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Optical density changes in dry-processed films.

Article Excerpt
The use of dry laser imagers has become widespread in radiology departments in Kuwait in the past 5 years. Most digital imaging modalities, including computed tomography, magnetic resonance imaging, ultrasound, nuclear medicine, computed radiography and digital radiography systems, use this type of imager to obtain hard copy images. (1) Some digital imaging modalities still use multiformat cameras attached to a laser imager, in which the films are processed using liquid chemicals. The storage and handling requirements of these 2 types of films are different due to the unprocessed chemicals left on the dry-processed films. This can affect the quality of images stored on these films when they are sent outside the hospital and subsequently exposed to heat, light or both. Radiologic technologists need to understand the consequences of different storage conditions and handling methods so they can advise patients properly. (1,2)

There are 2 major types of laser imagers used to create hard copy images from digital data on radio graphic films: wet laser imagers and dry laser imagers. In wet laser imagers, liquids are used to process the films through the 4 steps: developing, fixing, washing (wetting) and drying. The liquid chemicals can be expensive, produce hazardous waste and require a water supply and drainage facilities. (2) The introduction of dry laser imagers in 1996 eliminated the use of liquid chemical processing. (1) Modern dry laser imagers can produce images with an almost continuous gray scale, as do conventional wet laser imagers. (1) Because dry-processor laser imagers eliminate the need for liquid chemicals, they are safer and thus are expected to proliferate. (3) They also are easy to set up anywhere in the hospital and easy to connect to the computer network. (4) Moreover, dry laser imagers have an automatic quality control program built into the system and thus eliminate the need to perform daily sensitometry. (5) The dry imagers also have been found to be very stable, (6) and the quality of the images is comparable to wet laser images. (1)

Many types of dry laser printers have been developed for medical and nonmedical purposes in the past few years. These can be divided into 4 major types of printing: adherographic, photothermographic, thermographic and dye diffusion. (7) However, 2 of these technologies, namely thermographic and photothermographic, are used widely in medical imaging. (8-11) Whichever technology is used, the goal of dry laser imagers is to produce hard copy images with similar or better characteristics and image quality than wet laser imaging systems. The technical aspects of both technologies, the structure of films that are used and the chemical reactions that take place during film processing have been described in detail elsewhere. (7,9,10) The major problem with dry-processed films is that the unprocessed chemicals are left on the films themselves and can lead to further processing over long periods of time or if they are exposed to heat in the short term. It has been reported that exposure of dry-processed films to excessive heat or light can have adverse effects on the quality of images. (5,7,8) As reported earlier, (8) the authors have noticed changes in optical density (OD) on dry-processed films that patients left inside cars parked in the sun. The extent of OD changes due to environmental conditions has not been studied, and a lack of information about it exists in the current literature. (12) The source of these changes--whether the source is light, heat or both--needs to be investigated to ascertain optimal film storage conditions.

Many studies have been conducted to compare the image quality of wet- and dry-processed films. (1-6,10-17) Gahleither et al compared the thermal stability of...

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