Monthly Archives: January 2011

Computed Radiography and the Advancement of Small Private Practices

Computed Radiography is helping private practice offices move into the digital era.

In most cases, digital imaging with CR systems allows the practice to keep the same x-ray machine while eliminating the consumable costs for film, chemistry, filing materials as well as added water, and storage expenses.

The method of producing x-rays with computed radiography is very much the same as the method for plain film radiography.  X-rays are taken on cassettes with Imaging Phosphors.  The x-ray image is produced as the photons pass through the patient and are trapped in the electron traps of the image phosphor.  The Phosphors are sent through the Cassette Reader where a laser scans the phosphor and forces the photons to give off light.  This light is recorded and then sent to the computer through an analog digital converter.  The Imaging phosphor is “erased” by using white light scanning technology.  CR cassettes are reusable, but are prone to artifacts*.

The latest Journal of the American Society of Radiologic Technologists recently published a study investigating the likelihood of artifact on completed images. The study focuses on the effect of time delay between the last x-ray exposure and image acquisition time.  The study confirms that dark noise* is increased significantly (greater than 40%) for time delays of more than 24 hours. You can read the abstract here.

What does this mean for those using Computed Radiography systems?  The imaging phosphors are sensitive to background radiation of cosmic rays and radon in the walls of the building as well as ambient light.  In order to eliminate dark noise artifacts, and protect our patients from unnecessary exposure; the cassettes should be carefully scanned and erased. The cassette should not be used within 24 hours of the last wipe.


*Dark noise: Dark noise is an accumulation of heat-generated electrons in the sensor, which end up in the photosites and contribute a snow-like appearance to the image.

*Artifact : an area of the image that may look different than expected.