A study of exposure index value fluctuations in computed radiography and direct digital radiography using multiple manufacturers Poster No.: C-3011 Congress: ECR 2010 Type: Topic: Authors: Scientific Exhibit Radiographers - Technical Aspects M.-L. Butler 1, P. C. Brennan 2, J. Last 1, L. Rainford 1 ; 1 Dublin/IE, 2 Sydney/AU Keywords: Keywords: DOI: exposure index, radiation dose, manufacturer comparison Technical aspects, Radiation safety 10.1594/ecr2010/C-3011 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 13
Purpose Medical radiation is the largest source of man-made radiation (1) and it is important to adopt the linear no-threshold model, and assume all exposures carry some risk. Computed radiography (CR) and direct digital radiography (DR) were introduced into clinical departments in the 1980s. The phenomenon of exposure creep in association with the advent of CR and DR has been largely documented (2). In traditional film-screen radiography, over or under exposure to the patient was immediately apparent. In CR and DR, image processing can compensate by up to 100% for under exposure and up to 500% for over exposure, and still produce a clinically acceptable image (3). Manufacturers have responded to this by offering an exposure index (EI) value to clinicians. This value is a measure of radiation dose to the detector and is displayed with the image to the clinician. Different manufacturers use varying types of EI as displayed in Table 1 (4). Manufacturer Agfa Kodak Philips Siemens Fuji Table 1: Exposure Index Values by manufacturer Exposure Indicator lgm- logarithm of the median of the histogram EI- exposure index EI- exposure index EXI- exposure index S (sensitivity) number In a clinical setting a wide range of factors can influence the EI value such as patient size, artifacts, source to image receptor distance, collimation, centering and IP plate size (2). Whilst the EI value has been promoted as a means of quality assurance testing for best clinical practice, its clinical consistency is not apparent in any recent literature. Page 2 of 13
The current study aims to assess the consistency of the EI value at constant conditions and to document any fluctuations that may occur. Page 3 of 13
Methods and Materials Materials Four manufacturers were used for comparison; Agfa Gaevert CR, Carestream CR, Philips Digital Diagnost DR and Siemens DR Four common, but contrasting, clinical examinations were chosen for the study; skull, chest, abdomen and hand (5). Two anthropomorphic phantoms were used to produce clinically relevant images and simulate typical examination conditions. RANDO Phantom was used for the chest, abdomen and skull projections and PIXY anthropomorphic phantom (Radiology Support Devices, USA) was used for the hand projection. Method For each examination, the phantoms were positioned in line with clinical practice and international guidelines (6). For each system and each projection, the phantom was exposed 20 times. The phantom was not moved between exposures. When using the CR systems, the same imaging plate was used, as was the same digitizer. The imaging plate was processed and the corresponding EI value for each exposure was recorded. Page 4 of 13
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Images for this section: Fig. 0: RANDO Phantom http://www.maestro-research.org/ Page 6 of 13
Fig. 0: Positioning of Phantom School of Medicine and Medical Science, University College Dublin - Dublin/IE Page 7 of 13
Fig. 0: CR System School of Medicine and Medical Science, University College Dublin - Dublin/IE Page 8 of 13
Results The results for each manufacturer are displayed in tables 1-4. The ranges of EI values given represent the minimum and the maximum value recorded for the same examination at constant conditions. Examination EI Range Skull 1630-1660 Chest 2560-2660 Abdomen 1820-1890 Hand 1940-1960 Table 1: Kodak CR System Examination lgm Range Skull 1.88-2.21 Chest 1.67-1.82 Abdomen 1.82-1.92 Hand 1.85-2.03 Table 2: Agfa CR System Examination EI Range Skull 320 Chest 400 Abdomen 500 Hand 320 Table 3: Philips DR System Examination EI Range Page 9 of 13
Skull 487 Chest 475 Abdomen 309 Hand 583 Table 4: Siemens DR System Results show that the EI value is not consistent in CR, and thoroughly consistent in DR. This suggests that only varying clinical conditions such as exposure factor manipulation, collimation, SID and patient size will change the value in DR. The largest fluctuations were seen in the Agfa CR system. It should be noted that at increase of 0.3 in the lgm value, indicates a doubling of dose to the detector. Therefore, in the skull examination, the fluctuations seen would indicate to the clinician that double the exposure was given then is necessary according to manufacturers guidelines. Similarily, in the Kodak system, an increase of 300 EI indicates a doubling of exposure to the plate. In the chest examination, the EI value fluctuated by 100, which would suggest an increase or decrease of one third detector exposure. Page 10 of 13
Conclusion Given the evidence presented in this study, it is imperative that clinicians are aware of the fluctuations that are occurring in the EI value in CR systems outside of clinical conditions on which they have control. The challenge is posed to the clinician to be able to assess image quality outside of the EI value to ensure optimal clinical practice. The reliability of EI values as a feedback mechanism for CR is also uncertain Page 11 of 13
References 1. Mettler FA. Medical radiation exposure in the U.S. in 2006: preliminary results Health Phys 95(5):502-507, (2008). 2. Willis, C. Computed Radiography: a higher dose? Pediatr Radiol 32: 745-50 (2002). 3. Peters, S.E. and Brennan, P.B. Digital radiography: are the manufacturers' settings too high? Optimization of the Kodak digital radiography system with aid of the computed radiography dose index. Eur Radiol 12:2381-2387 (2002). 4. Willis CE. Strategies for dose reduction in ordinary radiographic examinations using CR and DR. Pediatr. Radiol 34 (Suppl 3): 196-200 (2004). 5. Hart D and Wall BF. Radiation Exposure of the UK Population from Medical and Dental X-ray examinations. National Radiological Protection Board: Chilton (2002). 6. Swallow RA, Naylor E, Roebuck EJ, Whitney AS. Clark's positioning in radiography. 11 th edition. London: Heinmann Professional Publishing Ltd. (1986) Page 12 of 13
Personal Information Ms Butler is a Lecturer and Biological Imaging researcher in University College Dublin, Ireland. Her research interests include radiation dose studies, medical image perception and forensic radiography. Page 13 of 13