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NDTMA 2015 Annual Conference
Conversion to Digital Radiography from Film Radiography Steve Mango Worldwide Technical Manager Carestream NDT Rochester, NY
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Overview: • Overview of digital • Basic computed radiography (CR) • Basic digital radiography (DDA) • Image quality measures • ASTM standards • Digital radiography system qualification • Customer acceptance of digital • Audit criteria
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
What is Digital Radiography? • Sources, shielding, image: same as film • Detector: different type for both CR & DR (film is a detector
also) • Everything after exposure to image formation is different
from film • Need computer and monitor • Image is an array of rows and columns of pixels • Each pixel has a value proportional to dose, which
eventually produces an analog “gray value” (brightness) on a display monitor
Digital radiography is a way for you to improve your throughput and reduce consumable expenditures while improving the end customer image experience.
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Digital Image Analog Image
What is a Digital Image?
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Other industries have converted (for example; photography)
• Medical and dental radiography have converted
• NDT is the last to go, still primarily film
• It’s not a matter of “if”; it is a matter of “when”
Reduce consumables, reduce re-‐work, eliminate chemical disposal charges, eliminate film storage costs, improve image evalua?on , share and store files electronically.
Digital Conversion
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
The user can; • adjust brightness
• adjust contrast
• apply magnification
• apply image processing
apply measurements, do calculations, and obtain statistics
• apply annotations
• include stamps
What’s so Great about Digital?
Saves inspector ?me and consumable cost while improving produc?vity.
NDTMA 2015 Annual Conference
What do your people need to learn to be prepared for digital?
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Digital Imaging Fundamentals – it not the same as film! • ASTM Standards pertaining to Digital • Digital System Qualification • Digital System Performance Baselining & Monitoring • Image Quality Measures • Computer Literacy • A Totally New User Interface!
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• ASNT training requirements • Level I: 24 total hours, 16 hours hands-on • Level II: 24 total hours, 16 hours hands-on
• NAS410 training requirements • NAS410 Level I: 16 total hours, 8 hours
hands on • NAS410 Level II: 40 total hours, 8 hours
hands-on • MAI training requirements
• MAI Level I: 8 hours formal training plus 20 hours OJT
• MAI Level II: 40 hours formal training plus 120 hours OJT
The Industry has standardized on training curricula for the transition to digital radiography with common guidelines from FWGIDR, DWGNDT, and MAI.
Varied requirements for digital certification
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Radiographic Testing (RT) film • Computed Radiography (CR) • Digital Radiography (DR)
• Digital Detector Array (DDA) • Linear Detector Array (LDA)
• Computed Tomography (CT)
Kinds of Radiography
NDTMA 2015 Annual Conference
Computed Radiography
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Invented in 1975 by George Lucky at Kodak
• First commercialized in the mid 1980’s • Digital image from “film like” plates • Work flow is more like film • Imaging plates are flexible like film • Dynamic range is “four decades” • (i.e., 1X to 10,000X)
Computed Radiography
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Imaging Plate (IP) – photostimulable phosphor • Laser scanner or reader • Computer, Software, and Monitor (image
viewing)
Components of Computed Radiography
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Translation stage
Galvo-driven scanning mirror
(Fast scan) Filter Detector
(PMT)
"Slow scan"
Stimulating Laser
Clock/sync *
A/D convert
Computer
Storage
Display Hard-copy
output device
Computed Radiography Imaging Process
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Computed Radiography: Imaging Plate
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Imaging Plates
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Imaging plate selection
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• One 14 X 17” plate typically costs about the same as one box (100 sheets) of film
• Imaging plates wear out over time • Film wears out too over time
• Proper care and handling of IPs is required to achieve favorable payback!
Imaging plates are a reusable media compared to film which is only used once. With proper handling of the imaging plates they can easily be used hundreds (or thousands) of ?mes. The longer they last, the faster the payback.
Imaging plate payback compared to film
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Comparison of CR to Film
NDTMA 2015 Annual Conference
Digital Radiography/DDAs
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Invented in the early 1960’s, the worlds first digital radiograph was via fluoroscopy
• Image is immediate • The detector is an electronic device • Workflow is less like film, more like a digital camera • DDA is rigid, not flexible • Highest sensitivity • Has excellent image quality due to frame averaging
Digital Radiography
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
DR System DR Flat Panel Detector (DDA)
Digital Radiography System
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Radiation source • Object manipulator (for different exposure positions) • Digital Detector Array, DDA • Analog to Digital Converter • Computer, Software & Monitor
Components of Digital Radiography
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Digital Radiography Imaging Process
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Contain a thin film transistor photodiode array pixel grid • Converts radiation to light
• Scintillators typically utilize Gadolinium Oxysulfide Terbium doped particle phosphors
• Scintillators can utilize Cesium Iodide Thallium doped needle phosphors
• Light is converted to electronic signal by the panel • amorphous silicon, α-Si
• Analog to Digital conversion produces pixel value
Digital Radiography Detectors - Indirect
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• DR detector contains sensitive electronics • Semi portable • Drop shock adversely affects detector • Temperature and moisture dependent • Radiation damage increases with kV; generally above
200kV • Periodic detector maintenance required
DR panels contain very sensi?ve electronics. In a sta?c environment, where the panel is not moved, the risk is reduced. However, panels can damage easily. Replacement panel costs run about $75K.
Digital Radiography Detector Handling
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Raw images obtained from a DDA must be calibrated (corrected) to create an ideal image.
These corrections consist of:
• Offset (dark image) – the noise level in the absence of radiation is characterized and subtracted from raw images.
• Gain – the individual pixel to pixel non uniformity (gain) is normalized (x-ray on) and applied to the raw images.
• Bad pixel correction – underperforming pixels are characterized, mapped, and corrected in the raw image.
Calibration and Corrections
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Offset is the most frequently required calibration. This can be performed as often as every image. As such, these are not normally saved.
• Gain calibrations last much longer. They are required for different energy and geometry conditions. They may need to be done if the scintillator develops irregularities due to burn in. These calibrations are saved, and are recalled as required.
• Bad pixel mapping is provided by the manufacturer, and is required very infrequently. As the DDA develops bad pixels with age and/or use, an updated bad pixel map may be required.
Calibration frequency
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Uncalibrated Calibrated
DDA Calibration Example
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Digital Radiography Bad Pixels
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Comparison of DR to Film
NDTMA 2015 Annual Conference
Image Quality Measures
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• With film, inspectors only had to understand film density • With digital radiography inspectors need to understand terms
such as; • pixel value, digital detector response (PV, DDR) • digital driving level (DDL) • contrast to noise ratio (CNR) • signal to noise ratio (SNR) • interpolated basic spatial resolution (iSRb) • equivalent penetrameter sensitivity (EPS)
• An understanding of digital image quality measures is required to qualify a system, gain customer approval, and produce optimum images
Digital Image quality measures
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Equal increments of Log Exposure (doubling mAs) should yield a straight line response of pixel values in a 12-bit Log system
Exposure Linearity
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Dynamic Range or Latitude
Film Latitude
Film
Digital Latitude
Digital
Exposure
Pixel value or density
CR has a huge dynamic range rela?ve to film. It’s easy to get a good shot the first ?me. Fewer reshoots, no double loading!
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Proportional to Dose! • Can not be treated the same as optical film density • The numerical representation of the pixel intensity depends
on the chosen scale (i.e., log vs linear) • Bit depth determines total range of pixel values
• Example 12 bit log = 2^12 = 4096, values 0 to 4095 • Example 16 bit linear = 2^16 = 65536, values 0 to
65535 • Pixel values are converted to analog brightness for viewing
Pixel Value (Pixel Intensity, DDR)
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• “Gray scale” (display) value is the number assigned to pixel value
• Window & level change the display values, not the underlying pixel values
• Display value is the “digital driving level” DDL
• DDL is the shade of gray on the monitor
• Monitor bit depth determines # of possible gray levels (8-bit = 256 levels)
Pixel Value Adjustment
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Pixel value difference between parts of image
• Radiographic contrast • Subject contrast: atomic no. (Z),
density, thickness • KV, filter, scatter • Detector sensitivity
• Contrast enhancement with processing • Use step wedge to define contrast
(image sensitivity) and latitude
Contrast
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Minimum percent change in an object which produces a perceptible change in the image
• Computed Radiography – lower contrast sensitivity • Digital Radiography – higher contrast sensitivity
Contrast Sensitivity
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Difference between pixel values of adjacent areas
• Divided by standard deviation of pixel value
• (N2 – N1)/ σ • N = pixel value • σ = standard deviation
Contrast to Noise Ratio (CNR)
Standards specify this contrast is measured inside the 4T hole, and adjacent to it
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• SNR = N/ σ N= pixel value; σ = standard deviation • Signal – desirable part of image: dose • Noise – undesirable part of image
• Scatter • Geometric distortion • Statistical variation or quantum noise
Signal to Noise Ratio (SNR)
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Amount of detail in the image • Minimum resolvable
separation between high contrast objects
• SR affected by many factors
Spatial Resolution (SR)
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Spatial Resolution (SR)
Resolution is limited by effective pixel size!
NDTMA 2015 Annual Conference
ASTM Standards for Digital Radiography
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
ASTM Standards for both CR and DR (DDAs) • Standard Guides (tutorials) • Standard Practices for Performance Evaluation and Long Term Stability • Standard Practices for Manufacturer Classification & Qualification • Standard Practices for Examination
Major revisions to CR standards in progress! DDA Standards due for update this year
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
ASTM E2445 CR Phantom
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
ASTM/USAF CR Phantom for low energy
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Valida?ng digital system performance at the start and finish of a project can be a sellable benefit to a customer (confirms work) as well as risk management for the inspec?on company.
HPX-1 Diagnostic Tool CR Phantom
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
SMPTE TV test pattern to evaluate display monitor performance
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• ASME Article 2, Appendix VIII • Replacement of film by CR
• ASME Article 2, Appendix IX • Replacement of film by DR
• ASME code, section V, Article 2 • 2T hole or essential wire must be displayed
ASME code acceptance
NDTMA 2015 Annual Conference
Digital Radiography System Qualification
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Example of a CR System Qualification
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• Establishes an exposure range for optimum image quality
• Determines the minimum pixel value to achieve a pre-determined image quality level
• Equivalent penetrameter sensitivity • Signal to noise ratio
• Allows users to know that they have good image quality based upon the pixel value (pixel intensity) that they achieve
• Must be “qualified” for specific systems/parameters!
Minimum pixel value qualification
NDTMA 2015 Annual Conference
Customer Acceptance of Digital
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
• What’s in it for them? Why change? • Is it as reliable as film? Demonstrate the same result as
film. • Productivity • Will it make them more profitable?
• ROI (Note; may not recoup investment with one job) • Operating expenses • Image management and storage
People can be reluctant to change. Digital imaging has a significant cost advantage rela?ve to film. It’s worth the effort to convert.
Customer acceptance of digital
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Source: Radiographic Inspection of Aircraft Components, Quality Digest, June 2006; Steven A. Mango.
RT inspection cost
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
How to assess / prepare / comply? Have comprehensive written procedures and be prepared to
demonstrate S/W features & image quality measures! • Window/level/zoom/pan/1:1 pixel mapping • Histogram, ROI stats, variable width line profile • Display of DDRs and DDLs • Neg/Pos image polarity • Annotations • DICONDE compliance, lossless image format • Process controls (SNR, EPS tests, etc.) • Written procedures include scanner settings, viewing cond.
Digital radiography audit criteria
NDTMA 2015 Annual Conference
Golden Nugget Hotel, Las Vegas, NV February 10-13, 2015
Thank You!