Presentation is loading. Please wait.

Presentation is loading. Please wait.

Components of Radiographic Image Quality Radiologic Technology 244 created: Fall 2005 Rev 12-01-2009.

Similar presentations


Presentation on theme: "Components of Radiographic Image Quality Radiologic Technology 244 created: Fall 2005 Rev 12-01-2009."— Presentation transcript:

1

2 Components of Radiographic Image Quality Radiologic Technology 244 created: Fall 2005 Rev

3 Review handouts

4 Main Factors Affecting Recorded Detail kVp & mAs kVp & mAs Technique Selection (Time) Technique Selection (Time) Motion Motion Object Unsharpness Object Unsharpness Focal Spot Size Focal Spot Size SID (Source to Image Distance) SID (Source to Image Distance) OID (Object to Image Distance) OID (Object to Image Distance) Material Unsharpness/ Film Screen Material Unsharpness/ Film Screen Combo Combo

5 Factors that affect Recorded Detail Geometric unsharpness Geometric unsharpness OID SID SIZE SHAPE OID SID SIZE SHAPE Motion unsharpness (blurring) Motion unsharpness (blurring) Intensifying Screens Intensifying Screens Film Speed / Composition Film Speed / Composition Film – Screen contact Film – Screen contact Kvp & Mas (density / visibility) Kvp & Mas (density / visibility)

6 GEOMETRIC QUALITIES DETAIL DETAIL DISTORTION DISTORTION MAGNIFICATION MAGNIFICATION

7 DETAIL The degree of sharpness in an object’s borders and structural details. The degree of sharpness in an object’s borders and structural details. How “clear” the object looks on the radiograph How “clear” the object looks on the radiograph

8 Recorded Detail Other names: Other names: -sharpness of detail -definition-resolution -degree of noise

9 What are these What does they measure?

10

11

12 Factors Affecting DENSITY PATIENT THICKNESS,PATHOLOGY PATIENT THICKNESS,PATHOLOGY MAS & KVP MAS & KVP SID SID

13

14

15 POOR POOR DETAIL DETAIL GOOD DETAIL

16 Motion Can be voluntary or involuntary Can be voluntary or involuntary Best controlled by short exposure times Best controlled by short exposure times Use of careful instructions to the pt. Use of careful instructions to the pt. Suspension of pt. respiration Suspension of pt. respiration Immobilization devices Immobilization devices

17

18 Decrease Motion Unsharpness Instruct patient not to move or breath Instruct patient not to move or breath Use Immobilization devices Use Immobilization devices Use Short exposure times Use Short exposure times Lock equipment in place Lock equipment in place

19 NAME 4 CAUSES

20 Blurring of image due to patient movement during exposure.

21 Focal Spot Size Smaller x-ray beam width will produce a sharper image. Smaller x-ray beam width will produce a sharper image. Fine detail = small focal spot (i.e. small bones) Fine detail = small focal spot (i.e. small bones) General radiography uses large focal spot General radiography uses large focal spot Beam from penlight size flashlight vs. flood light beam Beam from penlight size flashlight vs. flood light beam

22

23

24

25 FOCAL SPOT ANGLE

26 Object Unsharpness Main problem is trying to image a 3-D object on a 2-D film. Main problem is trying to image a 3-D object on a 2-D film. Human body is not straight edges and sharp angles. Human body is not straight edges and sharp angles. We must compensate for object unsharpness with factors we can control: focal spot size, SID & OID We must compensate for object unsharpness with factors we can control: focal spot size, SID & OID

27

28 SID Source to Image Distance The greater the distance between the source of the x-ray (tube) and the image receptor (cassette), the greater the image sharpness. The greater the distance between the source of the x-ray (tube) and the image receptor (cassette), the greater the image sharpness. Standard distance = 40 in. most exams Standard distance = 40 in. most exams Exception = Chest radiography 72 in. Exception = Chest radiography 72 in.

29 SID Shine a flashlight on a 3-D object, shadow borders will appear “fuzzy” Shine a flashlight on a 3-D object, shadow borders will appear “fuzzy” On a radiograph it’s called ______________ A true border – _____ A true border – _____ Farther the flashlight from object = sharper borders. Same with radiography. Farther the flashlight from object = sharper borders. Same with radiography.

30 OID Object to Image Distance The closer the object to the film, the sharper the detail. The closer the object to the film, the sharper the detail. OID , penumbra , sharpness  OID , penumbra , sharpness  OID , penumbra , sharpness  OID , penumbra , sharpness  Structures located deep in the body, radiographer must know how to position to get the object closest to the film. Structures located deep in the body, radiographer must know how to position to get the object closest to the film.

31

32 Distortion Misrepresentation of the true size or shape of an object Misrepresentation of the true size or shape of an object MAGNIFICATION (size distortion) TRUE DISTORTION (shape distortion)

33 Shape Distortion Misrepresentation of the shape of an object Misrepresentation of the shape of an object Controlled by alignment of the beam, part (object), & image receptor Controlled by alignment of the beam, part (object), & image receptor Influences: Central ray angulation & body part rotation Influences: Central ray angulation & body part rotation

34

35

36

37 Elongation Foreshortened Normal

38

39 Distortion (object & film not parallel) Distortion (x-ray beam not centered over object & film)

40 Central Ray Radiation beam diverges from the tube in a pyramid shape. Radiation beam diverges from the tube in a pyramid shape. Photons in the center travel along a straight line – central ray Photons in the center travel along a straight line – central ray Photons along the beam’s periphery travel at an angle Photons along the beam’s periphery travel at an angle When central ray in angled, image shape is distorted. When central ray in angled, image shape is distorted.

41 Distortion of multiple objects in same image (right) due to x-ray beam not being centered over objects.

42 Central Ray Angulation Body parts are not always 90 degrees from one another Body parts are not always 90 degrees from one another Central ray angulation is used to demonstrate certain details that can be hidden by superimposed body parts. Central ray angulation is used to demonstrate certain details that can be hidden by superimposed body parts. Body part rotation or obliquing the body can also help visualize superimposed anatomy. Body part rotation or obliquing the body can also help visualize superimposed anatomy. NAME 3 EXAMPLES NAME 3 EXAMPLES

43 MAGNIFICATION caused by: TUBE CLOSE TO THE PART (↓SID) TUBE CLOSE TO THE PART (↓SID) PART FAR FROM THE CASSETTE PART FAR FROM THE CASSETTE (↑ OID) (↑ OID) Compensate for MAG : ↑ OID by ↑ SID = “increase SID 7” for every 1” OID” “increase SID 7” for every 1” OID”

44 Size Distortion & SID Major influences: SID & OID Major influences: SID & OID As SID , magnification  As SID , magnification  Standardized SID’s allow radiologist to assume certain amt. of magnification factors are present Standardized SID’s allow radiologist to assume certain amt. of magnification factors are present Must note deviations from standard SID Must note deviations from standard SID

45

46 In terms of recorded detail and magnification, the best image is produced with a small OID and a large SID.

47 What can be done to improve the detail with a large OID? What can be done to improve the detail with a large OID?

48 Use a smaller FS

49 40” SID VS 72” SID

50

51 Size Distortion & OID If source is kept constant, OID will affect magnification If source is kept constant, OID will affect magnification As OID , magnification  As OID , magnification  The farther the object is from the film, the more magnification The farther the object is from the film, the more magnification

52 How can it be measured?

53 Measuring % of Magnification SIDSOD

54 What is the % of mag when you have a 72” SID and What is the % of mag when you have a 72” SID and 4” OID? 4” OID? DO the math………… DO the math…………

55 Material Unsharpness Equipment used can contribute to image unsharpness Equipment used can contribute to image unsharpness Fast film/screen combinations = decrease in image sharpness Fast film/screen combinations = decrease in image sharpness Slower film/screen combinations = increase in image sharpness Slower film/screen combinations = increase in image sharpness

56 Intensifying screens Lower patient dose Lower patient dose Changes resolution of image Changes resolution of image slow screens less LIGHT = better detail slow screens less LIGHT = better detail Faster – less detail (more blurring on edges) Faster – less detail (more blurring on edges)

57

58 Intensifying Screens: Review Located inside the cassette (film holder) Located inside the cassette (film holder) Calcium Tungstate Calcium Tungstate Blue to purple light Blue to purple light Rare Earth Rare Earth Green & Ultraviolet light Green & Ultraviolet light

59 POOR SCREEN CONTACT FOAM BACKING HELPS TO PLACE INTENSIFYING SCREENS IN DIRECT CONTACT WITH THE FILM – NO GAPS FOAM BACKING HELPS TO PLACE INTENSIFYING SCREENS IN DIRECT CONTACT WITH THE FILM – NO GAPS IF GAPS – MORE LIGHT CAN BE EMITTED IN SPACE, CAUSING THE IMAGE TO BE OF POOR DETAIL IF GAPS – MORE LIGHT CAN BE EMITTED IN SPACE, CAUSING THE IMAGE TO BE OF POOR DETAIL

60

61 WIRE MESH SCREEN CONTACT TEST

62

63 Screen Speed Efficiency of a screen in converting x-rays to light is Screen Speed. Efficiency of a screen in converting x-rays to light is Screen Speed.

64 Spectral Matching (F/S) What does it mean? What does it mean? Name the two types of screen phosphors Name the two types of screen phosphors What light spectrum do they emit? What light spectrum do they emit?

65 Spectral Sensitivity Film is designed to be sensitive to the color of light emitted by the intensifying screens. Blue LIGHT– Conventional Calcium Tungstate screen Blue LIGHT– Conventional Calcium Tungstate screen Green, Yellow-Green LIGHT Green, Yellow-Green LIGHT – Rare Earth screen – Rare Earth screen

66 Spectral Matching (F/S systems)

67 Red safe light

68

69 Safe lights What wattage bulb? What wattage bulb? Distance from counter top? Distance from counter top?

70 Review of Film Characteristics Size of silver halide crystals & emulsion thickness determine speed of film and degree of resolution Size of silver halide crystals & emulsion thickness determine speed of film and degree of resolution Speed – the response to photons Resolution – the detail seen Resolution – the detail seen

71 What are these What are these What are they made of What are they made of

72 Film Speed / Crystal size Larger crystals or Thicker crystal layer Larger crystals or Thicker crystal layer Faster response= less detail, and less exposure (chest x-ray) less exposure (chest x-ray) Finer crystals / thinner crystal layer Finer crystals / thinner crystal layer =Slower response, greater detail, more exposure (extremity)

73 IMAGE ON FILM SINGLE EMULSION = BETTER DETAIL SINGLE EMULSION = BETTER DETAIL DOUBLE EMULISON = LESS DETAIL DOUBLE EMULISON = LESS DETAIL PARALLAX PARALLAX With double emulsion – an image is created on both emulsions – then superimposed – slight blurring of edges With double emulsion – an image is created on both emulsions – then superimposed – slight blurring of edges

74 Extremity vs Regular cassettes

75 QUANTUM MOTTLE Film grain, or graininess, refers to the tiny black spots that make up the visible image, one grain from each silver halide crystal exposed MORE COMMON IN CR SYSTEMS NOW NOT ENOUGH PHOTONS TO CREATE IMAGE

76 Factors Affecting mAs LIST 6 factors LIST 6 factors

77 Factors Affecting mAs Patient factors: size of pt., density of tissue, pathology Patient factors: size of pt., density of tissue, pathology kVp kVp Distance - how Distance - how Grids Grids Film/Screen Combinations Film/Screen Combinations Processing Processing

78 Technique /Denisty CHANGES

79 Log denisty H & D curve

80 a densitometer, a densitometer, measures film blackness. measures film blackness. Film blackness is the relationship of the intensity of the light that hits the film from the view box (incident intensity) to the intensity of the light transmitted through the film (transmitted intensity). Film blackness is the relationship of the intensity of the light that hits the film from the view box (incident intensity) to the intensity of the light transmitted through the film (transmitted intensity). These measurements plotted on a graph produce a characteristic curve. The limitations of the human eye determine the useful density range in diagnostic radiography. These measurements plotted on a graph produce a characteristic curve. The limitations of the human eye determine the useful density range in diagnostic radiography. The diagnostically useful range of densities is 0.25 to 2.5. The diagnostically useful range of densities is 0.25 to 2.5. The later module on exposure calculation considers this in more detail. The later module on exposure calculation considers this in more detail.

81 Film latitude ? What does it mean how does it plot on the curve?

82

83

84 Main Factors Affecting Recorded Detail kVp & mAs kVp & mAs Motion Motion Object Unsharpness Object Unsharpness Focal Spot Size Focal Spot Size SID (Source to Image Distance) SID (Source to Image Distance) OID (Object to Image Distance) OID (Object to Image Distance) Material Unsharpness/ Film Screen Material Unsharpness/ Film Screen Combo Combo


Download ppt "Components of Radiographic Image Quality Radiologic Technology 244 created: Fall 2005 Rev 12-01-2009."

Similar presentations


Ads by Google