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Nondestructive Evaluation Program

X-ray Computed Tomography Image Quality Indicator (IQI) Development (CT IQI)

Active Technology Project

Project Introduction

Phase one of the program is to identify suitable x-ray Computed Tomography (CT) Image Quality Indicator (IQI) design(s) that can be used to adequately capture CT system performance. Since CT system performance quantification is considerably more complicated than 2D radiography, the approach to develop performance standards will be focused within a subset of materials such as aluminum, stainless steel, titanium, and/or polymers. These IQIs could include cylindrical or conical gauges containing various sizes of holes for assessment of contrast sensitivity, or implanted features for assessing resolution. We propose to use radial-symmetric objects for these standards so that the geometry of the part does not add additional layers of complexity to an already complex parameter space. Customary IQI devices for 2D radiography are typically flat, and since the CT system implements geometric reconstruction using up to 360 degrees of incident angles, flat objects offer an unrealistic basis for a standard (unless the inspected part is of similar geometry). While some CT IQIs are commercially available, none are widely or universally accepted as standard. Most CT IQIs are phantoms intended for medical inspection purposes or follow ASTM E1695, which dictates that resolution be based on the modulation transfer function calculated across the exterior edge of a round coupon. While this may be sufficient for an order of magnitude assessment, the image sharpness of the exterior edge is not representative of interior boundaries and only serves as an indirect measure. We aim to develop IQIs more consistent with NASA-related materials and using internal features/defects more representative of actual inspections.

Phase two of the program will focus on the quantification of the GSFC CT system using the produced CT performance standards. This will be followed by round-robin testing of the CT systems across the agency.  The IQIs will be used to assess CT detectability limits, contrast sensitivity, and resolution.  If additive manufacturing (AM) is utilized to generate the IQIs, a dual purpose, or secondary benefit to these IQIs is that the CT system may be used to ascertain AM material build defects and limitations.

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