Film latitude is an x-ray film characteristic that is usually obtained from the characteristic curve. This Latitude can be referred to as the range of exposure over which X-ray films tend to respond with densities within a range which is diagnostically useful. This range is usually 0. 25 – 2. 5 In clinical radiography, Latitude is the range of exposure with densities that exist within the range that is diagnostic. It is usually recorded as the width of range of exposure which will produce diagnostic range densities.
This can be seen in the following formula Latitude is inversely related to contrast thus indicating a relationship that cause a decrease in contrast as the latitude tends to increase. The relationship between the contrast and the latitude affect the overall shape of the D log E curve. Forgiving film is another important term which describes a situation whereby wide film latitude permits a considerable variation in the exposure while still retaining the densities within the diagnostic range.
In routine radiography, there is a need for greater exposure accuracy whenever a narrow latitude film is being used. The wide dynamic range response of imaging plate detector is known as the computed radiography. In x-ray, the response of the imaging to the plate is usually linear while that film-screen system is curve. Imaging plate tends to have increased exposure latitude over the film-screen simply because of the linear response it shows.
The merit of this is that there can be computer enhancement of those areas of the plate that receive very little radiation which prevent the densities clumping around the toe of the D log E curve. In regards to this, those areas with higher exposure to radiation can be separated and decrease into visible range also by the computer which also prevent the clumping of the densities around the should of the D log E curve.