Program Information
Exposure Indices and Target Values in Radiography: What Are They and How Can You Use Them?
I Reiser
A Walz-Flannigan
C Willis
I Reiser1*, A Walz-Flannigan2*, C Willis3*, (1) The University of Chicago, Chicago, IL, (2) Mayo Clinic, Rochester, MN, (3) MD Anderson Cancer Center, Bellaire, TX
Presentations
SU-B-BRC-0 (Sunday, March 19, 2017) 10:30 AM - 12:30 PM Room: Ballroom C
AAPM TG116 and IEC 62494 defined a consistent set of metrics to characterize detector exposure, namely, the exposure index (EI) and the deviation index (DI). These exposure indices were initially intended to prevent dose creep, a gradual increase of patient dose due to the wide dynamic range of digital detectors. Beyond providing technologists with immediate feedback on exposure factor, exposure indices are also available to physicists as surrogates of image quality. However, practical use of these metrics for protocol optimization, quality assurance, and quality improvement is impeded by a host of obstacles, including inter-vendor variability, a lack of published data on guidelines for using these metrics, and a lack of understanding on the part of the technologist, radiologist, and physicist. In particular, the EI is subject to interferences and its value is dependent on many variables including beam kVp and quality, patient thickness and composition, grid use, and vendor-specific calibration procedures. This 2-hour symposium will review in detail what each index represents, and how each is interrelated. Experimental data characterizing the dependence of EI on these variables will be presented to give the audience an understanding of how their system might respond under different clinical conditions. Current practices for using exposure index in protocol optimization will be outlined, as will methodology for validating EI accuracy. Issues related to interpretation of DI and its role in monitoring quality will also be discussed. The linkage between the detector EI and patient exposure will also be discussed.
Learning Objectives:
1. To understand the definition of and motivation for EI, EIT, DI, and their relation to AEC
2. To learn how these metrics can be validated and to understand their limitations
3. To obtain a working knowledge of how to use these metrics clinically and some possibilities for protocol design
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