Chapter 19 & 20 Image Chapter 19 & 20 Image Quality & TechniquesQuality & Techniques

• There are three geometric factors There are three geometric factors that affect radiographic quality.that affect radiographic quality.

• MagnificationMagnification

• DistortionDistortion

• Focal Spot BlurFocal Spot Blur

• We have explored these factors in We have explored these factors in the laboratory.the laboratory.

MagnificationMagnification

• All objects on the radiograph are All objects on the radiograph are larger that their actual size. This is larger that their actual size. This is called magnification.called magnification.

• The magnification factor is the image The magnification factor is the image size divided by the object size.size divided by the object size.

• At 40” (100 cm) factor is 1.1At 40” (100 cm) factor is 1.1

• At 72” (180 cm) factor is 1.05 At 72” (180 cm) factor is 1.05

MagnificationMagnification

• Usually we do not know the size of Usually we do not know the size of the object so we must determine the the object so we must determine the magnification factor another way.magnification factor another way.

• Image size S0DImage size S0D

• MF = ----------------= ------------MF = ----------------= ------------

• Object Size SIDObject Size SID

Minimizing MagnificationMinimizing Magnification

• Large SID: Use the less divergent Large SID: Use the less divergent beam.beam.– Chest X-rays are done at 72” SID to Chest X-rays are done at 72” SID to

minimize magnification.minimize magnification.– Lateral C-spine done at 72” Lateral C-spine done at 72”

• Small OID: Get patient as close to the Small OID: Get patient as close to the film as possible. film as possible. – Basic principle for positioning.Basic principle for positioning.

DistortionDistortion

• Distortion is the misrepresentation of Distortion is the misrepresentation of the true size and shape of the object the true size and shape of the object being radiographed.being radiographed.

• The amount of distortion depends The amount of distortion depends upon the thickness, position and upon the thickness, position and shape.shape.

ThicknessThickness

• Thick objects are Thick objects are more distorted more distorted than thin objects than thin objects because of the because of the greater change in greater change in Object Image Object Image Distance.Distance.

ThicknessThickness

• The position of The position of the object the object relative to the relative to the central axis will central axis will cause greater cause greater distortion with distortion with thick and/or thick and/or irregular shaped irregular shaped objects. objects.

Object PositionObject Position

• If the object plane If the object plane and image plane and image plane are parallel the are parallel the image will not be image will not be distorted.distorted.

• If the object plane If the object plane and image plane and image plane are not parallel, are not parallel, distortion will occur.distortion will occur.

Spatial DistortionSpatial Distortion

• When multiple objects When multiple objects at different OID’s at different OID’s occur, we get spatial occur, we get spatial distortion due to distortion due to unequal unequal magnification.magnification.

• Two arrows appear as Two arrows appear as one.one.

• When shifted laterally When shifted laterally more distortion occurs more distortion occurs

Object Shape DistortionObject Shape Distortion

• When the object When the object plane is not plane is not parallel to the parallel to the image plane as image plane as when inclined, when inclined, shape distortion shape distortion occurs.occurs.

• This will result in This will result in foreshortening.foreshortening.

Focal Spot BlurFocal Spot Blur

• Focal spot blur is Focal spot blur is caused by the caused by the effective size of the effective size of the focal spot, which is focal spot, which is larger at the cathode larger at the cathode side.side.

• Focal spot blur is the Focal spot blur is the most important most important factor in determining factor in determining spatial resolution.spatial resolution.

Focal Spot BlurFocal Spot Blur

• Focal spot blur is Focal spot blur is impacted by the impacted by the Object to Image Object to Image Distance.Distance.

Focal Spot Blur Heel EffectFocal Spot Blur Heel Effect

• There is more to the There is more to the heel affect than just heel affect than just the attenuation of the attenuation of the beam by the the beam by the anode.anode.

• The focal spot blur is The focal spot blur is smaller at the anode smaller at the anode side and larger at side and larger at the cathode side. the cathode side.

Taking advantage of the Taking advantage of the Anode Heel EffectAnode Heel Effect

E x a m T o w a r dC a t h o d e

T o w a r d A n o d e

F u l l s p i n eC h e s t

A b d o m e n N e c k

T - s p i n e A - P A b d o m e n N e c k

T - s p i n eL a t e r a l

N e c k A b d o m e n

H u m e r u s S h o u l d e r E l b o w

C o m m an d B u tto n 1

Did you see a problem ?Did you see a problem ?

• If the tube is mounted correctly for If the tube is mounted correctly for the AP Full spine, Chest and A-P the AP Full spine, Chest and A-P Thoracic Spine, the patient must Thoracic Spine, the patient must stand on his head for the lateral stand on his head for the lateral thoracic spine!!!!thoracic spine!!!!

• For erect radiography, the use of the For erect radiography, the use of the anode heel affect is limited.anode heel affect is limited.

Object Factors that Affect Object Factors that Affect QualityQuality

• Subject ContrastSubject Contrast

• Patient or part thicknessPatient or part thickness

• Tissue mass densityTissue mass density

• Affective atomic numberAffective atomic number

• Object shapeObject shape

• kVpkVp

Radiographic ContrastRadiographic Contrast

• Radiographic Contrast is how the film Radiographic Contrast is how the film looks.looks.

• It is the combination of receptor It is the combination of receptor contrast and subject contrast.contrast and subject contrast.

• Contrast occurs between structures Contrast occurs between structures of different densities.of different densities.

ThicknessThickness

• The thicker the body part or body The thicker the body part or body section, the greater attenuation of section, the greater attenuation of the beam. Contrast is relative to the the beam. Contrast is relative to the number of x-rays leaving the body.number of x-rays leaving the body.

• Remember that x-rays are merely Remember that x-rays are merely shadows of the anatomy based upon shadows of the anatomy based upon attentation of the beam. attentation of the beam.

ThicknessThickness

• Radiographs of thin patients will Radiographs of thin patients will have more contrast than those of have more contrast than those of large patients.large patients.

• Thicker object absorb more rays and Thicker object absorb more rays and will appear lighter than thin objects.will appear lighter than thin objects.

Tissue Mass DensityTissue Mass Density

• Different sections of the body have Different sections of the body have may equal thickness yet different may equal thickness yet different mass density.mass density.

• Two wrist may be the same thickness Two wrist may be the same thickness but the one that is swollen will have but the one that is swollen will have greater mass density due to water in greater mass density due to water in the tissues.the tissues.

Effective Atomic NumberEffective Atomic Number

• While Compton interactions with While Compton interactions with tissues are not impacted by the tissues are not impacted by the relative atomic number of tissues, relative atomic number of tissues, the photoelectric effect vary with the the photoelectric effect vary with the cube of the atomic number.cube of the atomic number.

• When the effective atomic number of When the effective atomic number of adjacent tissues is very different, adjacent tissues is very different, subject contrast is very high. subject contrast is very high.

Object shapeObject shape

• The object shape not The object shape not only influences the only influences the geometry but also geometry but also through its through its contribution to subject contribution to subject contrast.contrast.

• A vessel on end has A vessel on end has high contrast while high contrast while other have lower other have lower contrast.contrast.

Varying tissue densitiesVarying tissue densities

• Bone absorbs most x-rays leaving a Bone absorbs most x-rays leaving a white shadow.white shadow.

• Water absorbs less x-rays leaving a Water absorbs less x-rays leaving a light gray shadowlight gray shadow

• Fat absorbs fewer x-rays leaving a Fat absorbs fewer x-rays leaving a dark gray shadow.dark gray shadow.

• Air absorbs little x-rays and is black Air absorbs little x-rays and is black on the film.on the film.

Varying densities in the Varying densities in the BodyBody

• Air, oil, water and metal (natural) Air, oil, water and metal (natural) absorb different degrees of the x-absorb different degrees of the x-rays and produce contrast.rays and produce contrast.

• Heavy metals are used as contrast Heavy metals are used as contrast media to enhance contrast in the media to enhance contrast in the body in medical radiology. body in medical radiology. Principle ones are Barium and Principle ones are Barium and Iodine.Iodine.

kVpkVp

• We have little control over the We have little control over the previous factors controlling subject previous factors controlling subject contrast.contrast.

•BUT!!!!!BUT!!!!!• The The absolute magnitude of absolute magnitude of

subject contrastsubject contrast is greatly is greatly influenced by the influenced by the kVp of operation.kVp of operation.

kVpkVp

• kVp also influences film contrast but kVp also influences film contrast but not to the extend it controls subject not to the extend it controls subject contrast.contrast.

• Low kVp = high contrast = short Low kVp = high contrast = short scalescale

• High kVp = low contrast = broad High kVp = low contrast = broad scalescale

Motion BlurMotion Blur

• If any element of the x-ray moves If any element of the x-ray moves during exposure, we get motion blur.during exposure, we get motion blur.

• Patient motion is the most common Patient motion is the most common cause of motion blur.cause of motion blur.

• Motion blur is more common in erect Motion blur is more common in erect radiography.radiography.

Ways to Control Motion BlurWays to Control Motion Blur

• Use the shortest possible exposure Use the shortest possible exposure timetime

• Restrict patient motion by Restrict patient motion by instructions or restraining device.instructions or restraining device.

• Use a large SIDUse a large SID

• Use a small OIDUse a small OID

Tools to Improve Quality Tools to Improve Quality

• Patient PositioningPatient Positioning– Get the patient close to the film reduce Get the patient close to the film reduce

OID.OID.– Center the beam to the area of interest.Center the beam to the area of interest.– Get the area of interest parallel to the Get the area of interest parallel to the

beam or film.beam or film.– Restrain motion and communicate with Restrain motion and communicate with

the patient.the patient.– Use short exposure times.Use short exposure times.

Tools to Improve Quality Tools to Improve Quality

• Image receptorsImage receptors– Use the correct film & screen Use the correct film & screen

combination for the examination. combination for the examination. Extremity for wrist. Regular for spines.Extremity for wrist. Regular for spines.

– Intensifying screens reduce patient Intensifying screens reduce patient exposure at least 20 times.exposure at least 20 times.

– As the speed of the image receptor As the speed of the image receptor increases, radiographic noise and increases, radiographic noise and contrast resolution decreases. contrast resolution decreases.

Tools to Improve Quality Tools to Improve Quality

• Image receptorsImage receptors– Low contrast imaging procedures have Low contrast imaging procedures have

wider latitude and a larger margin of wider latitude and a larger margin of error in producing acceptable error in producing acceptable radiographs.radiographs.

– Use the highest speed system that will Use the highest speed system that will provide adequate contrast and density provide adequate contrast and density over the entire spectrum of over the entire spectrum of examinations.examinations.

Tools to Improve Quality Tools to Improve Quality

• Technique selectionTechnique selection– We must select the optimum technical We must select the optimum technical

factors.factors.– We must get the exposure time as low We must get the exposure time as low

as possible so high frequency machine as possible so high frequency machine are important.are important.

– Contrast controlled by the kVp usedContrast controlled by the kVp used– Density controlled by the mAs used.Density controlled by the mAs used.

Tools to Improve Quality Tools to Improve Quality

• kVp has a greater influence than kVp has a greater influence than mAs.mAs.

• Technique selection is a balancing Technique selection is a balancing act. Balancing contrast, density and act. Balancing contrast, density and exposure.exposure.

Chapter 20 Radiographic Chapter 20 Radiographic TechniqueTechnique

• Several factors influence the Several factors influence the selection of technical factors. The selection of technical factors. The primary factors that impact exposure primary factors that impact exposure and image quality are:and image quality are:

• SIDSID

• mAsmAs

• kVpkVp

Patient FactorsPatient Factors

• The anatomic The anatomic thickness and body thickness and body composition composition greatly impact the greatly impact the technical factors.technical factors.

• The technique The technique chart is based chart is based upon the Sthenic upon the Sthenic Body Type.Body Type.

Patient FactorsPatient Factors

• SthenicSthenic is strong & is strong & activeactive

• HyposthenicHyposthenic is thin is thin but healthybut healthy

• HyperstenicHyperstenic is is obeseobese

• AstenicAstenic is small, frail is small, frail sometime sometime emaciated, and often emaciated, and often elderlyelderly

Patient ThicknessPatient Thickness

• The thickness of The thickness of the patient should the patient should not be guessed.not be guessed.

• It should be It should be measured with measured with calipers.calipers.

• Patient thickness is Patient thickness is measured in cm.measured in cm.

Body compositionBody composition

• The type of tissue in the area of The type of tissue in the area of exposure will impact the technical exposure will impact the technical factors.factors.– The tissue types in the chest are different The tissue types in the chest are different

from the abdomen.from the abdomen.– Disease processes will also impact the Disease processes will also impact the

exposure factors. Obtaining a good clinical exposure factors. Obtaining a good clinical history is important. History must be history is important. History must be communicated to the radiographer.communicated to the radiographer.

Classifying PathologyClassifying Pathology

• Radiolucent Radiolucent (Destructive)(Destructive)

• Active TBActive TB• AtrophyAtrophy• Bowel obstructionBowel obstruction• CancerCancer• Degenerative arthritisDegenerative arthritis• EmphysemaEmphysema• OsteoporosisOsteoporosis• PneumothoraxPneumothorax

• RadiopaqueRadiopaque Constructive)Constructive)

• Aortic aneurysmAortic aneurysm• AscitesAscites• AtelectasisAtelectasis• CirrosisCirrosis• HypertrophyHypertrophy• MetastasisMetastasis• Pleural EffusionPleural Effusion• PneumoniaPneumonia• SclerosisSclerosis

Image Quality FactorsImage Quality Factors

• Image quality factors includeImage quality factors include– ODOD– ContrastContrast– Image DetailImage Detail– Image DistortionImage Distortion

• OD is the optical density or OD is the optical density or radiographic density. OD is controlled radiographic density. OD is controlled by the mAs and SID.by the mAs and SID.

Optical DensityOptical Density

• Numerically low OD is a low number Numerically low OD is a low number like 0.25.like 0.25.

• Dark is a high number like 2.20 to 4.0Dark is a high number like 2.20 to 4.0

• Light is underexposedLight is underexposed

• Dark is over exposedDark is over exposed

• If density is the only factor that needs If density is the only factor that needs to be changed, change the mAs.to be changed, change the mAs.

Optical DensityOptical Density

• A 30% change in mAs is needed to make A 30% change in mAs is needed to make a perceptible change in optical density.a perceptible change in optical density.

• Usually when a change in optical density Usually when a change in optical density is needed, the mAs is either doubled or is needed, the mAs is either doubled or halved.halved.

• kVp must be changed by 4% to produce kVp must be changed by 4% to produce the same change in optical density.the same change in optical density.– Changing kVp will also impact penetration Changing kVp will also impact penetration

and contrast.and contrast.

30 - 50 Rule30 - 50 Rule

• If the film is under exposed, double If the film is under exposed, double the mAs.the mAs.

• If the film is over exposed, cut the If the film is over exposed, cut the mAs in half.mAs in half.

• If the film is slightly underexposed, If the film is slightly underexposed, increase the mAs 30%.increase the mAs 30%.

• If the film is slightly overexposed, If the film is slightly overexposed, reduce the mAs 30%.reduce the mAs 30%.

30% Density Change30% Density Change

• The lower image The lower image was the first image was the first image taken. It was dark taken. It was dark but normally would but normally would be acceptable.be acceptable.

• The top image was The top image was the mAs reduced the mAs reduced 30%. The air fluid 30%. The air fluid levels in the sinus is levels in the sinus is easier to see.easier to see.

15% Rule15% Rule

• The OD can be changed with kVp but it will The OD can be changed with kVp but it will also impact exposure and contrast also.also impact exposure and contrast also.

• Increase of 15% in kVp is equal to cutting the Increase of 15% in kVp is equal to cutting the mAs in half. mAs in half.

• Decrease of 15% in kVp is equal to doubling Decrease of 15% in kVp is equal to doubling the mAs.the mAs.

• If the film is underexposed, increase kVp 15%.If the film is underexposed, increase kVp 15%.

• If the film is overexposed, decrease kVp 15%.If the film is overexposed, decrease kVp 15%.

ContrastContrast

• The function of contrast is to make The function of contrast is to make the anatomy more visible.the anatomy more visible.

• Contrast is the difference in density Contrast is the difference in density of adjacent structures.of adjacent structures.

• The relative penetrability of the x-ray The relative penetrability of the x-ray through different tissues determines through different tissues determines the image contrast.the image contrast.

ContrastContrast

• Contrast can be measured as the Contrast can be measured as the Gray Scale of Contrast. It is the range Gray Scale of Contrast. It is the range of optical density from white to black of optical density from white to black on the image.on the image.

• Contrast is controlled by kVp.Contrast is controlled by kVp.

Adjusting Contrast with 15% Adjusting Contrast with 15% RuleRule

• An 15% increase in kVp and a An 15% increase in kVp and a reduction of mAs by 50% will produce reduction of mAs by 50% will produce the same OD but lower contrast.the same OD but lower contrast.– Used to reduce exposure or reduce Used to reduce exposure or reduce

exposure time/exposure time/

• An 15% decrease in kVp and doubling An 15% decrease in kVp and doubling the mAs will produce the same OD the mAs will produce the same OD but higher contrast. but higher contrast.

Image DetailImage Detail

• The sharpness of image detail refers The sharpness of image detail refers to the ability to see structural lines or to the ability to see structural lines or borders of tissue in the image. borders of tissue in the image.

• The visibility of image detail is best The visibility of image detail is best measured by the contrast resolution.measured by the contrast resolution.

• The geometric factors of focal spot The geometric factors of focal spot selection, SID and OID will impact selection, SID and OID will impact sharpness. sharpness.

Image DetailImage Detail

• Visibility of image detail is impacted Visibility of image detail is impacted by factors such as image fog. by factors such as image fog. – Scatter radiation reduces the ability to Scatter radiation reduces the ability to

visualize lines of detail.visualize lines of detail.– Light fog or processing can impact the Light fog or processing can impact the

visibility of structures.visibility of structures.– Collimation, screen combination and the Collimation, screen combination and the

use of a grid are other factors that impact use of a grid are other factors that impact image detail. image detail.

DistortionDistortion

• The position of the x-ray tube greatly The position of the x-ray tube greatly impacts distortion of the image. The impacts distortion of the image. The image may be elongated or image may be elongated or foreshortened.foreshortened.

• The proper The proper PositioningPositioning of the tube, of the tube, anatomic part and image receptor anatomic part and image receptor greatly impacts distortion.greatly impacts distortion.

Types of Technique ChartsTypes of Technique Charts

• There are four primary means to There are four primary means to establish techniques.establish techniques.

• Variable kVpVariable kVp Fixed mAs Fixed mAs

• Fixed kVpFixed kVp with varying mAs. with varying mAs.

• High kVpHigh kVp with varying mAs with varying mAs

• Automatic Exposure ChartsAutomatic Exposure Charts when when AEC is used.AEC is used.

Variable kVp ChartsVariable kVp Charts

• The mAs is fixed and the kVp is varied The mAs is fixed and the kVp is varied based upon patient thickness.based upon patient thickness.

• Usually by a formula such as 2 x Usually by a formula such as 2 x thickness +30 = kVp for single phasethickness +30 = kVp for single phase

• 24 cm patient= 24*2+30=78kVp24 cm patient= 24*2+30=78kVp• For high frequency use 23 and for three For high frequency use 23 and for three

phase use 25.phase use 25.• Small patient used low kVp= high contrastSmall patient used low kVp= high contrast• Large patient used high kVp= low contrastLarge patient used high kVp= low contrast

Variable kVp ChartsVariable kVp Charts

• Contrast was very inconsistent.Contrast was very inconsistent.

• Very little latitude on smaller Very little latitude on smaller patients.patients.

• Higher radiation exposureHigher radiation exposure

•This type of chart should be This type of chart should be avoided.avoided.

Fixed kVp TechniqueFixed kVp Technique

• kVp is fixed and mAs varies by kVp is fixed and mAs varies by patient thickness. Usually 30% per patient thickness. Usually 30% per two cm.two cm.

• Uses Optimum kVp for the body partUses Optimum kVp for the body part

• Contrast is constant.Contrast is constant.

• Wider latitudeWider latitude

• Lower exposureLower exposure

Fixed kVp Technique Fixed kVp Technique VariationsVariations

• High kVpHigh kVp technique uses over 100 technique uses over 100 kVpkVp– No longer used for bone.No longer used for bone.– Long ago used for spine but images are Long ago used for spine but images are

too gray. Low contrasttoo gray. Low contrast– Mostly used for chest and barium Mostly used for chest and barium

contrast studies.contrast studies.

Fixed kVp Technique Fixed kVp Technique VariationsVariations• Automatic Exposure Technique ChartsAutomatic Exposure Technique Charts

– Uses optimum kVp and high backup mAs.Uses optimum kVp and high backup mAs.– Ion chamber or photo cell determines Ion chamber or photo cell determines

when correct density is achieved on film when correct density is achieved on film and terminates exposure.and terminates exposure.

– Proper positioning is critical to get the Proper positioning is critical to get the area of interest over the ion chamber. area of interest over the ion chamber.

Using the Technique ChartUsing the Technique Chart

• The chart is not the Bible but is a guide.The chart is not the Bible but is a guide.

• Works about 85% of the time so it is a Works about 85% of the time so it is a great starting point.great starting point.

• Lists factors used for each view based Lists factors used for each view based upon measurement of the patient.upon measurement of the patient.

• Can include as much as you want to Can include as much as you want to include.include.

Using the Technique ChartUsing the Technique Chart

• Recommended factors for chart:Recommended factors for chart:

• optimum kVp for viewoptimum kVp for view

• mAs based upon cm measurementmAs based upon cm measurement

• filters used filters used

• SID & tube angle usedSID & tube angle used

• Bucky or non-BuckyBucky or non-Bucky

• Cassette & film typeCassette & film type

Using the Technique ChartUsing the Technique Chart

• Charts should be: Charts should be: – accessibleaccessible– easy to readeasy to read– not hand writtennot hand written– based upon the type of machine and based upon the type of machine and

machine controls.machine controls.•mAs or mA and timemAs or mA and time

Technique VariablesTechnique Variables

• Variable machine & electrical outputVariable machine & electrical output– Incoming power and ability of machine to Incoming power and ability of machine to

compensate for variations in incoming compensate for variations in incoming power.power.

– Type of High-voltage PowerType of High-voltage Power•Single phase to High Frequency reduce mAs 50%Single phase to High Frequency reduce mAs 50%

•High Frequency to Single phase double mAsHigh Frequency to Single phase double mAs

– Grid ratioGrid ratio– Non-Bucky Holder Non-Bucky Holder

Technique VariablesTechnique Variables

• Variable machine & electrical outputVariable machine & electrical output– Relative Speed Value of cassettes & film Relative Speed Value of cassettes & film

combination.combination.– 400 speed to 200 speed = double mAs400 speed to 200 speed = double mAs– 200 speed to 400 speed = reduce mAs 200 speed to 400 speed = reduce mAs

50%50%

mAs & kVp RelationshipmAs & kVp Relationship

• There are some basic rules for mAs There are some basic rules for mAs and kVp that are used to adjust the and kVp that are used to adjust the technical factors.technical factors.

• Remember x-rays are like toast.Remember x-rays are like toast.

• Dark is too denseDark is too dense

• Light has inadequate densityLight has inadequate density

• This tells you which was to go.This tells you which was to go.

mAs RulesmAs Rules

• Since mAs controls density, it is Since mAs controls density, it is usually used to adjust density.usually used to adjust density.

• 30% increase needed to make a 30% increase needed to make a noticeable change in density.noticeable change in density.

• 50% mAs reduction will reduce 50% mAs reduction will reduce density 50%density 50%

• Doubling mAs will doubles density.Doubling mAs will doubles density.

mAs RulesmAs Rules

• If image is too dark reduce mAs 50%.If image is too dark reduce mAs 50%.

• If image is too light double mAs.If image is too light double mAs.

• Doubling mAs can be done by Doubling mAs can be done by doubling mA or time.doubling mA or time.

• Doubling time increases chance for Doubling time increases chance for motion blur.motion blur.

kVp RulekVp Rule

• kVp will also change density.kVp will also change density.

• A A light filmlight film from low kVp is called from low kVp is called under exposedunder exposed or under penetrated. or under penetrated.– Very white image because no x-rays Very white image because no x-rays

reached the film.reached the film.

• Too darkToo dark is is over exposed, some say over exposed, some say over penetrated. over penetrated. They are different.They are different.

kVp RulekVp Rule

• Over penetrated will result only if the kVp Over penetrated will result only if the kVp used is too high for the view. It will be used is too high for the view. It will be dark and very flat (lacking contrast)dark and very flat (lacking contrast)

• Density is very sensitive to changes in Density is very sensitive to changes in kVp.kVp.

• A 2 kVp (HF) to 4 kVp change is A 2 kVp (HF) to 4 kVp change is noticeable. About 4%.noticeable. About 4%.

• The 15% rule works with density The 15% rule works with density adjustment.adjustment.

kVp RulekVp Rule

• 15% increase in kVp will double 15% increase in kVp will double density.density.

• 15% decrease in kVp will reduce 15% decrease in kVp will reduce density 50%.density 50%.

• 15% increase in kVp = doubling mAs 15% increase in kVp = doubling mAs

• 15% decrease in kVp = half the mAs15% decrease in kVp = half the mAs

• 10 kVp = 15% change in the 60 to 90 10 kVp = 15% change in the 60 to 90 kVp range. kVp range.

Optimum kVpOptimum kVp

• Optimum kVp will provide the best Optimum kVp will provide the best contrast with the least amount of contrast with the least amount of radiation.radiation.

• If using the optimum kVp you should If using the optimum kVp you should not need to adjust kVp.not need to adjust kVp.

• kVp can be changed based upon kVp can be changed based upon body habitus and disease. body habitus and disease.

Optimum kVp Optimum kVp

• Small ExtremitySmall Extremity• Large ExtremityLarge Extremity• Cervical Spine AP or LatCervical Spine AP or Lat• APOMAPOM• Thoracic APThoracic AP• Thoracic LatThoracic Lat• Lumbar APLumbar AP• Lumbar ObliqueLumbar Oblique• Lumbar LateralLumbar Lateral• PelvisPelvis• AbdomenAbdomen• RibsRibs• ChestChest

• 55-6555-65• 65-7065-70• 70-7470-74• 75-7875-78• 7575• 8080• 7474• 8080• 9090• 8080• 7070• 7070• 110+110+

Dark filmDark film

• Dark & No contrast = reduce kVp no Dark & No contrast = reduce kVp no change to mAs change to mAs

• Black no structures seen reduce both.Black no structures seen reduce both.

• Dark = look at the optimum kVp range.Dark = look at the optimum kVp range.– If reducing kVp goes beyond optimum kVpIf reducing kVp goes beyond optimum kVp– reduce mAs 50% reduce mAs 50%

Light FilmLight Film

• If film is so light that no structures If film is so light that no structures are seen then it is under penetrated are seen then it is under penetrated so increase kVp.so increase kVp.

• kVp controls penetration.kVp controls penetration.

• If structures seen but lacks density If structures seen but lacks density increase double mAs.increase double mAs.

Patient FactorsPatient Factors

• Very muscular Very muscular oror large boned increase large boned increase mAs by 50%mAs by 50%

• Very muscular Very muscular andand large boned large boned increase mAs 50% and kVp 4 to 6 kVp.increase mAs 50% and kVp 4 to 6 kVp.

• Obese increase mAs 50%Obese increase mAs 50%

• Edema increase mAs 30%Edema increase mAs 30%

• Frail decrease kVp 5 to 15%Frail decrease kVp 5 to 15%

Patient FactorsPatient Factors

• Osteoporotic patient : over 60 years Osteoporotic patient : over 60 years old decrease mAs 30% to 50%old decrease mAs 30% to 50%

• 6 to 12 years old reduce mAs 30 to 6 to 12 years old reduce mAs 30 to 50%50%

• Infants to 6 years old decrease mAs Infants to 6 years old decrease mAs 75%75%

Item that Affect DetailItem that Affect Detail

• Spatial Resolution controlled by focal Spatial Resolution controlled by focal spot size and image receptor.spot size and image receptor.

• Detail influenced by:Detail influenced by:– SIDSID– OIDOID– Motion BlurMotion Blur– Density & Contrast of ImageDensity & Contrast of Image

Items that Affect ODItems that Affect OD

• Optical density is controlled by mAsOptical density is controlled by mAs

• OD influenced by:OD influenced by:– kVpkVp– SIDSID– ThicknessThickness– DensityDensity– CollimationCollimation

Items that Affect ODItems that Affect OD

• OD influenced by:OD influenced by:– Grid RatioGrid Ratio– Development time and temperatureDevelopment time and temperature– Image receptor speedImage receptor speed

Items that Affect ContrastItems that Affect Contrast

• Contrast controlled by kVpContrast controlled by kVp

• Contrast influenced by:Contrast influenced by:– mAsmAs– Development Time & TemperatureDevelopment Time & Temperature– CollimationCollimation– Grid ratioGrid ratio– Image receptorImage receptor

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