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Effect of added filtration on patient dose, exposure indexand image quality
Poster No.: C-1022
Congress: ECR 2013
Type: Educational Exhibit
Authors: N. Koistinaho, J. Kalliainen, H.-M. Kalliokoski, S. Flygare, M.Heikkilä, M. Peltokorpi, A. Henner; Oulu/FI
Keywords: Equipment, Plain radiographic studies, Radioprotection / Radiationdose, Education and training
DOI: 10.1594/ecr2013/C-1022
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Learning objectives
The aim of this study is to demonstrate how added filtration with different tube voltages(kV) affects image quality, exposure index and patient dose. We also wanted tounderstand better how image parameters affect to patient dose. It is important thatradiographers are able to optimize patient dose and image quality in everyday work.
The Philips OPTIMUS 50 equipment was insattlled to our school in 2010. This equipmentis used by the students for practicing radiographic positioning with PiXY phantom andlearning radiation dose and image quality optimisation. With this equipment students havelearned to use radiation safely and also evaluate good image criteria based on DIMONDIII.
Background
Factors that influence patient doses have been researched widely. Nevertheless, thereis a lack of studies about the effect of added filtration on patient dose and image quality.The effective dose of lumbar spine is relatively high because there is lots of radiationsensitive organs inside or near the radiation beam. Effective dose of lumbar spine is over
20 times higher than the dose of thorax (lumbar spine AP 2 mSv).1
The main principles guiding the use of radiation in healthcare are principle of justification,
optimization (ALARA, As Low As Reasonably Achievable) and individual protection.2
Optimizing the patient dose in the plain X-ray examination is based on Finnish law andEuropean guidelines and that's why the subject of this study is relevant.
The X-ray images (n=28) were taken in Oulu University of Applied Sciences in TheSchool of Social and Health Care, Northern Finland. The equipment we used werePhilips OPTIMUS 50, Philip Digital Diagnost Eleva Workspot with DAP-meter (Dose AreaProduct), Philips Digital Diagnost VM flat panel detector (CsI) and PiXY phantom.
X-rays with seven different tube voltages were producered by changing it at intervalsfive kV. Lowest tube voltage was 70 kV and highest 100 kV. X-rays were taken by eachtube voltages and four different filtrations. The main research parameters were kV, addedfiltration, the dose area product (DAP) and the exposure index (S-value). AEC (AutomaticExposure Control) was used. (Table 1.)
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Phantom was positioned to optimal lumbar spine projection. Central x-ray was above theiliac crest. Image field was wider than normally because line pair had to fit in the imagearea without obstructing the view of the bone structure. Line pair was used to assessimage quality. In examination radiation shield was used to model real imaging situation.
The images were evaluated by using Impax Client and BARCO-monitor (3 Mpx).DIMOND III good image criteria was used to assess images:
• "Complete visualisation of the lumbar spine and sacrum• Visually sharp imaging, as a single line, of the upper and lover-plate
surfaces in the centred beam area• Visualisation of the intervertebral spaces in the centred beam area• Visually sharp imaging of the pedicles, transverse processes, spinous
processes and intervertebral joints• Visualisation of the sacroiliac joints• Visually sharp imaging of the cortical and trapecular structures"3
Images for this section:
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Table 6: The record of measurements
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Fig. 1: Philips OPTIMUS 50 and Pixy-phantom
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Fig. 2: Philip Digital Diagnost Eleva Workspot
Fig. 3: Image area
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Fig. 4: Line pair tool
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Imaging findings OR Procedure details
According to Dimond III the range of kV in lumbar spine AP is 80-90 kV. In this phantomstudy lumbar spine AP was exposed with 70-100 kV with five kV steps.
Philips OPTIMUS 50 inherent filtration is 2.8 mmAl. Added filtrations used with eachkilovoltage step were 0 mmAl, 2 mmAl, 0,1 mmCu+1 mmAl and 0,2 mmCu+1 mmAl. AECwith middle chamber was used. Stable parameters were FFD 115 cm, grid focused on110 cm with grid ratio 12 and number of lamels 36/cm, sensitivity of AEC 400, and largefocus size (1 mm x 1 mm). Radiation beam was collimated 20 cm x 28 cm.
Images were analyzed by two different groups by using Impax Client and BARCO-monitors. Three different kV steps (70 kV, 85 kV and 100 kV) were selected becauseremarkable differences between images with smaller kV range was not found.
The results showed that patient dose (DAP) decreased with more added filtration withsame kV although mAs increased. With lower kV differences between DAP values weremore significant than with higher kV (Table 4). Added filtration didn't affect exposure indexsignificantly (Table 5). We didn't detect any differences in image quality between differentadded filtrations at the same kV-level (Table 1-3).
Images for this section:
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Fig. 5: BARCO-monitors 3 Mpx
Table 1: Added filtration and image quality at 70 kV
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Table 2: Added filtration and image quality at 85 kV
Table 3: Added filtration and image quality at 100 kV
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Table 4: Influence of added filtration on Dose Area Product (DAP)
Table 5: Influence of added filtration on Exposure Index (EI)
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Conclusion
It's important to understand how your equipment works. After that you can optimise image
quality parameters without the patient dose increase. 4
The results showed that patient dose (DAP) decreased with more added filtrationwith same kV although mAs increased. Added filtration didn't affect exposure indexsignificantly. Any differences were not detected in image quality between different addedfiltrations at the same kV-level.
The conclusion is that filtration can be added when imaging lumbar spine withoutdecreasing image quality substantially. Furthermore, patient dose reduces by addingfiltration.
With understanding the meaning of added filtration and the use of it in plain radiographythe radiographer can affect the patient dose significantly.
This project have deepened our know-how and deepended previously learned theory.Now we understand better how added filtration affect the patient dose and this informationwe can use in our daily work .
References
1. Säteilyturvakeskus. Röntgentutkimusten säteilyannoksia. 2011. http://www.stuk.fi/sateilyn_kaytto/terveydenhuolto/rontgen/fi_FI/annoksia/
2. Säteilylaki 27.3.1991/592. 1991.
http://www.finlex.fi/fi/laki/ajantasa/1991/19910592
3. The Dimond III group. Dimond III. 2004. http://www.dimond3.org/WEB_DIMOND3/Reports/WP%201/part_d_Chapter%20III.pdf
4. Alshleem, H. & Davidson, R. Quality parameters and assessment methods of digitalradiography images. The Radiographer 2012, Volume 59 (2).
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Personal Information
We are Niina Koistinaho, Johanna Kalliainen, Hanna-Mari Kalliokoski, Suvi Maiju Flygare,Marianne Heikkilä and Miia Peltokorpi, radiographer students from Finland. We study ourthird year at School of Social and Health Care at Oulu University of Applied Sciences.This poster was made in the guidance of our teacher Anja Henner, PhD, who can alsogive more information ([email protected]).
Images for this section:
Fig. 6: Remember to relax!
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