ACR - AAPM - SIIM Practice Guideline For Digital Radiography
By Thomas Bottiglia
Cambridge Institute of Allied Health and Technology
The science of Radiology has made tremendous advances over the past ten years with the introduction of digital technology. As radiographers, our #1 priority is to deliver optimal image quality with the least amount of radiation dose to the patient. Digital technology can help us achieve these principles faster and more efficient than ever before.
“CR” and “DR” are the two most commonly used terms we use to refer to digital imaging. “CR” or computed radiography has been around for 25 years and represents the most commonly used equipment in the radiology field. CR is a cassette-based system which uses a phosphor screen to produce a quality image. X-ray photons are absorbed in the storage phosphor also known as the imaging plate (IP). Following the exposure, plate readers scan a red laser beam over the IP surface. The laser light photons are detected by a photosensitive device or a photomultiplier tube (PMT) whose output is then digitized and stored. The raw image is then processed for display onto a computer screen.
“DR” or digital radiography is based on cassette-less operation. Although DR equipment is more costly then CR equipment, there are far more advantages. The #1 Advantage of DR is “Time”. DR systems read the transmitted x-ray signal immediately after the exposure has been taken. DR systems are rapidly evolving due to the rate of advances in modern electronic technology. The majority of DR systems utilize the use of a scintillator screen which incorporates thin fine transmitters (TFT) to capture the image. The transmission from x-ray photon to digital image is almost instantaneous.
There are many advantages and some limitations of computed and digital radiography. The main limitations are higher initial start-up costs, and the lack of familiarity with the electronic equipment on the part of both radiologists and technologists. Perhaps, the most important limitation is the “lack of” using optimal techniques while performing radiographic procedures which have led to a gradual increase in patient radiation dose. The replacement of conventional film screen images to the new digital systems requires less technique manipulation in order to achieve a good diagnostic image. Digital imaging technology uses higher energy or radiation dose which decreases noise on images and reduces the number of complaints from radiologists about image quality. Technologists have recognized this feature and have started to increase patient doses by manipulating radiographic techniques upward. An effective way to eliminate this problem is to develop validated radiographic technique charts for all performed examinations.
Some of the advantages for the use of digital radiography in the clinical practice include:
1. Significantly larger range of x-ray intensities that can be imaged by digital receptors compared to analog systems.
2. Independence of displayed contrast from kvp setting through adjustment of the display window width.
3. Independence of displayed brightness from mas setting through adjustment of the display window level.
4. Cost effectiveness over the use of conventional film and environmentally "unsafe” chemicals.
5. The availability of image processing with computer aided technology.
Radiology technologists must always remember to practice patient safety and adopt the concept of ALARA (as, low, as, reasonably, achievable) whenever they are performing radiographic procedures. No matter which type of digital radiographic equipment you are using, remember to think accordingly and modern technology will do the rest!
References
1. Article Titled: "ACR-AAPM-SIIM Practice Guideline For Digital Radiography", 2007 (Resolution 42)*
2. ACR Web Page: (http:// www.acr.org / guidelines)
