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Radiographic Inspections

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Title: Radiation Protection: Subject: HH Rad protection inservice Author: Lee Goldman Last modified by: Lee Goldman Created Date: 12/5/1997 3:00:44 PM – PowerPoint PPT presentation

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Title: Radiographic Inspections


1
Radiographic Inspections
  • Procedures for Digital and Conventional
    Radiographic Imaging Systems
  • Lee W. Goldman
  • Hartford Hospital

2
Filling in the Gap
3
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)

4
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

5
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

6
Sources of Requirements/Guidelines
7
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

8
Efficiency of Methodology
  • Combination of tests where appropriate
  • Time saving tools
  • Minimizing cassette/film usage (trips to the
    darkroom)

9
Organization of Work
  • Concise data forms avoid multiple pages
  • Sensible order verify detents before AEC tests
  • Effective reports Clear summary, recommendations

10
Frequency of Radiographic Findings
11
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

---?
12
Cardboard Cassettes or ReadyPack
13
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)

14
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

15
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

16
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

17
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.

18
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

19
Measuring kV Yesterday
20
Measuring kVp Today
21
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

22
Effect of Filtration on kV Meters
23
kVp Waveforms
  • Obtainable with meters having computer output
  • Very useful to recognize cause of calibration
    problems(ramps, spikes, dropped cycles or phases)

24
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!!

25
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

26
X-ray Beam Measurements
  • kVp accuracy AND reproducibility
  • Exposure rates (mR/mAs)
  • mA linearity
  • Exposure control
  • reproducibility
  • Half-Value Layer

27
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!!

28
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

29
Efficient Beam Measurements
  • Multiple Meters

30
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

31
Efficient Beam Measurements
Multifunction Meters
32
X-ray Beam Measurements
  • kVp accuracy AND reproducibility
  • Exposure rates (mR/mAs)
  • mA linearity
  • Exposure control
  • reproducibility
  • Half-Value Layer

33
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

34
X-ray Beam Measurements
  • kVp accuracy AND reproducibility
  • Exposure rates (mR/mAs)
  • mA linearity
  • Exposure control
  • reproducibility
  • Half-Value Layer

35
Evaluating Linearity
  • Both adjacent-station linearity as well as
    overall linearity (between any two mA stations)
    are important

36
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

37
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

38
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

39
Timer Accuracy
40
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

41
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

42
X-ray Beam Measurements
  • kVp accuracy AND reproducibility
  • Exposure rates (mR/mAs)
  • mA linearity
  • Exposure control
  • reproducibility
  • Half-Value Layer

43
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

44
X-ray Beam Measurements
  • kVp accuracy AND reproducibility
  • Exposure rates (mR/mAs)
  • mA linearity
  • Exposure control
  • Half-Value Layer

45
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

46
Collimation
  • X-ray/light field congruence and alignment
  • Light field Illumination
  • Anode cutoff
  • Damaged off-focus radiation limiters
  • Positive Beam Limitation

47
Collimation Congruence
48
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

49
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

50
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

51
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

52
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53
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?)

54
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)

55
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)

56
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)

57
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

58
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

59
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60
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

61
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
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