1 Components of Image Quality & Radiographic Artifacts Radiologic Technology A SPRING 2012.
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Transcript of 1 Components of Image Quality & Radiographic Artifacts Radiologic Technology A SPRING 2012.
11
Components of Components of Image Quality Image Quality
& & Radiographic Radiographic
ArtifactsArtifacts
Radiologic Technology ARadiologic Technology A
SPRING 2012SPRING 2012
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X-ray Exposure FactorsX-ray Exposure Factors
Radiographic Density & ContrastRadiographic Density & Contrast
Components of Components of Image Quality Image Quality
Radiographic ArtifactsRadiographic Artifacts
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Review Review
Primary radiation exits the tubePrimary radiation exits the tube
Interacts with various densities in the body Interacts with various densities in the body
Photons may be absorbedPhotons may be absorbed
Scattered Scattered
Passed through without any interference Passed through without any interference to the cassette or image receptor (IR)to the cassette or image receptor (IR)
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How well we can see something on the imageHow well we can see something on the image
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Image detail Image detail is affected by:is affected by:
Photographic Photographic propertiesproperties
and and Geometric propertiesGeometric properties
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Photographic Photographic PropertiesProperties
1.1.Contrast Contrast
2.2.DensityDensity
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Factors Affecting Factors Affecting DensityDensity Primary control factorPrimary control factor
– mAmA– Time (seconds)Time (seconds)
Influencing factorsInfluencing factors– kVpkVp– GridsGrids– Beam restrictionBeam restriction– Body structures (size of pt, pathologyBody structures (size of pt, pathology– ProcessingProcessing– SID & OIDSID & OID– Film Screen combinations Film Screen combinations
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Primary Controlling Primary Controlling Factor of DensityFactor of Density mAs mAs
mA = mA = AMOUNTAMOUNT of electrons sent of electrons sent across the tube combined with TIME across the tube combined with TIME (S) = mAs(S) = mAs
mAs controls mAs controls DENSITY DENSITY on radiographon radiograph primary function of mAs is DENSITYprimary function of mAs is DENSITY
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Imagine this…Imagine this… If the mA station is changed from 200 to If the mA station is changed from 200 to
400 mA, twice as many electrons will 400 mA, twice as many electrons will flow from the cathode to the anode.flow from the cathode to the anode.
From 10 mA to 1000 mA = 100 x moreFrom 10 mA to 1000 mA = 100 x more
mA controls mA controls how manyhow many electrons are electrons are coming at the targetcoming at the target
mAs is a combination of mAs is a combination of how manyhow many and and for for how longhow long (seconds)(seconds)
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10 mA 1000 mA
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Changing Mas – Changes DensityChanging Mas – Changes Density + 25 % + 50 % + 25 % + 50 % masmas
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Influencing Factor Influencing Factor on Density:on Density:
kVpkVp
1414
Change in kVpChange in kVp kVp controls the energy level of the kVp controls the energy level of the
electrons and subsequently the energy electrons and subsequently the energy of the x-ray photons.of the x-ray photons.
A change from 72 kVp will produceA change from 72 kVp will producex-rays with a lower energy than atx-rays with a lower energy than at82 kVp82 kVp
Difference between a ball traveling 72 Difference between a ball traveling 72 mph and 82 mph (how much energy did mph and 82 mph (how much energy did it take to throw the ball at the rates?)it take to throw the ball at the rates?)
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+ 15% kvp - 15% + 15% kvp - 15% kvpkvp
Increasing kVp = increase energy reaching the IR
This will also influence the density on the image
1616
Radiolucent vs. Radiolucent vs. RadiopaqueRadiopaque
RadiolucentRadiolucent materials materials allow x-ray photons to pass allow x-ray photons to pass through easily (soft tissue).through easily (soft tissue).
RadiopaqueRadiopaque materials are materials are not easily penetrated by x-not easily penetrated by x-rays (bones)rays (bones)
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Creating the ImageCreating the Image
1.1. Transmission Transmission – no interactionno interaction– Responsible for Responsible for
dark areasdark areas2.2. ScatterScatter
1.1. (grays) – produces (grays) – produces no diagnostic infono diagnostic info
3.3. AbsorptionAbsorption1.1. (photoelectric (photoelectric
effect)effect)– Responsible for Responsible for
light areaslight areas
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ImagesImages
DENSITYDENSITY = THE AMOUNT OF = THE AMOUNT OF BLACKENING “DARKNESS” ON BLACKENING “DARKNESS” ON THE RADIOGRAPH (mAs)THE RADIOGRAPH (mAs)
CONTRASTCONTRAST – THE DIFFERENCES – THE DIFFERENCES BETWEEN THE BLACKS TO THE BETWEEN THE BLACKS TO THE WHITES (kVp)WHITES (kVp)
1919
Why you see what you Why you see what you see…see… The films or images have different levels of The films or images have different levels of
density – different shades of graydensity – different shades of gray
X-rays show different features of the body in X-rays show different features of the body in various shades of gray. various shades of gray.
The gray is darkest in those areas that do not The gray is darkest in those areas that do not absorb X-rays well – and allow it to pass absorb X-rays well – and allow it to pass throughthrough
The images are lighter in dense areas (like The images are lighter in dense areas (like bones) that absorb more of the X-rays.bones) that absorb more of the X-rays.
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Patient Body Size Patient Body Size and and
PathologyPathology
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3 Different Body Habitus3 Different Body HabitusHypersthenic Sthenic HyposthenicHypersthenic Sthenic Hyposthenic
Thank you to the 3 men in my life ! DCharman
Dr. Charman, Eric Guzman, Adam Guzman
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PATHOLOGY Pleural Effusion Excessive
fluid in lung
More dense than air
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PneumoniaPneumonia
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The right lung is almost completely collapsed;
vascular shadows can not be seen in this area (arrow).
Pneumothorax
Lung collapses
No tissue in space
Easy to penetrate with x-ray photons
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LungLungCancerCancer
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LUNG CANCERLUNG CANCER
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Density and ImagesDensity and Images
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Goal: Producing optimal radiographsGoal: Producing optimal radiographs
DENSITYDENSITY
Too dark Too light
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Controlling Factor ofControlling Factor ofContrastContrast
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Controlling Factor of Controlling Factor of ContrastContrast
1.1. Kilovolts to anode side – kVpKilovolts to anode side – kVp
2.2. Kilovolts controls Kilovolts controls how fasthow fast the the electrons are sent across the tubeelectrons are sent across the tube
3.3. kVp – controls kVp – controls CONTRAST CONTRAST on on imagesimages
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Producing optimal radiographsContrast Scale
Long scale short scale
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Scale of Contrast?Scale of Contrast? Which one is “better” Which one is “better” How does the kVp affect these How does the kVp affect these images?images?
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Beam Restriction Beam Restriction and and GridsGrids
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ScatterScatter
– Creates fogCreates fog– Lowers contrast (more grays)Lowers contrast (more grays)
Increases as Increases as – kV increaseskV increases– Field size increasesField size increases– Thickness of part increasesThickness of part increases
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Effects of collimation Effects of collimation (beam restriction) on (beam restriction) on scatterscatter
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Collimate to Collimate to area of interest area of interest -reduces -reduces scatter and scatter and radiation dose radiation dose to the patientto the patient
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GridsGrids
A device with lead strips that is A device with lead strips that is placed between the patient and placed between the patient and the cassettethe cassette
Used on larger body parts to Used on larger body parts to reduce the number of scattering reduce the number of scattering photons from reaching the imagephotons from reaching the image
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Basic Grid Basic Grid ConstructionConstruction
• Radiopaque lead stripsRadiopaque lead strips
• Separated by radiolucent interspace Separated by radiolucent interspace material - Typically aluminummaterial - Typically aluminum
Allow primary radiation to reach the Allow primary radiation to reach the image receptor (IR)image receptor (IR)
Absorb most scattered radiationAbsorb most scattered radiation
Primary disadvantage of grid use Primary disadvantage of grid use – Grid lines on filmGrid lines on film
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GRIDSGRIDS
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Grid is placedGrid is placedbetween patient (behind between patient (behind table or upright bucky) & table or upright bucky) & cassettecassette
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Grids absorb scatter –Grids absorb scatter –prevents it from reaching prevents it from reaching the imagethe 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 GRIDS CAN CAN
LEAVE LEAVE LINESLINES
ON THE ON THE IMAGE IMAGE
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GEOMETRIC PropertiesGEOMETRIC Properties1.1. Recorded DetailRecorded Detail
2.2. DISTORTIONDISTORTION1.1. Size Size distortion distortion
1.1. MagnificationMagnification
2.2. ShapeShape distortion distortion1.1. Elongation Elongation 2.2. ForeshorteningForeshortening
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RECORDED DETAILRECORDED DETAIL
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RECORDED DETAILRECORDED DETAILThe degree of sharpness The degree of sharpness in an object’s borders in an object’s borders and structural details.and structural details.
How “clear” the object How “clear” the object looks on the radiographlooks on the radiograph
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Recorded DetailRecorded Detail
The degree of sharpness in an object’s The degree of sharpness in an object’s borders and structural details.borders and structural details.
Other names:Other names:
-sharpness of detail-sharpness of detail
-definition-definition
-resolution-resolution
-degree of -degree of noisenoise
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RESOLUTION TEST
TOOLS
LINE PAIRS/ MM
Depicts how well you can see the differences in structures
More lines=more detail
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Factors that affectFactors that affectRecorded DetailRecorded Detail Geometric unsharpnessGeometric unsharpness
OID SID SIZE SHAPEOID SID SIZE SHAPE Motion unsharpness (blurring)Motion unsharpness (blurring) Intensifying Screens Intensifying Screens Film Speed / CompositionFilm Speed / Composition Film – Screen contactFilm – Screen contact Kvp & Mas (density / visibility)Kvp & Mas (density / visibility)
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MOTION MOTION
AKAAKA
BlurringBlurring
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MotionMotion Can be voluntary or involuntaryCan be voluntary or involuntary
Best controlled by short exposure Best controlled by short exposure timestimes
Use of careful instructions to the pt.Use of careful instructions to the pt.
Suspension of pt. respirationSuspension of pt. respiration
Immobilization devicesImmobilization devices
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Decrease Motion Decrease Motion UnsharpnessUnsharpness
1.1. Instruct patient not to move or Instruct patient not to move or breathbreath
2.2. Use Immobilization devicesUse Immobilization devices
3.3. Use Short exposure timesUse Short exposure times
4.4. Lock equipment in placeLock equipment in place
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Blurring of image due to patient movement during exposure.
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Object UnsharpnessObject Unsharpness
Main problem is trying to image a 3-D Main problem is trying to image a 3-D object on a 2-D film.object on a 2-D film.
Human body is not straight edges and Human body is not straight edges and sharp angles.sharp angles.
We must compensate for object We must compensate for object unsharpness with factors we can unsharpness with factors we can control: focal spot size, SID & OIDcontrol: focal spot size, SID & OID
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SID SID Source to Image DistanceSource to Image Distance
The greater the source X-ray tube) The greater the source X-ray tube) to image (cassette) distance, the to image (cassette) distance, the greater the image sharpness.greater the image sharpness.
Standard distance = 40 in. most Standard distance = 40 in. most examsexams
Exception = Chest radiography 72 Exception = Chest radiography 72 in.in.
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The SID will influence magnification. The farther away – the less magnified
↑SID ↓ MAGNIFICATION
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SIDSID Shine a flashlight on a 3-D object, Shine a flashlight on a 3-D object,
shadow borders will appear “fuzzy” shadow borders will appear “fuzzy” -On a radiograph called -On a radiograph called
PenumbraPenumbra
Penumbra (fuzziness) obscures Penumbra (fuzziness) obscures true border – true border – umbraumbra
Farther the flashlight from object = Farther the flashlight from object = sharper borders. Same with sharper borders. Same with radiography.radiography.
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OIDOIDObject to Image DistanceObject to Image Distance The closer the object to the film, the The closer the object to the film, the
sharper the detail.sharper the detail.
OID OID , penumbra , penumbra , sharpness , sharpness OID OID , penumbra , penumbra , sharpness , sharpness
Structures located deep in the body, Structures located deep in the body, radiographer must know how to position radiographer must know how to position to get the object closest to the film.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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DistortionDistortion Misrepresentation of the true size Misrepresentation of the true size
or shape of an objector shape of an object
– MAGNIFICATIONMAGNIFICATION – size distortionsize distortion
– TRUE DISTORTION TRUE DISTORTION – shape distortionshape distortion
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MAGNIFICATIONMAGNIFICATION
TUBE CLOSE TO THE PART (SID)TUBE CLOSE TO THE PART (SID)
PART FAR FROM THE CASSETTE PART FAR FROM THE CASSETTE (OID)(OID)
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http://http://www.coursewareobjects.com/www.coursewareobjects.com/objects/mroimaging_v1/mod04i/objects/mroimaging_v1/mod04i/0416a.htm0416a.htm
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Size Distortion & OIDSize Distortion & OID
If source is kept constant, OID will If source is kept constant, OID will affect magnificationaffect magnification
As OID As OID , magnification , magnification
The farther the object is from the The farther the object is from the film, the more magnification 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
7676Minimal magnification small OID
Magnification - large OID
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Size Distortion & SIDSize Distortion & SID Major influences: SID & OIDMajor influences: SID & OID
As SID As SID , magnification , magnification
Standardized SID’s allow Standardized SID’s allow radiologist to assume certain amt. radiologist to assume certain amt. of magnification factors are of magnification factors are presentpresent
Must note deviations from Must note deviations from standard SIDstandard SID
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8080
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40” SID VS 72” SID 40” SID VS 72” SID
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SHAPE DISTORTIONSHAPE DISTORTION
ElongationElongation
and and
ForeshorteningForeshortening
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Shape DistortionShape Distortion
Misrepresentation of the shape of Misrepresentation of the shape of an objectan object
Controlled by alignment of the Controlled by alignment of the beam, part (object), & image beam, part (object), & image receptorreceptor
Influences: Central ray angulation Influences: Central ray angulation & body part rotation& body part rotation
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A = goodA = goodB & C = shape distortionB & C = shape distortion (elongation of part) (elongation of part)
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D & E = D & E = shape distortionshape distortion (foreshortening of part) (foreshortening of part)
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Image DistortionImage Distortion
When the part to be imaged – When the part to be imaged – does not lay parallel with the IR does not lay parallel with the IR (cassette)(cassette)
If the Central Ray is not If the Central Ray is not perpendicular to the part perpendicular to the part – CR should be at right angle with the CR should be at right angle with the
cassettecassette
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Central Ray AngulationCentral Ray Angulation Body parts are not always 90 Body parts are not always 90
degrees from one anotherdegrees from one another
Central ray angulation is used to Central ray angulation is used to demonstrate certain details that demonstrate certain details that can be hidden by superimposed can be hidden by superimposed body parts.body parts.
Body part rotation or obliquing the Body part rotation or obliquing the body can also help visualize body can also help visualize superimposed anatomy.superimposed anatomy.
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Central RayCentral Ray Radiation beam diverges from the tube Radiation beam diverges from the tube
in a pyramid shape.in a pyramid shape.
Photons in the center travel along a Photons in the center travel along a straight line – straight line – central raycentral ray
Photons along the beam’s periphery Photons along the beam’s periphery travel at an angletravel at an angle
When central ray in angled, image When central ray in angled, image shape is distorted.shape is distorted.
9090
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Elongation Foreshortened Elongation Foreshortened NormalNormal
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Distortion (object & film not parallel)
Distortion (x-ray beam not centered over object & film)
9696
Distortion of multiple objects in same image (right) due to x-ray beam not being centered over objects.
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Focal Spot SizeFocal Spot Size
Smaller x-ray beam width will produce a Smaller x-ray beam width will produce a sharper image.sharper image.
Fine detail = small focal spot (i.e. small Fine detail = small focal spot (i.e. small bones)bones)
General radiography uses large focal General radiography uses large focal spotspot
Beam from penlight size flashlight vs. Beam from penlight size flashlight vs. flood light beamflood light beam
9898
ANODE
ANODE
9999
THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED
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FOCAL SPOT ANGLEFOCAL SPOT ANGLE
SMALLER ANGLE – SMALLER BEAM AT PATIENT
101101
ARTIFACTS:ARTIFACTS:AN UNWANTED DENSITYAN UNWANTED DENSITYON THE FILMON THE FILM
http://www.xray2000.co.uk/
102102
Artifacts - TypesArtifacts - Types
Processing ArtifactsProcessing Artifacts
Exposure ArtifactsExposure Artifacts
Handling & Storage Handling & Storage ArtifactsArtifacts
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Processing ArtifactsProcessing Artifacts
Emulsion pickoffEmulsion pickoff Chemical fogChemical fog Guide-shoe marksGuide-shoe marks Water marksWater marks Chemical spotsChemical spots Guide-shoe & roller scratchesGuide-shoe & roller scratches
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Developer Spots
105105Water 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.
108108
Exposure ArtifactsExposure Artifacts
MotionMotion Improper patient positionImproper patient position Wrong screen-film matchWrong screen-film match Poor film/screen contactPoor film/screen contact Double exposureDouble exposure Warped cassetteWarped cassette Improper grid positionImproper grid position
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ArtifactArtifact
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Blurred image due to patient motion
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PATIENT ARTIFACT - PATIENT ARTIFACT - JEWERLYJEWERLY
113113
Handling & Storage Handling & Storage ArtifactsArtifacts Light fogLight fog Radiation fogRadiation fog StaticStatic Kink marksKink marks ScratchesScratches Dirty cassettesDirty cassettes
114114
Crimping /cresent Crimping /cresent markmark
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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.
120120
Light fog
121121
Kink mark or nail pressure mark
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castcast
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POOR SCREEN POOR SCREEN CONTACTCONTACT
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Patient motionPatient motion
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motionmotion
126126
Double Double exposureexposure
ChildChild
127127
PoorPoorscreen screen contactcontact
128128
Double exposureDouble exposure
129129
??
130130
??
131131
132132
Pt clothing
133133
Hip replacement
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2 chest tubes in the patient
135135Patient swallowed batteriesWhat size are they?
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137137
PATHOLOGY NOT PATHOLOGY NOT ARTIFACTARTIFACT
138138
Name &Name & cause causeof this?of this?
139139
scratches
140140
Digital image
Mis-
Registration
error
141141
Roller marks from film stuck –
then pulled from processor
142142
Hardware
In cervical
spine
143143
Dust in imaging plate can Dust in imaging plate can cause white marks on cause white marks on image image
Both in film/screen and Both in film/screen and computed radiographycomputed radiography
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E E G MONITOR
145145
What do you
See?
2 exposures
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147147
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Evaluating ImagesEvaluating Images
What do you think?What do you think?
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See anythingSee anythingwrong wrong
with with this this
image?image?
150150
Contrast? What influences this? (kVp in Contrast? What influences this? (kVp in f/s)f/s)
151151
Collimation – reducing the size of beamCollimation – reducing the size of beamhelps to improve the image, and reduce the helps to improve the image, and reduce the dose to the patientdose to the patient
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?