Flat-panel X-ray Sensor that Directly Converts X-rays into Electrical Signals – SHIMADZU Corporation

Flat-panel X-ray Sensor that Directly Converts X-rays into Electrical Signals – SHIMADZU Corporation
Source: The Japan Machinery Federation

An x-ray sensor that converts x-rays directly into electrical signals has been developed for the digitization of x-ray imaging, which has been analog for the past 100 years or so. The device consists of a TFT panel for the liquid crystal display mounted with a layer of amorphous selenium (a-Se), which is normally used for a photoreceptor drum in copier machines. The TFT panel receives the electric charge generated by x-ray radiation on the layer of amorphous selenium for conversion into an electrical signal. The device can handle both still images and moving images. It also reduces the exposure of x-rays to patients. In September 2003, a digital angiographic system (for imaging blood vessels inside such internal organs as the heart) equipped with a newly developed 9-inch-square X-ray sensor was commercialized, followed by an x-ray imaging system of a 17-inch-square size in November 2004.

Building a sensor that receives x-rays penetrating straight through
Since being invented in the late 19th century, the x-ray diagnosis system as typified by x-ray photos has been mainly imaged using film, but digitization of the system has lagged far behind. The reason for this is the property of x-rays to penetrate straight through anything (thus enabling fluorography of the human body), including even lenses. Therefore, the condensing of refracted light has been impossible. Typical digital cameras convert light captured by the lenses into an electrical signal by using a light-sensitive element called the CCD, which is small enough to be placed on a fingertip. The fluorograph of a patient’s chest is digitally imaged by means of x-rays, for example, and requires the kind of CCD that has the same area as the size of the chest. Of course, there is no such a thing in the world, and even if one were manufactured, the cost will be exorbitant.
However, digitization has been accelerating in other fields of medical systems, so the x-ray diagnosis system could not be allowed to lag behind. Mr. Sato was entrusted with this development.
“We needed a large-sized, light-sensitive device that could replace the CCD. We then considered the feasibility of a TFT panel that is widely used for PC liquid crystal displays.”
The TFT panel is normally used as an output device that converts electrical signals into images, but their idea was to use it for entering data, and converting images (x-rays) into electric signals. The TFT panel can provide an area large enough to accommodate the chest size of patients.
They concretized the structure of a TFT panel mounted with a layer of amorphous selenium, which generates carriers of conduction when radiated with x-rays that in turn are received by the TFT panel for conversion into electrical signals. There was, however, a major problem.
“Our company specializes in the development of medical diagnosis systems, and therefore, we didn’t have any know-how about TFT panels, not to mention the technology for vaporization deposition (for vaporizing the amorphous selenium to be coated on the TFT panel).”
It would take too much time to newly develop in-house an unfamiliar technology beyond the company’s field of expertise. This is why they launched a joint development with Sharp, given its TFT panel-related technology, and Yamanashi Electronics with its vaporization deposition technology for amorphous selenium.

Arguments caused by clashing opinions. Yet, problems were solved one by one.
A small-sized trial production revealed few problems in commercializing this development. Then they engaged in full-fledged commercial development of a 9-inch-square X-ray sensor in the late 1990s.
“The prototype was developed mainly for checking the overall functions, with sufficient thickness of the deposited layer at several hundreds of μm, but a commercialized product requires a thickness of 1 mm, which is 10 times the thickness of the prototype. We vaporized and deposited amorphous selenium and tried to obtain an image by applying 10,000 volts, but repeatedly failed to obtain a layer of uniform thickness, and the TFT panel wiring picked up a noise signal. We completely failed to produce what we wanted.”
Shimadzu usually spends an average of two years for product development, but in this case they spent three years without achieving any substantial results. Usually a project like this would be discontinued, but the environment surrounding the company was changing very quickly at that time. In view of an all-out market entry of foreign medical diagnosis equipment makers into the Japanese market, Shimadzu decided to dedicate its resources to x-ray diagnosis systems, which are the company’s proprietary field. Due to an unexpected turn of events, the future of the company now rested on their shoulders, and they simply could not afford to fail.
“We were not only under a lot of pressure but growing so impatient at not having achieved substantial progress that we had some arguments among the team members (laughing). We needed to clarify and adjust the technical problems of which each company was in charge, so we verified and separated the problems related to the TFT and deposition layer developments and eliminated them one by one.”

In September 2003, five years after launching the project, they developed the world’s first direct-conversion flat-panel detector. The newly developed x-ray sensor processed high-resolution digital images equivalent to two million image pixels, as well as video images. Given the high sensitivity, the dosage of X-ray radiation could be reduced to half or even one-third that of conventional methods, thus contributing to the reducing the exposure of radiation to patients. Two years later, they succeeded in developing 17-inch-square X-ray sensors.
“An effect always has its cause. People tend to see what they want to see, but unless one humbly focuses on the cause, a solution will never be found.”
Thus, an accumulation of their persistent trials bore fruit. The x-ray sensor that Mr. Sato and his team commercialized is now being mounted on the x-ray diagnosis systems for visualizing the circulatory system or internal organs of the body, thus performing their functions with regard to medical care activities.

SHIMADZU Corporation
Established in 1875 and backed by a long history of 131 years, Shimadzu Corporation succeeded in developing x-ray imaging for the first time in Japan in 1996. Since then, the company has developed and manufactured various medical diagnosis devices, analytic equipment, and measuring instruments that mainly utilize x-ray diagnosis systems. Its technological capability has earned the company high regard both in Japan and abroad. Moreover, the memory is still vivid of when, in December 2002, Mr. Koichi Tanaka of Shimadzu Corporation was awarded the Nobel Prize for his development of a new structural analytic method for biologic polymers, thus becoming the 12th Japanese Nobel Prize laureate.