Factors affecting the radiographic image and film faults

Factors affecting the radiographic . image and film faults

Image quality I. Contrast II. Image geometry III. Characteristics of the X-ray beam

I. Contrast n Subject contrast n Film contrast n Fog and scatter

Subject contrast n Differences in tissue thickness n Differences in tissue density n k. V or penetrating power of the radiation beam

Film contrast n The characteristic curve of the film n Optical density n Type of film- direct or indirect action n Processing

Fog and scatter Fogged film Scatter radiation from within the patient’s tissues

Perception of the radiographic image n Partial images-we all see the same partial images but we don’t necessarily perceive the same object n Contrast n Context

Effect of partial image

The effect of contrast

The effect of context

Image geometry n n n Positioning of the film, object and x-ray beam Focal spot size and principle of line focus Focal spot-object distance (FSOD), objectto film-distance (OFD)

Ideal image geometry requirements

Focal spot size, heat distribution and image sharpness n n n Focal spot 1 mm Heat needs to be distributed over as large as possible area Principle of line focus

Focal spot-to filmdistance(FSFD)

FSFD n Increasing the distance between the focal spot and the object results in an image with increased sharpness and less magnification of the object

Object-to film- distance (OFD)

n Decreasing the distance between the object and the film increases the sharpness and result in less magnification of the object

Image shape distortion

Cont’d

Practical factors influencing image quality n n n The X-ray equipment The image receptor/screen combination Processing The patient The operator and radiographic technique

Typical film faults I. n Film too dark Overexposure Overdevelopment Fogging Thin patients tissues

Films with inadequate contrast n Processing errors n Exposure errors

Image unsharp and blurred n n n Movement of the patient during the exposure Excessive bending of the film during the exposure Poor film/screen contact within the cassette

Film marked n n - Film packet bent by the operator Careless handling of the film in the darkroom : Finger prints Finger nails Bending Static electricity

Operator positioning faults n n n 1. Incorrect placement of the film packet Back to front, image of the lead foil evident ( film also too pale) Inadvertently used twice, double exposure (films also too dark) Not covering the area of interest