Optimised low dose CT protocols: the half slice thickness approach.
Wednesday, March 2, 2016 (ECR) – Computed tomography (CT) is an essential imaging modality that can be used to solve many clinical problems. Moreover, it is available all over the globe and in many areas even on a 24/7 basis. Over the last ten years much has been done to lower the radiation doses used in CT through technical innovations and the application of protocols based on the ALARA (As Low As Reasonably Achievable) principle. But the optimisation of CT protocols still offers a lot of potential.
“Optimisation of protocols represents a complex task and every year tons of papers are released with several suggestions,” said Prof. Erich Sorantin of the Division of Paediatric Radiology at Graz Medical University, Austria, at the ECR 2016 press conference. In theory, the optimisation process should be easy to do, should not involve a lot of staff and of course no additional hardware should be needed. Based on his longstanding experience in the clinical field and teaching countless workshops on CT protocol generation, Sorantin has come up with a new method, called the half slice thickness approach.
The theory behind it is quite simple and exploits the inverse relationship between image noise, one of the major image quality determinants, and dose. To obtain the same image quality at half slice thickness, a double dose would be needed. To achieve a dose reduction, the process is reversed: after a particular study and patient discharge, radiographers reconstruct the study with half slice thickness and radiologists check image quality – if the diagnostic quality is still appropriate then 100% excess dose is used. Therefore, for the next study the initial dose is reduced by 20% and this process should be repeated until the image quality is no longer diagnostically acceptable. The half slice thickness approach is easy to do and involves only radiologists and radiographers, no hardware investments are needed – making it a good starting point for dose optimisation.
For paediatric CT, the optimisation process is more difficult to do, since many anatomical, physiological, and metabolic differences have to be worked into the parameter settings. Moreover, children are more sensitive to radiation than adults. There is scientific evidence that lower CT doses are used for children in dedicated paediatric radiology centres. Therefore, children should undergo CT where optimised protocols are available and where the clinical consequences of the study can be carried out, he recommended.
Erich Sorantin: Professor and Acting Head of the Division of Paediatric Radiology, Department of Radiology, Medical University Graz, Austria
Thursday, March 3, 16:00–17:30, Room D2
SF 8d CT radiation dose optimisation: are we doing enough?
- Chairmen’s introduction
I.M. Björkman-Burtscher (Lund/SE) and C. Malamateniou (London/UK)
- CT radiation dose optimisation: what has been achieved so far?
J. Santos; Coimbra/PT
- Dose reduction techniques in paediatric CT: from A to Z
E. Sorantin; Graz/AT
- Challenges and opportunities in CT dose optimisation: what can we do in the future?
S.J. Foley; Dublin/IE
- Panel discussion: What are the suggested priorities and actions for CT dose optimisation?