Components of Image Quality

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Components of Image Quality Radiographic
Artifacts

• Radiologic Technology A
• Spring 2009

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• X-ray Exposure Factors
• Radiographic Density Contrast
• Components of Image Quality
• Radiographic Artifacts

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Review Chapter 7

• Primary radiation exits the tube
• Interacts with various densities in the body
• Photons may be absorbed
• Scattered
• Passed through without any interference to the
  cassette or image receptor (IR)

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How well we can see something on the image
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Image detail is affected byPhotographic
propertiesand Geometric properties
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Photographic Properties

• Contrast
• Density

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X-ray Exposure Factors

• TECHNIQUE SELECTION
• Radiographer selects the
• Kilovoltage peak (kVp)
• Milliamperage (mA) time (s)
• Milliamperage x time mAs
• (milliamperage multiplied by a set time
  measured in seconds)

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Kilovoltage Peak

• kVp
• One kilovolt 1000 volts
• The amount of voltage selected for the x-ray
  tube.
• Range 30 to 150 kVp
• kVp controls __________ ?

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Milliamperage

• One milliampere (mA) one thousandth of an
  ampere.
• The amount of current supplied to the x-ray tube
• How many x-rays will be produced
• Range 10 to 1200 mA

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Time

• In seconds
• How long x-rays will be produced
• 0.001 to 6 seconds

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Milliampere Seconds

• Technologists think in terms of mAs
• Calculated by mA x seconds
• Ex 100mA X 0.2s 20 mAs
• How many x-rays will be produced and for how
  long.
• Modern x-ray machines only allow control of
• mAs controls _______________ ?

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Factors Affecting Density

• Primary control factor
• mA
• Time (seconds)
• Influencing factors
• kVp
• Grids
• Beam restriction
• Body structures (size of pt, pathology
• Processing
• SID OID
• Film Screen combinations

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Primary Controlling Factor of Density

• mAs
• mA AMOUNT of electrons sent across the tube
  combined with TIME (S) mAs
• mAs controls DENSITY on radiograph primary
  function of mAs is DENSITY

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Imagine this

• If the mA station is changed from 200 to 400 mA,
  twice as many electrons will flow from the
  cathode to the anode.
• From 10 mA to 1000 mA 100 x more
• mA controls how many electrons are coming at the
  target
• mAs is a combination of how many and for how long
  (seconds)

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10 mA
1000 mA
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Changing Mas Changes Density
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50 mas
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Influencing Factor on DensitykVp
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??? kVp more energy more photons passing though
tissue striking the image

• 15 kVp doubling of exposure to the film
• ? 15 kVp halving of exposure to the film
• 15 rule will also change the contrast of the
  image because kV is the primary method of
  changing image contrast.
• Remember
• 15 change ( ??) KVP has the same effect as
  doubling or ½ the MAS on density

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Change in kVp

• kVp controls the energy level of the electrons
  and subsequently the energy of the x-ray photons.
• A change from 72 kVp will produce
• x-rays with a lower energy than at
• 82 kVp
• Difference between a ball traveling 72 mph and 82
  mph (how much energy did it take to throw the
  ball at the rates?)

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15 kvp - 15 kvp
This will also influence the density on the image
Increasing kVp increase energy reaching the IR
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Radiolucent vs. Radiopaque

• Radiolucent materials allow x-ray photons to pass
  through easily (soft tissue).
• Radiopaque materials are not easily penetrated by
  x-rays (bones)

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Creating the Image

• Transmission (no interaction)
• Responsible for dark areas
• Scatter (grays) produces no diagnostic info
• Absorption (photoelectric effect)
• Responsible for light areas

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Images

• DENSITY THE AMOUNT OF BLACKENING DARKNESS ON
  THE RADIOGRAPH (mAs)
• CONTRAST THE DIFFERENCES BETWEEN THE BLACKS TO
  THE WHITES (kVp)

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Why you see what you see

• The films or images have different levels of
  density different shades of gray
• X-rays show different features of the body in
  various shades of gray.
• The gray is darkest in those areas that do not
  absorb X-rays well and allow it to pass through
• The images are lighter in dense areas (like
  bones) that absorb more of the X-rays.

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Image Production

• Primary Radiation The beam of photons, B4 it
  interacts with the pts body.
• Remnant Radiation The resulting beam that is
  able to exit from the patient.
• Scatter Radiation Radiation that interacts with
  matter only continues in a different direction
  not useful for image production.
• Attenuation Primary radiation that is changed
  (partially absorbed) as it travels through the pt.

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Patient Body Size and Pathology
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3 Different Body HabitusHypersthenic Sthenic
Hyposthenic
Dr. Charman,
Eric Guzman, Adam
Guzman
Thank you to the 3 men in my life ! ? DCharman
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PATHOLOGY Pleural Effusion Excessive fluid in
lung More dense than air
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pneumonia
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The right lung is almost completely
collapsed vascular shadows can not be seen in
this area (arrow).
Lung collapses No tissue in space Easy to
penetrate with x-ray photons
pneumothorax
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LUNGCancer
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LUNG CANCER
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Density and Images
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Goal Producing optimal radiographsDENSITY
Too dark Too light
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Controlling Factor ofContrast
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Controlling Factor of Contrast

• Kilovolts to anode side kVp
• Kilovolts controls how fast the electrons are
  sent across the tube
• kVp controls CONTRAST on images

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Producing optimal radiographsContrast Scale
Long scale short scale
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Scale of Contrast?
Which one is better
How does the kVp affect these images?
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Short Scale vs. Long Scale
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Beam Restriction and Grids
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Scatter

• Creates fog
• Lowers contrast (more grays)
• Increases as
• kV increases
• Field size increases
• Thickness of part increases

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Effects of collimation (beam restriction) on
scatter
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• Collimate to area of interest -reduces scatter
  and radiation dose to the patient

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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

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GRID NO GRIDCONTROLS CONTRAST
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Basic Grid Construction

• Radiopaque lead strips
• Separated by radiolucent interspace material -
  Typically aluminum
• Allow primary radiation to reach the image
  receptor (IR)
• Absorb most scattered radiation
• Primary disadvantage of grid use
• Grid lines on film

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GRIDS
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Grid is placedbetween patient (behind table or
upright bucky) cassette
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Grids absorb scatter prevents it from reaching
the image
GRID STOPS SCATTER
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Contrast changes with the use of a grid Less
scatter radiation shorter scale better
contrast
With Grid No Grid
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GRIDS CAN LEAVE LINES ON THE IMAGE
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GEOMETRIC Properties

• Recorded Detail
• DISTORTION
• Size distortion
• Magnification
• Shape distortion
• Elongation
• Foreshortening

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RECORDED DETAIL
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RECORDED DETAIL

• The degree of sharpness in an objects borders
  and structural details.
• How clear the object looks on the radiograph

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Recorded Detail

• The degree of sharpness in an objects borders
  and structural details.
• Other names
• -sharpness of detail
• -definition
• -resolution
• -degree of noise

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RESOLUTION TEST TOOLS
LINE PAIRS/ MM Depicts how well you can see the
differences in structures More linesmore detail
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Factors that affectRecorded Detail

• Geometric unsharpness
• OID SID SIZE SHAPE
• Motion unsharpness (blurring)
• Intensifying Screens
• Film Speed / Composition
• Film Screen contact
• Kvp Mas (density / visibility)

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MOTION AKABlurring
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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

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Decrease Motion Unsharpness

• Instruct patient not to move or breath
• Use Immobilization devices
• Use Short exposure times
• Lock equipment in place

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Blurring of image due to patient movement during
exposure.
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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

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SID Source to Image Distance

• The greater the source X-ray tube) to image
  (cassette) distance, the greater the image
  sharpness.
• Standard distance 40 in. most exams
• Exception Chest radiography 72 in.

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The SID will influence magnification. The
farther away the less magnified ?SID ?
MAGNIFICATION
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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.

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OIDObject 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.

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The position of the structure in the body will
influence how magnified it will be seen on the
image The farther away the more magnified
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Distortion

• Misrepresentation of the true size or shape of an
  object
• MAGNIFICATION
• size distortion
• TRUE DISTORTION
• shape distortion

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MAGNIFICATION

• TUBE CLOSE TO THE PART (SID)
• PART FAR FROM THE CASSETTE (OID)

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• http//www.coursewareobjects.com/objects/mroimagin
  g_v1/mod04i/0416a.htm

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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

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

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Minimal magnification small OID
Magnification - large OID
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Size Distortion SID

• Major influences SID OID
• As SID ?, magnification ?
• Standardized SIDs allow radiologist to assume
  certain amt. of magnification factors are present
• Must note deviations from standard SID

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40 SID VS 72 SID
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SHAPE DISTORTIONElongationand Foreshortening
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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

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A goodB C shape distortion
(elongation of part)
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D E shape distortion (foreshortening of
part)
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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
• CR should be at right angle with the cassette

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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.

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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 beams periphery travel at an
  angle
• When central ray in angled, image shape is
  distorted.

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Elongation Foreshortened Normal
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Distortion (x-ray beam not centered over object
film)
Distortion (object film not parallel)
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Distortion of multiple objects in same image
(right) due to x-ray beam not being centered over
objects.
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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

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ANODE
ANODE
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THE SMALLER THE BEAM TOWARDS THE PATIENT - THE
BETTER THE DETAIL OF THE IMAGE PRODUCED
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FOCAL SPOT ANGLE
SMALLER ANGLE SMALLER BEAM AT
PATIENT
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ARTIFACTSAN UNWANTED DENSITYON THE FILM
http//www.xray2000.co.uk/
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Artifacts - Types

• Processing Artifacts
• Exposure Artifacts
• Handling Storage Artifacts

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Processing Artifacts

• Emulsion pickoff
• Chemical fog
• Guide-shoe marks
• Water marks
• Chemical spots
• Guide-shoe roller scratches

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Developer Spots
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Water spot
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Discolored film due to hypo (fixer)
retention. Chemicals not washed off over time
will turn film brown
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Scratch marks from rollers in automatic processor.
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Exposure Artifacts

• Motion
• Improper patient position
• Wrong screen-film match
• Poor film/screen contact
• Double exposure
• Warped cassette
• Improper grid position

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Artifact
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Blurred image due to patient motion
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PATIENT ARTIFACT - JEWERLY
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Handling Storage Artifacts

• Light fog
• Radiation fog
• Static
• Kink marks
• Scratches
• Dirty cassettes

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Crimping /cresent mark
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Double Exposure 2 exposures made on top of each
other from poor handling of cassettes
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Static electricity
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Dirt on screen mimicking a foreign object.
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Scratch marks from improper handling.
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Light fog
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Kink mark or nail pressure mark
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cast
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POOR SCREEN CONTACT
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Patient motion
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motion
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Double exposureChild
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Poorscreen contact
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Double exposure
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Hands over upper abdomen
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Is itmotion or double exposure?
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Pt clothing
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Hip replacement
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2 chest tubes in the patient
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Patient swallowed batteries What size are they?
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PATHOLOGY NOT ARTIFACT
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Name causeof this?
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scratches
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Digital image Mis- Registration error
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Roller marks from film stuck then pulled from
processor
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Hardware In cervical spine
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• Dust in imaging plate can cause white marks on
  image
• Both in film/screen and computed radiography

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E E G MONITOR
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What do you See? 2 exposures
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Evaluating Images

• What do you think?

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• Does this show good detail?
• Is all of the anatomy present?
• How is the density / contrast?

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• Does this show good detail?
• YES
• Is all of the anatomy present?
• No (part of the little finger is not seen)
• How is the density / contrast?
• Density a little light underexposed
• Contrast is good

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See anythingwrong with this image?
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Contrast? What influences this? (kVp in f/s)
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Collimation reducing the size of beamhelps to
improve the image, and reduce the dose to the
patient
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?