Image quality of X-ray- Contrast, Resolution, Foggy image ,Distortion?


image quality of X-ray

X-ray Image Contrast

Contrast is the difference between adjacent densities. The adjacent densities can range from white to black and various shades of grey in between.

The contrast between different parts of the image is what forms the image and the image and the greater the contrast, the more visible features become. Radiographic contrast has two main contributors: subject contrast and detector (film ) contrast.

Film contrast refers to density differences that result due to the type of film used, how it was exposed, and how it was processed. Since there are other detectors besides film, this could be called detectors contrast, but the focus here will be on film. Exposing a film to produce higher film densities will generally increase the contrast in the radiograph.

There are two types of contrast subjective and objective

  1. Subjective contrast is dependent on eye of the observer, as the ability differs from person to person to different contrast.
  2. The Objective contrast is the difference between densities or difference between black and white, it can be measured by photometer.
Optimum contrast can be obtained by using correct radiation quality/ kV, quality/ mAs, filtration of scattered radiation, radiation material and processing techniques

Resolution

Resolution is one of the important parameters used in the measure of the image quality. Resolution means recorded sharpness of the image which means the ability to show smaller objects accuratelly.

Resolution is resolving capacity of the image and is expressed in line pairs per unit length, for example line pair/mm. normally a fixture is made with radio opaque substance like metal wires, equi-spaced at the dimensions of diameter of wire. It is the ability of an imaging process to distinguish  adjacent structures in an object. It is an important measure of image quality.

This resolution can be two types, the spatial and the contrast resolution. 

Spatial resolution is the ability to image small structures that have high subject contrast such as bone-soft tissue interface. When all of the factors are correct, conventional raadiography has excellent spatial resolution.

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