Radiation dose-, contrast media- and image quality optimization in computed tomography

Computed tomography (CT) was introduced to medicine in the early 1970s, which brought slice imaging into wide use for the first time. Today, CT is an essential part of radiological diagnostics, and is used for a wide range of clinical applications. One downside of CT imaging is the health risks related to the ionizing radiation. In the 80s it was believed that CT would soon be replaced completely by MRI due, in part, to the ionizing radiation required in CT. A further downside are the health risks related to the use of iodine-based contrast media. Both radiation- and contrast media dose have a trade-off with image quality. However, many technical advances have been made, and progress is still ongoing, to improve and broaden the applications of CT. Such advances necessitate a re-evaluation of imaging protocols and continued optimization of radiation dose, contrast media dose and imaging quality. This is the subject of this PhD project.

Study I: The aim of this study was to evaluate the potential of low-kV dual-source (DS) and dual-energy (DE) to reduce CM-doses while maintaining soft-tissue and iodine CNR in phantoms of varying size, and to quantify the corresponding radiation dose increases. It was found that low-kV dual-source imaging could be used to reduce CM doses by 44–53% with maintained iodine-, soft tissue- and other materials CNR in a wide range of abdominal sizes, to the cost of about 20–100% increased radiation dose, depending on size. The dual-energy technique allowed a reduction of CM dose by 20% at similar radiation dose as the standard 120 kV protocol.

Study II: The aim of this study was to implement and evaluate a scanning regimen, based on the results from Study I, to reduce CM-doses for patients believed to be at risk of CIN. It was concluded that the protocols from Study I could be used to reduce CM doses by 40–50%, depending on patient size, with maintained CNR in patients with a BMI-range of 15–36 kg/m2. The size-specific dose estimates increased by 70%.

Study III: The aim of this study was to compare the outcome in image noise and radiation dose in the subsequent CT scan following a single anterior-posterior (AP) vs a combined lateral plus AP (LAT+AP) localizer when using automatic tube-current modulation (ATCM). The results suggested that using LAT+AP localizer yields more consistent noise and radiation dose than a single AP. The effect was small, except for a subgroup of females with laterally protruding breast tissue, which may have been overexposed by about 57% in the thorax region.

Study IV: The aim of this study was to evaluate if standard-dose CT can be replaced with low-dose CT for characterization of non-specific findings bone in scintigraphy. Based on these results, sub-mSv CT seems feasible for morphological characterization of skeletal changes in areas with increased tracer uptake on bone scintigraphy, although a larger study is needed.

List of scientific papers

I. Low tube voltage dual source computed tomography to reduce contrast media doses in adult abdomen examinations: A phantom study. Thor D., Brismar T.B., and Fischer M.A., Medical Physics. 2015. 42(9): p. 5100-9.
https://doi.org/10.1118/1.4927791

II. Dual source abdominal computed tomography: the effect of reduced X-ray tube voltage and intravenous contrast media dosage in patients with reduced renal function. Svensson, A.*, Thor D.*, Fisher M.A., Brismar T.B. Acta Radiologica. 2019. 60(3): p.293-300. *Shared first authorship.
https://doi.org/10.1177/0284185118783213

III. Effect of localizer orientation on ATCM consistency. Thor D., Poludniowski G., Söderberg M., Brismar T.B. [Manuscript]

IV. Is sub-mSv CT for evaluation of non-specific findings in bone scintigraphy of oncological patients feasible? Zakko Y., Thor D., Savitcheva I., Sundvall A., Wassberg C., Koskinen S.K., and Axelsson R. Acta Radiologica. 2019.
https://doi.org/10.1177/0284185119874481