INSTRUMENTATIONINSTRUMENTATION

ELECTRICAL REQUIREMENTS ELECTRICAL REQUIREMENTS AND EFFICIENCYAND EFFICIENCY

Effective voltageEffective voltage High frequency inverter technology (over High frequency inverter technology (over

10,000Hz) 10,000Hz) Constant potential output (<13% ripple)Constant potential output (<13% ripple) kVp should be set according to machine’s kVp should be set according to machine’s

ripple content.ripple content.

Advantages of Advantages of High-Frequency/Constant Potential High-Frequency/Constant Potential

UnitsUnits Ability to use lower kVp settingsAbility to use lower kVp settings Greater efficiency which results in shorter Greater efficiency which results in shorter

exposure times exposure times Less patient motion.Less patient motion. Lower x-ray dose to the patient.Lower x-ray dose to the patient. Tube will last longer because output is higher.Tube will last longer because output is higher. Less interference from reciprocity law failure.Less interference from reciprocity law failure. More compactMore compact

KV SELECTIONKV SELECTION

ComptonCompton

PhotoelectricPhotoelectric

Technical Factors DefinedTechnical Factors Defined

kVp – peak kilovolts; measure of the kVp – peak kilovolts; measure of the highest energy applied to electrons during highest energy applied to electrons during the exposure.the exposure.

mAs- The number of electrons accelerated mAs- The number of electrons accelerated to the target during a given exposure.to the target during a given exposure.

keV – ( kilo-electron volts) The energy keV – ( kilo-electron volts) The energy received by the electrons.received by the electrons.

PHOTOELECTRIC EFFECTPHOTOELECTRIC EFFECT

Depends on atomic number of substanceDepends on atomic number of substance Molybdenum (atomic #42) produces Molybdenum (atomic #42) produces

characteristic peaks at 17.4-19.6keV.characteristic peaks at 17.4-19.6keV. Glandular tissue (atomic #’s 7,8)Glandular tissue (atomic #’s 7,8) Fatty tissue (atomic # 6)Fatty tissue (atomic # 6) Calcifications (atomic #’s 15,20)Calcifications (atomic #’s 15,20) Low kV beam essential to maximize Low kV beam essential to maximize

photoelectric interactions.photoelectric interactions. 25-27kV optimal25-27kV optimal

COMPTONCOMPTON

AVOID COMPTON AVOID COMPTON Deals with electron densitiesDeals with electron densities No contrast differentiation between fat and No contrast differentiation between fat and

glandular tissue with electron density. glandular tissue with electron density. Accounts for most interactions within Accounts for most interactions within

tissues above 28kVtissues above 28kV

Target Material/FilterTarget Material/Filter

Molybdenum – 17-20 keV 25 kVpMolybdenum – 17-20 keV 25 kVp

Rhodium – 20-23 keV 30 kVpRhodium – 20-23 keV 30 kVp

Tungsten – 15-25 keV 22-26 kVpTungsten – 15-25 keV 22-26 kVp

RECIPROCITY LAW FAILURERECIPROCITY LAW FAILURE

Exposure must be <1sec to avoid thisExposure must be <1sec to avoid this Grids make it difficult to avoidGrids make it difficult to avoid Invites client motionInvites client motion Increases dosageIncreases dosage Capture of excessive scattered radiation on the Capture of excessive scattered radiation on the

filmfilm Instead of making exposures beyond the RLF of Instead of making exposures beyond the RLF of

the film, increase density of film by raising kVp the film, increase density of film by raising kVp setting.setting.

GRIDSGRIDS

DesignDesign

RatioRatio

Effect on DoseEffect on Dose

Effect on ImagesEffect on Images

COMPRESSIONCOMPRESSION

Decreased motionDecreased motion Decreased geometric unsharpnessDecreased geometric unsharpness Increased contrastIncreased contrast Separates superimposed tissuesSeparates superimposed tissues Decreased doseDecreased dose Increased uniform film densityIncreased uniform film density

COMPRESSION PADDLESCOMPRESSION PADDLES

Made of thin PlexiglasMade of thin Plexiglas Straight chest wall edgeStraight chest wall edge Sufficient height and angle of chest wallSufficient height and angle of chest wall Squared rather than roundedSquared rather than rounded Remains parallel when compressedRemains parallel when compressed Vertical alignment between chest wall Vertical alignment between chest wall

edge and image receptoredge and image receptor Final compression manually controlledFinal compression manually controlled

MAGNIFICATIONMAGNIFICATION

No grid:No grid: causes increase in tube loading, causes increase in tube loading, dose and motion due to prolonged dose and motion due to prolonged exposure time.exposure time.

Disadvantages of mag:Disadvantages of mag: Increased doseIncreased dose Decreased sharpnessDecreased sharpness

FSS decreased to improve sharpness: FSS decreased to improve sharpness: .2mm with 1.5x mag.2mm with 1.5x mag .1mm with 2x mag.1mm with 2x mag

MAGNIFICATION CONT….MAGNIFICATION CONT….

Magnification factors range from 1.4x to 2xMagnification factors range from 1.4x to 2x

1.5x mag can see 13 line pairs/mm1.5x mag can see 13 line pairs/mm

2x only sees 7 line pairs2x only sees 7 line pairs

X-RAY TUBEX-RAY TUBE

HVL – amount of AL that when added to HVL – amount of AL that when added to the beam, will decrease intensity by 1/2. the beam, will decrease intensity by 1/2. An indirect measurement of the x-ray An indirect measurement of the x-ray beam and expressed in mm-AL.beam and expressed in mm-AL.

Includes:Includes: Beryllium windowBeryllium window Moly filterMoly filter MirrorMirror Compression paddleCompression paddle

X-RAY TUBEX-RAY TUBE

Heel effectHeel effect Electron stream driven by ___Electron stream driven by ___ Amount of electrons controlled by ___Amount of electrons controlled by ___ When angle of anode is increased:When angle of anode is increased:

can withstand larger stream of electrons (greater can withstand larger stream of electrons (greater heat) heat)

results in smaller effective focal spot which provides results in smaller effective focal spot which provides better resolutionbetter resolution

more pronounced heel effect (reduction in intensity of more pronounced heel effect (reduction in intensity of beam from chest to nipple)beam from chest to nipple)

X-RAY TUBEX-RAY TUBE

Focal Spot ProjectionFocal Spot Projection

Reference AxisReference Axis

AUTOMATIC EXPOSURE AUTOMATIC EXPOSURE CONTROLCONTROL

Radiation that is transmitted through an Radiation that is transmitted through an object is converted into an electronic object is converted into an electronic signal, which terminates the exposure signal, which terminates the exposure when the predetermined level of radiation when the predetermined level of radiation has been reached.has been reached.

AUTOMATIC EXPOSURE AUTOMATIC EXPOSURE CONTROLCONTROL

Single Pickup PhototimersSingle Pickup Phototimers Confined to the center of the chest wall edgeConfined to the center of the chest wall edge Can move ~3 inches from chestCan move ~3 inches from chest Difficult to determine adequate placementDifficult to determine adequate placement

Smart PhototimersSmart Phototimers A series of photocellsA series of photocells Averages signals of each cellAverages signals of each cell

Smart PhototimersSmart Phototimers

Track from one kVp setting to anotherTrack from one kVp setting to another Compensate for differences in breast thicknessCompensate for differences in breast thickness Obtain an adequate density for all varying breast Obtain an adequate density for all varying breast

densitiesdensities Compensate for reciprocity law failure of the filmCompensate for reciprocity law failure of the film Provide a kVp and mAs readoutProvide a kVp and mAs readout Reproduce accurate densities on each filmReproduce accurate densities on each film

SINGLE EMULSION FILMSINGLE EMULSION FILM

More silver halide and gelatin per More silver halide and gelatin per emulsion layer than double emulsionemulsion layer than double emulsion

Longer immersion time in developer due to Longer immersion time in developer due to thicker emulsionthicker emulsion

More susceptible to artifactsMore susceptible to artifacts Anti-halation layerAnti-halation layer Base + fog no more than .16-.20Base + fog no more than .16-.20

H&D CURVEH&D CURVE

High contrast films have a steeper High contrast films have a steeper average gradientaverage gradient

Fast films respond to lower exposures Fast films respond to lower exposures creating higher optical density with less creating higher optical density with less light exposure.light exposure.

DOUBLE EMUSION FILMDOUBLE EMUSION FILM

Contrast is less but 60% fasterContrast is less but 60% faster

Less susceptible to processor problems Less susceptible to processor problems and artifactsand artifacts

CASSETTES/SCREENSCASSETTES/SCREENS

Fluorescent layers either calcium Fluorescent layers either calcium tungstate (blue) or rare earth phosphor tungstate (blue) or rare earth phosphor (green orthochromatic film)(green orthochromatic film)

An increase in screen speed will not cause An increase in screen speed will not cause as much of an increase in quantum mottle as much of an increase in quantum mottle (noise) as film would.(noise) as film would.

The thicker the screen, the greater the The thicker the screen, the greater the blur, but the faster the screen becomes, blur, but the faster the screen becomes, thus the lower the dose.thus the lower the dose.

PROCESSINGPROCESSING

Extended processed films remain in Extended processed films remain in developer 47 seconds (as opposed to 23 developer 47 seconds (as opposed to 23 sec in standard).sec in standard).

Diffusion of developer through the thicker Diffusion of developer through the thicker emulsion requires:emulsion requires: Longer immersion in developerLonger immersion in developer Increase in developer tempIncrease in developer temp Movement of film through rollers to give Movement of film through rollers to give

developer better access to silver halide developer better access to silver halide

EXTENDED PROCESSINGEXTENDED PROCESSING

Increased contrastIncreased contrast

Increased film speedIncreased film speed

Decreased doseDecreased dose

Increased noiseIncreased noise

STANDARD PROCESSINGSTANDARD PROCESSING

Decreased noiseDecreased noise

Increased doseIncreased dose