conversion to digital radiography from film radiography

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



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



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.



Digital Image Analog Image

What is a Digital Image?



•  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



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.


What do your people need to learn to be prepared for digital?


•  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!



•  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



•  Radiographic Testing (RT) film •  Computed Radiography (CR) •  Digital Radiography (DR)

•  Digital Detector Array (DDA) •  Linear Detector Array (LDA)

•  Computed Tomography (CT)

Kinds of Radiography


Computed Radiography




•  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



•  Imaging Plate (IP) – photostimulable phosphor •  Laser scanner or reader •  Computer, Software, and Monitor (image

viewing)

Components of Computed Radiography



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



Computed Radiography: Imaging Plate



Imaging Plates



Imaging plate selection



•  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



Comparison of CR to Film


Digital Radiography/DDAs




•  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



DR System DR Flat Panel Detector (DDA)

Digital Radiography System



•  Radiation source •  Object manipulator (for different exposure positions) •  Digital Detector Array, DDA •  Analog to Digital Converter •  Computer, Software & Monitor

Components of Digital Radiography



Digital Radiography Imaging Process



•  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



•  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



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



•  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



Uncalibrated Calibrated

DDA Calibration Example



Digital Radiography Bad Pixels



Comparison of DR to Film


Image Quality Measures




•  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



Equal increments of Log Exposure (doubling mAs) should yield a straight line response of pixel values in a 12-bit Log system

Exposure Linearity



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!



•  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)



•  “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



•  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



•  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



•  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



•  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)



•  Amount of detail in the image •  Minimum resolvable

separation between high contrast objects

•  SR affected by many factors

Spatial Resolution (SR)



Spatial Resolution (SR)

Resolution is limited by effective pixel size!


ASTM Standards for Digital Radiography




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



ASTM E2445 CR Phantom



ASTM/USAF CR Phantom for low energy



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



SMPTE TV test pattern to evaluate display monitor performance



•  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


Digital Radiography System Qualification




Example of a CR System Qualification



•  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


Customer Acceptance of Digital




•  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



Source: Radiographic Inspection of Aircraft Components, Quality Digest, June 2006; Steven A. Mango.

RT inspection cost



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



Thank You!

conversion to digital radiography from film radiography

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