Methods and utilities to assist in the optimization of image quality and radiation dose in X-ray Computed Tomography
Time: Mon 2020-06-15 13.00
Subject area: Physics
Doctoral student: Robert Bujila , Medicinsk bildfysik
Opponent: Professor Nico Buls, Brije Universitet, Bryssel, Belgien
Supervisor: Professor Mats Danielsson, Fysik
X-ray Computed Tomography (CT) is a highly utilized tool in diagnos- tic radiology. CT provides radiologists with unobstructed views of patient anatomy. However, image quality in CT is highly dependent on the imaging task, scan technique, beam quality and radiation dose. The size of the patient must be considered and the radiation dose must be subsequently adapted to achieve consistent image quality. As CT is a modality that utilizes radia- tion to generate images, the purpose of this thesis was to explore tools and methodologies that can be utilized to optimize image quality with respect to radiation dose.
In Paper I, fundamental image quality metrics were modeled whereby the effect of radiation dose/beam quality on these metrics could be estimated. The applications of these models were demonstrated by estimating the de- tectability of low contrast details across different radiation doses/beam qual- ities using a mathematical model observer.
Dose indices are reported by CT scanners to indicate the level of radiation that has been utilized during a scan. As the level of radiation dose is a central aspect in optimization work, methods were deployed to verify the accuracy of CT dose indices for wide beam CT scanners in Paper II.
CT scanners employ so called Automatic Tube Current Modulation (ATCM) to adapt the level of radiation dose to obtain consistent image quality across varying sized patients. In Paper III, a comprehensive study was executed to better understand the complex nature of ATCM as it relates to different vendor implementations as ATCM plays a central role in the optimization of CT scans.
As the beam quality used during an examination has a central role for both dosimetry and image quality, a toolkit was developed that can be used to model x-ray spectra emerging from an x-ray tube in Paper IV. The toolkit underwent a rigorous validation and has since been made available online.
In conclusion, this thesis has resulted in a number of methods and utilities that can help unfold the complex relationship between image quality and radiation dose on a practical level in CT.