A history rich in innovation

In London, in fall 1971, a radiologist and an engineer found themselves jumping up and down for joy – as one of them later recalled – “like football players who had just scored a winning goal.” It had been 76 years since the discovery of X-rays, and the two researchers held in their hands a completely new type of X-ray image – known as a tomogram – that depicted a brain in unprecedented quality.
The history of computed tomography at Siemens began when the heads of development went on a trip to London in 1972. Later the same year, a CT development department was established in the fundamental research unit at Siemens in Erlangen – and Siemens went on to launch its first CT scanner in 1975. The SIRETOM head scanner acquired two tomographic images of the brain per scan in close to five minutes. Just two years later, a head scan using a Siemens whole-body scanner took just five seconds – and it was also possible to examine the chest, abdomen, and joints.

In order to deliver an image even before the scan was complete, SOMATOM was equipped with the fastest serially produced image processor in the world in 1983. Nevertheless, the first ten years had not brought any fundamental changes in CT scanner technology. The scanner’s performance was limited primarily by the way in which the measurement system worked, first accelerating and rotating through 360° before braking, stopping, rotating in the other direction, and coming to a stop again. Siemens overcame this limitation in 1987 with SOMATOM Plus, which achieved continuous rotation by supplying power to the gantry via slip rings, instead of cables as before.
The significantly higher speed resulted in significantly more data, which Siemens transmitted using an optoelectronic system. Other components of SOMATOM Plus were also adapted to the higher speeds – for example, the X-ray tube had twice the output of previous tubes and cooled down much faster.

Continuous rotation laid the foundation for spiral CT, a technique in which the body is X-rayed in a spiral pattern. This method means that the image reconstruction software also needs to take account of the movement of the table.
From the mid-1990s onward, it was possible to visualize the vast quantities of data generated by spiral CT in 3D for the first time. Also unique were the Ultra Fast Ceramic (UFC) detectors, which replaced the xenon gas of earlier systems and absorbed the X-rays almost entirely, converting them into electrical signals in a relatively loss-free manner. In conjunction with increasingly advanced software, this technology also brought significant reductions in radiation dose.
In 1998, Siemens took another key step forward with the introduction of multislice CT. This technology split the detector into multiple rows, which processed signals from the X-ray tube independently of one another and could therefore record multiple slices per rotation. The system was able to visualize whole organs in high definition – including, for the first time, the coronary vessels.

Just under three years later, Siemens took the next major step by introducing the world’s first 16-slice CT scanner. Thanks to this rapid increase in capabilities, with 16 slices and a rotation time of 0.4 seconds, physicians were now able to visualize even the fine side branches of the coronary vessels.
At the same time, heat generation during long scans placed a burden on the X-ray tube, and the pivot bearings were subject to considerable mechanical strain. The answer was to develop a rotating envelope tube known as the Straton X-ray tube. In this design, the entire vacuum tube rotated and was therefore much more robust and compact. It also discharged about ten times more heat.
In order to usher in a technological revolution, it was then necessary to completely redesign the basic framework of the CT scanner: the first Dual Source CT with two tube-detector systems. Instead of rotating through 180 degrees per slice in order to collect the necessary data, SOMATOM Definition needed to rotate through just 90 degrees. This, in conjunction with a rotation time of just 0.33 seconds, lead to a temporal resolution of just 0.083 seconds, for example to produce pin-sharp images of the beating heart.

Integrating a photodiode and a signal converter into a chip in the Stellar detector reduced electronic noise and dose by up to 30 percent, while allowing visualization of structures down to a size of 0.30 millimeters. Reducing radiation dose was also a key factor in the development of the Vectron X-ray tube, which enabled physicians to scan larger patients with a lower tube voltage and hence a lower dose.
SOMATOM Force has ultimately pushed all the high-end components from Siemens Healthineers to their limits. Weighing in at 1.6 tons, its gantry rotates around the patient four times per second and achieves a resolution of 0.24 millimeters and the radiation exposure for a lung scan, for example, is 0.1 millisievert.
The engineers are developing new tools in order to make constructive use of this huge quantity of three-dimensional data. One need only look at Cinematic Rendering images to get an idea of the capabilities of sophisticated image processing software. At the same time, artificial intelligence is gaining a foothold in CT imaging – helping users not only to prepare for scans but also to evaluate the results: myExam Companion helps them achieve optimum scan preparation, and AI-Rad Companion Chest CT¹ can relieve the burden on radiologists when it comes to interpreting medical images.

The concept of photon-counting computed tomography is based on completely new detector technology and major redevelopments of all system components, as well as hardware and software. It opens up new horizons with an unprecedented combination of very sharp images, extremely short acquisition times, improved image contrast, and more diagnostically useful content. It also requires lower X-ray and contrast agent doses and therefore constitutes more than just a new, improved generation of CT scanners. Rather, CT imaging has effectively been redefined.