Radiographic Quality

DENSITY (1)

• What exactly is meant by term radiographic density?

• Radiographic density referred to as the overall blackening of the film. Density is dependent on amount of radiation received by the film.

• It is not the technologist’s purposes to produce an overall black film.

• Technologist is concerned with what is termed proper density.

DENSITY (2)

• A radiographic image that possesses proper density provides suitable visualization of all of the structures of interest.

• Any variance from this value of density is detrimental to radiographic quality.

• Insufficient density, degrading image quality as excessive density –in fact, perhaps more so.

Schematic drawing showing differentialabsorption of x–rays by the tissues of thebody in conventional radiography. From most to least radiodense these are (1) bone or calcium; (2) all soft tissues and liquids (muscle, blood, brain, heart, liver, urine, etc.) except (3) fat; (4) air or other gases.

DENSITY

Influencing factors?

Controlling factors?

I

FACTORS THAT INFLUENCE and CONTROL VISIBLE RECORDED DETAIL

Factors that influence visible recorded detailWhat are they???

Patient factorsTissue thicknessPhysiqueAgeDevelopmentPathology –additive and destructiveTissue opacity (density)

Factors that influence visible recorded detailWhat are they???

Patient factorsTissue thicknessPhysiqueAgeDevelopmentPathology –additive and destructiveTissue opacity (density)

- - Technique (mA; s; kV; distance)Technique (mA; s; kV; distance)

- - Receptor quantum efficiencyReceptor quantum efficiency

- - Image processingImage processing--Anode heel effectAnode heel effect --Orthopedic castsOrthopedic casts--FiltrtionFiltrtion

- - Technique (mA; s; kV; distance)Technique (mA; s; kV; distance)

- - Receptor quantum efficiencyReceptor quantum efficiency

- - Image processingImage processing--Anode heel effectAnode heel effect --Orthopedic castsOrthopedic casts--FiltrtionFiltrtion

Density control factorsDensity control factors

•A minimal change of 30% is A minimal change of 30% is necessary to produce noticeable necessary to produce noticeable difference in radiographic difference in radiographic density.density.

To increase densityTo increase density30%30% mAs increase requiredmAs increase required

•Density: Kvp/mAs Density: Kvp/mAs 15%15% rulerule

15%15% kv ↑ =50% mAskv ↑ =50% mAs↓ ↓

KilovoltageKilovoltage

•Abdomen: Abdomen: old 200mAx0.5 s =100 mAsold 200mAx0.5 s =100 mAs

new 200 mAx0.6 s= 120 new 200 mAx0.6 s= 120 mAsmAs • Elbow: Elbow: old 100mAx 0.1 s=10 mAs old 100mAx 0.1 s=10 mAs

new new 100mAx0.13.3 s= 13.3 mAs100mAx0.13.3 s= 13.3 mAs

A “step in time” A “step in time”

Distance - Inverse Square Law• intensity of radiation falling on flat

surface from point source is inversely proportional to square of distance from point source– if distance 2X, intensity drops by 4X

• Assumptions– point source– no attenuation

• Cause– increase in exposure area with

distance

Intensity 1/d2

d

Intensification factor formulaIntensification factor formula

Intensifying screenIntensifying screenScreen intensification factorScreen intensification factor

Intensifying screenIntensifying screenScreen intensification factorScreen intensification factor

intensification factorintensification factor= = exposure without screensexposure without screens

Exposure with screensExposure with screens

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Screen intensification factor•At 50 kv the intensification factor is 60•At 60 kv the intensification factor is 80•At 70 kv the intensification factor is 100

Screen intensification factor•At 50 kv the intensification factor is 60•At 60 kv the intensification factor is 80•At 70 kv the intensification factor is 100

Intensifying screen speeds and exposuresIntensifying screen speeds and exposures Intensifying screen speeds and exposuresIntensifying screen speeds and exposures

Screen type Speed value Exposure value

Ultraslow speed (detail) 1/4 4 times par

Slow speed 1/2 2 times par

Par speed (standard) 1 1

High speed 2 ½times par

Ultrahigh speed 3 1/3 times par

New phosphor material and rare earth screens peed*

4 t0 12 ¼to 1/12 times par

*Screen speed depends upon the type phosphor used, and the type and speed of the film it is used with

EExposure required to maintain radiographic densityxposure required to maintain radiographic density

With difference screen speeds (table top radiographyWith difference screen speeds (table top radiography)) using 60 kvp and having intensification factor of 80using 60 kvp and having intensification factor of 80

Screen type Speed value Exposure value

Nonscreen 400 mAs

Ultraslow speed ¼ 20 mAs

Slow speed ½ 10 mAs

Par speed 1 5 mAs

High speed 2 2.5 mAs

Ultrahigh speed 3 1.66 mAs

New phosphor material or rare earth speed

4 to 12 1.25 to 0.415 mAs

•Manual processing →difficult Manual processing →difficult to control quality.to control quality.• Automatic processingAutomatic processing

enable the enable the technologist to standardize film technologist to standardize film processingprocessing..

Film processingFilm processing

→→

•Has an influence on uniformity Has an influence on uniformity of overall density of the image.of overall density of the image.•In specific application, you can In specific application, you can employ this effect to advantage*employ this effect to advantage*

Anode heel effectAnode heel effect

**you must place the thicker and/or more dense area toward the cathode end of the x-ray tubeyou must place the thicker and/or more dense area toward the cathode end of the x-ray tube**you must place the thicker and/or more dense area toward the cathode end of the x-ray tubeyou must place the thicker and/or more dense area toward the cathode end of the x-ray tube

Anode heel effectAnode heel effect

**you must place the thicker and/or more dense area toward the cathode end of the x-ray tubeyou must place the thicker and/or more dense area toward the cathode end of the x-ray tube**you must place the thicker and/or more dense area toward the cathode end of the x-ray tubeyou must place the thicker and/or more dense area toward the cathode end of the x-ray tube

•Orthopedic casts adds both Orthopedic casts adds both thickness and opacity to the partthickness and opacity to the part•RememberRemember double the mAs for double the mAs for increased part thickness; increased part thickness; increased the kvp by 10 % for increased the kvp by 10 % for increased part opacity.increased part opacity.

Orthopedic castsOrthopedic casts

•Added filtration above 2.5 mm Al Added filtration above 2.5 mm Al increase exposure factors to increase exposure factors to maintain density.maintain density.•Remember; added filtration is Remember; added filtration is used as a means of reducing used as a means of reducing patient exposure to radiation.patient exposure to radiation. Filters should not be removed Filters should not be removed during routine examination. during routine examination.

FiltrationFiltration

Radiopacity and radiolucency are relativeterms. The central gray squares are all ofthe same density.

The left triangle seems lighter than the right one. This is only an illusion - they are equal in density.

Questions please