Evaluation and Optimization of Exposure Index in Lumbar Spine and Pelvis X-Ray

Evaluation and Optimization of Exposure Index in Lumbar Spine and Pelvis X-Ray Poster No.: C-1492 Congress: ECR 2012 Type: Scientific Exhibit Authors: R. M. Lopes, L. H. Domingos ; Mortágua/PT, Azoia de Cima/PT Keywords: Genetic defects, Dosimetry, Digital radiography, Computer applications DOI: 10.1594/ecr2012/C-1492 1 2 1 2 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 The exposure index (EI) in digital radiography has been used as an indicator of the speed and relative sensitivity of the scanner when it is focused by the X-rays. It is a measure of the level of signal produced by a digital detector for a given exposure by the patient, being 2 (1) proportional to the ratio of signal to noise (SNR ) and it is related to image quality. The International Electrotechinical Commission (IEC), American Association of Physics in Medicine (AAPM) and Medical Imaging and Technology Alliance (MITA), as well as physicists and manufacturers of digital radiology equipment from around the world have standardized on IE for the different detectors in digital radiology (2;3). All these efforts (1) resulted in IEC 62494-1 called "exposure index of digital imaging systems for x-ray". However, this isn't being applied yet. EI is just a value that provides feedback to the radiographer in order to obtain the image quality at the lowest dose but, the EI doesn't (1) indicate directly the dose debited to the patient dose. The dose in the detector is dependent on the combination of several factors, such as, an anatomic region in study, a presence or absence of organ most sensitive to radiation, collimation, kilovolts (kv), milliampere (ma), exposure time and filtration of X-ray. EI doesn't replace the dose area product (DAP) or entrance skin dose (ESD), because they are internationally accepted calculation of radiation dose in patient. The EI in Carestream equipment represents the average value of pixels in the anatomic region of interest and is determined directly from the code of values by estimating the exposure incident in image plate (IP). This represents a logarithmic relationship with air (4) 5;6) kerma incidence. It is calculated by the formula EI # 1000 log10 (exposure in mr) : +2000 An exposure of 1mR (80kVp, 0.5 mm Cu, 1 mm Al filtration) will result in an exposure index of 2000. An exposure of 10 mr will result in an exposure index of 3000, while, an exposure of 0.1 mr will result in a value of 1000 for general used IP's. The IP's of high resolution aren't quite as sensitive due to a thinner phosphor layer, modifying the EI for 1700. Doubling the exposure will increase from 300 in the EI value (7;8). Carestream recommends that all X-rays should be situated between 1700 and 1900 as exposure's index (9;10). The reproducibility of the exposure system is clearly the mirror on the reproducibility of the EI (11). Page 2 of 13

The EI is revealed as a useful tool in the evaluation of dose proportionality charged for the structure to radiate, allowing the radiographer to adapt the parameters in order to follow the "As Low As Reasonable Achievable" (ALARA) principle. However, despite the EI doesn't relate directly to the patient dose, it is utmost importance to monitoring and evaluation of EI in order to optimize the radiation dose in each exposure, ensuring the improvement of health care provided. Methods and Materials EI were recorded for all exams performed during the months of July and August 2011, in a District Hospital in Portugal, where were registered 822 patients (402 of lumbar spine X-rays antero-posterior (AP) and 378 have done lateral also); 420 made to Pelvis X-ray) aged between 1 and 100 years (table 1). The EI was collected through the scanner Kodak Direct View CR 975 System and X-ray equipment are Philips Optimus 65 ZBH7 and Shimadzu RAD speed. The 35x43 IP was used. All data were processed and analyzed in SPSS v.17. Through an analysis to the fig. 1, we can conclude that the age's class with the largest number of patients and who made the X-rays, is [71-80]. Images for this section: Table 1: Ages variance. Page 3 of 13

Fig. 1: Relationship between the age's classes with the number of patients who carried out the different exams. Page 4 of 13

Results The standard deviation (s) presented with high discrepancy, causing a big difference in the mean, therefore, prepared an analysis for the values of 1700, 1800 and 1900 (table 2). AP Lumbar Spine: It appears that most of the values are between 1800 and 1900 since they are statistically significant positive for 1800 and negative to 1900. Lateral Lumbar Spine: It appears that the majority of EI values are below of 1700 because the values are statistically significant for negative. Pelvis: It is evident that most of the EI values are between 1800 and 1900, since these are statistically significant positive for 1800 and negative to 1900. In table 3, we show the rates of EI values. AP Lumbar Spine: It is observed that 43.3% (174 exams) of EI are between 1700 and 1900 and about 37.8% (152 exams) are above the upper reference limit. Lateral Lumbar Spine: It is found that 72.5% (274 exams) of the values of EI are situated less than 1700 and only 4.8% (18 exams) of EI are above the upper reference limit. Pelvis: It is shown that 46.4% (195 exams) of EI, are higher than 1900, 34.5% (145 exams) are situated in the reference values and only 19.0% (80 exams) are less than 1700. Then, calculations were carried out in order to relate the age's classes with different EI exams. Page 5 of 13

AP Lumbar Spine (table 4) As # <0.05, we can conclude that there is a correlation between the age's classes and EI. In the following age's classes, [11-20], [31-40], [41-50] and [71-80], more than 40% of EI are above the reference values. In the classes of # 10 and [91-100] we cannot observe any exam greater than 1900. Lateral Lumbar Spine (table 5) As #> 0.05, we can see that there isn't any correlation between age classes and EI. In all classes, at least 60% of patients had EI below the minimum reference value (<1700) and all, except the age's classes # 10 years, have less than 10% of the values above 1900. Pelvis (table 6) As # <0.05, can be seen that there is a correlation between the age classes and EI. In the age's class [81-90], 56.6% of EI are above the reference value. The ages' classes [41-50] [51-60] [71-80], more than 40% of EI are higher than 1900. In the age's class # 10, 53.6% of the EI values are less than 1700. Since #>0.05, there isn't a correlation between the patients EI with or without hip/hips prosthesis/prostheses (table 7). The total of the 67 pelvis x-rays that show the prostheses, 32 (46.4%) had an EI greater than 1900. Images for this section: Table 2: Mean and standard deviation of the different EI exams. Page 6 of 13

Table 3: Rates and number of exams showing various EI. NE - Number of expected exams. NO - Number of observed exams Table 4: Relationship between age's classes and AP lumbar spine EI. Page 7 of 13

Table 5: Relationship between age's classes and lateral lumbar spine EI. Page 8 of 13

Table 6: Relationship between age's classes and pelvis EI. Page 9 of 13

Table 7: Relationship between pelvis EI with or without prostheses. Page 10 of 13

Conclusion AP Lumbar Spine It can be concluded that 43.3% of EI of AP lumbar spine x-rays are presented within the standard values of Carestream, however, about 37.8% have higher values. Lateral Lumbar Spine It is concluded that 72.5% of EI lateral lumbar spine are lower than the reference values, which indicates a proper delivery of health care. Pelvis It is evident that 46.4% of EI of pelvis x-ray are above the reference values. Through the values of AP lumbar spine and pelvis EI, it would be appropriate to revise the exposure factors, in order to reduce the detector dose, relating a EI decrease. In AP lumbar spine, it appears that in the age classes [11-20], [31-40], [41-50] and [71-80] is possible to reduce the detector dose and consequently, decrease a patient dose, since, at least 40% of EI are above the reference value. In the pelvis x-rays, the age classes [81-90] and [90-100], more 50% EI are above the reference value and the age classes of [41-50], [51-60] and [71-80] more than 40% of EI are above the reference value. It is a fact that patients having hips prostheses doesn't influence the EI and detector dose. We consider interesting to repeat the study, with attention to patients standard biotype, assessing the correlation between DAP and ESD in order to verify the variability and reliability of EI in Carestream scanners. In short, through data we can conclude that it is possible in some tests, to reduce the EI in order to fit them on the reference values of Carestream, conclusively, to reduce the debited dose by improving the provision of health care. References Page 11 of 13

1. Seiberg JA, Morin RL, The standardized exposure index for digital radiography: an opportunity for optimization of radiation dose to the pediatric population, Pediatric Radiology, 2011, USA, Springer; 2. Shepard SJ, Wang J, Flynn M et al. An exposure indicator for digital radiography: AAPM Task Group 116 (executive summary), 2009, Med Phys 36:2898-2914; 3. International Standard IEC 62494-1 Medical electrical equipment-exposure index of digital X-ray imaging systems- Part 1: definitions and requirements for general radiography. International Electrotechnical Commission, 2008, ISBN 2-8318-9944-3 4. Peters SE, Brennan PC, Digital Radiography: are the manufacture's settings too high? Optimisation of the Kodak digital radiography system with aid of the computed radiography dose index, European Radiology, 2002, 12:2381-2387; 5. Bogucki TM, Trauernicht DP, Kocher TE. Characteristics of a storage phosphor system for medical imaging. Technical and Scientific Monograph 6. Rochester, USA: Kodak Health Sciences, 1995; 6. Report of AAPM Task Group 10, Acceptance Testing and Quality Control of Photostimulable Storage - Phosphor Imaging Systems, American Association of Physics in Medicine, 2006; 7. Seibert JA, Computed Radiography Technology, Department of Radiology, University 0f California Davis Medical Center Sacramento, California, 2004; 8. Computed Radiography (CR) and Digital Radiography (DR) State xray Inspection Protocol, Conference of Radiation Control Program Directors, Inc. January 2010, available at URL: http://www.crcpd.org/pubs/ cr&dr_protocol.pdf; 9. Warren-Forward H, et al. An Assessment of Exposure Indices in Computed Radiography for the Posterior-anterior Chest and the Lateral Lumbar Spine, The Brithish Journal of Radiology, 80, 2007, 26-31; 10. Gavin C. Kodak Health Imaging Business Relations Manger, 2005, Personal Communication; 11. Butler, M. L. et al. Are exposure índex values consistent in clinical practice? A multi-manufacturer investigation. Radiation Protection Dosimetry, 2010, pp. 1-4; 12. ACR-AAPM-SIIM, Practice Guideline For Digital Radiography, Resolution 42, 2007; Personal Information Luís Domingos Student of College of Health Technology of Coimbra, Portugal Page 12 of 13

Email: luis24.5@gmail.com; Rogério Lopes Student of College of Health Technology of Coimbra, Portugal Email: rogeriolopes87@gmail.com; Page 13 of 13