Congress:
EuroSafe Imaging 2017
Keywords:
Radiation safety, Imaging sequences, CT, Radioprotection / Radiation dose, Hybrid Imaging, Computer applications, Action 2 - Clinical diagnostic reference levels (DRLs), Action 3 - Optimisation, diagnostic reference levels, image quality, Dosimetric comparison
Authors:
S. Power, S. O'Neill, K. Murphy, P. Mc Laughlin, F. Moloney, K. James, M. A. Maher, F. Shanahan, O. O’Connor
DOI:
10.1594/esi2017/ESI-0052
Background/Introduction
Since its introduction in the 1970s computed tomography (CT) has revolutionised diagnostic decision making.
However,
the rapid increase in CT utilisation has brought with it significant medical and public concern with regards to the doses of ionising radiation delivered during scanning (1).
There is an inherent responsibility on the medical community to keep radiation doses “as low as reasonably achievable” (ALARA).
With improved technology,
significant advances have been made with regards to radiation dose reduction (1).
One of the most significant advances in dose reduction technology in recent times has been iterative reconstruction.
When used in conjunction with filtered back projection,
this technology improves noise and spatial qualities within a CT image (2).
This technique allows images of improved quality to be acquired at significantly lower radiation doses (3).
Adaptive statistical iterative reconstruction (ASIR) is a noise efficient reconstruction algorithm which is computationally fast and proven to result in images with good low-contrast detail,
preserved image quality and with typical radiation dose reductions of greater than 30%(4,5).
Pilot studies using ASIR has found that radiation dose can be successfully reduced by 50% in CT colonography (6),
44% in coronary CT angiography(7),
and approximately 50% in CT abdomen and pelvis studies(8) without significantly affecting image quality.
However,
the next step in the optimisation of image quality and radiation dose involves advanced iterative reconstruction algorithms such as Model Based Iterative Reconstruction (MBIR) to further increase radiation dose.
MBIR can incorporate a physical model of the CT system into the reconstruction process to characterize the data acquisition process,
including noise,
beam hardening,
and scatter (9).
This advanced iterative reconstruction process offers the potential to further enhance image quality at even lower radiation doses than ASIR.
Irish centres have played a central role in the development of clinical research assessing the potential application of these iterative reconstruction techniques to clinical practice.
We have focused on the application of these dose reduction techniques in the imaging of patients with chronic conditions such as cystic fibrosis (10,11) and inflammatory bowel disease(5,12-15) but also common conditions such as acute abdominal pain and carotid artery disease (16).
Patient with chronic medical conditions can accumulate significant doses during their lives (13,17) – this type of radiation exposure is particularly important in an era where we are moving from a “linear no threshold” model of oncogenic risk to a threshold model where only patients who accumulate over 50-100mSv of cumulative radiation during their lifetime statistically increase their risk of malignancy (18,19).