Image Quality and Artifacts - Im by pengtt

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									        Components of

 Radiographic Image
             Quality
Radiologic Technology 244
        created: Fall 2005
           Rev 12-01-2009
Review handouts
         Main Factors Affecting
           Recorded Detail
   kVp & mAs
       Technique Selection (Time)
   Motion
   Object Unsharpness
   Focal Spot Size
   SID (Source to Image Distance)
   OID (Object to Image Distance)
   Material Unsharpness/ Film Screen
                          Combo
         Factors that affect
          Recorded Detail
 Geometric unsharpness
        OID SID SIZE SHAPE
 Motion unsharpness (blurring)
 Intensifying Screens
 Film Speed / Composition
 Film – Screen contact
 Kvp & Mas (density / visibility)
     GEOMETRIC QUALITIES
   DETAIL

   DISTORTION

   MAGNIFICATION
           DETAIL

The  degree of sharpness in
 an object’s borders and
 structural details.
How “clear” the object looks
 on the radiograph
              Recorded Detail
   Other names:
       -sharpness of
    detail
       -definition
       -resolution
       -degree of noise
What are these
What does they
measure?
Factors Affecting DENSITY
 PATIENT THICKNESS,PATHOLOGY
 MAS & KVP
 SID
POOR
DETAIL




GOOD
DETAIL
               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
 Decrease Motion Unsharpness
 Instruct patient not to move or breath
 Use Immobilization devices
 Use Short exposure times
 Lock equipment in place
NAME 4 CAUSES
Blurring of image
due to patient
movement during
exposure.
               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
FOCAL SPOT ANGLE
       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
                    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.
    SID
 Shine a flashlight on a
  3-D object, shadow
  borders will appear
  “fuzzy”
On a radiograph it’s
  called
  ______________
 A true border – _____
 Farther the flashlight
  from object = sharper
  borders. Same with
  radiography.
                   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.
                    Distortion
   Misrepresentation of
    the true size or shape
    of an object

MAGNIFICATION (size
 distortion)

TRUE DISTORTION
 (shape distortion)
          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
Elongation Foreshortened Normal
                       Distortion (x-ray
Distortion (object &   beam not centered
film not parallel)     over object & film)
             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.
Distortion of multiple objects in same
image (right) due to x-ray beam not
being centered over objects.
      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.
 NAME 3 EXAMPLES
        MAGNIFICATION
          caused by:
   TUBE CLOSE TO THE PART (↓SID)

   PART FAR FROM THE CASSETTE
    (↑ OID)

Compensate for MAG : ↑ OID by ↑ SID =
 “increase SID 7” for every 1” OID”
       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
In terms of recorded detail and
magnification, the best image is
produced with a small OID and a
large SID.
   What can be done to
    improve the detail
    with a large OID?
Use a smaller FS
40” SID VS 72” SID
        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
How can it be measured?
Measuring % of Magnification



SID
SOD
    Measuring % of Magnification
    What is the %
    of mag when
    you have a 72”
    SID and
    4” OID?

 DO   the
    math…………
      Material Unsharpness
 Equipment used can contribute to image
  unsharpness
 Fast film/screen combinations = decrease
  in image sharpness
 Slower film/screen combinations =
  increase in image sharpness
           Intensifying screens
   Lower patient dose

   Changes resolution of image

   slow screens less LIGHT = better detail

   Faster – less detail (more blurring on edges)
    Intensifying Screens: Review
 Located inside the
  cassette (film
  holder)
 Calcium Tungstate
       Blue to purple light
   Rare Earth
       Green & Ultraviolet
        light
    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
     WIRE MESH
SCREEN CONTACT TEST
                Screen Speed
   Efficiency of a screen in converting x-rays to
    light is Screen Speed.
     Spectral Matching (F/S)
 What does it mean?
 Name the two types of screen phosphors
 What light spectrum do they emit?
           Spectral Sensitivity
Film is designed to be
   sensitive to the color
   of light emitted by the
   intensifying screens.
 Blue LIGHT–
   Conventional Calcium
   Tungstate screen
 Green, Yellow-Green
   LIGHT
 – Rare Earth screen
Spectral Matching (F/S systems)
Spectral Matching (F/S systems)


                           Red safe
                           light
              Safe lights
 What wattage bulb?
 Distance from counter top?
    Review of Film Characteristics
 Size of silver halide
  crystals & emulsion
  thickness determine
  speed of film and degree
  of resolution
Speed – the response to
  photons
 Resolution – the detail
  seen
   What are
    these

   What are
    they made
    of
    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)
            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
Extremity vs Regular cassettes
            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
         Factors Affecting mAs
   LIST 6 factors
          Factors Affecting mAs
   Patient factors: size of pt.,
    density of tissue,
    pathology
   kVp
   Distance - how
   Grids
   Film/Screen
    Combinations
   Processing
Technique /Denisty CHANGES
Log denisty   H & D curve
   a densitometer,
   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).
   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 later module on exposure
    calculation considers this in
    more detail.
       Film latitude ?
     What does it mean
how does it plot on the curve?
     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

								
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