Computed Radiography Health Article

Definition

Computed radiography, or CR, is a digital image acquisition and processing system for radiography that uses computers and laser technology. It was developed in the mid-1980s. CR images can be recorded on laserprinted film or transmitted and stored digitally. This technological change has a significant impact on hospital operating costs and efficiency because radiography is the most common method of diagnostic imaging. It accounts for 70% of all imaging procedures, in comparison to 10% for CT scans and 6% for MRIs.

Purpose

The purpose of CR is to produce accurate radiographic images without the use of film, thereby streamlining the storage, display, and transmission of patient data. Because CR allows the radiographer to correct images immediately following exposure, the need for retake exposures is dramatically reduced. In a CR system, corrections made in the image are relayed to the radiographer through an s number. This value tells the radiographer whether the system had to brighten or darken the image, and to what degree, in order to produce a usable image. The adjusted image can then be printed on a film by a laser printer.

In addition to providing clear diagnostic images that can be adjusted before printing, CR simplifies the process of transmission for purposes of consultation. CR images can easily be sent to other physicians or facilities for consultation via computer networks. Furthermore, CR systems permit considerable reductions in the cost of storage space for diagnostic images. Given the rapid rise in operating costs of full-service radiology departments, many newer facilities and some larger hospitals have installed CR systems.

Radiation levels

One problematic aspect of CR is that it requires a higher dose of radiation to produce an image comparable to those produced by the film-screen method. The higher dose is necessary because the plate speed is approximately half that of the current screens used in film-screen combinations. The speed of the plate is directly related to the amount of radiation needed to create the x-ray image. Keeping the patient's exposure to radiation "ALARA," or "as low as is reasonably achievable," has always been one of the goals of radiologic imaging. On the other hand, some radiologists note that patients may receive lower total dosages of radiation from CR imaging because fewer repeat exposures are required.

Performance considerations

A second problematic aspect of CR is that although its contrast resolution is better than that of conventional radiographic films, its spatial resolution is not as good. This drawback is especially apparent in mammograms and chest radiographs. One study that compared six different systems for chest radiography found that the CR system performed the least well, even though it was tested under the normal operating conditions for its setting.

Description

Computed radiography is an imaging technology in which a phosphor imaging plate replaces the older combination of film-screen radiography. Phosphors are substances that become luminescent (emit light) when they are excited by ultraviolet light or other forms of radiation. The imaging plate consists of either aluminum or a steel frame with honeycombed carbon fiber on one side. This side is the x-ray attenuating side. Inside is the phosphor imaging plate, which replaces the older film-screen cassette. The plate is contained in standard-size radiographic cassettes that can be used in existing radiographic tables and stands.

The radiographer positions the patient and inserts the imaging plate cassette with the carbon-fiber side facing the x-ray tube. When the phosphor inside the imaging plate is exposed to x rays, its electrons are excited to higher energy levels. The radiographer then places the plate in a scanner, in which a helium-neon laser irradiates the excited electrons in the phosphor. The electrons emit light and return to a lower energy level. The light given off is converted first to an analog electrical signal which is then digitized, or converted into numerical data. The data can be recorded as an image on laser-printed film or transmitted and stored digitally.

Picture-archiving communications systems (PACS)

Picture-archiving communication systems, or PACS, are computer systems that allow several physicians to view radiographic images from multiple locations at the same time, whether in different departments of the same hospital or from remote facilities. CR images can be scanned, reviewed by the technologist for accuracy, and made available within three minutes to both the radiologist and the admitting physician. PACS improve hospital efficiency by eliminating the risk of losing or misplacing x-ray films as well as minimizing the need for storage space.