Evaluation of exposure index (IgM) in orthopaedic radiography

Abstract

The exposure index (lgM) obtained from a radiographic image may be a useful feedback indicator to the radiographer about the appropriate exposure level in routine clinical practice. This study aims to evaluate lgM in orthopaedic radiography performed in the standard clinical environment. We analysed the lgM of 267 exposures performed with an AGFA CR system. The mean value of lgM in our sample is 2.14. A significant difference (P 5 0.000 0.05) from 1.96 lgM reference is shown. Data show that 72% of exposures are above the 1.96 lgM and 42% are above the limit of 2.26. Median values of lgM are above 1.96 and below 2.26 for Speed class (SC) 200 (2.16) and SC400 (2.13). The interquartile range is lower in SC400 than in SC200. Data seem to indicate that lgM values are above the manufacturer's reference of 1.96. Departmental exposure charts should be optimised to reduce the dose given to patients.

Digital radiography exposure indices: A review

“…Thereby providing the radiographer with a guide to optimal technique factors to use on subsequent CXRs on the same patient 12. Variation in EI values between genders has also been demonstrated with women often obtaining higher values compared to their male counterparts 22,39. The lack of an adequate exposure chart for female patients has been suggested as a possible cause of this gender variation 39.…”

Development of an online automatic computed radiography dose data mining program: A preliminary study

“…The dose limit is another extreme and an EI beyond this point represents overexposure. Following are the recommended values of image quality baselines and dose limits for different CR systems: AGFA -1.76 (baseline) and 2.26 (limit) [6]; and 500 (baseline); and Kodak -1700 (baseline) and 2200 (limit) [12]. It is noted that dose increasing yields a smaller S-number in Fuji system while dose decreasing produces a larger value.…”

“…For example, a S-number of 74 indicates overexposure while a value of 501 represents underexposure. This arrangement is different from other manufacturers [6,9,12]. The web server executes appropriate Active Server Pages (ASP) scripts (ASP-VBScript), i.e.…”

“…This problem can propagate because good image quality is always favoured by radiologists but overexposure is difficult to identify when looking at CR images [2,4,5]. This problem can be overcome through quality assurance (QA) programming by evaluating exposure indices of CR images regularly [1,2,6]. Exposure indices are dose feedback indicators provided by CR manufacturers to show relative radiation amounts that reach image plates such as AGFA's logarithm of median exposure (Lgm), Fuji's sensitivity number (S-number) and Kodak's exposure index (EI) [6][7][8][9].…”

“…This problem can be overcome through quality assurance (QA) programming by evaluating exposure indices of CR images regularly [1,2,6]. Exposure indices are dose feedback indicators provided by CR manufacturers to show relative radiation amounts that reach image plates such as AGFA's logarithm of median exposure (Lgm), Fuji's sensitivity number (S-number) and Kodak's exposure index (EI) [6][7][8][9]. This information is stored in the Digital Imaging and Communication in Medicine (DICOM) header of an image but in different tags (AGFA's Lgm in tag 0019,1015 [1]; Fuji's S-number in tag 0018,6000 [2,7] and Kodak's EI in tag 0018,1405 [8]).…”