Digital X-Ray

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Digital X-RayDigital radiography is a form of X-ray imaging, where digital X-ray sensors are used instead of traditional photographic film. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also less radiation can be used to produce an image of similar contrast to conventional radiography.

Instead of X-ray film, digital radiography uses a digital image capture device. This gives advantages of immediate image preview and availability; elimination of costly film processing steps; a wider dynamic range, which makes it more forgiving for over- and under-exposure; as well as the ability to apply special image processing techniques that enhance overall display of the image.

Digital radiology may represent the greatest technological advancement in medical imaging over the last decade. The use of radiographic films in x ray imaging might become obsolete in a few years. An appropriate analogy that is easy to understand is the replacement of typical film cameras with digital cameras. Images can be immediately acquired, deleted, modified, and subsequently sent to a network of computers.

The benefits from digital radiology are enormous. It can make a radiological facility or department filmless. The referring physician can view the requested image on a desktop or a personal computer and often report in just a few minutes after the examination was performed. The images are no longer held in a single location; but can be seen simultaneously by physicians who are kilometres apart. In addition, the patient can have the x-ray images on a compact disk to take to another physician or hospital.

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DR Monitor

 

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Digital XRay FAQ

1. Do I need a darkroom when I buy a digital X ray system?

No. A darkroom is not required. However, images can be printed using laser or thermal printers that are similar to computer printers which will produce good quality images on specialised films without chemical processing.

2. Do I have to throw away my old X ray equipment when I move to digital imaging?

Not necessarily. The old X ray machine can be used as CR (computed radiography) by providing CR cassette. The machine can still be used as before using conventional cassette.

3. Do I have to be a computer expert to use digital imaging?

No. The software to manage digital images is user-friendly and quite easy to use.

4. Do I need to have special training to interpret digital X rays?

You will need some specific training to obtain the full advantages of digital radiology but not for the interpretation of X ray images.

5. The salesman says CR is better than DR? What do these terms mean, and is this true?

CR means 'computed radiography' and this technique uses photo-stimulable phosphor plates to obtain the digital images. The great advantage is that you can still use your present X ray systems just by changing the cassettes. DR means 'digital radiography' and requires the use of newer X ray systems with an integrated digital detector. At the moment, this last option is still more expensive but allows improving the workflow (i.e., it is no longer necessary to handle the cassettes)

6. Can I perform angiographic procedures with a digital radiography X ray unit?

This is not a good option. Angiography procedures require specifically designed X ray systems.

7. Can digital X ray units be mobile?

Yes, the most common solution is to use CR (computed radiography) with mobile x-ray systems, but there are already mobile X ray units with a digital detector (called 'flat panel detector' integrated on it) commercially available in the market. With these systems, the imaging tool is not a radiographic film but a phosphor plate. The digital detector receives the radiation going through the patient and converts it into a digital image that can be immediately visualized on a monitor.

8. If the image of one of the patients examined a few days ago is not found in the DR workstation, what should I do before repeating the examination?

One should look for the image in the PACS with a similar name, the day and time of the examination for the same modality. Try also to find the image by the identification number of the patient.

9. How do I recognize if a digital chest image has been obtained with 120 kV or with 70 kV?

It is not easy to recognize by viewing the digital image the exposure parameters employed. If a direct radiography (DR) system was used, the exposure parameters normally should be available in the DICOM (Digital Imaging and Communication in Medicine) header in PACS.

10. Should I process numerically the overexposed digital images to get image useful for diagnosis?

It is possible to process the image or adjust the display in many situations so as to make it good for diagnosis. But there may be situations where some relevant areas of the image are saturated (the pixel content has the maximum value). In such cases, the exposure will need to be repeated as scaling down saturated areas will not maintain corresponding relationship in all areas of the image.

11. How may I know the number of series and the number of images acquired during a procedure when a digital fluoroscopy system has been used?

It is not easy to know it. Sometimes in the DICOM header, a tag with identified number is archived. Another tag indicates the number of images acquired in every series. The only retrospective information that could be obtained is the number of series 'non archived' before the one existing in the PACS, e.g. if the archived series is the number 3, two other series were obtained before and not archived. It is not possible to know if other ulterior series were obtained.

12. Should I expect reduction in patient dose with digital radiography systems?

Although digital imaging systems have potential for dose reduction, the experience shows that many facilities impart more doses to patients. The primary reason is that over-exposure goes undetected, unlike with film where the image turns dark or black. In digital imaging, in contrast, the image becomes better when there is overexposure. Further, there is a tendency to take more images than necessary. In a study performed in several hospitals in the US, in-patient utilization (number of examinations per in-patient day) increased after transition to digital systems, while out-patient utilization (number of examinations per visit) also increased, although the number of examinations per visit nationally were decreased. It is very easy to delete images before archiving, and technologists tend to repeat exposure if the positioning is wrong or if there is motion blur. Such repeats normally go undetected. Thus digital imaging has the potential to increase the number of exposures and hence patient dose

13. How do I recognise if my digital image has been obtained with more dose than necessary?

It is not easy to recognise these overexposures if the radiographic technical data (exposure parameters) or the dose values are not recorded by the X ray system or in the DICOM header. The wide dynamic range of digital detectors and the automatic post-processing create difficulty in recognising overexposures

14. How can I know if the image to be reported is the first exposure for this patient or if it has been repeated?

It is possible, but one has to put some efforts. If obtained images are automatically sent to the PACS, a query to the images obtained the same day for the same patient could give the information. Other possibility is to look at the DICOM header and identify.