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
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