Introduction to radiological interpretation

Interpretation of radiographs can be regarded as an unravelling process – uncovering all the information contained within the black, white and grey radiographic images. The main objectives are:

• To identify the presence or absence of disease

• To provide information on the nature and extent of the disease

• To enable the formation of a differential diagnosis.

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. It is easy to 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 the main diagnostic aid.

This chapter provides an introductory approach to show dental care professionals how radiographs should be interpreted, specifying the viewing conditions required and suggesting systematic guidelines.

Essential requirements for interpretation

The essential requirements for interpreting dental radiographs can be summarized as follows:

• Optimum viewing conditions

• Understanding the nature and limitations of the black, white and grey radiographic image

• Knowledge of what the radiographs used in dentistry should look like, enabling a critical assessment of individual image quality

• Detailed knowledge of the range of radiographic appearances of normal anatomical structures

• Detailed knowledge of the radiographic appearances of the pathological conditions affecting the head and neck

• A systematic approach to viewing the entire radiograph and to viewing and describing specific lesions

• Access to previous images for comparison.

Optimum viewing conditions

For film-captured images these include:

• An even, uniform, bright light viewing screen (preferably of variable intensity to allow viewing of films of different densities) (see Fig. 16.1)

Fig. 16.1 A Wardray viewing box incorporating an additional central bright-light source for viewing overexposed dark films. B The SDI X-ray reader – an extraneous light excluding intraoral film viewer with built-in magnification.

• A quiet, darkened viewing room

• The area around the radiograph should be masked by a dark surround so that light passes only through the film

• Use of a magnifying glass to allow fine detail to be seen more clearly on intraoral films

• The radiographs should be dry.

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. 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. 16.2).

Fig. 16.2 Eizo high-resolution medical grade image monitor.

The nature and limitations of the radiographic images

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 3. Revision of both these chapters is recommended. To reiterate, the final image, whether captured on film or digitally, is ‘a two-dimensional picture of three-dimensional structures superimposed on one another and represented as a variety of black, white and grey shadows’ – a shadowgraph.