Radiographic Imaging Image Production

1. Radiographic ImagingImage Production

2. Terms Related to Image Production • Primary Radiation • Refers to the x-ray beam after it exits the x-ray tube and before it interacts with the patient’s body • Remnant Radiation • The remainder of radiation after it passes through the patient’s body. • This is what produces the image on the radiographic film • Secondary Scatter Radiation • Radiation that may not be able to reach the film but does not carry any useful information

3. Terms Related to Image Production • Attenuation • The process by which primary radiation is changed or absorbed as it travels through the patient • Radiolucent • Material that allow x-ray photons to pass through easily (air) • Radiopaque • Materials that do not allow x-ray photons to pass through easily (bone)

4. Film / Screen RadiographyThe Imaging Chain • Latent Image • The image that is invisible on the radiographic film until processing occurs • In order to release that image the film must be developed.

5. Technical Exposure Factors • Exposure Factors directly under the influence of the radiographer • MAs • K Vp • SID

6. mAs • Milliampere seconds • Controls the amount of radiation coming from the x-ray tube and time the x-rays are being produced • Controls the quantityor number of x-ray photons produced

7. kVp • Kilovoltage peak or potential • Measures the potential difference forcing the current through the x-ray tube • It affects the energy or quality or power of the x-ray photons

8. SID • Source to image distance • The distance between the point of x-ray emission and the image receptor • Also known as focal film distance (FFD)or target film distance (TFD)

9. Geometric factors • Purpose of Radiography- To obtain as accurate an image as possible of the structure being radiographed. • Attributes contributing to this accuracy: • Sharpness • Size and Shape of the image of the object. • Following geometric factors affect the radiographic factors: • Image magnification • Image distortion • Image unsharpness

10. Image Magnification Magnification Factor = • Geometric rules applicable, due to divergence of light rays in a beam • Object nearer to source – shadow enlarges. • Object away from source – shadow size decreases. • Shorter the distance between object & source- Greater magnification. • NOTE: Magnification of some degree is usually present in every clinical radiograph because the image formed is a two dimensional representation of a three dimensional structure. Focus Film Distance Focus Object Distance • To reduce magnification, part to be examined should be as close to the film as possible

11. Image Distortion • Misrepresentation of shape and size. • Unequal magnification of different portions of same object. • Factors affecting Image distortion: • Shape of the object • Oval opaque object- Circular • Rectangular opaque object- Square • Image of thicker object is distorted more than thin objects • Position of the object • Image not distorted if object positioned parallel to film. • Image of inclined object is smaller- Foreshortening of image. • Angle of inclination increases- Extent of foreshortening increases • Spatial distortion occurs – when object of same size positioned at different distances from the film.

12. Image Unsharpness Penumbra/ Edge gradient (Pen- Almost; umbra-Shadow) • Region of partial illumination that surrounds the complete umbra causing undesirable blurred region on the radiograph. • Maximum sharpness of image is achieved by placing the object of great interest towards the anode side of the x-ray tube. • Factors affecting formation of penumbra: • Large effective focal spot size. • Short focal-film distance • Long object-film distance • Also, object to be radiographed should be placed as near to the film as possible so that so that the penumbra formed is smaller than the size of the effective focal spot.

13. Motion Unsharpness • Loss of radiographic quality due to the movement of either the patient or x-ray tube or film during x-ray exposure. • Movement of film and tube – does not pose problem • Movement of patient– not easily controlled Absorption Unsharpness • Due to gradual change in x-ray absorption across the boundary or periphery of the object. • This leads to unsharp edges. Screen Unsharpness • Due to light diffusion in screen phosphor layer. • Use of intensifying screen reduces exposure factor but causes image unsharpness

14. Factors Affecting Radiographic Quality A. Density • The overall blackening of the film

15. Variables That Affect Density • Patient size and tissue composition • The density of the tissues affect the visible density on the radiographic film • The denser the tissue, the lighter the corresponding film • mAs • The chief controlling factor of exposure and density • Increasing mA or time increases the radiographic density

16. Variables That Affect Density • kVp • kVp affects density differently than mAs. In order for there to be a significant increase in density a 15% change in kVp must be made. • Distance • Distance is inversely related to density • A decrease of distance of the source of x-rays to film increases the density and vice versa

17. Factors Affecting Radiographic Quality B. Beam Modification • Anything that changes the nature of the radiation beam. • The beam may be modified before it enters the patient (primary beam modification) or before it interacts with the film (scatter control)

18. Factors Affecting Beam Modification • Filtration • The use of attenuating or absorbing material between the x-ray tube and the patient that filters out non-diagnostic, low energy, x-ray photons. • Beam limitation devices • Anything that will change the size of the primary x-ray beam

19. Factors Affecting Radiographic Quality C. Grids • A device that is designed to remove as many scattered photons exiting the patient as possible before they reach the film. • Consist of thin lead strips interspersed with spacing material • Placed between the patient and the film to intercept scattered photons leaving the patient.

20. Factors Affecting Radiographic Quality D. Processing • Chemicals used to process or develop the radiographic film may affect the density • Most common change in density is temperature • Temperature to hot, increases radiographic density • Temperature to cold, decreases radiographic density

21. Factors Affecting Radiographic Quality E. Patient Factors • Because tissues in the body attenuate x-rays differently, tissues with similar attenuation will have similar density as well as contrast.

22. Contrast • The visible difference between adjacent radiographic densities. • The black and white and all shades of gray of the x-ray film

23. Factors Affecting Radiographic Contrast • kVp • The chief controlling factor of contrast • The higher the kVp, the lower the contrast • The lower the kVp, the higher the contrast

24. Factors Affecting Radiographic Contrast • mAs • A secondary factor for contrast. No change in mAs can make up for inadequate penetration (kVp)

25. Factors Affecting Radiographic Contrast • Beam Modification • Anything that decreases scatter, increases contrast.

26. Factors Affecting Radiographic Contrast • Contrast media • Substances that attenuates the beam to a different degree than the surrounding tissue • Used to enhance areas of the body that have the same attenuation of surrounding tissue • Contrast media increases contrast on film

27. Factors Affecting Radiographic Contrast • Processing • Inadequate processing degrades the radiographic contrast

28. Recorded Detail • The distinct representation of an object’s true borders or edges • It is often called sharpness of detail, definition or resolution

29. Factors Affecting Radiographic Recorded Detail • Motion • Voluntary motion • Motion caused by the movement of the patient. • Best controlled by good patient instructions • Involuntary motion • Motion caused by uncontrolled motion of the body such as the heart beat or peristalsis • Best controlled by short exposure times

30. Factors Affecting Radiographic Recorded Detail • Object unsharpness • The inherent unsharpness of an object due to its shape and location • Focal spot size • A small focal spot is used when fine detail is needed

31. Factors Affecting Radiographic Recorded Detail • Source to image distance (SID) • As SID increases detail increase • Penumbra -A fuzzy border of an object that is obscure • Umbra-The true boarder • Object to Image Distance (OID) • The smaller the OID, the better the recorded detail • Material Unsharpness • Faster systems produce greater unsharpness of detail

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