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Components of Radiographic Image Quality. Radiologic Technology 244 created: Fall 2005 Rev 12-01-2009. Review handouts. Main Factors Affecting Recorded Detail. kVp & mAs Technique Selection (Time) Motion Object Unsharpness Focal Spot Size SID (Source to Image Distance)

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Components of radiographic image quality

Components of Radiographic ImageQuality

Radiologic Technology 244

created: Fall 2005

Rev 12-01-2009



Main factors affecting recorded detail
Main Factors Affecting Recorded Detail

  • kVp & mAs

    • Technique Selection (Time)

  • Motion

  • Object Unsharpness

  • Focal Spot Size

  • SID (Source to Image Distance)

  • OID (Object to Image Distance)

  • Material Unsharpness/ Film Screen

    Combo


Factors that affect recorded detail
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)


Geometric qualities
GEOMETRIC QUALITIES

  • DETAIL

  • DISTORTION

  • MAGNIFICATION


Detail
DETAIL

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

  • How “clear” the object looks on the radiograph


Recorded detail
Recorded Detail

  • Other names:

    -sharpness of detail

    -definition

    -resolution

    -degree of noise


Components of radiographic image quality

What are these

What does they

measure?


Components of radiographic image quality

Factors Affecting DENSITY

  • PATIENT THICKNESS,PATHOLOGY

  • MAS & KVP

  • SID


Components of radiographic image quality

POOR

DETAIL

GOOD DETAIL


Motion
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


Decrease motion unsharpness
Decrease Motion Unsharpness

  • Instruct patient not to move or breath

  • Use Immobilization devices

  • Use Short exposure times

  • Lock equipment in place




Focal spot size
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



Object unsharpness
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


Sid source to image distance
SID Source to Image Distance

  • The greater the distance between the source of the x-ray (tube) and the image receptor (cassette), the greater the image sharpness.

  • Standard distance = 40 in. most exams

  • Exception = Chest radiography 72 in.


Components of radiographic image quality
SID

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

    On a radiograph it’s called ______________

  • A true border – _____

  • Farther the flashlight from object = sharper borders. Same with radiography.


Oid object to image distance
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.


Distortion
Distortion

  • Misrepresentation of the true size or shape of an object

    MAGNIFICATION (size distortion)

    TRUE DISTORTION (shape distortion)


Shape distortion
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



Components of radiographic image quality

Distortion (x-ray beam not centered over object & film)

Distortion (object & film not parallel)


Central ray
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 beam’s periphery travel at an angle

  • When central ray in angled, image shape is distorted.


Components of radiographic image quality

Distortion of multiple objects in same image (right) due to x-ray beam not being centered over objects.


Central ray angulation
Central Ray Angulation x-ray beam not being centered over objects.

  • 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.

  • NAME 3 EXAMPLES


Magnification caused by
MAGNIFICATION x-ray beam not being centered over objects.caused by:

  • TUBE CLOSE TO THE PART (↓SID)

  • PART FAR FROM THE CASSETTE

    (↑ OID)

    Compensate for MAG : ↑ OID by ↑ SID =

    “increase SID 7” for every 1” OID”


Size distortion sid
Size Distortion & SID x-ray beam not being centered over objects.

  • Major influences: SID & OID

  • As SID , magnification 

  • Standardized SID’s allow radiologist to assume certain amt. of magnification factors are present

  • Must note deviations from standard SID


Components of radiographic image quality

In terms of recorded detail and magnification, the x-ray beam not being centered over objects.best image is produced with a small OID and a large SID.


Components of radiographic image quality


Use a smaller fs
Use a smaller FS x-ray beam not being centered over objects.


40 sid vs 72 sid
40” SID VS 72” SID x-ray beam not being centered over objects.


Size distortion oid
Size Distortion & OID x-ray beam not being centered over objects.

  • If source is kept constant, OID will affect magnification

  • As OID , magnification 

  • The farther the object is from the film, the more magnification


How can it be measured
How can it be measured? x-ray beam not being centered over objects.


Measuring of magnification
Measuring % of Magnification x-ray beam not being centered over objects.

SID

SOD


Measuring of magnification1
Measuring % of Magnification x-ray beam not being centered over objects.

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

    4” OID?

  • DO the math…………


Material unsharpness
Material Unsharpness x-ray beam not being centered over objects.

  • Equipment used can contribute to image unsharpness

  • Fast film/screen combinations = decrease in image sharpness

  • Slower film/screen combinations = increase in image sharpness


Intensifying screens
Intensifying screens x-ray beam not being centered over objects.

  • Lower patient dose

  • Changes resolution of image

  • slow screens less LIGHT = better detail

  • Faster – less detail (more blurring on edges)


Intensifying screens review
Intensifying Screens: Review x-ray beam not being centered over objects.

  • Located inside the cassette (film holder)

  • Calcium Tungstate

    • Blue to purple light

  • Rare Earth

    • Green & Ultraviolet light


Poor screen contact
POOR SCREEN CONTACT x-ray beam not being centered over objects.

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

  • IF GAPS – MORE LIGHT CAN BE EMITTED IN SPACE, CAUSING THE IMAGE TO BE OF POOR DETAIL


Wire mesh screen contact test
WIRE MESH x-ray beam not being centered over objects.SCREEN CONTACT TEST


Screen speed
Screen Speed x-ray beam not being centered over objects.

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


Spectral matching f s
Spectral Matching (F/S) x-ray beam not being centered over objects.

  • What does it mean?

  • Name the two types of screen phosphors

  • What light spectrum do they emit?


Spectral sensitivity
Spectral Sensitivity x-ray beam not being centered over objects.

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

  • Blue LIGHT– Conventional Calcium Tungstate screen

  • Green, Yellow-Green LIGHT

  • – Rare Earth screen


Spectral matching f s systems
Spectral Matching (F/S systems) x-ray beam not being centered over objects.


Spectral matching f s systems1
Spectral Matching (F/S systems) x-ray beam not being centered over objects.

Red safe light


Safe lights
Safe lights x-ray beam not being centered over objects.

  • What wattage bulb?

  • Distance from counter top?


Review of film characteristics
Review of Film Characteristics x-ray beam not being centered over objects.

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

    Speed – the response to photons

  • Resolution – the detail seen


Components of radiographic image quality

  • What are these x-ray beam not being centered over objects.

  • What are they made of


Film speed crystal size
Film Speed / Crystal size x-ray beam not being centered over objects.

  • Larger crystals or Thicker crystal layer

    Faster response= less detail, and

    less exposure (chest x-ray)

  • Finer crystals / thinner crystal layer

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


Image on film
IMAGE ON FILM x-ray beam not being centered over objects.

  • SINGLE EMULSION = BETTER DETAIL

  • DOUBLE EMULISON = LESS DETAIL

  • PARALLAX

    With double emulsion – an image is created on both emulsions – then superimposed – slight blurring of edges


Extremity vs regular cassettes
Extremity vs Regular cassettes x-ray beam not being centered over objects.


Components of radiographic image quality

QUANTUM MOTTLE x-ray beam not being centered over objects.Film grain, or graininess, refers to the tiny black spots that make up the visible image, one grain from each silver halide crystal exposedMORE COMMON IN CR SYSTEMS NOWNOT ENOUGH PHOTONS TO CREATE IMAGE


Factors affecting mas
Factors Affecting mAs x-ray beam not being centered over objects.

  • LIST 6 factors


Factors affecting mas1
Factors Affecting mAs x-ray beam not being centered over objects.

  • Patient factors: size of pt., density of tissue, pathology

  • kVp

  • Distance - how

  • Grids

  • Film/Screen Combinations

  • Processing


Technique denisty changes
Technique /Denisty CHANGES x-ray beam not being centered over objects.


Log denisty h d curve
Log denisty H & D curve x-ray beam not being centered over objects.


Components of radiographic image quality

  • a x-ray beam not being centered over objects.densitometer,

  • measures film blackness.

  • Film blackness is the relationship of the intensity of the light that hits the film from the view box (incident intensity) to the intensity of the light transmitted through the film (transmitted intensity).

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

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

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


Film latitude what does it mean how does it plot on the curve
Film latitude ? x-ray beam not being centered over objects.What does it meanhow does it plot on the curve?


Main factors affecting recorded detail1
Main Factors Affecting Recorded Detail x-ray beam not being centered over objects.

  • kVp & mAs

  • Motion

  • Object Unsharpness

  • Focal Spot Size

  • SID (Source to Image Distance)

  • OID (Object to Image Distance)

  • Material Unsharpness/ Film Screen

    Combo