Radiographic Inspections Procedures for Digital and Conventional Radiographic

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

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

Filling in the Gap

Filling in the Gap

Reasons for Rad or R/F Inspection State regulatory requirement n 3 rd party payer

Reasons for Rad or R/F Inspection State regulatory requirement n 3 rd party payer requirement n Employer expectations (see following) n Standards of good practice (see above) n 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)

Philosophy of Inspections The goal of radiographic and fluoroscopic (R/F) inspections should be to

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 n image quality n image consistency n This may entail going beyond commonly accepted standards to striving for stricter yet generally achievable performance levels

Philosophy of Inspections Accomplishing this goal require thoroughness on the part of the inspecting

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 n organization of work n attention to frequent problem areas n

Sources of Requirements/Guidelines

Sources of Requirements/Guidelines

Guidelines and Acceptance Limits n n n Many items commonly evaluated physicists have performance

Guidelines and Acceptance Limits n n n 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

Efficiency of Methodology Combination of tests where appropriate n Time saving tools n Minimizing

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

Organization of Work n n n Concise data forms: avoid multiple pages Sensible order:

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

Frequency of Radiographic Findings

Frequency of Radiographic Findings

Inspection Factors for Digital Systems n Many inspection components--no difference – k. Vp, m.

Inspection Factors for Digital Systems n Many inspection components--no difference – k. Vp, m. R/m. As, linearity, timer accuracy, HVL) n For beam measurements (k. Vp, m. R/Mas, etc) – Move tube off of digital receptor if possibile – If not, use lead blocker n Some (may) require digital receptor to record – Collimation – Grid alignment – Focal spot size – SID Indication ---?

Cardboard Cassettes or Ready. Pack

Cardboard Cassettes or Ready. Pack

Radiographic Inspection Components Visual Inspection n Beam Measurements (k. Vp, m. R, HVL, etc)

Radiographic Inspection Components Visual Inspection n Beam Measurements (k. Vp, m. R, HVL, etc) n Receptor Tests: Grids, PBL, Coverage n Tube Assembly Tests: Collim, Foc Spot, SID n AEC (table and upright) n Darkroom Tests (if applicable) n

Visual Inspection n Visually evident deficiencies often ignored/worked around by staff n Reporting deficiencies

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

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As)

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As) n m. A linearity n – Adjacent station – Overall n Exposure control – Timer accuracy – Timer and/or m. As linearity Reproducibility n Half-Value Layer n

k. Vp Evaluation: Significance n Among most common issue, even with HF generators n

k. Vp Evaluation: Significance n Among most common issue, even with HF generators n Poor k. V calibration can: – Increase dose if k. V’s too low – Cause poor m. A linearity, leading to possible repeats n Image contrast: affected, but relatively minor effect for ranges of miscalibration usually encountered

Causes of k. V Miscalibration n Inadequate provisions for k. V adjustments – May

Causes of k. V Miscalibration n Inadequate provisions for k. V adjustments – May have only one overall k. V adjustments to raise or lower all k. Vps and one to adjust k. V ramp – Result: difficult to properly calibration all stations n Miscalibrated compensation circuits: – Initial sags or spikes as tube begins to energize – May significantly affect short exposure times n Important to evaluate k. V accuracy at several m. A/k. V combinations, and possibly all m. A’s.

Causes of HF k. Vp Miscalibration Pulse freq calibration: infrequent but seen on units

Causes of HF k. Vp Miscalibration Pulse freq calibration: infrequent but seen on units invasively calibrated at generator rather than at tube n Power line limitations: more common if powered by 1 -phase line with inadequate power n Units incorporating energy storage device helps n

Measuring k. V: Yesterday

Measuring k. V: Yesterday

Measuring k. Vp: Today

Measuring k. Vp: Today

k. Vp Measurements (Con’t) n Invasive measurement: – still standard for many service personnel)

k. Vp Measurements (Con’t) n Invasive measurement: – still standard for many service personnel) n Non-invasive k. V meters (highly recommended): – Measurements at many settings practical--allows comprehensive eval of accuracy & reproducibility n Understand characteristics of your k. V 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

Effect of Filtration on k. V Meters

Effect of Filtration on k. V Meters

k. Vp Waveforms n n Obtainable with meters having computer output Very useful to

k. Vp Waveforms n n Obtainable with meters having computer output Very useful to recognize cause of calibration problems(ramps, spikes, dropped cycles or phases)

k. Vp: Action Limits n CFR: refers only to manufacturer’s specifications Manufacturer specs: often

k. Vp: Action Limits n CFR: refers only to manufacturer’s specifications Manufacturer specs: often quite loose (eg, +/-7%) Common recommendations: 5% or 4 -5 k. V n For consistency: n n differences between k. V calibration at different m. A stations may be more important than across-theboard errors: eg: 100 m. A --> 80 k. Vp measured to be 84 200 m. A --> 80 k. Vp measures to be 76 Both may yield similar intensities at receptor!!

k. Vp Action Limits-Considerations Inconsistencies may be more important than across-the-board errors n More

k. Vp Action Limits-Considerations Inconsistencies may be more important than across-the-board errors n More important for multi-unit sites (technique consistency matters more) n Older Generators: n n – Often difficult to accurately calibrate all m. A/k. V – 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

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As)

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As) n m. A linearity n Exposure control n reproducibility n Half-Value Layer n

Beam Exposure Measurements PROBLEM FREQUENCIES n Poor linearity (adjacent or a common problem n

Beam Exposure Measurements PROBLEM FREQUENCIES n Poor linearity (adjacent or a common problem n Timer and Reproducibility issues occur less frequently n Problems may appear only: – with certain m. A settings – Under certain conditions – At certain k. V ranges Important to evaluate many k. V/m. A settings!!

Efficient Beam Measurements Valuable to make both k. V and exposure measurements at many

Efficient Beam Measurements Valuable to make both k. V and exposure measurements at many k. V/m. A settings. n Appropriate to measure k. V and exposure measurements simultaneously. n May accomplish this via: n – Appropriate (multipe) tools and test geometry – Multifunction meters

Efficient Beam Measurements Multiple Meters

Efficient Beam Measurements Multiple Meters

Geometry with Multiple Detectors n n Scatter from k. V meter (or other material)

Geometry with Multiple Detectors n n Scatter from k. V meter (or other material) can significantly affect exposure measurement Procedures: – Tight collimation – Block scatter from dosimeter (air gap, foam spacer, lead blocker

Efficient Beam Measurements Multifunction Meters

Efficient Beam Measurements Multifunction Meters

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As)

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As) n m. A linearity n Exposure control n reproducibility n Half-Value Layer n

Exposure Rates (m. R/m. As) n Measure at several m. A/k. V settings covering

Exposure Rates (m. R/m. As) n Measure at several m. A/k. V settings covering the commonly used clinical ranges – Can measure along with k. Vp (no add’l exposures) – Measure at relevant distance (eg, 30”) n Normal ranges very broad: – Affected by filtration, age, k. V and m. A calibration – Common range (30”): 12 +/- 50% (3 -phase, HF) – Narrow limits which have been published (6 m. R/m. As +/- 1 at 100 cm) are not realistic n Greatest value is for patient dose estimates

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As)

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As) n m. A linearity n Exposure control n reproducibility n Half-Value Layer n

Evaluating Linearity Both adjacent-station linearity as well as overall linearity (between any two m.

Evaluating Linearity Both adjacent-station linearity as well as overall linearity (between any two m. A stations) are important

m. A Linearity (con’t) n Definition: L = (Rm. A-1 - Rm. A-2)/(Rm. A-1

m. A Linearity (con’t) n Definition: L = (Rm. A-1 - Rm. A-2)/(Rm. A-1 + Rm. A-2) where R is m. R/m. As at m. A-1 and m. A-2 n Usual Requirement: L < 0. 1 for any pair of adjacent m. A stations n Exposure rates may differ by ~20% yet pass n Prob signif contributor to technique errors n We recommend: L < 0. 1 for any pair of m. A L < 0. 05 for adjacent pairs

m. A Linearity (con’t) For some HF and Falling Load Generators: n Don’t allow

m. A Linearity (con’t) For some HF and Falling Load Generators: n Don’t allow selection of m. A n 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 m. As rather than m. A may be more pertinent n

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As)

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As) n m. A linearity n Exposure control n – Timer accuracy – Timer or m. As linearity reproducibility n Half-Value Layer n

Timer Accuracy

Timer Accuracy

Exposure Control & Timer Accuracy n Measure as part of linearity tests – Also

Exposure Control & Timer Accuracy n Measure as part of linearity tests – Also at longer and shorter times if necessary n For HF generators: – exposures terminated at desired m. As, not time. – More meaningful to evaluate exposure control via linearity of exposure versus m. As

Timer Accuracy: Action Limits n Recommend: – – – Greater attention to m. As

Timer Accuracy: Action Limits n Recommend: – – – Greater attention to m. As and timer exposure linearity Attention to accuracy of short exposure times Awareness of non-invasive timer characteristics

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As)

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As) n m. A linearity n Exposure control n reproducibility n Half-Value Layer n

Reproducibility Usual Criteria: coeff of variaton < 0. 05 n Our experience: Rarely a

Reproducibility Usual Criteria: coeff of variaton < 0. 05 n Our experience: Rarely a problem per se n Causes when found: n – 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 n We recommend: limited test (3 exposures) at several settings, with followup if necessary n

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As)

X-ray Beam Measurements k. Vp accuracy AND reproducibility n Exposure rates (m. R/m. As) n m. A linearity n Exposure control n Half-Value Layer n

HVL Measurement n n n Failures do occur Should test new tubes prior to

HVL Measurement n n n 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 k. Vp Criteria from CFR

Collimation X-ray/light field congruence and alignment n Light field Illumination n Anode cutoff n

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

Collimation: Congruence

Collimation: Congruence

Collimation: Congruence n n n Simple tools can suffice Relatively frequent issue, particularly for

Collimation: Congruence n n n 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

Light Field Illumination/Contrast n CFR Specifications: – Illum: >160 lux at 100 cm –

Light Field Illumination/Contrast n CFR Specifications: – Illum: >160 lux at 100 cm – Contrast: I 1/I 2 > 4 (I 1, I 2 are illuminations 3 mm in and out from light edge, respectively) n Often never inspected n Common problem on some collim designs n Recommend: test if visually dim or edge definition is poor

Anode Cutoff and Off-focus Limiters n n n Evaluated from full-field exposures: – both

Anode Cutoff and Off-focus Limiters n n n 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

Positive Beam Limitation n n n No longer FDA-required Still available/common for non-digital systems

Positive Beam Limitation n n n 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

n Measurement: –OK to use star pattern test with digital image but –difficult to

n Measurement: –OK to use star pattern test with digital image but –difficult to properly expose with NEMA k. V, m. A (need lowest m. As, 1 mm Cu) n n Results rarely useful Pinhole/slit tests: –Not clinically relevant –Needed to resolve failure n Resolution-based test (as in MQSA) at appropriate distance/position could be useful (limits? ) Focal Spot Size

SID Accuracy n Measurement: – Location of focal spot usually not marked or visible

SID Accuracy n 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 n Causes of failure: New installations: n – incorrectly located/mounted scale – miscalibrated digital display n Causes of Failure: Existing installations – incorrect or mispositioned tape measure – Incorrectly used tape (tape handle ‘tip’ or ‘flat’)

Grid Alignment/Appropriateness Common problem area due to: n n Incorrect grid: 72” upright grid

Grid Alignment/Appropriateness Common problem area due to: n n 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)

Grid Cutoff vs Lateral Misalignment Grid cutoff (absorption of primary x-rays) versus amount of

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 10: 1 grid, 103 lines/inch)

Stationary Grid Artifacts with CR n Problem if grid lines parallel to CR horizontal

Stationary Grid Artifacts with CR n Problem if grid lines parallel to CR horizontal scan direction n Need > 65 -70 lines/cm for clinically acceptable images

Testing Grids n If exposure possible with tube off lat detent: – Load cassette

Testing Grids n If exposure possible with tube off lat detent: – Load cassette crosswise in receptor – Position x-ray at lateral detent and proper SID – Expose (~3 m. As at 50 k. Vp) 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 n If cannot move off detent: – one exposure--should have relatively uniform signal or density across image

Radiograpic Inspection: Summary 1) Visual inspection and recording of information 2) k. Vp and

Radiograpic Inspection: Summary 1) Visual inspection and recording of information 2) k. Vp and m. R/m. As together at 4 k. Vs, 3 m. A’s 3) m. R at fixed m. As for all m. A; also measure time, k. Vp 4) HVL measurement 5) Light/X-ray field alignment 6) Star pattern focal spot test with SID verification 7) PBL test with film 14 x 17” 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

Portable Radiography Inspection n Battery-powered: – m. R/m. As and k. V formerly frequent

Portable Radiography Inspection n Battery-powered: – m. R/m. As and k. V formerly frequent problems; rare with modern versions n Capacitor-discharge – More uncommon – Difficult to test n Outlet-powered and all portable types: – Collimation most frequent problem