copied and improved soon. This, coupled with the rapid growth of demand, means that new competitors have strong motivation to enter the market. EMI responded by launching its second-generation head and full-body scanner at the end of 1975. Further reduce the time to only 20 seconds. However, the pace of innovation will only get faster and faster.
By 1976, the CT industry was booming. Siemens released its first full-body CT: somatom in 1977.
SOMATOM，1977
EMI company can’t produce enough CT scanners to meet the demand, and the waiting time for orders is as long as one year. In the fourth year of production alone, the CT department of EMI created nearly 20% of the net profit of the whole company.
However, in the same year, their market share in the United States dropped from 98% in 1974 to only 37%.
The annual meeting of the Radiological Society of North America in 1975 showed EMI that they had more to worry about. Many new companies in this field have demonstrated their new scanners, including Siemens, GE, Picker, Varian and other giants in the medical electronics world. EMI: the end of the play
In 1977, EMI regained some market share in the United States, but its peak was only a little over 40%, and it faced a difficult journey.
EMI lacks the technical resources of companies like GE, Toshiba and Siemens. Nor does it really know how to sell its products to radiologists and established participants in the traditional medical imaging industry. Godfrey Hounsfield is a major advantage, but at this point, most innovations are incremental, not revolutionary, and genius may not be important in moving forward.
Huntsfield was killed in 1981.
Make a knight. (Image from the Internet)
In the end, the high-performance marketing and sales teams behind other companies, coupled with their huge technical infrastructure, proved the problems that EMI could not handle.
In the 1980s, EMI chose to withdraw from the market and focus on its core music business.
Between 1973 and 1983, nearly 20 manufacturers produced CT scanners. After 1983, the development of CT continued, with nearly 10 manufacturers competing for the CT market.
In 1986, Godfrey and his friends were outside a chocolate factory in the Loire Valley.
Huntsfield liked to walk in the mountains and lived frugally. He was unmarried all his life and died in 2004. (Image from the Internet)
The changes in the 1990s and 21st century are as rapid as those in the field of medical imaging. Music taste, the transition from physical media to digital media, and the Internet have all weakened EMI’s business. In 2007, Terra Firma, a private equity group, acquired EMI for $4.73 billion.
EMI group (image from network)
After that, EMI sold its assets, and the record operation and music copyright around the world were divided up by the other three.
In 2012, EMI was split and acquired, the record part was acquired by Universal Records, and the copyright department of lyrics was acquired by consortia such as Sony and Mubadala. After Universal Records sold the record department to BMG (Bertelsmann Music Group) and Warner Records, and most of the assets of EMI Records Department belonged to Warner.
In 2018, Sony Entertainment took another shot, occupying a total of 90% of the shares of EMI’s lyrics copyright department, consolidating its position as the world’s largest lyrics copyright company.
The name of EMI still exists, but the company that started with the phonograph company no longer exists.
George martin George Martin of the Beatles was knighted by Queen Elizabeth II in 1996 and died in 2016 at the age of 90. (Image from the Internet)
The CT scanner developed by EMI is really one of the greatest innovations in the 20th century. What’s more, this groundbreaking medical equipment was developed by the same company in charge of the Beatles.
The pain of EMI is that they mainly regard themselves as a music company. They lack resources and professional knowledge, so they can’t compete with multinational companies with the necessary resources and technical expertise, and they can’t keep up with the subsequent battles in innovation and marketing.
50 patents issued by China National Intellectual Property Administration that affect the world (pictures from the Internet)
The CT scanner may be a short adventure for EMI, but Ricky and the Beatles continue to soar.
For EMI, it seems to be back to moderns in 1960s. In 2009, the Beatles’ reissue sold more than 600,000 copies in one week.
Click play to enjoy Yellow Submarine.
By Lennon-McCartney
Date of record: May 26th and June 1st, 1966.
Producer: George Martin
Ringo Starr: lead singer, drum
John Lennon: backup singer, acoustic guitar
Paul McCartney: backup singer, bass
George Harrison: backup singer, tambourine
Mal Evans: backup singer, bass drum
Neil Aspinall, George Martin, Geoff Emerick, Pattie Harrison, Brian Jones, Marianne Faithfull, Alf Bicknell: backup singers.
In March 2018, Ringo Starr Ringo Starr was knighted at Buckingham Palace in recognition of his contribution to the music industry. (Image from the Internet)
postscript
Today, our radiologists and radiologists are also facing problems similar to EMI.
What do radiologists see when they look in the mirror? Producer of high quality images? The producer of accurate and timely reports? The big brother of the image? What additional sources of value do they need to add if they want to thrive in future changes?
Who is the competitor of radiology?
What can they offer?
The fact that radiologists first realize those, or radiologists traditionally control access to imaging equipment, to what extent does this guarantee their future?
With the continuous development of CT scanning, what steps can be taken in the field of radiology to improve its value for patients, referring doctors and medical insurance payers, and how to promote this value to those who rely on it more effectively?
Major milestones in the development of CT, such as spiral CT, PET/CT and Shuang Yuan CT, will certainly not be the last development in the history of CT-as Godfrey Huntsfield said: "Many discoveries may be lurking in the corner, waiting for someone to bring them into life. （Many discoveries are probably lurking around the corner, just waiting for someone to bring them to life.）”
The story of EMI and CT scanner provides us with profound lessons. Radiologists understand the interaction between medicine and business, which is at least as important today as it was fifty years ago.
Follow me and learn more about dry goods.
References:
[1] Laureaci Nobla Allan Cormack i Godfrey Hounsfield [Nobel Prize winners, Allan Cormack and Godfrey Hounsfield]. Pol Przegl Radiol Med Nukl. 1979 Nov-Dec; 43(6):334.
[2] Friedland G W . Allan Macleod Cormack, MSc. 1998.
[3] Isherwood I . Sir Godfrey Hounsfield – Nobel Laureate[J]. European Radiology, 2004, 14(11):2152-2153.
[4] Martland, Peter. A business history of the Gramophone Company Ltd 1897-1918.[D]. University of Cambridge, 1992.
[5] Burns R W . EMI, Shoenberg and television (1931-1934)[M]. IET Digital Library, 1998.
[6] Alexander R C . The Inventor of Stereo: The Life and Works of Alan Dower Blumlein[J]. 2000.
[7] Hounsfield Facility: 3D X-ray imagin. Available at: https://www.nottingham.ac.uk/microct/about-us/sir-godfrey-hounsfield.aspx
[8] Bartlett C A . EMI and the CT Scanner (B)[J]. Harvard Business Review, 1983.
[9] Ambrose E , Gould T , Uttley D . Jamie Ambrose[J]. Bmj British Medical Journal, 2006, 332(7547):977.
[10] Hounsfield G N . Computerized transverse axial scanning (tomography): Part 1. Description of system[J]. British Journal of Radiology, 1973.
[11] Paxton R , Ambrose J . Proceedings: A review of the results of EMI scanning in the first 650 patients.[J]. Br J Radiol, 1974, 47(560):515.
[12] Alexander R E , Gunderman R B . EMI and the first CT scanner[J]. Journal of the American College of Radiology, 2010, 7(10):778-781.
[13]Seising, Rudolf. Robert S. Ledley, 1926–2012[J]. Artificial Intelligence in Medicine, 2013, 57(1):1-7.
[14] Kiker W E , Ledley R S . The ACTA Scanner[C]// Application of Optical Instrumentation in Medicine III. 1975.
[15] Twigg H L , Axelbaum S P , Schellinger D . Computerized body tomography with the ACTA scanner[J]. JAMA The Journal of the American Medical Association, 1975, 234(3):314-317.
[16] Weinstein MA, Berlin AJ Jr, Duchesneau PM. High resolution computed tomography of the orbit withthe Ohio Nuclear Delta head scanner. AJR Am J Roentgenol. 1976 Jul; 127(1):175-7.
[17] Mitchell W. Playing leap-frog with elephants: EMI and CT scanner competition in the 1970s. Ann Arbor: University of Michigan Ross Business School; 1989.
[18] patents affecting the world. Available at: http://www.cnipa.gov.cn/col/col2149/index.html
October 8, 2021