Internal Application Development Project, Research Paper Example

Objective: Determine Inspection Capabilities of Digital and Computed Radiography

Introduction

This research report documents the identified capabilities, and information deduced from the research which involved conducting a round-robin test, and also gives recommendations for future study. Funded by an internal application development project, ($30,000), this study focused at determining the capabilities demonstrated by new digital radiography (DR) and computed radiography (CR) technologies. Currently, Pratt & Whitney Rocket dyne Canoga Park uses both film radiography and image intensifier DR radiography (an older form of the newly advancing digital radiography used in industrial nondestructive testing inspection). This project report thus directly supports the understanding of the two leading types of new digital radiography technologies to aid in the selection of a system to support RS-68 and J-2X engine programs.

Background

As one of the most inspiring breakthroughs in X-ray imaging, film radiography has been a core task at Rocket dyne for quite a number of years. The first RTR system was built by a team from Rocket dyne in the early 1990s and it had the capacity to .Having been initially used for the acceptance of welds on Delta programs and Atlas, the system is still in use today for THAAD, RS68, MKV and GBI.

Radiography refers to the application of electromagnetic ionizing radiations such as X-rays to pass through materials to view inside objects. An X-Ray imaging system comprises two main elements: the “X-ray emitting source,” and the “image capture device” (Gurley 47). The “X-ray emitting source” provides the energy through the specimen and transmits relevant data to the “image capture device.”

This exercise will not address “X-ray emitting source” as part of the research.

The study thus focuses on the different types of “image capture devices” and image presentation equipment.

In modern radiology, there are three major “image capture devices” in used for image capture and presentation.

Image Capture Devices

Film = The base line standard is exposed and developed in much the same way as  a photographic film and involves the use of a dark room and some type of chemical development .This film is then viewed directly using some type of light emitting viewer.

The film does not involve the use of many types of equipment as the film acts both as the image display and the detector. The technique is however disadvantageous in that it is sensitive to photons of light emitted by adjacent intensifying screens and at the same time the film is to some extent sensitive to light other than X-rays hence does not produce fine detail.

Computed Radiography (CR). Its the first digital equipment to have been used in medical imaging and uses very similar equipment to conventional radiography except that in place of a film, an imaging plate (IP) made of photo-stimulable phosphor sheet is used to create the image (Pizzutiello 77).

Under CR, instead of subjecting an exposed film to a darkroom for developing in chemical tanks or an automatic film processor imaging plate is instead run through a special laser scanner, or CR reader, thus causing liberation of light from the image stored in the phosphor sheet following the lasers impartation of energy into the sheet (Carlton 123). This light emitted is then digitized producing a digital radiograph. The digital image can then be viewed on a high quality monitor (See note # XX) and enhanced using software that works in more or less the similar way to other conventional digital image-processing software. This software is offers the capability to adjust contrast, brightness, filtration, and zoom. The CR is a relatively cheap radiographic technique providing many advantages of imaging digitally.  CR is however slow in that only one cassette can be fed into the laser since it processes one at a time rather than multiple sheets and thus the delay caused can a hindrance in identification of radiographic technique such as positioning.

Digital radiography or Direct X-ray (DX) is refers to filmless X-ray image capturing, whereby unlike in CR cassettes or traditional photographic films, digital sensors are used (Davis 23). In DR, the image is directly captured onto a flat panel detector. With the every exposure being done on the same X-ray detector, images are produced almost instantaneously. The fact that images are produced instantaneously makes DR the most suitable for automated radiography (Gurley 57). This also builds on the basis that the panel fixed inside the cell does not need removal from the room for processing of the image and this makes image production efficient and a larger scope of work can be done. The technique is however expensive especially when upgrading form conventional cassette films as it requires that alterations be done in tables for radiographic examination and existing cassette holders. It is thus an expensive technique to acquire (Eisenberg 67).

In one of the earliest digital radiography implementers: PWR Canoga Park, the technology is known as a real-time radiography or RTR. In essence the technology is a Direct Digital radiography by way of an image intensifier rather than the newer flat panel detectors.

CR DR Display Monitors

With the modern advancement in technology, Liquid Crystal Displays (LCD) now dominates the monitor industry. Some radiologists though prefer the Cathode Ray Tubes (CRT) for digital imaging. Both the two monitors have different qualities in terms of resolution (Bushong 43).

During this research, we had many questions about the type of LCD monitor best suited for digital image viewing. Before selecting on the monitor we would use, we considered various aspects that were interested in such as: Either monochrome or color? The number of megapixels intended? DOCONDT required, and back light brightness control.

Progress So Far

There has been intense evolution in new digital radiographic technology in the medical field in the last 10 or so years. Currently, more and more companies are individually adopting the technology. Today, the technique is widely applied in other such as the    American Society Testing & Materials work projects to standardize the process control and technique requirements for proper inspection practices (Pizzutiello 88). In a bid to adopt this technology, PWR is in the process of procuring a digital system which will be housed in cell 6 of the Strategic Fabrication Center at the De Soto site. The need to better understand and quantify actual hardware has prompted the company to seek acquisition of this technology. The new technology addressed by this report, evaluates the progress made over the past 10 years in terms of focus on image quality providence as relates to the experience with actual PWR designs in an effort to aid the development and selection of the next generation real-time system. For instance, PWC has uncovered new Computed radiography (CR) procedures for review that they hope to implement by Feb.2010. In another instance, ASME ASTM and the PCC federal working group are working to include DR and CR in new radiography guidelines (Cambridge education firm 37).

 Testing Approach

Specimens

Natural flaws best

Boeing edm

Step wedge

The approach involved using film to shoot and map PWR and use RTR as benchmark

No time was assigned to RTR due constraints on time and money.

The plan approach was to use a verity of different PW and venders but was limited by lack of funding.

Basing on low project funding, P&W Canada offered to sponsor a “one-company” analysis which was funded indirectly to bring the project sites closer. This would make evaluation easier as the project relied on the computed radiography system located at PWC Montreal and the digital radiographic system located at TBD.

Boeing at Seattle loaned us its “electrode discharge machine” or (EDM) samples. Internal naturally occurring flaws were used and a step wedge was selected for the study.

Samples were selective due to lack of enough funding to cater for large samples since fabrication of test specimens is costly and takes long periods of time to develop. However, the selected specimens provided the weld and flaw types found in PWR designs.  Having just completed a probability of detection test, Boeing Seattle had just completed a probability of detection test and loaned us their test specimen set for this study. The specimens were thin-walled titanium in-place tube welds with various size “electrode discharge machine” or (EDM) notches. Two specimens containing two welds each were selected for the evaluation. Naturally occurring flaws were provided by a single thick-walled Inconel tube containing three welds. Additionally, Inconel 718 step wedge was included to demonstrate radiographic contrast and sensitivity.  Specimens are illustrated in Figure X.

The step wedge was selected basing on the material and thickness range used at PWR Canoga Park. This step wedge and “image quality indicator” (IQI) combination were employed as the most appropriate and easy way to chart and present image quality data. Because of the increasing thickness, and the fact that we used an IQI for .25” material, each technology would fail to show key characteristics of the IQI at some point as the thickness was increased.

2.5 (IQI) or Penetrameters were placed on all the steps. This would provide details of the sensitivity and contrast based on internal specification requirements.

One of the methods of controlling the quality of a radiograph is by the use of image quality indicators (IQIs). IQIs also referred to as penetrameters, provide a means of visually informing the film interpreter of the contrast sensitivity and definition of the radiograph (Carlton 197). The IQI indicates that a specified amount of change in material thickness will be detectable in the radiograph, and that the radiograph has a certain level of definition such that density changes are not lost due to unsharpness. With lack of such reference point, consistency and quality could not be maintained and defects could go undetected.

Image quality levels are typically designated using a two part expression such as 2-2T. The first term referring to the IQI thickness expressed as a percentage of the region of interest of the part being inspected (Eisenberg 107). The second term refers to the diameter of the hole that must be revealed and is expressed as a multiple of the IQI thickness. Therefore, a 2-2T call-out would mean that the shim thickness should be two percent of the material thickness and that a hole that is twice the IQI thickness must be detectable on the radiograph. The presentation of a 2-2T IQI in the radiograph verifies that the radiographic technique is capable of showing a material loss of 2% in the area of interest (Gurley 128).

Works Cited

Bushong, Stewart C. Radiologic Science for Technologists: physics, biology, and protection.St. Louis, MO: Mosby, 1997

Carlton, Richard R. Principles of Radiographic Imaging: an art and a science. Albany, NY: Delmar Thomson Learning. 2001

Davis, Ryan. Blueprints in radiology. Malden, MS: Blackwell Pub. 2003

Eisenberg, Ronald L. Comprehensive Radiographic Pathology. (3rd ed.). St. Louis: Mosby.2003

Gurley, LaVerne T. Introduction to Radiologic Technology. (5th ed.)  St. Louis, MO: Mosby, 2002

Pizzutiello, Robert J. Introduction to medical radiographic imaging. Rochester, NY: Health Sciences Division, Eastman Kodak Co, 1993