Appendix_3.pdf

Computed Radiography Systems for USAF Airframe Crack Detection Applications and Development of System Performance Requirements

(Evaluation Report)

2 February 2012

Evaluation Report

(SA103002)

Report No. AFRL/RXS 12-002

AUTHOR(S)

Materials Integrity Branch (AFRL/RXSA) Wright-Patterson Air Force Base, Ohio 45433-7718

REQUESTER

NDIEWG

AFRL/RXS-OL

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PD-AFLCMC-EZPT-17-01 Appendix 3

1216544567C Highlight

AFRL/RXS 12-002

iv

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TABLE OF CONTENTS

Page

PURPOSE

BACKGROUND

FACTUAL DATA

DISCUSSION

CONCLUSIONS

RECOMMENDATIONS

FIGURES

APPENDICES

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Computed Radiography Systems for USAF Airframe Crack Detection Applications and Development of System Performance Requirements

PURPOSE

The purpose of this report is to summarize the findings of the USAF Computed Radiography (CR) Crack Detection Program and the development of recommended system specifications and test procedures to be used to qualify CR systems to be used for USAF airframe crack detection applications.

BACKGROUND

The Air Force Research Laboratory/Materials Integrity Branch (AFRL/RXSA) developed a set of recommended CR system specifications and an associated test procedure that will be used to „qualify‟ the performance of a CR system. Both of these items are documented as separate appendices in this report, so that field and depot units can use the documents either in combination or individually.

Both of these documents were developed using information generated from a test program titled “Computed Radiography for Crack Detection,” which was awarded to the University of Dayton Research Institute (UDRI) and managed by the Air Force Research Laboratory/Nondestructive Evaluation Branch AFRL/RXLP. AFRL/RXSA was the USAF technical lead on the program. Data from this program were used to establish the necessary performance requirements of CR systems to ensure crack detection performance equivalent to film radiography for typical USAF airframe crack inspection applications. „Typical‟ was defined by the USAF user community as through-thickness cracks 0.25 inches in length or longer, in crack layers with thicknesses of 0.040-0.375 inches, within aluminum structures with „total thicknesses‟ between 0.375 and 1.125 inches. Although the majority of the program evaluated this range of applications, limited work was also performed on total thicknesses up to 2 inches, and in steel crack layers up to 0.250 inches thick. Validation was demonstrated with a Probability of Detection (PoD) study. The program was completed in 2011, and detailed technical data from the program is documented in AFRL technical report# AFRL-RX-WP-TR- 2011-4347 “Computed Radiography Crack Detection Validation Study.”

The USAF defines a „CR system‟ as the complete system used to perform the inspection.

As a minimum, the CR system includes: the X-ray tube (and focal spot size), imaging plate type, scanner model and settings, viewing monitor model, and system software and firmware. If any one of these components is changed, the system performance could be affected. If sufficient comparison testing is performed, as determined by the responsible engineering office, similarity of system variables may be established (e.g., two different manufacturer‟s imaging plates may be shown to perform similarly and be considered interchangeable).

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FACTUAL DATA

System Performance Required for Crack Detection

The crack detection study evaluated a relatively wide range of CR system variables covering a similarly wide range of crack detection capability. The study determined that two performance metrics, in particular, were key in determining if a CR system would perform as well as film for the range of USAF crack detection applications evaluated. These two metrics were: (1) spatial resolution and (2) signal-to-noise ratio (SNR).

Spatial resolution was evaluated using the foil line pair gauges in the USAF CR Process Control Standard (CRPCS) (Figure 1). SNR was measured using a related metric called Equivalent Penetrameter Sensitivity (EPS) using a 2024 aluminum version of the ASTM E746 Relative Image Quality Indicator (RIQI) (Figure 2). The ASTM E746 RIQI uses four EPS plaques placed on a 0.75 inch thick absorber.

It was determined that CR systems with 6 lp/mm spatial resolution or higher in both the x and y orientations, in addition to an EPS performance of 1.28% or less, performed as well as film for detection of cracks in typical USAF airframe applications. These system performance requirements were used to develop the “USAF Computed Radiography System Performance Qualification Test Procedure for Airframe Crack Detection Applications” (Appendix A).

CR systems which meet these performance criteria are usually systems which sample data at 50 micron resolution, and use imaging plates (IP) commonly referred to as „high resolution‟ (HR) IPs.

Other System Features

In addition to crack detection performance, other system features were found to be necessary and/or beneficial for crack detection inspections, or inspections in general (e.g., FOD, water, etc.). These requirements and features were identified either during the study, adopted from previous USAF CR product descriptions, or adopted from an unpublished draft system qualification checklist developed by the Federal Working Group on Industrial Digital Radiography (FWG-IDR).

Many of these features are considered to be requirements (e.g., environmental, image data, software functions, etc.), while some are optional (e.g., ability to handle odd shaped IPs, non-mandatory software tools, etc.), and others are specific to the user (i.e., tailorable, such as system size and weight, number of USB ports on computer, etc.).

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DISCUSSION

Since CR is still a relatively new and evolving technology, there are several technical aspects and „lessons learned‟ that warrant additional discussion to ensure the user has a fundamental understanding of how to select and use a CR system.

Imaging Plates

Most imaging plate manufacturers make several models of imaging plates. The primary differences between imaging plate types is materials, coatings, and grain size. Materials are proprietary. Thicker IP coatings prevent wear, but may reduce image quality. Coarse grained IPs tend to be faster (i.e., require less dose) and have relatively low SNR (i.e., „noisier‟), while fine grained image plates are typically slower but have higher SNR. There are exceptions, and technology is continually changing the state-of-the-art. Also, depending on the application, adjusting scanner settings (e.g., laser power, PMT gain) can often make exposure times for „slow‟ IPs more practical. The drawback is the potential for reduced image quality in terms of spatial resolution or SNR.

IPs that performed best for crack detection are considered by most manufacturers to be „high resolution‟ (HR) IPs. Most manufacturers also make an „ultra‟ high resolution (UHR) IP as well, but in limited testing, UHR IPs have shown poorer SNR at the 50 micron sampling resolution (i.e., EPS>1.28%). Limited testing of UHR IPs at 25 micron sampling demonstrated the required EPS values for crack detection (i.e., EPS<1.28%), but most CR systems cannot sample at 25 micron, and those that can may be limited to processing smaller IPs (e.g., 8x10) due to large image file sizes.

To clarify a common misconception, it should also be noted that „50 micron IP,‟ „100 micron IP,‟ etc. are misnomers. Sampling resolution is determined by the scanner. Any IP can be sampled at any micron resolution. The only exceptions are when an IP has a barcode on it that is used to tell the scanner what sampling resolution to use (see Processing Cassettes, below).

ProcessingCassettes

Depending on the CR system, processing cassettes may or may not be required. Some systems use a hard cassette with an internal microchip which „tells‟ the scanner at what resolution to sample the imaging plate (i.e., 50, 100, 200 micron, etc.). Some systems use hard cassettes with a transparent window, allowing the scanner to „read‟ a barcode affixed to the imaging plate to determine the sampling resolution. Many systems, however, whether or not they require a processing cassette, will require the user to select the sampling resolution through the workstation interface.

Scanners

Although all scanners operate similarly by transporting an IP past a scanning laser, specific features of scanners can be significantly different. Some features to be aware of include:

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IP wear. IP wear may depend on scanner design. Drum type scanners tend to score the surface of the IP as it is dragged across the surface of the drum. This primarily occurs on the non-imaging side of the IP but, over time, can affect image quality. Many other systems with internal rollers may cause minor IP damage, but most newer systems are designed to avoid abrasion of the IP surface and/or incorporate roller designs that are very gentle on the IP surface.

Custom IP handling. A common user requirement for USAF airframe inspection is the ability to process custom shaped IPs. This is necessary in many cases due to access limitations (e.g., nearby structural interferences, etc.). For film applications, this was accomplished by simply cutting the film into relatively simple shapes, which most automatic film processors could easily handle. With CR, some hard cassette systems will only process rectangular IPs in standard sizes (e.g., 8x10 inches, 14x17inches), some systems can handle relatively simple custom shapes (e.g., hard cassette systems with custom „templates,‟ „drum‟ scanners), and other systems can handle nearly any shape IP by employing unique features (e.g., integral glass cassette within scanner; use of a sticky „carrier‟ plate that the cut IP can be laid on for transport through the scanner). Likewise, for the less common requirement to process IPs of non-standard lengths (i.e., >17 inches), only a few scanner models can accommodate.

Artifacts. Dust, lint, and debris can be trapped within a cassette or on an IP, so care must be taken to keep these areas clean. However, some scanner designs are more prone to introducing contaminants that cause these artifacts, possibly due to location of internal optics, type of openings for transporting IPs, and/or airflow through the scanner. Though not a significant concern for crack detection applications, these contaminates appear as white artifacts and can be misinterpreted as defects (e.g., tungsten inclusions in welds).

Viewing Monitors

CR systems may have one or multiple monitors. In all cases, the monitor for viewing the CR image must be a high resolution monitor containing 3 or 5 million pixels (i.e., 3MP or 5MP).

In most cases, the high resolution monitor is monochrome (i.e., black and white), but may be color. When a second monitor is employed, it is typically a low resolution monitor strictly for displaying the user interface. In no case should the low resolution monitor be used to interpret CR images. The only significant detriment observed with the 3MP monitors was aliasing of line pair gauge images when used with software that can rotate the image at angles other than 90 degrees (a.k.a. infinite rotation). In other words, if the image was rotated to any angle other than 90o/180 o/270o, „diagonal stripes‟ appear between lines in the line pair gauges (Figure 3). As a result, use of infinite rotation capability is not recommended with 3MP monitors unless approved by the cognizant engineering authority.

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Image Data

Most CR systems now advertise to be „DICONDE compliant.‟ DICONDE (Digital Imaging and Communication in Nondestructive Evaluation) is a standard for image data acquisition, review, storage, and archival. One of the benefits of using a DICONDE compliant system is that the user is ensured image information is recorded along with the image, and all of this information can be viewed on any DICONDE compliant system, regardless of whose system it was acquired on. Some information is recorded automatically (e.g., scanner ID, spatial resolution, etc.) while other information is input by the user before scanning the IP (e.g., component name, date, etc.). In some cases, the workstation software will prompt the user for data not required by DICONDE (e.g., kV, mA, time, etc.) and, in most cases, the software will allow for recording of custom notes. In addition, some manufacturers‟ software can automatically display selected DICONDE data on the image.

Software Ffilters

Image post-processing filters are common among all CR systems. Post-processing filters alter the image in an attempt to improve image quality; however, if used improperly, these same filters can easily mask relevant indications. Some filters are relatively simple (e.g., smoothing, sharpening, edge enhancement, etc.) while others are complex and proprietary. Although only a limited evaluation of post-processing filters was performed in the USAF crack detection study, use of filters for interpreting images of cracks is currently prohibited.

Additional Literature and Resources

In recent years, more information on CR has become available, some publically and some through member organizations. If further information is desired on select CR topics, the following references are recommended:

1. AFRL-RX-WP-TR-2009-4069 “Development of the USAF Computed Radiography (CR) Process Control”. Explanation of the rationale used to develop the USAF CR Process Control procedures and test standard.

2. AFRL-RX-WP-TR-2011-4347 (public release version) “Computed Radiography Crack Detection Validation Study”. A detailed summary of the USAF crack detection study.

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3. ASTM E2033 “Standard Practice for Computed Radiology”. Covers application details and a fairly thorough tutorial of CR.

4. ASTM E2339 “Standard Practice for Digital Imaging and Communication in Nondestructive Evaluation (DICONDE)”.

5. Federal Working Group on Industrial Digital Radiography (FWGIDR). The FWGIDR is chartered by the Defense Working Group (DWG), and has a public website (http://www.dwgndt.org/fwgidr.htm) that contains white papers covering several topics including:

o Recommended Training Curriculum for Digital Radiography Personnel o Guide for the Qualification of Digital Radiography Systems and Processes o Hardware for High Energy Applications o Guide for Standardization and Management of Digital NDT Data

CONCLUSION

The information provided above and in the appendices will aid the user in making an informed decision when selecting a CR system for crack detection inspection applications.

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FIGURES

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(a)

(b)

Figure 3. Example of (a) good line pair vs. (b) aliased line pair

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APPENDICES

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APPENDIX A

“USAF Computed Radiography System Performance Qualification Test Procedure for Airframe Crack Detection Applications”, 24 Oct 2011, AFRL/RXSA

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USAF COMPUTED RADIOGRAPHY

SYSTEM PERFORMANCE QUALIFICATION TEST PROCEDURE FOR

AIRFRAME CRACK DETECTION APPLICATIONS

24 Oct 2011

AFRL/RXSA

USAFCOMPUTED RADIOGRAPHY SYSTEM PERFORMANCE QUALIFICATION

TEST PROCEDURE FOR AIRFRAME CRACK DETECTION APPLICATIONS

1. INTRODUCTION.

1.1 General Description. The following computed radiography (CR) general practice is to be used to perform system qualification for use of CR for crack detection. It is intended that this general practice be performed by technicians or engineers who have completed all pertinent training on the use of film based radiography, are cognizant of standard radiographic principles, are familiar with the operation of CR systems, and all appropriate radiation safety procedures are in place and operative.

1.2 General Requirements. This procedure prescribes general set-up and test requirements for system qualification for crack detection using CR systems. CR system qualification test results shall be reviewed and approved by the appropriate authority. Likewise, if conditions exist that are not adequately covered, contact the appropriate authority. For Air Force units contact the weapon system‘s ALC NDI Manager or AFRL/RXSA. For Navy units contact the FRC NDI Program Manager.

2. TEST MATERIALS.

2.1 USAF Computed Radiography (CR) Process Control Standard (PCS), NSN 6635-01-555-4372 (Figure 1)

2.2 USAF EPS Test Standard. Raycheck RIQR2024EPS plaques mounted on Raycheck RIOI-AP absorber block. (Figure 2)

Figure 1. USAF Computed Radiography (CR) Process Control Standard (PCS), NSN 6635-01-555-4372

4.2.2.2 Model

4.2.2.3 Serial number

4.2.2.4 Eraser settings (e.g. gain)

4.2.3 Imaging plate

4.2.3.1 Manufacturer

4.2.3.2 Type/model (e.g. IPS)

4.2.4 Processing Cassette (if applicable)

4.2.4.1 Manufacturer

4.2.4.2 Type/model

4.2.5 System Controller/Workstation

4.2.5.1 Manufacturer

4.2.5.2 Model

4.2.5.3 Serial number

4.2.6 Data acquisition and reviewing (or image processing) software

4.2.6.1 Manufacturer

4.2.6.2 Software name and version/revision

4.2.7 Viewing monitor

4.2.7.1 Manufacturer

4.2.7.2 Model (also note whether monochrome or color)

4.2.7.3 Size (diagonal, inches), 17 inch minimum required

4.2.7.4 Resolution (megapixels), 3MP minimum required

4.2.8 X-ray tube (including control unit and cooler) – see note below

4.2.8.1 Manufacturer

4.2.8.2 Model

4.2.8.3 Serial number

4.2.8.4 Focal spot (mm, per EN12543)

4.2.8.5 Tube filters (material and thickness, if used)

4.2.9 X-ray tube control unit

4.2.9.1 Manufacturer

4.2.9.2 Model

4.2.9.3 Serial number

4.2.10 X-ray tube cooler

4.2.10.1 Manufacturer

4.2.10.2 Model

4.2.10.3 Serial number

NOTE

Most USAF applications will use Lorad KVP160 x-ray tubes, therefore if a different tube is used for testing, the test results must be verified using a Lorad x-ray tube unless prior approval by the appropriate authority identified in section 1.

Once qualified, the minimum system components that shall not be interchangeable include: x-ray tube manufacturer/model, CR scanner manufacturer/model, CR scanner settings, IP type, IP cassette type/model. (non-interchangeable components are shaded in Appendix B, Table B-1).

Focal spot measurements are typically measured in accordance with one of two specifications. In general, EN12543 is the older of the two specifications and is used to measure the Lorad KVP160 tube focal spot as 1.5mm. A newer specification occasionally used is IEC336, which on average measures focal spots to be roughly half of the size measured by EN12543. Care should be taken to record focal spot data IAW EN12543 to ensure tube performance is compared properly.

4.3 Process Control Testing—The CR system shall satisfy the CR process control requirements stated in Appendix C.

4.4 System Performance Tests.

4.4.2.4.2 Record kV, exposure, %EPS, and approximate pixel value (e.g. for a system with a max pixel value of 65500, round to the nearest 1000) for the image as shown in App B Table B-2.

4.4.2.4.3 Repeat at increasing exposure times of 15 seconds (or exposures of 75 mA-sec) until four consecutive EPS readings are at or below 1.28%EPS, AND the numerical average of the four readings is 1.24% or less (i.e. all readings 1.28% or less, and at least two of the four readings 1.19% or less). Record this as the AVERAGE EPS value for this specific system in App B Table B-1.

If image is saturated (i.e. maximum pixel value is achieved) prior to completing 4.3.2.4.3, reduce kV and return to step 4.3.2.3.

4.4.2.4.4 Record the MINIMUM QUALIFIED EXPOSURE AT 48 INCHES for this specific system as the numerical average exposure (mA and time) of these four data points.

Maximum exposure time shall not exceed 3 minutes (or 900 mA-sec) at 48 inches.

Minimum qualified exposure is typically achieved between 1-2 minutes, or 300-600 mA-sec.

To reduce exposure time, system optimization recommendations include: Changing to a finer grain (lower noise) imaging plate; Adjusting scanner settings if applicable (Consult with manufacturer for guidance); Increasing mA if possible; or Evaluate power source for noise (i.e.

line conditioner or voltage regulator may be required).

An example of the EPS evaluation is presented in Appendix D.

4.4.2.4.5 Establish the minimum qualified pixel value as the lowest pixel value of these four data points. Record this as the MINIMUM QUALIFIED PIXEL VALUE for this specific system in Appendix B Table B-1.

A lower minimum pixel value allows a larger useable range of data in the radiograph. If a lower minimum qualified pixel value is desired, it is recommended to repeat the tests with a lower kV.

5. SUMMARY OF QUALIFICATION CRITERIA FOR CR SYSTEM PERFORMANCE. Using the above procedures,

5.1 No less than 6.0 lp/mm spatial resolution in both orientations.

5.2 Less than or equal to 1.24% EPS, with minimum qualified exposure of less than 5mA and 180 seconds (900 mA-sec) at 48 inches Source-to-Detector distance.

APPENDIX B – Checklists for System Qualification

Table B-1 CR SYSTEM DESCRIPTION AND PERFORMANCE METRICS CHECKLIST

CR System #1 CR System #2 CR System #3 CR System #4 gain laser power other (specify) other (specify)

A

B

4.4.2.4.3

4.4.2.4.5

4.4.2.2 amperage (mA) time (sec) 4.4.2.4.4

MIN QUAL EXP

(at 48 in) manufacturer model number serial number of system tested

4.4.1 System

Performance

Results /

Acceptance Criteria for Process

Controls spatial resolution lp/mm image noise

AVERAGE %EPS

energy (kV) filters (if used)

4.2.9 Control Unit

manufacturer model number serial number of system tested

4.2.10

MIN QUAL PIXEL VALUE

name revision

4.2.7 Viewing Monitor

manufacturer model serial number display size (inches, diagonal) resolution (megapixels, MP)

4.2.5 System Controller/Workstation

manufacturer model serial number

4.2.6

Data Acquisition and/or

Review Software #1 name revision

Data Acquisition and/or

Review Software #2 maximum pixel value

4.2.2 CR Eraser (*if separate from Scanner)

manufacturer* model number*

4.2.4 Processing Cassette (if applicable)

manufacturer type type/model eraser settings (specify)

Details serial number internal software (firmware)

4.2.3 Imaging Plates (IP)

manufacturer type/model sampling resolution manufacturer model number

CR System Component

4.2.8 X-ray Tube

manufacturer model number serial number of system tested focal spot (mm) serial number*

Cooler

4.2.1

Test Date

Qualifying Organization

Testing Organization

Test locationpara equipment settings

CR Scanner (Reader)

Shaded cells are parameters and results to be specified for Qualified Systems.

The resulting performance metrics are listed below the solid black line.

Table B-2. Exposure vs. EPS Performance Test Sheet mA sec mA-sec

CR System # exposure approx.

pixel value

% EPSkV Notes

APPENDIX C

Computed Radiography Process Control Test Procedure for Crack Detection Systems

1. INTRODUCTION.

1.1 General Description. The following computed radiographic (CR) general practice is to be used to perform process control checks on CR equipment and materials. It is intended that this general practice be performed by apprentice level technicians or higher with minimal additional training.

a) Like traditional film radiography, the entire computed radiography (CR) process must be closely controlled with process control tests to produce expected results. In the case of CR, the primary concerns are:

Operating performance of the CR system, which includes the imaging plate (IP) reader, eraser, and monitor, and

Degradation of the IPs

b) Most of the process control tests require some type of test target to establish an initial level of performance which is then used as a baseline measurement so subsequent tests can identify performance degradation. Test targets are provided in the USAF Process Control Standard (PCS) as illustrated in Figure 1, and in the EPS Test Standard (for crack detection applications only) in Figure 2. Good record keeping of process controls is also important in maintaining reliability.

Figure 1a. USAF Computed Radiography (CR) Process Control Standard (PCS)

4521x138, NAVAIR ISSC-ChPt Code 43430, DSN 451-8380. For Army units contact: SFAE-AV-AS-AG, NDT CoE, Bldg. 7770, Redstone Arsenal, 256-313-0211, DSN 897-0211.

a) For General Use CR systems (used for applications other than crack detection), process control tests shall be performed every calendar quarter. For Crack Detection CR systems, process control tests are required daily when the system is in use.

b) The CR Process Control tests are split into three types: 1) Display Monitor tests, 2), System tests and 3) IP tests. Refer to Table 1 for a summary of the tests, and Table 2 for a list of possible causes and recommended corrective actions for each test.

i. For General Use CR systems (used for applications other than crack detection), two tests are required: 1) evaluation of a Display Monitor test pattern, and 2) one exposure of the CR process control standard followed by a series of evaluations of the CR image, both visually and with software tools. In some instances, two exposures may be required to perform all evaluations.

ii. For Crack Detection CR systems, the General Use tests are required plus one additional System test (EPS test) is required to measure image noise.

c) System tests are laid out with an initial test setup/data capture procedure that applies to all tests, followed by individual evaluation procedures so that any one test can be performed individually if necessary.

d) When necessary, system specific software procedures are detailed for each manufacturer‘s system CR systems in paragraph 6 through paragraph 8. If procedures for a manufacturer‘s latest software are not listed, consult with the manufacturer for guidance.

e) The IP tests evaluate the IPs only, by providing a method to document IP artifacts which may be useful for determining if a CR image contains non-relevant indications. IP tests are optional and are discussed in paragraph 5.

f) All IPs and cassettes in inventory should be serialized. Consult the system manufacturer for means of serializing as a first choice.

g) Recommended marking methods include notation along the edge of the unexposed side of the IP and the backside of cassettes using a permanent marker. Recommended serialization format is ‗‗Organization/Office symbol-IP MFG- 0001‘‘

2. ACCESS.

NA

3. PART PREPARATION.

NA

f) Documentation. Document pass/fail of the test and any corrective actions taken IAW the process control documentation requirements listed in T.O. 33B-1-1.

Display brightness is monitored by internal software.

If display brightness is inadequate, the software will alert the user that corrective action is required.

4.2 Initial Test Setup/Data Capture Procedure for System Tests.

a) Record the date of the test, and model and serial number(s) of CR reader and CR eraser if applicable.

b) Select a 14-inch x 17-inch IP and cassette. For Crack Detection systems, the same IP type identified in Table 3 shall be used. For General Use systems, any IP type can be used. Record model and serial number of the IP, and the hard or soft cassette.

The first time this test is performed on the system is considered the baseline test. Once a baseline test has been performed, subsequent tests shall use the same type of IP, cassette, parameters, and CR reader settings.

The time elapsed between exposures and processing of the IP for process control tests shall be less than 60 minutes to ensure repeatable data.

Evaluation procedures assume the operator has had adequate training on their specific CR software to be able to perform common post-processing functions such as image optimization using contrast/brightness or equivalent, and magnification.

Evaluation of all images shall be performed using the raw data (no software filters).

c) Record the model and serial number of the PCS. The PCS shall be centered on a 14-inch x 17-inch IP, and oriented such that it covers the entire IP. A minimum of 1/8-inch thick back screen of lead is required for all exposures.

d) Expose the PCS to X-rays. Recommended test parameters: 50kV, 3mA, 20 second exposure, and a

48-inch source to-Source-to-Detector Distance (SDD). Record all exposure parameters.

e) Select the CR reader settings (i.e. sensitivity, pixel pitch, speed, etc.), and record.

f) Scan the IP and display the CR image on the display monitor.

g) Image Acceptance Criteria. Confirm all PCS targets are visible and background area is not greater than 95% of the system‘s max digital value and intensity on line pair target is no less than 10% max digital value.

h) Archive the raw CR image. Record image file name.

4.3 System Test Evaluation for Geometric Distortion. Evaluation of image for overall distortion using special software measurement tools.

The environment of CR viewing area SHOULD be pleasant and SHALL be free of objectionable background light, which MAY cause reflection on the monitors.

a) Adjust the magnification, if necessary, so that the CR image of the entire PCS fits within the viewable area of the display monitor and all geometric distortion markers in the PCS are visible (note: the markers are small ball bearings within the PCS, highlighted with arrows in Figure 4).

b) Using the CR image processing software, calibrate the software measurement tool on the known distance (12.5 inches) between two of the geometric distortion markers across the short direction of the IP (markers 1-3 or 2-4).

MARKER MARKER

2 4

MARKER MARKER

1 3

Figure 4. Simulated CR Image of PCS for Geometric Distortion Table 4. Geometric Distortion Acceptance Criteria

Measurement Direction Markers Acceptance Criteria

Long Diagonal

1-2 (or 3-4) 1-4 (or 2-3)

15.5 ±0 15 in

19.9 ±0.15 in

c) Measure the distance between the geometric distortion markers along one long side and one diagonal on the CR image. See Table 4 for markers to be measured.

d) Acceptance criteria are listed in Table 4.

4.4 System Test Evaluation for Slippage, Scan Line Dropout, Shading and Afterglow. A visual evaluation of the CR image for multiple irregularities.

a) Adjust the magnification, if necessary, so that the CR image of the entire PCS fits within the viewable area of the display monitor.

b) Visually evaluate the image for linear Slippage, Scan Line Dropout, Shading and Afterglow in the short and/or long directions of the CR image. Brightness or equivalent ONLY, may be adjusted during this evaluation to optimize image. See Figure 5 for examples and descriptions of each irregularity.

c) Slippage indications (e.g. indications highlighted by white outline) are evident as a light or dark ‗‗stripes‘‘ or ‗‗bands‘‘ oriented in the short dimension of the CR image (Figure 5, Top left).

Slippage can occur in more than one location in the image, and may occur as wide or narrow indications depending on the amount of slip. Not all CR readers are susceptible to slip.

Figure 5. Simulated CR Images Illustrating Slippage, Scan Line Dropout, Shading, and Afterglow

d) Scan line dropout is evident as a bright white line spanning the entire long dimension of the CR image (Figure 5, Top right). Scan line dropout can occur in multiple places within the same image and may occur as wide or narrow indications.

e) Shading is evident as light and dark ‗‗bands‘‘ oriented in the long direction of the CR image.

(Figure 5, Bottom Left)

f) Afterglow is evident as ‗‗streaking‘‘ or ‗‗overshoot‘‘ at light to dark transition regions in the short dimension of the IP and is most noticeable at the edges of the afterglow target. (Figure 5, Bottom Right)

g) Acceptance criteria. None of the irregularities discussed in paragraph 4.3. shall be visible.

4.5 Laser Beam Jitter Evaluation. Visually evaluate image of jitter target for straight and continuous edges.

a) Adjust the image to an absolute magnification of 1.

b) Visually evaluate the long edges of the entire length of the jitter target in the CR image.

Brightness or equivalent ONLY, may be adjusted during this evaluation. Edges should appear straight and continuous (Figure 6).

Figure 6. Simulated CR Image of Jitter Target

c) Acceptance Criteria. Distorted edges along the jitter target (Figure 7), which may occur at one or more locations, are not permitted.

Figure 7. Example of Jitter

4.6 Spatial Resolution Evaluation. Visually evaluate image for ability to resolve small details or features.

a) Adjust the magnification so that the CR image of one line pair gauge fills the viewable area of the display monitor (Figure 8).

Figure 8. Line Pair Gauge for Spatial Resolution Evaluation

b) Visually optimize image using brightness and contrast (i.e. window/level). During evaluation of the CR image of the line pair gauges, the operator shall be positioned 12-18 inches from the display monitor.

c) Visually evaluate the CR image of the line pair gauge and determine the smallest line pairs per mm (LP/mm) that are separated by a continuous visible space along the entire length of the line pair. Record the LP/mm and line pair gauge ID (A or B).

d) While maintaining the same magnification level and image viewing parameters, manipulate the image to view the other line pair gauge and evaluate it in the same manner. Record the LP/mm and line pair gauge ID (A or B).

It is not uncommon for the spatial resolution between line pair gauges A and B to be different due to inherent differences in scanning resolution of the laser scanner in each direction (i.e. ―fast-scan‖ vs. ―slow-scan‖ directions).

e) Acceptance Criteria. A minimum of 6.0 lp/mm is required in both orientations.

Figure 9. Contrast Sensitivity Gauge for Sensitivity Evaluation

4.7 Contrast Sensitivity Evaluation. Visually evaluate image for ability to detect low contrast features.

a) Adjust the magnification so that the CR image of the contrast gauge fills the viewable area of the display monitor (Figure 9).

b) Visually optimize image using brightness/contrast, window/level, or equivalent.

c) Visually evaluate the CR image of the contrast gauge and record the number of steps that can be visually identified.

If the steps in the contrast gauge are not visible, in the baseline test, it may be necessary to repeat the exposure for this test with different exposure parameters and record the parameters specifically for this test.

Recommended ‗‗alternate‘‘ exposure parameters for the contrast gauge are 60kV, 5mA, and 36sec, at 48 inches.

d) Acceptance Criteria. Three steps must be visually identified on the contrast sensitivity gauge, which equates to 2% contrast sensitivity (2% step highlighted by the arrow in Figure 8).

4.9 Residual Image Evaluation. Evaluate image for proper erasure using special software tools.

a) Erase the IP by processing it through the CR eraser.

Most CR systems automatically erase the IP after reading. If so, the erasure step is not required.

b) Scan the erased IP and display the CR image on the monitor.

c) Evaluate the CR image of the erased IP by measuring the pixel digital value and/or intensity over the entire image using the imaging software tools. See paragraph 6 through paragraph 8 for system specific software procedures.

d) Acceptance Criteria/Corrective Action. The maximum intensity shall be less than 1% of the maximum digital value of the CR system.

APPENDIX D

Example of EPS Evaluation for System Qualification

1) Record energy, exposure, pixel value, and %EPS for each image. (Table D1)

Table D1. EPS Performance Data for System Tested mA sec mA-sec

65 5 15 75 4000 1.49

65 5 30 150 8000 1.33

65 5 45 225 12000 1.28

65 5 60 300 16000 1.28

65 5 75 375 20000 1.19

65 5 90 450 24000 1.28

65 5 105 525 28000 1.19 exposure

%EPS

approx.

pixel value kV

2) The shaded rows indicate the first four exposures that have an EPS at or below 1.28%, AND the numerical average of the four readings is 1.24% or less.

(1.28+1.19+1.28+1.19)/4 = 1.24

3) Minimum qualified exposure (at 48 inches) is the average exposure of these four data points

At 5 mA, average time = (60+75+90+105)/4 = 83 seconds or

Average exposure = (300+375+450+525)/4 = 413mA-sec

4) Minimum qualified pixel value is the lowest pixel value of the four data points = 16000

The mA and time from step 3, along with the kV from Table D1, will be used to evaluate image noise as part of process control testing for this specific system (T.O. 33B-1-2, WP 106 01)