Digital Radiography Training
Understanding the new digital technology and its application to everyday imaging is complicated at best. The questions asked about the relevancy of the digital technology in today’s cost conscious healthcare market, seem to fade in the rush to implement the digital technology regardless of the cost. It can be compared to the switch from the plastic medium of the 78 and 45 records to the music CD. At the time, the consumer was not given a choice, and the music industry said we would receive better reproduction of sound if we went digital. Long after the conversion had been made, and the old 78 and 45 records had become collector items, the industry admitted that the sound was worse on a CD than in the record medium, and not a whole lot had been gained by the switch. But nothing changed and we continue with inferior sound produced and delivered on the music CD. In any discussion of radiographic image quality with screen film systems, we will find that production of the image is a series of tradeoffs. If you want to have speed, you must sacrifice resolution and have image noise. If you want to lower radiation dose, you must lower radiographic contrast and sacrifice information. Digital radiography also has tradeoffs and image quality can be sacrificed for convenience. But before we rush to judgement, let’s study the components of what a digital department might include and how they will change our daily working.
For those of us who are computer users (someone who knows who to turn on the machine and use a mouse) and not computer operators (someone who knows what software is and how to make the machine use it), going digital is very confusing. There are many systems to integrate and utilize and it’s very scary. There is the radiology information system (RIS) and the hospital information system (HIS), which may or may not be linked together. In other words, they may not talk to one another. This means all information or data on the patient will have to be entered into two systems. This increases the time for electronic paperwork. And no one seems to have the answer to the dilemma for comparison studies of having a portion of your images in the electronic format and the archive of images in the standard film format.
Let us start our Non Techno Geek lesson by building a glossary of terms, which will assist you in the identification of each of the technologies, which may be classified as digital. Let me forewarn you that this technology is filled with buzzwords and abbreviations for the technology.
Glossary of Terms
Picture Archiving and Communication System (PACS) – a three-component system to acquire, store, and transmit images. The three components are the display system, the network, and the storage system. Images acquired in digital format are stored or filed in a magnetic or optical memory storage device (similar to the CD). The images can be transmitted throughout the facility via a network of computers interfaced or connected together. They are displayed on monitors, which may vary in resolution.
Digital Imaging (DI) – uses radiation (x-rays) to form an electronic image in or on a radiation detector. Imaging technologies such as Computed Tomography (CT), Magnetic Resonance Imaging (MRI) and Digital Subtraction Angiography (DSA) have produced digital images since the 1970 – 80’s. Ultrasound and Nuclear Medicine also produce their images in a digital format. General radiography has traditionally produced images directly on the receptor, the film. New technology is changing this methodology for general radiography.
Direct Radiography (DR) – is an effective method for capturing the high resolution x-ray image data in a digital format. This technology uses an amorphous selenium-coated thin-film-transistor (TFT) array to capture and convert x-ray energy directly into digital signals. This produces an image that can be immediately viewed on a video monitor and after acceptance can be transmitted to other locations.
Computed Radiography (CR)- uses a storage phosphor screen (photostimulable) with energy storage capability as a x-ray image receptor. The screen is contained in standard-sized (somewhat smaller) cassettes that are reusable. This technology is used with existing x-ray equipment and requires no equipment changes. After exposure, the cassettes are transferred to a reader system. Here the imaging plate (screen) is scanned with a finely focused laser beam that stimulates luminescence proportional to the original x-ray exposure. The luminescence signal is converted to an electrical signal and now is digitized.
Resolution – is defined as the ability to image very small objects that are placed very close together. Is measured in line pairs per inch, line pairs per millimeter, etc. It is a description of how well an imaging system is visualizing or reproducing the information contained in the object being imaged. Resolution is frequently evaluated as part of quality assurance programs to assure that equipment is functioning at the correct level.
Dynamic Range – is a range of color values over which an imaging system is capable of responding. Visually, dynamic range refers to the number of shade s of gray that can be displayed. The dynamic range of a computer system is much better than the human eye. However, if the dynamic range of the system level is too low, the image will be too high contrast.
Windowing – processing an image after is is acquired can improve the optical density and contrast. The characteristic of windowing includes the window level and the window width. Window level identifies the type of tissue to be imaged, i.e. lung, abdomen, etc. Window width identifies the gray scale representation of that tissue. The wider the window width, the longer the gray scale. Narrow window width produces high contrast.
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