Abstract
Objectives: To investigate the impact of patient off-centring, tube voltage and localiser direction on dose and CT number accuracy. Correlations between CT number and dose change were also explored.
Methods: A discovery CT750 HD-128 slice (GE Healthcare) scanner was used to scan the trunk of a PBU-60 anthropomorphic phantom. Using the system’s automatic tube current modulation (ATCM), images were acquired by employing 0° and 180° localisers for different combinations of tube voltage (80, 120 and 140 kVp) and vertical off-centring (±30, ±60 and ±100 mm). The displayed volume CT dose index (CTDIvol) and CT number were recorded.
Results: The maximum change in dose (191% - 196%) was observed when there was closer proximity of the phantom to the x-ray tube (±100 mm above and below the gantry iso-centre Fig 1 (a). The maximum change in CT number (180° localiser and 80 kVp) as a function of vertical off-centring was 43 HU Fig 1. (b). A strong positive correlation was reported between the variation in dose and CT number (r = 0.969, p < 0.001); 95% CI (0.93, 0.99).
Conclusion: As the literature reports that a considerably large percentage of CT patients are off-centred vertically, and more likely below the gantry iso-centre, this study recommends employing the 0° localiser and applying lower tube voltage where applicable. It is also crucial for those involved in CT imaging to have an in-depth understanding of the limitations of CT systems to avoid potential pitfalls in clinical decision-making when using CT numbers as an absolute value for tissue lesion characterisation.
Methods: A discovery CT750 HD-128 slice (GE Healthcare) scanner was used to scan the trunk of a PBU-60 anthropomorphic phantom. Using the system’s automatic tube current modulation (ATCM), images were acquired by employing 0° and 180° localisers for different combinations of tube voltage (80, 120 and 140 kVp) and vertical off-centring (±30, ±60 and ±100 mm). The displayed volume CT dose index (CTDIvol) and CT number were recorded.
Results: The maximum change in dose (191% - 196%) was observed when there was closer proximity of the phantom to the x-ray tube (±100 mm above and below the gantry iso-centre Fig 1 (a). The maximum change in CT number (180° localiser and 80 kVp) as a function of vertical off-centring was 43 HU Fig 1. (b). A strong positive correlation was reported between the variation in dose and CT number (r = 0.969, p < 0.001); 95% CI (0.93, 0.99).
Conclusion: As the literature reports that a considerably large percentage of CT patients are off-centred vertically, and more likely below the gantry iso-centre, this study recommends employing the 0° localiser and applying lower tube voltage where applicable. It is also crucial for those involved in CT imaging to have an in-depth understanding of the limitations of CT systems to avoid potential pitfalls in clinical decision-making when using CT numbers as an absolute value for tissue lesion characterisation.
| Original language | English |
|---|---|
| Publication status | Published - 30 Apr 2023 |
| Event | ASMIRT 2023 Conference - International Convention Centre, Sydney, Australia Duration: 27 Apr 2023 → 30 Apr 2023 https://conference.asmirt.org/2023/ https://conference.asmirt.org/2023/wp-content/uploads/2023/05/ASMIRT-2023-program-FINAL-V8.pdf (Program) https://onlinelibrary.wiley.com/toc/20513909/2023/70/S1 (Abstracts) |
Conference
| Conference | ASMIRT 2023 Conference |
|---|---|
| Abbreviated title | Champions of change. Honouring the past, embracing the present, shaping the future |
| Country/Territory | Australia |
| City | Sydney |
| Period | 27/04/23 → 30/04/23 |
| Other | The theme for this year’s Conference is Champions of change – Honouring the past | Embracing the present | Shaping the future. We are looking for you, our current and future champions, to submit workshop proposals and abstracts. The conference will comprise an engaging program including a mixture of invited speakers, proffered papers, vibrant physical posters, specialised workshops and so much more. Honour the past by sharing previous learnings and knowledge and how they still relate to current practice Embrace the present by networking, collaborating and reconnecting with your peers and others in the profession Shape the future by sharing your latest research and workplace protocols, professional standards and ongoing improvement of practice and person centred care across our profession. |
| Internet address |