Timeline of Developments in Digital Imaging Technology

The first digital radiography system using the basic principle of the conversion of x-ray energy into digital signals utilizing scanning laser stimulated luminescence (SLSL) was developed by Fuji and introduced in the early 1980s.

1980. Computed Radiography (CR) was the first available digital technology for projection radiography. CR uses a photostimulable detector, which replaces the traditional screen-film cassettes. In this process, storage phosphor plates are exposed inside the cassettes with standard dimensions for typical plain radiography and no change or generator, x-ray tube, and bucky wall or table mounted system is necessary. The basis CR imaging cycle is comprised of three steps: expose, readout, and erase.

1987. Amorphous selenium-based image plates. Amorphous selenium (a-Se) is a photoconductor used as x-ray detector material. This material catches the x-rays and converts them to either charge or lower energy photons. Amorphous selenium was used as a photoconductor in print copying machines as well as in x-ray imaging technique known as xeroradiography for decades.

1990. Charged Coupled Device (CCD) is a light-sensitive integrated circuit that stores and displays the data for an image in such a way that each pixel in the image is converted into an electrical charge of intensity of which is related to a color in the color spectrum. In many clinical environments, CCD x-ray detectors replaced film, as it allows digital copies of images to be captured and stored much more quickly.

1994. Selenium drum detectors consist of a selenium-coated aluminum drum that spins slowly during irradiation. When x-ray photos hit the surface of the drum they cause a change of the surface charger proportionally dependent on their local radiation intensity. During this process, the shift is detected and processed by an analog-digital converter.

1995. Amorphous silicon Cesium Iodide (CsI) scintillator Flat Panel Detector (FPD) and selenium-based FPD. There are two types of Flat Panel Detectors used in digital x-ray: Direct, using a-Se (amorphous selenium) to convert x-rays directly to electricity; and indirect using a-Si (amorphous silicon) and phosphor plates. These plates are semiconductor products constructed based on thin-film transistor (TFT) film. The direct type, a-Se detector, converts x-ray photons when exposed, without the use of a scintillator. The indirect a-Se FPD use a phosphor plate to convert x-ray photos to normal light, and detects that light. CsI typically yields more detailed, higher resolution images. You can read more about the differentiation between Gadox and CsI here.

1997. Gadolinium-based (scintillator) FPD. According to The Radiological Society of North America (RSNA), gadolinium-based contrast agents have been used for diagnosis and treatment guidance in more than 100 million patients worldwide over the past 25 years. These agents are said to enhance the quality of Magnetic Resonance (MR) images by altering the magnetic properties of nearby water molecules in the body. Contrast agents help physicians diagnose and treat a wide variety of medical conditions. This is done through improving the visibility of organs, blood vessels or tissues.

2001. Gadolinium-based (scintillator) portable FPD requires no cables between the FPD and mobile x-ray unit. The wireless FPD can reduce x-ray exposure dose and is powered by lithium batteries, which can be removed and replaced. The absence of cable removes the sterilization issues typically resulting from contact between the cable and people or equipment when used in emergency situations or in an OR.

2001. Dynamic FPD fluoroscopy digital subtraction angiography (DSA). DSA is a fluoroscopy technique used in interventional radiology to clearly visualize the blood vessels in a bony or design soft tissue environment.
2006. Digital tomosynthesis, which creates a three-dimensional picture of the breast using x-rays, is different than a standard mammogram in the same way a Computed Tomography (CT) scan of the chest is different from a standard chest x-ray; one is three-dimensional and the other is flat.

2009. Wireless DR (FPD) incorporate the proven technology of amorphous silicon photodiode array and thin film translator (TFT) underneath, which convert invisible x-ray photos into visible photons and then into electric charges. An example of a wireless DR FPD is the ExamVue DR 14” x 17” wireless cassette-sized detector, which easily fits into standard bucky tray cabinets for upgrading a film-based or CR system to digital x-ray system.

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