Minimum Requirements for Digital Radiography …

1 Ewert and Zscherpel1 Requirements for RT-DECNDTP raha, Oct. MethodsMinimum Requirements for Digital Radiography Equipment and Measurement Procedures by Different Industries and Standard Ewert and Uwe ZscherpelBAM Federal Institute for Materials Research and Testing, Berlin, GermanyEwert and Zscherpel2 Requirements for RT-DECNDTP raha, Oct. MethodsIntroduction-Film Radiography has been developed for quality assurance in industry over decades. - It is basis for contractual agreements of Supplier and Radiography shall achieve the same image qualityor better, but with higher image quality Requirements of different standards as ASTM, ASME and ISO are compared.

2 - The essential parameters for optimization and prediction of IQI visibility are discussed. - Requirements for equipment selectionare derived for CR and DDAs. - Newly developed classification procedures for RT-D equipment are introduced. Ewert and Zscherpel3 Requirements for RT-DECNDTP raha, Oct. MethodsBasic Requirements in Radiography RequirementFilmDigitalStandardsISO, CEN, ASTM, ASMEISO, CENASTM, ASME, MAIE xposureExceed Minimum optical densityExceed Minimum required SNRN(Normalized Signal to Noise Ratio)DDAs: Exceed Minimum required CNRCR: expose to EPS plateau (MAI) Detector requirementsUse required film system classor betterUse detectors which achieve the required SNRN anddo not exceed the detector unsharpnesslimitDo not exceed image unsharpness limitsMaximum image unsharpnessDo not exceed the geometrical unsharpness limitsDo not exceed the image unsharpness limitsDo not exceed the image unsharpnesslimitsImage qualityAchieve required IQI contrast sensitivityAchieve IQI contrast sensitivity + duplex wire resolutionAchieve required IQI contrast sensitivityEwert and Zscherpel4 Requirements for RT-DECNDTP raha, Oct.

3 MethodsKey Technologies for Film Replacement Computed Radiography (CR) with storage phosphor imaging plates Digital Detector Arrays(DDA)CRDDAE wert and Zscherpel5 Requirements for RT-DECNDTP raha, Oct. MethodsImage Quality in Radiography - Influence of SNR and CNR -LengthIntensityContrastSignal(base material)LengthIntensityContrastSignal(b ase material)Notch visible!Contrast/Noise is highSignal/Noise is highNotch not visible!Contrast/Noise is lowSignal/Noise is lowNotch is visible in the profile if C > NoiseEwert and Zscherpel6 Requirements for RT-DECNDTP raha, Oct. MethodsTypical noise sources in Digital Radiography :1.

4 EXPOSURE CONDITIONS:Photon noise, depending on exposure dose ( mA sor GBq min). This is the main factor! SNR increases with higher exposure Limitation for the maximum achievable SNR:1. DETECTOR:Structural noise of DDAs and Imaging Plates also called fixed pattern noise (due to variations in pixel to pixel response and inhomogeneities in the phosphor layer). 2. OBJECT:1. Crystalline structure of material ( nickel based steel, mottling)2. Surface roughness of test objectNoise Sources in Radiographic ImagesEwert and Zscherpel7 Requirements for RT-DECNDTP raha, Oct. MethodsMeasurement of Contrast to Noise Ratio in DDA Practice CNR shall be measured in the 4T hole for proof of image quality.

5 A Minimum CNR of is required by ASTM E 2698. This value needs to be revised! CNR = = I = 473 Noise = 71 SNR = 155 ASTM E 1025 I I=contrastNoiseby ASTM E 2698 Ewert and Zscherpel8 Requirements for RT-DECNDTP raha, Oct. MethodsCNR = = = 1 2 mmNoise = 1000 Signal = 3000050 m pixel sizeSRbimage = 50 mHuman Observer Model: Perception Threshold PTCNR bconstSRdPTPT const- constant human perception threshold 10d diameter of just visible holeCNR - contrast to noise ratioSRb basic spatial resolution (effective pixel size) Large area flaws are better visible than small ones at same Contrast-to-Noise Ratio Each row has indications with same CNR = Cdepth/ Each column has holes with same diameterFlat bottom holes of different depth and diameterd - diameterof holeRose approach, 1946 ASTM E 2698 requires CNR > revision!

6 Ewert and Zscherpel9 Requirements for RT-DECNDTP raha, Oct. Methods ASTM Draft, Practice for the Use of Digital Detector Arrays and Computed Radiology for Aerospace Casting Inspections requires a Minimum basic spatial resolution of the detector (SRbdetector) if images have been taken without magnification or a Minimum basic spatial resolution in the magnified image SRbimage). System Selection for ASTM Standard Practice 9imagebSREffective pixel size of Digital image ()Ewert and Zscherpel10 Requirements for RT-DECNDTP raha, Oct. Methods ASTM Draft, Practice for the Use of Digital Detector Arrays and Computed Radiology for Aerospace Casting Inspections and E 2698 Standard Practice for Radiological Examination Using Digital Detector Arrays require for Digital images with DDAs in the 2T IQI hole: The ASTM E 2698 value (CNR = ) is optimized for testing of thin objects with thickness < and typical DDAs in the range of mm < SRb< 130 m.

7 Generally, CNRminfor all Digital images can be described more accurate by the equation: Verification of CNRminfor ASTM Standard Practice holeIQIimagebdiameterSRCNR CNRB ased on old Rose equation as shown before for PTconstantEwert and Zscherpel11 Requirements for RT-DECNDTP raha, Oct. MethodsContrast Sensitivity as Required by Different Standards Almost all standards require image quality indicators on each production radiograph. The operator has to evaluate if the required image quality has been achieved. He decides about acceptance or rejection of the production radiographs. Different international standards require different contrast sensitivities, which yields different inspection quality.

8 The thickness sensitivity improves with material thickness. Ewert and Zscherpel12 Requirements for RT-DECNDTP raha, Oct. MethodsBasic Requirements for IQI Visibility of International Standards in ComparisonASME BPVC SC V, Ar. 2, andISO 17636-class A are about equivalentASTM E1742, E 2104, ISO 17636-class B are about equivalent below t=12 mm (1/2 )Step Holes, ISO17636-2, 2013 Plate Holes, ASMEBPVC SC V Ar. 2 Plate Holes, ASTME 1742, E 2104 ISO 19232-3 ISO 19232-2 ASTM E 1025 Ewert and Zscherpel13 Requirements for RT-DECNDTP raha, Oct. MethodsAdditional Requirements for Unsharpness and Basic Spatial Resolution In all film Radiography standards the permitted geometric unsharpness(Ug) is limited and the film unsharpness is neglected.

9 In Digital Radiography the detector unsharpness (Udetector) contributes significantly to the image unsharpness (Uim) or total unsharpness(UT). Therefore, the permitted detector unsharpness (Udetector) is limited in different standard systems, which is relevant for detector selection. The detector unsharpness shall be always smaller than the permitted geometric unsharpness (Udetector< Ug). The basic spatial resolution is defined as unsharpness in Digital Radiography (SRb= U). Ewert and Zscherpel14 Requirements for RT-DECNDTP raha, Oct. MethodsMeasurement of Basic Spatial ResolutionDuplex wire IQIISO 19232-5 ASTM E 2002 The detector unsharpness udetectorshall be controlled by reference exposures with the duplex wire Wire IQI, 90 kV, 1m SDD, small focusASTM E 2002 Two new wire pairsEwert and Zscherpel15 Requirements for RT-DECNDTP raha, Oct.

10 MethodsStandard ISO 17636-2 (2013): Table , Maximum detector or image unsharpness (2 SRb)DDACRE wert and Zscherpel16 Requirements for RT-DECNDTP raha, Oct. MethodsUnsharpness Requirements of Different International Standards No International Harmonization -0,000,010,020,030,040,050,060,070,080,0 1,02,03,04,05,06,0 Unsharpness in inchThickness in inchUnsharpness requirementsE 1742 ISO 17636 class B ISO 17636 class A MAIE 1030 (2004) E 1030, 1032E 2104 Co-60, High EnergyEwert and Zscherpel17 Requirements for RT-DECNDTP raha, Oct. MethodsUnsharpness Requirements in Different Int. StandardsEwert and Zscherpel18 Requirements for RT-DECNDTP raha, Oct.