IMAGE QUALITY IMAGE QUALITY REVIEWREVIEW
RT 244 2007RT 244 2007
What affects DENSITYWhat affects DENSITYon the radiographic on the radiographic image?image?
Factors Affecting mAs Factors Affecting mAs & Density& Density Patient factors:Patient factors:
– size of pt., density / pathology of tissuesize of pt., density / pathology of tissue kVpkVp CollimationCollimation DistanceDistance GridsGrids Film/Screen Combinations Film/Screen Combinations Processing Processing
Factors Affecting mAsFactors Affecting mAs
Patient factors: size of pt., density Patient factors: size of pt., density of tissue, pt. complianceof tissue, pt. compliance
kVpkVp DistanceDistance GridsGrids Film/Screen CombinationsFilm/Screen Combinations ProcessingProcessing
Influences technique & Influences technique & density on imagedensity on image
Patient’s Body Habitus Patient’s Body Habitus (size)(size)
PATHOLOGY
?
pneumothorax
Lung collapses
No tissue in space
Easy to penetrate with x-ray photons
LUNGLUNGCancerCancer
DON’T !
WE WANT
YOU
HEALTHY
&
NOT
SMELLY !
LUNG CANCERLUNG CANCER
Creating the ImageCreating the Image
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
Effects of collimation Effects of collimation on scatteron scatter
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
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
Grid is placedGrid is placedbetween patient (behind table between patient (behind table or upright bucky) & cassetteor upright bucky) & cassetteIf placed BACWARDS CAN CAUSE If placed BACWARDS CAN CAUSE GRID ERRORSGRID ERRORS
GRIDS GRIDS CAN CAN
LEAVE LEAVE LINESLINES
ON THE ON THE IMAGE IMAGE
DETAIL & Quality :DETAIL & Quality :How well we can see something on the imageHow well we can see something on the image
DETAILDETAIL
The 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
Recorded DetailRecorded Detail
The degree of sharpness in an The degree of sharpness in an object’s borders and structural object’s borders and structural details.details.
Other names:Other names:
-sharpness of detail-sharpness of detail
-definition-definition
-resolution-resolution
-degree of -degree of noisenoise
2 principal characteristics 2 principal characteristics of any image are of any image are Spatial & Contrast Spatial & Contrast ResolutionResolution Spatial resolution Spatial resolution
– Resolution is the ability to image two Resolution is the ability to image two separate objects and visually separate objects and visually distinguish one from the otherdistinguish one from the other
– Spatial resolution is the ability to Spatial resolution is the ability to image small objects that have high image small objects that have high subject contrast (eg. bone-soft subject contrast (eg. bone-soft tissue interface, calcified lung tissue interface, calcified lung nodules)nodules)
2 principal characteristics 2 principal characteristics of any image areof any image are Spatial & Contrast Spatial & Contrast ResolutionResolution Spatial resolution Spatial resolution
– Determined by focal-spot size and Determined by focal-spot size and other factors that contribute to blurother factors that contribute to blur
– Diagnostic x-ray has excellent Diagnostic x-ray has excellent spatial resolution. It is measured in spatial resolution. It is measured in line pairs per mm. line pairs per mm. (CT measured in cm)(CT measured in cm)
Factors that affect the Factors that affect the detail of an imagedetail of an image
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 / CompostionFilm Speed / Compostion Film – Screen contactFilm – Screen contact Kvp & Mas (density / visibility)Kvp & Mas (density / visibility)
Main Factors Affecting Main Factors Affecting Recorded DetailRecorded Detail kVp & mAskVp & mAs MotionMotion Object UnsharpnessObject Unsharpness Focal Spot SizeFocal Spot Size SID (Source to Image Distance)SID (Source to Image Distance) OID (Object to Image Distance)OID (Object to Image Distance) Material UnsharpnessMaterial Unsharpness
GEOMETRIC QUALITIESGEOMETRIC QUALITIES
DETAILDETAIL
DISTORTIONDISTORTION
MAGNIFICATIONMAGNIFICATION
RESOLUTION TEST
TOOLS
LINE PAIRS/ MM
Depits how well you can see the differences in structures
More lines=more detail
POOR POOR
DETAILDETAIL
GOOD GOOD DETAILDETAIL
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 Use of careful instructions to the
pt.pt. Suspension of pt. respirationSuspension of pt. respiration Immobilization devicesImmobilization devices
Decrease Motion Decrease Motion UnsharpnessUnsharpness Instruct patient not to move or Instruct patient not to move or
breathbreath Use Immobilization devicesUse Immobilization devices Use Short exposure timesUse Short exposure times Lock equipment in placeLock equipment in place
Blurring of image due to patient movement during exposure.
Object UnsharpnessObject Unsharpness
Main problem is trying to image a Main problem is trying to image a 3-D object on a 2-D film.3-D object on a 2-D film.
Human body is not straight edges Human body is not straight edges and sharp angles.and 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
SID SID Source to Image DistanceSource to Image Distance
The greater the distance between the The greater the distance between the source of the x-ray (tube) and the source of the x-ray (tube) and the image receptor (cassette), the greater image receptor (cassette), the greater the image sharpness.the image sharpness.
Standard distance = 40 in. most Standard distance = 40 in. most examsexams
Exception = Chest radiography 72 in.Exception = Chest radiography 72 in.
*See page 74 in your book*See page 74 in your book
The position of the tube (SID) to IR Will influence how the structures appear on the image The farther away – the less magnified ↑SID ↓ MAGNIFICATION
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 true Penumbra (fuzziness) obscures true border – border – umbraumbra
Farther the flashlight from object = Farther the flashlight from object = sharper borders. Same with sharper borders. Same with radiography.radiography.
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 radiographer must know how to position to get the object closest to the position to get the object closest to the film.film.
*See page 74 in your book*See page 74 in your book
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
Focal spot size – determined by filament in cathode & surface area used at anode
DistortionDistortion
Misrepresentation of the true size Misrepresentation of the true size or shape of an objector shape of an object
--MAGNIFICATIONMAGNIFICATION (size (size distortion)distortion)
--TRUE DISTORTION TRUE DISTORTION (shape (shape distortion)distortion)
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)
In terms of recorded detail and magnification, the best image is produced with a small OID and a large SID.
40” SID VS 72” SID 40” SID VS 72” SID
MAGNIFICATION MAGNIFICATION PROBLEMSPROBLEMS
SIDSID
SODSOD
SID – OID = SODSID – OID = SOD
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
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
A = goodA = goodB & C = shape distortionB & C = shape distortion (elongation of part) (elongation of part)
D & E = D & E = shape distortionshape distortion (foreshortening of part) (foreshortening of part)
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
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 partperpendicular to the part
Elongation Foreshortened NormalElongation Foreshortened Normal
Distortion (object & film not parallel)
Distortion (x-ray beam not centered over object & film)
Central RayCentral Ray
Radiation beam diverges from the Radiation beam diverges from the tube in a pyramid shape.tube in a pyramid shape.
Photons in the center travel along Photons in the center travel along a straight line – a straight line – central raycentral ray
Photons along the beam’s Photons along the beam’s periphery travel at an angleperiphery travel at an angle
When central ray in angled, When central ray in angled, image shape is distorted.image shape is distorted.
Distortion of multiple objects in same image (right) due to x-ray beam not being centered over objects.
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 Body part rotation or obliquing the body can also help visualize the body can also help visualize superimposed anatomy.superimposed anatomy.
Main Factors Affecting Main Factors Affecting Recorded DetailRecorded Detail
kVp & mAskVp & mAs MotionMotion Object UnsharpnessObject Unsharpness Focal Spot SizeFocal 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
ComboCombo
Factors Affecting mAsFactors Affecting mAs
Patient factors: size of pt., density Patient factors: size of pt., density of tissue, pt. complianceof tissue, pt. compliance
kVpkVp DistanceDistance GridsGrids Film/Screen CombinationsFilm/Screen Combinations ProcessingProcessing
Focal Spot SizeFocal Spot Size
Smaller x-ray beam width will produce Smaller x-ray beam width will produce a sharper image.a sharper image.
Fine detail = small focal spot (i.e. Fine detail = small focal spot (i.e. small bones)small 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
*See page 73 in your book*See page 73 in your book
ANODE
ANODE
THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED
FOCAL SPOT ANGLEFOCAL SPOT ANGLE
SMALLER ANGLE – SMALLER BEAM AT PATIENT
REVIEWREVIEWIntensifying ScreensIntensifying Screensand Filmand Film
““Fast” Screen Fast” Screen CassettesCassettes Equipment used can contribute Equipment used can contribute
to image unsharpnessto image unsharpness Fast film/screen combinations Fast film/screen combinations
= decrease in image = decrease in image sharpnesssharpness
Slower film/screen Slower film/screen combinations = increase in combinations = increase in image sharpnessimage sharpness
Fast screen vs Slower Fast screen vs Slower screenscreen
QUANTUM MOTTLEQUANTUM MOTTLE Not enough PHOTONS – can create a mottled Not enough PHOTONS – can create a mottled or grainy image - or grainy image - MORE COMMON IN CR MORE COMMON IN CR SYSTEMSSYSTEMS
SAME TECHNIQUE CHANGE IN SAME TECHNIQUE CHANGE IN SCREEN SPEEDSCREEN SPEED
SLOWER FASTER
CASSETTES with CASSETTES with IntensifyingIntensifying
Screens Screens
The CASSETTE The CASSETTE holds the film in a holds the film in a light tight containerlight tight container
It consist of front It consist of front and back and back intensifying screensintensifying screens
Intensfying screensIntensfying screens
Lower patient dose (less photons Lower patient dose (less photons needed)needed)
Changes resolution of imageChanges resolution of image
Slow screens less LIGHT = better detailSlow screens less LIGHT = better detail
Faster – less detail (more blurring on Faster – less detail (more blurring on edges)edges)
Intensifying Screens:Intensifying Screens:
Located inside the Located inside the cassette (film holder)cassette (film holder)
Contains Phosphors:Contains Phosphors: Calcium TungstateCalcium Tungstate
– Blue to purple lightBlue to purple light Rare EarthRare Earth
– Green & Ultraviolet Green & Ultraviolet lightlight
CHANGING CR SPEEDCHANGING CR SPEED
F/S SPEED CHANGESF/S SPEED CHANGES
CR SPEED CLASSCR SPEED CLASS
WIDER LATITUDE & WIDER LATITUDE & DYNAMIC RANGE WITH DYNAMIC RANGE WITH CRCR
POOR SCREEN POOR SCREEN CONTACTCONTACT FOAM BACKING HELPS TO PLACE FOAM BACKING HELPS TO PLACE
INTENSIFYING SCREENS IN INTENSIFYING SCREENS IN DIRECT CONTACT WITH THE FILM DIRECT CONTACT WITH THE FILM – NO GAPS– NO GAPS
IF GAPS – MORE LIGHT CAN BE IF GAPS – MORE LIGHT CAN BE EMITTED IN SPACE, CAUSING THE EMITTED IN SPACE, CAUSING THE IMAGE TO BE OF POOR DETAILIMAGE TO BE OF POOR DETAIL
Tight contact needed Tight contact needed between film & between film & screensscreens
WIRE MESHWIRE MESHSCREEN CONTACT SCREEN CONTACT TESTTEST
When there is a space between the contact When there is a space between the contact of the film to the intensifying screens, a of the film to the intensifying screens, a larger amount of light is allowed to reach larger amount of light is allowed to reach the film – causing “more density” on fimthe film – causing “more density” on fim
Lack of contact between film and cassette can cause “blurring” of the image
LOADING FILM IN LOADING FILM IN CASSETTECASSETTE
IMAGE ON FILMIMAGE ON FILM SINGLE EMULSION = BETTER DETAILSINGLE EMULSION = BETTER DETAIL
DOUBLE EMULISON = LESS DETAILDOUBLE EMULISON = LESS DETAIL
PARALLAX PARALLAX
With double emulsion – an image is With double emulsion – an image is created on both emulsions – then created on both emulsions – then superimposed – slight blurring of edgessuperimposed – slight blurring of edges
PARALLAX –PARALLAX –each emulsion has an imageeach emulsion has an imagesingle image overlaped single image overlaped edges edges edge sharp less sharpedge sharp less sharp
Film CharacteristicsFilm Characteristics (more in week 9) (more in week 9)
Film contains silver halide Film contains silver halide crystalscrystals
2 layers – emulsion & base2 layers – emulsion & base emulsion thickness determine emulsion thickness determine
speed of film and degree of speed of film and degree of resolutionresolution
Speed – the response to photonsSpeed – the response to photons Resolution – the detail seenResolution – the detail seen
Film Speed / Crystal Film Speed / Crystal sizesize Larger crystals or Thicker crystal Larger crystals or Thicker crystal
layerlayer
Faster response= less detail, andFaster response= less detail, and
less exposure (chest x-ray)less exposure (chest x-ray) Finer crystals / thinner crystal layerFiner crystals / thinner crystal layer
=Slower response, greater =Slower response, greater detail, more exposure (extremity)detail, more exposure (extremity)
Processing FilmProcessing Film (wk 10)(wk 10)
Film contains silver crystals Film contains silver crystals If crystals exposed to photons – If crystals exposed to photons –
will convert to black after placed will convert to black after placed in processing chemicalsin processing chemicals
If not exposed – will remain clear If not exposed – will remain clear on filmon film
Goal : Produce Goal : Produce Optimal Images for Optimal Images for diagnosisdiagnosis
Too dark too light
Out of focus good image