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IMAGE QUALITY REVIEW

What affects DENSITY on the radiographic image?. . Factors Affecting mAs

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IMAGE QUALITY REVIEW

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    1. IMAGE QUALITY REVIEW RT 244 2007

    2. What affects DENSITY on the radiographic image?

    3. Factors Affecting mAs & Density Patient factors: size of pt., density / pathology of tissue kVp Collimation Distance Grids Film/Screen Combinations Processing

    4. Factors Affecting mAs Patient factors: size of pt., density of tissue, pt. compliance kVp Distance Grids Film/Screen Combinations Processing

    5. Influences technique & density on image

    8. LUNG Cancer

    10. LUNG CANCER

    11. Creating the Image Scatter Creates fog Lowers contrast (more grays) Increases as kV increases Field size increases Thickness of part increases

    12. Effects of collimation on scatter

    13. Collimate to area of interest -reduces scatter and radiation dose to the patient

    14. Grids A device with lead strips that is placed between the patient and the cassette Used on larger body parts to reduce the number of scattering photons from reaching the image

    15. Grid is placed between patient (behind table or upright bucky) & cassette If placed BACWARDS CAN CAUSE GRID ERRORS

    16. GRIDS CAN LEAVE LINES ON THE IMAGE

    17. DETAIL & Quality : How well we can see something on the image

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

    19. Recorded Detail The degree of sharpness in an object’s borders and structural details. Other names: -sharpness of detail -definition -resolution -degree of noise

    20. 2 principal characteristics of any image are Spatial & Contrast Resolution Spatial resolution Resolution is the ability to image two separate objects and visually distinguish one from the other Spatial resolution is the ability to image small objects that have high subject contrast (eg. bone-soft tissue interface, calcified lung nodules)

    21. 2 principal characteristics of any image are Spatial & Contrast Resolution Spatial resolution Determined by focal-spot size and other factors that contribute to blur Diagnostic x-ray has excellent spatial resolution. It is measured in line pairs per mm. (CT measured in cm)

    22. Factors that affect the detail of an image

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

    24. Main Factors Affecting Recorded Detail kVp & mAs Motion Object Unsharpness Focal Spot Size SID (Source to Image Distance) OID (Object to Image Distance) Material Unsharpness

    25. GEOMETRIC QUALITIES DETAIL DISTORTION MAGNIFICATION

    29. POOR DETAIL GOOD DETAIL

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

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

    36. Object Unsharpness Main problem is trying to image a 3-D object on a 2-D film. 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

    37. 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. Standard distance = 40 in. most exams Exception = Chest radiography 72 in. *See page 74 in your book

    39. SID Shine a flashlight on a 3-D object, shadow borders will appear “fuzzy” -On a radiograph called Penumbra Penumbra (fuzziness) obscures true border – umbra Farther the flashlight from object = sharper borders. Same with radiography.

    41. OID Object to Image Distance The closer the object to the film, the sharper the detail. 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. *See page 74 in your book

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

    46. MAGNIFICATION TUBE CLOSE TO THE PART (SID) PART FAR FROM THE CASSETTE (OID)

    54. 40” SID VS 72” SID

    55. MAGNIFICATION PROBLEMS SID SOD SID – OID = SOD

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

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

    58. A = good B & C = shape distortion (elongation of part)

    59. D & E = shape distortion (foreshortening of part)

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

    61. Image Distortion When the part to be imaged – does not lay parallel with the IR (cassette) If the Central Ray is not perpendicular to the part

    65. Elongation Foreshortened Normal

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

    70. Central Ray Angulation 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. Body part rotation or obliquing the body can also help visualize superimposed anatomy.

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

    72. Factors Affecting mAs Patient factors: size of pt., density of tissue, pt. compliance kVp Distance Grids Film/Screen Combinations Processing

    73. Focal Spot Size Smaller x-ray beam width will produce a sharper image. Fine detail = small focal spot (i.e. small bones) General radiography uses large focal spot Beam from penlight size flashlight vs. flood light beam *See page 73 in your book

    77. FOCAL SPOT ANGLE

    79. REVIEW Intensifying Screens and Film

    80. “Fast” Screen Cassettes Equipment used can contribute to image unsharpness Fast film/screen combinations = decrease in image sharpness Slower film/screen combinations = increase in image sharpness

    81. Fast screen vs Slower screen

    82. QUANTUM MOTTLE Not enough PHOTONS – can create a mottled or grainy image - MORE COMMON IN CR SYSTEMS

    83. SAME TECHNIQUE CHANGE IN SCREEN SPEED

    84. CASSETTES with Intensifying Screens The CASSETTE holds the film in a light tight container It consist of front and back intensifying screens

    85. Intensfying screens Lower patient dose (less photons needed) Changes resolution of image Slow screens less LIGHT = better detail Faster – less detail (more blurring on edges)

    89. Intensifying Screens: Located inside the cassette (film holder) Contains Phosphors: Calcium Tungstate Blue to purple light Rare Earth Green & Ultraviolet light

    90. CHANGING CR SPEED

    91. F/S SPEED CHANGES

    92. CR SPEED CLASS

    93. WIDER LATITUDE & DYNAMIC RANGE WITH CR

    96. POOR SCREEN CONTACT 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

    97. Tight contact needed between film & screens

    98. WIRE MESH SCREEN CONTACT TEST

    99. When there is a space between the contact of the film to the intensifying screens, a larger amount of light is allowed to reach the film – causing “more density” on fim

    101. LOADING FILM IN CASSETTE

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

    103. PARALLAX – each emulsion has an image single image overlaped edges edge sharp less sharp

    104. Film Characteristics (more in week 9) Film contains silver halide crystals 2 layers – emulsion & base emulsion thickness determine speed of film and degree of resolution Speed – the response to photons Resolution – the detail seen

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

    106. Processing Film (wk 10) Film contains silver crystals If crystals exposed to photons – will convert to black after placed in processing chemicals If not exposed – will remain clear on film

    107. Goal : Produce Optimal Images for diagnosis

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