The Standardized Exposure Indicator
This chapter addressed essential features of the international standardized EI for DR imaging systems. First, two “old” propriety scales for the EI, the inverse scale and the proportional scale, were reviewed briefly followed by an outline of a generalized method for determining the EI. The next topic described are three conditions for the IEC standardized EI that must be met: (a) the standardized EI is related to the detector exposure and the standardized EI is obtained from the pixel values in the region of interest, (b) the standardized EI uses a linear proportional scale related to the detector exposure/signal (i.e., doubling the detector dose doubles the standardized EI value), and (c) consideration of the radiation beam quality (kVp, half-value layer, and added filtration) used for the calibration of the EI and the precision of the scale. Additionally, selected terminology of the IEC standardized EI are defined and include the exposure index (EI), the target EI (EIT), deviation index (DI), and the value of interest (VOI).
The IEC standardized EI is now proportional to the detector exposure and requires the user to establish EIT values for all examinations in order to ensure optimization of the dose to the patient without compromising the image quality. These values (EI and EIT) can now be used to calculate the DI. The DI provides immediate feedback to the technologist as to whether the correct exposure was used for the examination. The chapter concludes with an example of a dose-image quality optimization study for the purpose of providing insights as to how a department may go about establishing EIT values objectively.
It is important to note that sections of this chapter have been previously published in Journal of Medical Imaging and Radiation Sciences 45 (2014) 144–158, entitled “The New Exposure Indicator for Digital Radiography,” and some of the content has been taken from my PhD thesis, entitled Optimization of the Exposure Indicator as a Dose Management Strategy in Computed Radiography. PhD Dissertation (Charles Sturt University, New South Wales, Australia, 2014).
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