Radiographic Inspections

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Radiographic Inspections

• Procedures for Digital and Conventional
  Radiographic Imaging Systems
• Lee W. Goldman
• Hartford Hospital

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Filling in the Gap
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Reasons for Rad or R/F Inspection

• State regulatory requirement
• 3rd party payer requirement
• Employer expectations (see following)
• Standards of good practice (see above)
• It is not uncommon that inspections include the
  minimum set of tests and evaluations needed to
  fulfill the expectation or legal requirement
  (perhaps due to time constraints and priorities)

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Philosophy of Inspections

• The goal of radiographic and fluoroscopic (R/F)
  inspections should be to provide value by
  evaluating and (if necessary) improving
• radiation safety
• image quality
• image consistency
• This may entail going beyond commonly accepted
  standards to striving for stricter yet generally
  achievable performance levels

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Philosophy of Inspections

• Accomplishing this goal require thoroughness on
  the part of the inspecting physicist. Since time
  is money, emphasis must be placed on
• efficiency of inspection methodology
• organization of work
• attention to frequent problem areas

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Sources of Requirements/Guidelines
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Guidelines and Acceptance Limits

• Many items commonly evaluated physicists have
  performance levels specified by the Code of
  Federal Regulations (CFR) 21 Part 1020
• For other items, recommendations from various
  organizations (AAPM, etc)are fairly consistent
• State law may impose stricter limits, require
  more frequent evaluations and include more test
  items
• If not legally mandated, acceptance criteria may
  depend on environment, equipment used, etc.
• Might recommend stricter criteria if reasonably
  achievable and provides appropriate benefits

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Efficiency of Methodology

• Combination of tests where appropriate
• Time saving tools
• Minimizing cassette/film usage (trips to the
  darkroom)

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Organization of Work

• Concise data forms avoid multiple pages
• Sensible order verify detents before AEC tests
• Effective reports Clear summary, recommendations

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Frequency of Radiographic Findings
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Inspection Factors for Digital Systems

• Many inspection components--no difference
• kVp, mR/mAs, linearity, timer accuracy, HVL)
• For beam measurements (kVp, mR/Mas, etc)
• Move tube off of digital receptor if possibile
• If not, use lead blocker
• Some (may) require digital receptor to record
• Collimation
• Grid alignment
• Focal spot size
• SID Indication

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Cardboard Cassettes or ReadyPack
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Radiographic Inspection Components

• Visual Inspection
• Beam Measurements (kVp, mR, HVL, etc)
• Receptor Tests Grids, PBL, Coverage
• Tube Assembly Tests Collim, Foc Spot, SID
• AEC (table and upright)
• Darkroom Tests (if applicable)

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Visual Inspection

• Visually evident deficiencies often
  ignored/worked around by staff
• Reporting deficiencies often leads to corrective
  actions
• Include
• Lights/LEDs working
• Proper technique indication
• Locks and interlocks work
• No broken/loose dials, knobs
• Any obvious electrical or mechanical defects

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X-ray Beam Measurements

• kVp accuracy AND reproducibility
• Exposure rates (mR/mAs)
• mA linearity
• Adjacent station
• Overall
• Exposure control
• Timer accuracy
• Timer and/or mAs linearity
• Reproducibility
• Half-Value Layer

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kVp Evaluation Significance

• Among most common issue, even with HF generators
• Poor kV calibration can
• Increase dose if kVs too low
• Cause poor mA linearity, leading to possible
  repeats
• Image contrast affected, but relatively minor
  effect for ranges of miscalibration usually
  encountered

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Causes of kV Miscalibration

• Inadequate provisions for kV adjustments
• May have only one overall kV adjustments to raise
  or lower all kVps and one to adjust kV ramp
• Result difficult to properly calibration all
  stations
• Miscalibrated compensation circuits
• Initial sags or spikes as tube begins to energize
• May significantly affect short exposure times
• Important to evaluate kV accuracy at several
  mA/kV combinations, and possibly all mAs.

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Causes of HF kVp Miscalibration

• Pulse freq calibration infrequent but seen on
  units invasively calibrated at generator rather
  than at tube
• Power line limitations more common if powered by
  1-phase line with inadequate power

• Units incorporating energy storage device helps

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Measuring kV Yesterday
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Measuring kVp Today
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kVp Measurements (Cont)

• Invasive measurement
• still standard for many service personnel)
• Non-invasive kV meters (highly recommended)
• Measurements at many settings practical--allows
  comprehensive eval of accuracy reproducibility
  
• Understand characteristics of your kV meter
• Minimum exposure time for accurate measurement
• Accuracy 2 beware of imposing tight limits
• Effect of mid- or HF (meters that sample
  waveform)
• Selection of waveform type
• Properly calibrated filtration range

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Effect of Filtration on kV Meters
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kVp Waveforms

• Obtainable with meters having computer output
• Very useful to recognize cause of calibration
  problems(ramps, spikes, dropped cycles or phases)

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kVp Action Limits

• CFR refers only to manufacturers specifications
• Manufacturer specs often quite loose (eg, /-7)
  
• Common recommendations 5 or 4-5 kV
• For consistency
• differences between kV calibration at different
  mA stations may be more important than
  across-the-board errors eg
• 100 mA --gt 80 kVp measured to be 84
• 200 mA --gt 80 kVp measures to be 76
• Both may yield similar intensities at receptor!!

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kVp Action Limits-Considerations

• Inconsistencies may be more important than
  across-the-board errors
• More important for multi-unit sites (technique
  consistency matters more)
• Older Generators
• Often difficult to accurately calibrate all mA/kV
  
• Recalibrations may shift error to other ranges
• More important to accurately calibrate limited
  but clinically important limited range
• May attempt improvements during next service or
  during servicing for other corrective actions

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X-ray Beam Measurements

• kVp accuracy AND reproducibility
• Exposure rates (mR/mAs)
• mA linearity
• Exposure control
• reproducibility
• Half-Value Layer

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Beam Exposure Measurements

• PROBLEM FREQUENCIES
• Poor linearity (adjacent or a common problem
• Timer and Reproducibility issues occur less
  frequently
• Problems may appear only
• with certain mA settings
• Under certain conditions
• At certain kV ranges
• Important to evaluate many kV/mA settings!!

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Efficient Beam Measurements

• Valuable to make both kV and exposure
  measurements at many kV/mA settings.
• Appropriate to measure kV and exposure
  measurements simultaneously.
• May accomplish this via
• Appropriate (multipe) tools and test geometry
• Multifunction meters

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Efficient Beam Measurements

• Multiple Meters

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Geometry with Multiple Detectors

• Scatter from kV meter (or other material) can
  significantly affect exposure measurement
• Procedures
• Tight collimation
• Block scatter from dosimeter (air gap, foam
  spacer, lead blocker

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Efficient Beam Measurements
Multifunction Meters
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X-ray Beam Measurements

• kVp accuracy AND reproducibility
• Exposure rates (mR/mAs)
• mA linearity
• Exposure control
• reproducibility
• Half-Value Layer

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Exposure Rates (mR/mAs)

• Measure at several mA/kV settings covering the
  commonly used clinical ranges
• Can measure along with kVp (no addl exposures)
• Measure at relevant distance (eg, 30)
• Normal ranges very broad
• Affected by filtration, age, kV and mA
  calibration
• Common range (30) 12 /- 50 (3-phase, HF)
• Narrow limits which have been published (6 mR/mAs
  /- 1 at 100 cm) are not realistic
• Greatest value is for patient dose estimates

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X-ray Beam Measurements

• kVp accuracy AND reproducibility
• Exposure rates (mR/mAs)
• mA linearity
• Exposure control
• reproducibility
• Half-Value Layer

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Evaluating Linearity

• Both adjacent-station linearity as well as
  overall linearity (between any two mA stations)
  are important

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mA Linearity (cont)

• Definition
• L (RmA-1 - RmA-2)/(RmA-1 RmA-2)
  where R is mR/mAs at mA-1 and mA-2
• Usual Requirement L lt 0.1 for any pair of
  adjacent mA stations
• Exposure rates may differ by 20 yet pass
• Prob signif contributor to technique errors
• We recommend L lt 0.1 for any pair of mA
• L lt 0.05 for
  adjacent pairs

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mA Linearity (cont)

• For some HF and Falling Load Generators
• Dont allow selection of mA
• May allow selection of load
• 60/80/100
• Low/Half/Full, etc)
• May evaluate linearity for different load
• Note For these (and some other HF) units,
  linearity of mAs rather than mA may be more
  pertinent

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X-ray Beam Measurements

• kVp accuracy AND reproducibility
• Exposure rates (mR/mAs)
• mA linearity
• Exposure control
• Timer accuracy
• Timer or mAs linearity
• reproducibility
• Half-Value Layer

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Timer Accuracy
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Exposure Control Timer Accuracy

• Measure as part of linearity tests
• Also at longer and shorter times if necessary
• For HF generators
• exposures terminated at desired mAs, not time.
• More meaningful to evaluate exposure control via
  linearity of exposure versus mAs

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Timer Accuracy Action Limits

• Recommend
• Greater attention to mAs and timer exposure
  linearity
• Attention to accuracy of short exposure times
• Awareness of non-invasive timer characteristics

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X-ray Beam Measurements

• kVp accuracy AND reproducibility
• Exposure rates (mR/mAs)
• mA linearity
• Exposure control
• reproducibility
• Half-Value Layer

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Reproducibility

• Usual Criteria coeff of variaton lt 0.05
• Our experience Rarely a problem per se
• Causes when found
• Abnormally terminated exposures (errors)
• Tripped circuit breaker
• Often occur only at certain technique settings
• CFR test 10 exposures within 1 hour, checking
  line voltage prior to each exposure
• We recommend limited test (3 exposures) at
  several settings, with followup if necessary

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X-ray Beam Measurements

• kVp accuracy AND reproducibility
• Exposure rates (mR/mAs)
• mA linearity
• Exposure control
• Half-Value Layer

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HVL Measurement

• Failures do occur
• Should test new tubes prior to clinical use
• Test procedure should allow easy setup, proper
  geometry (adequate space between dosimeter and
  aluminum sheets
• Measure at desired measured kVp
• Criteria from CFR

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Collimation

• X-ray/light field congruence and alignment
• Light field Illumination
• Anode cutoff
• Damaged off-focus radiation limiters
• Positive Beam Limitation

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Collimation Congruence
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Collimation Congruence

• Simple tools can suffice
• Relatively frequent issue, particularly for
  portables
• Some uncertainty in marking light field edges
• CFR Criteria 2 of SID for L/X congruence and
  indicator accuracy (1.5 at 72 SID !!)
• Can usually do better try for 1 of SID
  congruence

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Light Field Illumination/Contrast

• CFR Specifications
• Illum gt160 lux at 100 cm
• Contrast I1/I2 gt 4 (I1,I2 are
  illuminations 3 mm in and out from light edge,
  respectively)
• Often never inspected
• Common problem on some collim designs
• Recommend test if visually dim or edge
  definition is poor

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Anode Cutoff and Off-focus Limiters

• Evaluated from full-field exposures
• both lengthwise and crosswise orientations
• May combine with PBL or grid alignment tests
• Anode Cutoff failure to reach anode edge of film
  with adequate intensity
• Off-focus limiters
• Can become bent inward, blocking primary x-ray
• Poorly delineated edge of x-ray field occuring
  before reaching each of image receptor

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Positive Beam Limitation

• No longer FDA-required
• Still available/common for non-digital systems
• Test for each cassette size
• Can often use single test cassette by overriding
  PBL or switching to manual mode
• Place angled cassette on table of in front of
  receptor to capture full field
• Limits from CFR
• Common causes of Failure
• Mechanical failure of sensors
• Calibrated for metric but english sizes used, etc

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Focal Spot Size

• Measurement
• OK to use star pattern test with digital image
  but
• difficult to properly expose with NEMA kV, mA
  (need lowest mAs, 1 mm Cu)
• Results rarely useful
• Pinhole/slit tests
• Not clinically relevant
• Needed to resolve failure
• Resolution-based test
• (as in MQSA) at appropriate
• distance/position could be
• useful (limits?)

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SID Accuracy

• Measurement
• Location of focal spot usually not marked or
  visible
• Determine magnification of known-object size
  convenient to combine with star pattern f.s. test
• Digital displays should check 2-3 distances
• Criteria 2 of SID
• Causes of failure New installations
• incorrectly located/mounted scale
• miscalibrated digital display
• Causes of Failure Existing installations
• incorrect or mispositioned tape measure
• Incorrectly used tape (tape handle tip or
  flat)

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Grid Alignment/Appropriateness

• Common problem area due to
• Incorrect grid 72 upright grid for orthopedic
  office
• Angulation due to installation errors or sag
  (with age)
• Incorrect lateral detents (table and upright
  receptors)
• Stationary grid artifacts with CR (corduroy
  effect)

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Grid Cutoff vs Lateral Misalignment

• Grid cutoff (absorption of primary x-rays) versus
  amount of lateral decentering of x-ray tube focal
  spot from the grid focal line. Lateral
  decentering is relatively common due to
  misplacement or changes in detent positions
  (measurements are for a typical 101 grid, 103
  lines/inch)

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Stationary Grid Artifacts with CR

• Problem if grid lines parallel to CR horizontal
  scan direction
• Need gt 65-70 lines/cm for clinically acceptable
  images

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Testing Grids

• If exposure possible with tube off lat detent
• Load cassette crosswise in receptor
• Position x-ray at lateral detent and proper SID
• Expose (3 mAs at 50 kVp) with full x-ray field
• Repeat with lateral shift of /- 1 and /-2
• Can use one cassette, exposing narrow strips
• Maximum density of signal should be at detent
• Image density or signal should be rel uniform
• If cannot move off detent
• one exposure--should have relatively uniform
  signal or density across image

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Radiograpic Inspection Summary

• 1) Visual inspection and recording of information
• 2) kVp and mR/mAs together at 4 kVs, 3 mAs
• 3) mR at fixed mAs for all mA also measure time,
  kVp
• 4) HVL measurement
• 5) Light/X-ray field alignment
• 6) Star pattern focal spot test with SID
  verification
• 7) PBL test with film 14x17 test inspected for
  coverage
• 8) Grid alignment (also inspected for coverage)
• 9) Table and upright receptor AEC tests (if
  applicable)
• 10) Darkroom fog evaluation (if applicable)
• 11) Vendor-specific digital receptor tests, if
  available

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Portable Radiography Inspection

• Battery-powered
• mR/mAs and kV formerly frequent problems rare
  with modern versions
• Capacitor-discharge
• More uncommon
• Difficult to test
• Outlet-powered and all portable types
• Collimation most frequent problem