Components of Radiographic Image Quality

Components of Components of

Radiographic ImageRadiographic ImageQualityQuality

Radiologic Technology 244Radiologic Technology 244created: Fall 2005created: Fall 2005

Rev 12-01-2009Rev 12-01-2009

Review handoutsReview handouts

Main Factors Affecting Main Factors Affecting Recorded DetailRecorded Detail

kVp & mAskVp & mAs Technique Selection (Time)Technique Selection (Time)

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 that affectFactors that affectRecorded DetailRecorded Detail

Geometric unsharpnessGeometric unsharpness

OID SID SIZE SHAPEOID SID SIZE SHAPEMotion unsharpness (blurring)Motion unsharpness (blurring) Intensifying Screens Intensifying Screens Film Speed / CompositionFilm Speed / CompositionFilm – Screen contactFilm – Screen contactKvp & Mas (density / visibility)Kvp & Mas (density / visibility)

GEOMETRIC QUALITIESGEOMETRIC QUALITIES

DETAILDETAIL

DISTORTIONDISTORTION

MAGNIFICATIONMAGNIFICATION

DETAILDETAIL

The degree of sharpness in The degree of sharpness in an object’s borders and an object’s borders and structural details.structural details.

How “clear” the object looks How “clear” the object looks on the radiographon the radiograph

Recorded DetailRecorded Detail

Other names:Other names:

-sharpness of -sharpness of detaildetail

-definition-definition

-resolution-resolution

-degree of -degree of noisenoise

What are these

What does they

measure?

Factors Affecting DENSITYFactors Affecting DENSITYPATIENT THICKNESS,PATHOLOGYPATIENT THICKNESS,PATHOLOGYMAS & KVPMAS & KVPSIDSID

POOR POOR

DETAILDETAIL

GOOD GOOD DETAILDETAIL

MotionMotionCan be voluntary or involuntaryCan be voluntary or involuntaryBest controlled by short exposure timesBest controlled by short exposure timesUse of careful instructions to the pt.Use of careful instructions to the pt.Suspension of pt. respirationSuspension of pt. respiration Immobilization devicesImmobilization devices

Decrease Motion UnsharpnessDecrease Motion Unsharpness

Instruct patient not to move or breathInstruct patient not to move or breathUse Immobilization devicesUse Immobilization devicesUse Short exposure timesUse Short exposure timesLock equipment in placeLock equipment in place

NAME 4 CAUSES

Blurring of image due to patient movement during exposure.

Focal Spot SizeFocal Spot Size

Smaller x-ray beam width will produce a sharper Smaller x-ray beam width will produce a sharper image.image.

Fine detail = small focal spot (i.e. small bones)Fine detail = small focal spot (i.e. small bones) General radiography uses large focal spotGeneral radiography uses large focal spot Beam from penlight size flashlight vs. flood light Beam from penlight size flashlight vs. flood light

beambeam

FOCAL SPOT ANGLEFOCAL SPOT ANGLE

Object UnsharpnessObject Unsharpness Main problem is trying Main problem is trying

to image a 3-D object to image a 3-D object on a 2-D film.on a 2-D film.

Human body is not Human body is not straight edges and straight edges and sharp angles.sharp angles.

We must compensate We must compensate for object for object unsharpness with unsharpness with factors we can factors we can control: focal spot control: focal spot size, SID & OIDsize, 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 image source of the x-ray (tube) and the image receptor (cassette), the greater the image receptor (cassette), the greater the image sharpness.sharpness.

Standard distance = 40 in. most examsStandard distance = 40 in. most examsException = Chest radiography 72 in.Exception = Chest radiography 72 in.

SIDSID

Shine a flashlight on a Shine a flashlight on a 3-D object, shadow 3-D object, shadow borders will appear borders will appear “fuzzy” “fuzzy”

On a radiograph it’s called On a radiograph it’s called ____________________________

A true border – A true border – __________ Farther the flashlight Farther the flashlight

from object = sharper from object = sharper borders. Same with 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 position to radiographer must know how to position to get the object closest to the film.get the object closest to the film.

DistortionDistortion

Misrepresentation of Misrepresentation of the true size or shape the true size or shape of an objectof an object

MAGNIFICATIONMAGNIFICATION (size (size distortion)distortion)

TRUE DISTORTION TRUE DISTORTION (shape (shape distortion)distortion)

Shape DistortionShape Distortion

Misrepresentation of the shape of an Misrepresentation of the shape of an objectobject

Controlled by alignment of the beam, part Controlled by alignment of the beam, part (object), & image receptor(object), & image receptor

Influences: Central ray angulation & body Influences: Central ray angulation & body part rotationpart rotation

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 tube in Radiation beam diverges from the tube in a pyramid shape.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 travel Photons along the beam’s periphery travel at an angleat an angle

When central ray in angled, image shape When central ray in angled, image shape is distorted.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 degrees Body parts are not always 90 degrees from one anotherfrom one another

Central ray angulation is used to Central ray angulation is used to demonstrate certain details that can be demonstrate certain details that can be hidden by superimposed body parts.hidden by superimposed body parts.

Body part rotation or obliquing the body Body part rotation or obliquing the body can also help visualize superimposed can also help visualize superimposed anatomy.anatomy.

NAME 3 EXAMPLESNAME 3 EXAMPLES

MAGNIFICATIONMAGNIFICATIONcaused by:caused by:

TUBE CLOSE TO THE PART (TUBE CLOSE TO THE PART (↓↓SID)SID)

PART FAR FROM THE CASSETTE PART FAR FROM THE CASSETTE

((↑ ↑ OID)OID)

Compensate for MAG : Compensate for MAG : ↑ ↑ OID by OID by ↑ ↑ SID =SID =

“ “increase SID 7” for every 1” OID”increase SID 7” for every 1” OID”

Size Distortion & SIDSize Distortion & SID

Major influences: SID & OIDMajor influences: SID & OIDAs SID As SID , magnification , magnification Standardized SID’s allow radiologist to Standardized SID’s allow radiologist to

assume certain amt. of magnification assume certain amt. of magnification factors are presentfactors are present

Must note deviations from standard SIDMust 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 What can be done to improve the detail improve the detail with a large OID?with a large OID?

Use a smaller FSUse a smaller FS

40” SID VS 72” SID 40” SID VS 72” SID

Size Distortion & OIDSize Distortion & OID

If source is kept constant, OID will affect If source is kept constant, OID will affect magnificationmagnification

As OID As OID , magnification , magnification The farther the object is from the film, the The farther the object is from the film, the

more magnification more magnification

How can it be measured?How can it be measured?

Measuring % of MagnificationMeasuring % of Magnification

SIDSID

SODSOD

Measuring % of MagnificationMeasuring % of Magnification

What is the % What is the % of mag when of mag when you have a 72” you have a 72” SID andSID and

4” OID?4” OID?

DO the DO the math…………math…………

Material UnsharpnessMaterial Unsharpness

Equipment used can contribute to image Equipment used can contribute to image unsharpnessunsharpness

Fast film/screen combinations = decrease Fast film/screen combinations = decrease in image sharpnessin image sharpness

Slower film/screen combinations = Slower film/screen combinations = increase in image sharpnessincrease in image sharpness

Intensifying screensIntensifying screens

Lower patient doseLower patient dose

Changes resolution of imageChanges resolution of image

slow screens less LIGHT = better detailslow screens less LIGHT = better detail

Faster – less detail (more blurring on edges)Faster – less detail (more blurring on edges)

Intensifying Screens: ReviewIntensifying Screens: Review

Located inside the Located inside the cassette (film cassette (film holder)holder)

Calcium TungstateCalcium TungstateBlue to purple lightBlue to purple light

Rare EarthRare EarthGreen & Ultraviolet Green & Ultraviolet

lightlight

POOR SCREEN CONTACTPOOR SCREEN CONTACT

FOAM BACKING HELPS TO PLACE FOAM BACKING HELPS TO PLACE INTENSIFYING SCREENS IN DIRECT INTENSIFYING SCREENS IN DIRECT CONTACT WITH THE FILM – NO GAPSCONTACT WITH THE FILM – 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

WIRE MESHWIRE MESHSCREEN CONTACT TESTSCREEN CONTACT TEST

Screen SpeedScreen Speed

Efficiency of a screen in converting x-rays to Efficiency of a screen in converting x-rays to light is light is Screen Speed.Screen Speed.

Spectral Matching (F/S)Spectral Matching (F/S)

What does it mean?What does it mean?Name the two types of screen phosphorsName the two types of screen phosphorsWhat light spectrum do they emit?What light spectrum do they emit?

Spectral SensitivitySpectral Sensitivity

Film is designed to be Film is designed to be sensitive to the color sensitive to the color of light emitted by the of light emitted by the intensifying screens.intensifying screens.

Blue LIGHT– Blue LIGHT– Conventional Calcium Conventional Calcium Tungstate screenTungstate screen

Green, Yellow-Green Green, Yellow-Green LIGHTLIGHT

– – Rare Earth screenRare Earth screen

Spectral Matching (F/S systems)Spectral Matching (F/S systems)

Spectral Matching (F/S systems)Spectral Matching (F/S systems)

Red safe light

Safe lightsSafe lights

What wattage bulb?What wattage bulb?Distance from counter top?Distance from counter top?

Review of Film CharacteristicsReview of Film Characteristics

Size of silver halide Size of silver halide crystals & emulsion crystals & emulsion thickness determine thickness determine speed of film and degree speed of film and degree of resolutionof resolution

Speed – the response to Speed – the response to photonsphotons

Resolution – the detail Resolution – the detail seenseen

What are What are thesethese

What are What are they made they made ofof

Film Speed / Crystal sizeFilm Speed / Crystal size

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 detail, =Slower response, greater detail, more exposure (extremity)more exposure (extremity)

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

Extremity vs Regular cassettesExtremity vs Regular cassettes

QUANTUM MOTTLEQUANTUM MOTTLE Film grainFilm grain, or graininess, refers to the tiny black spots that , or graininess, refers to the tiny black spots that

make up the visible image, one grain from each silver make up the visible image, one grain from each silver halide crystal exposedhalide crystal exposed

MORE COMMON IN CR SYSTEMS NOWMORE COMMON IN CR SYSTEMS NOWNOT ENOUGH PHOTONS TO CREATE IMAGENOT ENOUGH PHOTONS TO CREATE IMAGE

Factors Affecting mAsFactors Affecting mAs

LIST 6 factorsLIST 6 factors

Factors Affecting mAsFactors Affecting mAs

Patient factors: size of pt., Patient factors: size of pt., density of tissue, density of tissue, pathologypathology

kVpkVp Distance - howDistance - how GridsGrids Film/Screen Film/Screen

CombinationsCombinations ProcessingProcessing

Technique /Denisty CHANGESTechnique /Denisty CHANGES

Log denisty H & D curveLog denisty H & D curve

a a densitometerdensitometer, , measures film blackness.measures film blackness. Film blackness is the Film blackness is the

relationship of the intensity of relationship of the intensity of the light that hits the film from the light that hits the film from the view box (the view box (incident incident intensityintensity) to the intensity of the ) to the intensity of the light transmitted through the light transmitted through the film (film (transmitted intensitytransmitted intensity). ).

These measurements plotted These measurements plotted on a graph produce a on a graph produce a characteristic curve.characteristic curve. The limitations of the human The limitations of the human eye determine the useful eye determine the useful density range in diagnostic density range in diagnostic radiography. radiography.

The diagnostically useful range The diagnostically useful range of densities is 0.25 to 2.5. of densities is 0.25 to 2.5.

The later module on exposure The later module on exposure calculation considers this in calculation considers this in more detail. more detail.

Film latitude ?Film latitude ?What does it meanWhat does it mean

how does it plot on the curve?how does it plot on the curve?

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