How CT happened: the early development of medical computed tomography

Abstract. As we arrive at the 50th anniversary of the first computed tomography (CT) scan of a live patient, we take this opportunity to revisit the history of early CT development. It is not an exaggeration to say that the invention of CT may represent the greatest revolution in medical imaging since the discovery of x-rays. We cover events over a period of about two decades that started with the realization that accurate cross-sectional soft-tissue detail is possible and could be a significant advance. We describe in some detail the development of the first CT system and then the rapid technical advances during the following years that included the entry of many companies into the field and the circumstances that led many of those entrants to exit the field. Rather than focusing on the specific technical details (which can be found elsewhere), we include stories and events in the hope that broader lessons can be learned. As the first x-ray-based digital imaging modality, CT brought into common use an exceptional tool that benefits countless patients every day. It also introduced dramatic changes to biomedical imaging as a field that continues to influence progress to this day.


Mini-Computers: The critical component for success
Hounsfield worked on the design of the EMIDEC 1100 mainframe computer and knew its capabilities. It was fast for its time, but that was all relative. It had 1024 words of memory and three magnetic drums that stored less than a 3.5" floppy of the 90s. It could add 2 numbers in 140 msec.
In the prototype EMI Mark the projection data was collected by a reel-to-reel tape drive, sent across town for overnight reconstruction on an ICL1905 mainframe, and returned the next day for display, analysis and Polaroid image capture and medical record archiving.
On March 22, 1965, the PDP-8, a 12-bit (two 6-bit words) minicomputer produced by Digital Equipment Corporation (DEC) was launched. It was the first commercially successful minicomputer, with over 50,000 units being sold over the model's lifetime. [ https://en.wikipedia.org/wiki/PDP-8] At $18,500, it was the first computer to be sold for under $20,000 with a smaller subsequent PDP-8/S being the first computer to be sold for under $10,000!. In 1967, the new ASCII character convention dictated 8-bit words (& multiples thereof), to accommodate all 128 characters. That changed everything. The Nova family was a series of 16-bit minicomputers released by Data General (DG) in 1969 by the designer of the PDP-8 and other DEC colleagues. It differed from the PDP-8, by adopting the new standard with 32K 16-bit words. Advertised as "the best small computer in the world", https://en.wikipedia.org/wiki/Data_General_Nova#History NOVA quickly gained a following, especially in scientific and educational markets. It outperformed and cost less than half the equivalent from DEC at a base price of US$3,995. In a simulated test at EMI CRL labs, a Nova 820, recently acquired by the Cognitive Systems Group, beat out the PDP-8 and became the device of choice to launch into the world's hospital market.
Prior to the availability of the minicomputer the market was estimated to be 20 units because of the challenge of reconstructing the data at an offline mainframe. The minicomputer was the final key critical component in a selfcontained scanner system that could reside in a hospital radiology department (see below on the world's first minicomputers.

Some drivers of CT market changes
THE RUSH TO ACQUIRE CT TECHNOLOGY | CHALLENGES AND SOLUTIONS: The US was clearly the fasted growing market. After the first presentations in 1972 at Montefiore in the Bronx in May and at RSNA in Chicago in November, there was a huge pent up demand for CT. By the end of 1973 there were 8? EMI Mark-I scanners installed in the US. Each scanner cost about $350,000 and a typical installation-construction cost was $150,000 in a large metropolitan area teaching hospital.
Freestanding Centers: The first non-hospital-based system was xxx in 197x, which was approximately the 40 th EMI Mark-I installed. This led to many other entrepreneurs and private Radiology groups setting up their freestanding center, which avoided the large costs that teaching hospitals had to incur because of hospital infrastructure and red tape.
Mobile CT Scanning: Yet another advance was placing CT scanners in portable trucks which resided in hospital parking lots. In 1977, the first mobile CT system, an EMI 1010 was launched in the LA area as a joint venture between American Medical Inc., a large hospital company and the predecessor company to RadNet Inc., today the largest freestanding imaging center company in the country. At the time, many hospitals were uncertain about purchasing their own system and/or were caught up in the long process of trying to qualify for a Certificate of Need (CON). In the 70's CON regulations were prevalent throughout the country and sharing a CT system solved many concerns and allowed the hospital to see if the demand would justify their own purchase and build a use case for later CON approval.
The engineering required to build a reliable mobile CT system with it massive and sensitive computers that required a temperature, moisture and vibration control was considerable but the engineers at EMI, AMI and Calumet Coach were up to the task. At the peak, there were over 500 truly mobile CT systems serving about 1500 hospitals and many were operating around the clock 7 days a week because of the intense demand and emergency cases requiring an immediate CT exam.