Title: Radiographic Inspections
1Radiographic Inspections
- Procedures for Digital and Conventional
Radiographic Imaging Systems - Lee W. Goldman
- Hartford Hospital
2Filling in the Gap
3Reasons 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)
4Philosophy 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
5Philosophy 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
-
6Sources of Requirements/Guidelines
7Guidelines 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
8Efficiency of Methodology
- Combination of tests where appropriate
- Time saving tools
- Minimizing cassette/film usage (trips to the
darkroom)
9Organization of Work
- Concise data forms avoid multiple pages
- Sensible order verify detents before AEC tests
- Effective reports Clear summary, recommendations
-
10Frequency of Radiographic Findings
11Inspection 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
---?
12Cardboard Cassettes or ReadyPack
13Radiographic 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)
14Visual 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
15X-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
16kVp 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
17Causes 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.
18Causes 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
19Measuring kV Yesterday
20Measuring kVp Today
21kVp 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
22Effect of Filtration on kV Meters
23kVp Waveforms
- Obtainable with meters having computer output
- Very useful to recognize cause of calibration
problems(ramps, spikes, dropped cycles or phases)
24kVp 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!!
25kVp 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
26X-ray Beam Measurements
- kVp accuracy AND reproducibility
- Exposure rates (mR/mAs)
- mA linearity
- Exposure control
- reproducibility
- Half-Value Layer
27Beam 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!!
28Efficient 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
29Efficient Beam Measurements
30Geometry 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
31Efficient Beam Measurements
Multifunction Meters
32X-ray Beam Measurements
- kVp accuracy AND reproducibility
- Exposure rates (mR/mAs)
- mA linearity
- Exposure control
- reproducibility
- Half-Value Layer
33Exposure 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
34X-ray Beam Measurements
- kVp accuracy AND reproducibility
- Exposure rates (mR/mAs)
- mA linearity
- Exposure control
- reproducibility
- Half-Value Layer
35Evaluating Linearity
- Both adjacent-station linearity as well as
overall linearity (between any two mA stations)
are important
36mA 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
37mA 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
38X-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
39Timer Accuracy
40Exposure 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
41Timer 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
42X-ray Beam Measurements
- kVp accuracy AND reproducibility
- Exposure rates (mR/mAs)
- mA linearity
- Exposure control
- reproducibility
- Half-Value Layer
43Reproducibility
- 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
44X-ray Beam Measurements
- kVp accuracy AND reproducibility
- Exposure rates (mR/mAs)
- mA linearity
- Exposure control
- Half-Value Layer
45HVL 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
46Collimation
- X-ray/light field congruence and alignment
- Light field Illumination
- Anode cutoff
- Damaged off-focus radiation limiters
- Positive Beam Limitation
47Collimation Congruence
48Collimation 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
49Light 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
50Anode 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
51Positive 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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53Focal 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?)
54SID 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)
55Grid 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)
56Grid 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)
57Stationary Grid Artifacts with CR
- Problem if grid lines parallel to CR horizontal
scan direction - Need gt 65-70 lines/cm for clinically acceptable
images
58Testing 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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60Radiograpic Inspection Summary
- 1)Â 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)Â HVL measurement
- 5) Light/X-ray field alignment
- 6)Â Star pattern focal spot test with SID
verification - 7)Â PBL test with film 14x17 test inspected for
coverage - 8)Â Grid alignment (also inspected for coverage)
- 9)Â Table and upright receptor AEC tests (if
applicable) - 10)Â Darkroom fog evaluation (if applicable)
- 11)Â Vendor-specific digital receptor tests, if
available
61Portable 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