LECTURE 1 The Radiographic Image

Transcription

1 LECTURE 1 The Radiographic Image Prepared by:- KAMARUL AMIN ABU BAKAR UiTM Faculty of Health Sciences Medical Imaging Department 11/23/2011 KAMARUL AMIN (C) 1

2 Lesson Objectives At the end of the lesson, the student should able to explain:- The definition of density, contrast, unsharpness, and distortion. The factors affecting them. 11/23/2011 KAMARUL AMIN (C) 2

3 DENSITY 11/23/2011 KAMARUL AMIN (C) 3

4 DENSITY Represents the degree of darkening of an exposed x-ray film (white to black). The overall density of the film affects the diagnostic value of the film (ideal density, too light, too dark). 11/23/2011 KAMARUL AMIN (C) 4

5 Cont d.. Black areas on a developed radiograph are produced by deposits of black metallic silver in the film emulsion that result from exposure to x-rays and their subsequent processing. Degree of blackness on a radiograph depends on the amount of x-rays reaching the film. 11/23/2011 KAMARUL AMIN (C) 5

6 Cont d.. Also known as the logarithm of opacity or optical density (OD). OD: the ratio of the amount of light incident on the film to the amount of light transmitted through the film. 1. Light incident the light striking the radiograph from the back (viewing box). 2. Light transmitted the light which is seen coming through the radiograph while being viewed either by human eye or densitometer. OD = LOG 10 light incident light transmitted 11/23/2011 KAMARUL AMIN (C) 6

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9 LOW DENSITY HIGH DENSITY 11/23/2011 KAMARUL AMIN (C) 9

10 Factors Affecting Density Exposure Factors Patient Size Distance Object Density Film Processing Film/Screen Combination Collimation Grids Anode Heel Effect Filtration 11/23/2011 KAMARUL AMIN (C) 10

11 Cont d.. Exposure Factors (mas, kvp). An unnecessary increase in any of these factors results in an increase in film density. A. mas The chief controlling factor of exposure and density. Directly control the total number or amount of x-ray photons reaching the films. Increasing ma or time increases the density and Decreasing ma or time will decrease the density. 11/23/2011 KAMARUL AMIN (C) 11

12 Cont d.. B. 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. Directly control the penetration or quality of x-ray photons. There is a peak or optimal kvp for each body part. 11/23/2011 KAMARUL AMIN (C) 12

13 Cont d.. Patient Size: the larger the patient s body, the more x-rays that are needed to produce an ideal film density. i.e.: Increase in thickness, means that the patient can absorb more x-rays which will results in a lighter image. 11/23/2011 KAMARUL AMIN (C) 13

14 Cont d.. 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. Known as the Inverse Square Law. e.g.:if distance is doubled, density decreases four times. 11/23/2011 KAMARUL AMIN (C) 14

15 Cont d.. Object Density: determined by type of material (metals, structure (e.g. bone, tissue), composite, etc.) and by amount of material. Types of tissue affects density. For example, higher density tissues will cause less x-rays to reach film, therefore have lighter areas on the film at that place. Density (darkness) decreases when object density increases. 11/23/2011 KAMARUL AMIN (C) 15

16 RADIOLUCENT Dark Gray to Black Low object density results in high film density OR allows x-ray to easily penetrate (e.g. air, soft tissue) 11/23/2011 KAMARUL AMIN (C) 16

17 RADIOPAQUE White to Light Gray High object density results in low film density OR x-rays do not easily penetrate (e.g. bone, metals) 11/23/2011 KAMARUL AMIN (C) 17

18 Activities.. Instruction: Please indicate which parts are the radiolucent and radiopaque for each images. 11/23/2011 KAMARUL AMIN (C) 18

19 Cont d.. Film Processing: due to light, mishandling and automatic film processor. The developing time increase time will increase density The temperature of the developer increase temperature will increase density Mishandling and light can occur due to wet hands, open cassettes in light areas, high beam safelight, leakage, etc. 11/23/2011 KAMARUL AMIN (C) 19

20 Cont d.. Film/Screen Combination Screens were used to enhance the radiation so that fewer x-ray photons (less dose) / more light photons are used to create a radiographic image with optimum density. The color of the glow of the intensifying screen must match the color sensitivity of the film (spectral matching). Good film/screen combination = GOOD Density 11/23/2011 KAMARUL AMIN (C) 20

21 Cont d.. Collimation Limiting the size or increase collimation will decrease density. i.e. it reduces the scattered radiation that will adds density to the film. 11/23/2011 KAMARUL AMIN (C) 21

22 Cont d.. Grids Grids also absorb scattered radiation before reaching the film. It will reduce the density. 11/23/2011 KAMARUL AMIN (C) 22

23 Cont d.. Anode Heel Effect Density is greater near cathode end. Density is lesser near the anode end. 11/23/2011 KAMARUL AMIN (C) 23

24 Cont d.. Filtration Improve quality of beam by absorbing low photon energies. Good quality of beam has high penetration and improve the density. More penetration = more interaction with matter = more x-ray photons interact with film. 11/23/2011 KAMARUL AMIN (C) 24

25 CONTRAST 11/23/2011 KAMARUL AMIN (C) 25

26 CONTRAST Defined as visible difference between two adjacent radiographic densities. Primary function is to visible image details. Is divided into Radiographic Contrast Subject Contrast 11/23/2011 KAMARUL AMIN (C) 26

27 Radiographic Contrast Density between two adjacent areas on a radiograph. Many black and white areas means you have contrast. If a radiograph has many grays and a small density difference between 2 adjacent areas, then it has low contrast. Need right amount of contrast. (Include grays, blacks and whites so eye can easily see details). 11/23/2011 KAMARUL AMIN (C) 27

28 Subject Contrast Defined as the difference in density and mass between two adjacent anatomic structures. Depends on: Thickness of the anatomic part. Density of the anatomic part. 11/23/2011 KAMARUL AMIN (C) 28

29 Short Scale High Contrast Black and White (Few shades of gray) 11/23/2011 KAMARUL AMIN (C) 29

30 Low Contrast Long Scale Many shades of gray 11/23/2011 KAMARUL AMIN (C) 30

31 Question: Which one is Low Contrast and High Contrast? 11/23/2011 KAMARUL AMIN (C) 31

32 Factors Affecting Contrast Controlling Factor: kvp Level Grids Beam Restriction Filtration Subject Contrast Film Processing 11/23/2011 KAMARUL AMIN (C) 32

33 Cont d.. kvp LEVEL The controlling factor for contrast. kvp affects energy (penetrating ability) of x- rays. The penetrability will control the differential absorption of x-ray. 11/23/2011 KAMARUL AMIN (C) 33

34 Cont d.. As HIGH kvp = more penetration = more scatter = low contrast = long scale As LOW kvp = less penetration = less scatter = high contrast = short scale 11/23/2011 KAMARUL AMIN (C) 34

35 Cont d.. 11/23/2011 KAMARUL AMIN (C) 35

36 Cont d.. Grids Reduce the amount of scattered radiation reaching the film. And this will improve the contrast as less density has been added to the film. 11/23/2011 KAMARUL AMIN (C) 36

37 Cont d.. Increase Scattered Radiation = Low Contrast = HIGH kvp = High Penetrability Decrease Scattered Radiation = High Contrast = LOW kvp = Low Penetrability 11/23/2011 KAMARUL AMIN (C) 37

38 Cont d.. Beam Restriction It limits the area being irradiated. Close or Increase collimation will reduce scattered by reducing Compton s Interaction. Less scattered reduces the number shades of gray, thereby increasing contrast. 11/23/2011 KAMARUL AMIN (C) 38

39 Cont d.. Filtration As filtration is increased, the penetrability of the beam will also increase. The increase of high average penetration/energies will produce low contrast as many gray tones will produce. 11/23/2011 KAMARUL AMIN (C) 39

40 Cont d.. Subject Contrast Results from varying object densities within patient. For example, BONE will have more white on the film than SOFT TISSUE. Bone HIGH contrast low kvp Soft tissue LOW contrast high kvp 11/23/2011 KAMARUL AMIN (C) 40

41 Cont d.. Film Processing Inadequate processing degrades the radiographic contrast. Optimum temperature, time, replenishment chemicals, water flow and etc. will produce GOOD contrast. 11/23/2011 KAMARUL AMIN (C) 41

42 RECORDED DETAILS 11/23/2011 KAMARUL AMIN (C) 42

43 RECORDED DETAILS The distinct representation of an object s true borders or edges. It is often called sharpness of detail, definition or resolution. Terms used to describe image sharpness, clarity, distinctness, and perceptibility. 11/23/2011 KAMARUL AMIN (C) 43

44 Factors Affecting Details Motion Focal Spot Size Source-Image-Distance (SID) Object-Image-Distance (OID) Film/Screen Combination 11/23/2011 KAMARUL AMIN (C) 44

45 Cont d.. Motion The most common cause. Voluntary motion Motion caused by the movement of the patient and equipment. 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 11/23/2011 KAMARUL AMIN (C) 45

46 11/23/2011 Which one KAMARUL is blurred AMIN (C) image? 46

47 Cont d.. Focal Spot Size A small focal spot is used when fine detail is needed. A large focal spot can cause unsharpness of recorded details. However, using of large focal spot size can lengthen the x-ray tube life. It is because the x-ray produced by larger focal spot will cause bigger divergence of the beam. 11/23/2011 KAMARUL AMIN (C) 47

48 Cont d.. Source-Image-Distance (SID) As SID increases detail increase. Longer SID can reduce penumbra effect. Penumbra A fuzzy border of an object that is obscure. Umbra The true border. 11/23/2011 KAMARUL AMIN (C) 48

49 Cont d.. Object Image Distance (OID) Distance from anatomical part to the film. Decrease the OID will increase details. Increase the OID will decrease the details. Increase of OID cause the magnification to occur. 11/23/2011 KAMARUL AMIN (C) 49

50 Increase OID, Increase magnification, Decrease Details. Target 16 OID Target 16 Decrease OID, Decrease magnification, Increase Details 11/23/2011 KAMARUL AMIN (C) 50

51 Cont d.. Film-Screen Combination Slow Speed = Increase Details High Speed = Decrease Details Speed primarily affected by Phosphors Size of Intensifying Screen and Crystals Size of Film. Larger Size = Poor Details Smaller Size = Greater Details 11/23/2011 KAMARUL AMIN (C) 51

52 DISTORTION 11/23/2011 KAMARUL AMIN (C) 52

53 DISTORTION Any misrepresentation of anatomic structure on an image that has changing of its size or shape. There are TWO (2) types of distortion : A) Size B) Shape 11/23/2011 KAMARUL AMIN (C) 53

54 Factors Affecting Distortion A) SIZE Magnification Caused by excessive OID Caused by insufficient SID Causes anatomic structures to appear larger from an original size. 11/23/2011 KAMARUL AMIN (C) 54

55 SOURCE-IMAGE-DISTANCE (SID) 11/23/2011 KAMARUL AMIN (C) 55

56 OBJECT-IMAGE-DISTANCE (OID) 11/23/2011 KAMARUL AMIN (C) 56

57 Cont d.. B) SHAPE Caused by:- 1. Film-Object relationship - Improper structure with the film. 2. Beam alignment - Improper angulations of tube with the structure/part. 11/23/2011 KAMARUL AMIN (C) 57

58 Cont d.. It has TWO (2) types:- 1. Elongation Causes anatomic structure to appear longer than original size. 2. Fore shortening Causes anatomic structure to appear shorter than original size. 11/23/2011 KAMARUL AMIN (C) 58

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61 ~END OF LECTURE 1~ 11/23/2011 KAMARUL AMIN (C) 61