To achieve these objectives and maximize the diagnostic yield, interpretation should be carried out under specified conditions, following ordered, systematic guidelines.
Unfortunately, interpretation is often limited to a cursory glance under totally inappropriate conditions. Clinicians often fall victim to the problems and pitfalls produced by spot diagnosis and tunnel vision. This is in spite of knowing that in most cases radiographs are their main diagnostic aid.
These ideal viewing conditions give the observer the best chance of perceiving all the detail contained within the radiographic image. With many simultaneous external stimuli, such as extraneous light and inadequate viewing conditions, the amount of information obtained from the radiograph is reduced. Film-captured radiographs should be viewed once they have dried as films still wet from processing may show some distortion of the image.
Digital images should be viewed on bright, high-resolution monitors in subdued lighting (see Fig. 19.2). Table 19.1 outlines the minimum and ideal specifications of the monitor (image display device) as recommended in the UK by the Health Protection Agency and by the Royal College of Radiologists.
|Minimum specification||Ideal specification|
|Screen resolution||≥1280 × 1024 (~1.3 megapixels)||≥1500 × 2000|
|Screen size (viewable diagonal)||≥42cm (~17″)||≥50cm (~20″)|
|Maximum luminance||>170 cd/m2||≥500cd/m2|
|Luminance contrast ratio||≥250 : 1||≥500 : 1|
|Greyscale bit depth||8-bit greyscale (24-bit colour)||≥10-bit greyscale|
The importance of understanding the nature of different types of radiographic images – film-captured or digital (depending on the type of image receptor used) and their specific limitations was explained in Chapter 1. How the visual images are created by processing – chemical or computer – was explained in Chapter 5. Revision of both of these chapters is recommended. To reiterate, the final image whether captured on film or digitally is ‘a/>