Congress:
EuroSafe Imaging 2017
Keywords:
CT, Radioprotection / Radiation dose, Radiation physics, Action 13 - Stakeholder engagement and collaboration, Action 5 - Performance indicators for radiation protection management, Action 2 - Clinical diagnostic reference levels (DRLs), Action 12 - Cooperation with international radiation protection initiatives and other stakeholders including IAEA, WHO, ICRP, HERCA, European Commission, Action 9 - Development of criteria for safe imaging procedures, Action 3 - Optimisation, diagnostic reference levels, image quality, Diagnostic procedure, Radiation safety, Quality assurance
Authors:
M. R. Onur, A. D. Karaosmanoglu, E. Akpinar, M. Karcaaltincaba, D. Akata, M. N. Özmen
DOI:
10.1594/esi2017/ESI-0007
Description of activity and work performed
- Parameters affecting the radiation dose
- Consequences of their modification
1.
Detector configuration
- Number of data channels in the z-axis
- Effective detector thickness of each of these data channel
Detector configurations on different equipments
- number of data channels
- type of data channels
- manner of data channel combinations in a detector array
Radiation dose emitted from X-ray tube
- Tube potential
- Tube current
- Detector configuration
2.
Tube Current
Increased tube current
- Decreased image noise
- Increased radiation dose
- Increased image quality
Automatic tube current modulation (ATCM) increase the mAs to increase the mAs in those parts of the body with the greatest attenuation and decreases the mAs in those parts of the body with lower attenuation.
Pitfalls in ATCM |
Improper patient positioning and centering |
Methalic orthopaedic hardware |
High pitch |
Discrepancy in the position of the arms between the scout and axial images |
3.
Tube Potential
Radiation dose decreases with the use of low kVp while still preserving acceptable image quality.
Image noise in the setting of low kVp may be lowered with increase in tube current.
Automatic tube potential selection (ATPS) enables to the voltage that is adequate for acceptable image quality with the lowest CTDIvol at different body regions.
4.
Reconstruction Algorithm
Iterative reconstruction (IR)
- Only parameter used after image acquisition
- Reduces radiation dose
- Improves image quality
- Different vendors provide different IR techniques with different vendors
5.
Patient positioning
Improper positioning (Fig.
1-3)
- Displacement in both horizontal or vertical axes
- Breaks down bowtie filtering
- Increased noise
- Increased patient dose due to ATCM
Horizontal and vertical impositioning cause increased noise.
AEC increases radiation dose to compensate the noise.
ATCM can be turned-off if there is difficulty in properly positioning the patient at the isocenter of the scanner :
- Scoliotic patients
- Patients who can not lie in the gantry
- excessive elevation of the patient’s head with pillows
6.
Scan Range
- Limitation of scan area to the clinically relevant body region
- Appropriate pitch values
- Dynamic z-collimation: prevent dose waste at the beginning and the end of the scan area
7.
Reconstructed Slice Thickness
- Low reconstructed slice thickness cause increased noise.
- ATCM increases radiation dose to reduce noise
8.
Pitch
Low pitch (< 1) --- overlap of anatomy,
high radiation dose
High pitch (> 1) --- gaps in the anatomy,
low radiation dose
Pitch may be between 1-1.5 in routine body protocols
(Fig.
4-7)