image quality review

IMAGE QUALITY IMAGE QUALITY REVIEWREVIEW

Dr Mohamed El Safwany, MD.Dr Mohamed El Safwany, MD.

Intended learning Intended learning outcomeoutcome The student should learn at the The student should learn at the

end of this lecture radiological end of this lecture radiological image quality review .image quality review .

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

Influences technique & Influences technique & density on imagedensity on image

Patient’s Body Habitus Patient’s Body Habitus (size)(size)

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

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

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

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.

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

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

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)

40” SID VS 72” SID 40” SID VS 72” 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

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)

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

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

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

Text BookText Book

David Sutton’s RadiologyDavid Sutton’s Radiology Clark’s Radiographic positioning Clark’s Radiographic positioning

and techniquesand techniques

AssignmentAssignment

Two students will be selected for Two students will be selected for assignment.assignment.

QuestionQuestion

Define motion unsharpness?Define motion unsharpness?

Thank YouThank You

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