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CR computed Radiography

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By Arvindsutar
CR Computed radiography (CR) is the digital replacement of conventional X-ray film radiography and offers enormous advantages for inspection tasks – the use of consumables is virtually eliminated and the time to produce an image is drastically shortened.

How exactly does CR technology work?

In computed radiography, when imaging plates are exposed to X-rays or gamma rays, the energy of the incoming radiation is stored in a special phosphor layer. A specialized machine known as a scanner is then used to read out the latent image from the plate by stimulating it with a very finely focused laser beam. When stimulated, the plate emits blue light with intensity proportional to the amount of radiation received during the exposure. The light is then detected by a highly sensitive analog device known as a photomultiplier (PMT) and converted to a digital signal using an analog-to-digital converter (ADC). The generated digital X-ray image can then be viewed on a computer monitor and evaluated. After an imaging plate is read, it is erased by a high-intensity light source and can immediately be re-used - imaging plates can typically be used up to 1000 times or more depending on the application.

Medical applications

Computed Radiography systems are the most common in medical applications because they have proven reliability over more than two decades, flexibility to address a variety of clinical applications and lower costs to take multiple exam rooms digital. DR in the form of a portable detector starts at around $150,000.00, while a basic low volume CR can start as low as $30,000.00 (but higher volume, hospital-grade applications can be higher.) DR systems are generally sold as a full x-ray room replacements and tied to a single x-ray generator. CR IPs can be retrofitted to existing exam rooms and used in multiple x-ray sites since IPs are processed through a CR reader (scanner) that can be shared between multiple exam rooms.

Advantages

  • No silver based film or chemicals are required to process film.
  • Reduced film storage costs because images can be stored digitally.
  • Computed radiography often requires fewer retakes due to under- or over-exposure which results in lower overall dose to the patient.
  • Image acquisition is much faster - image previews can be available in less than 15 seconds.
  • By adjusting image brightness and/or contrast, a wide range of thicknesses may be examined in one exposure, unlike conventional film based radiography, which may require a different exposure or multiple film speeds in one exposure to cover wide thickness range in a component.
  • Images can be enhanced digitally to aid in interpretation.
  • Images can be stored on disk or transmitted for off-site review.
  • Ever growing technology makes the CR more affordable than ever today. With Chemicals, dark room storage and staff to organize them, you could own a CR for the same monthly cost while being environmentally conscious, depending upon the size of the Radiographic Operation.

Disadvantages

  • In medical applications, manual handling of the cassette housing the IP is considered a disadvantage versus DR but it also offers more flexibility for patient positioning.
  • CR is still not an approved method for higher quality radiologic applications (aerospace), due to the possibility of digital manipulation to the captured image, the inherent geometric unsharpness and resultant lower spatial resolution as compared to film (radiographic) images, SNR (signal vs. noise)issues and sensitivity to scattered radiation, and the general lack of procedural consensus among primes and OEM's.
  • There also are no quality (image resolution)standards for general radiography, only for mammography (21 CFR 900.12 (e)), however, competition among manufacturers has raised the bar and newer CR technologies with increased detective quantum efficiency (DQE) and higher spatial resolution have emerged.

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