The dependency of image quality on acquisition protocol and image processing in chest tomosynthesis

The digital tomosynthesis (DTS) technique is a next generation of the old tomography technique, the use of which has been extended during the past decade. The interest in this technique has increased more and more in Radiology due to its ability to provide threedimensional images by acquiring a number of projection radiographs at lower radiation dose and potentially lower cost than CT in certain clinical situations. Furthermore, there are two main advantages of DTS in comparison with conventional radiography. The first one is that the reconstructed slices reduce the problem of overlaying anatomical structures in a twodimensional image created by conventional radiography. The second one is that DTS has better depth resolution than conventional radiography. The primary aims of the studies in this thesis have been to determine a chest DTS protocol with shorter exposure time then the vendor recommended protocol (12 s) with retained image quality and to investigate the difference in image quality between the protocols with acquisition time 6.3 s and 12 s.

In order to compare all available chest DTS protocols, an anthropomorphic phantom with a 12 mm module placed in the center of the right lung was used for the first study. The second study was performed as a prospective human study where the best performing protocols from the first study were compared. In both studies, the observers were instructed to evaluate the image quality based on the pre-defined criteria. The criteria were developed in accordance with the European guidelines and previous studies in combination with the clinical experience of the observers. The data from both studies were analysed with visual grading characteristics (VGC) analysis and the area under the VGC curve (AUGVGC) was used as figure-of-merit.

The result of the studies indicates that the chest DTS protocol with the acquisition time of 6.3 s has similar image quality as the reference protocol with acquisition time of 12 s for all quality criteria. The shorter acquisition time may have a great clinical significant for the patient with respiratory impairment. In the future, further studies should be performed to evaluate the diagnostic value of chest DTS in compare with CT in some clinical situations, reduction of radiation dose and cost efficiency within healthcare.

List of scientific papers

I. Jadidi M, Sundin A, Aspelin P, Båth M, Nyrén S. Evaluation of a new system for chest tomosynthesis: aspects of image quality of different protocols determined using an anthropomorphic phantom. Br J Radiol. 2015;88(1053):20150057.
https://doi.org/10.1259/bjr.20150057

II. Jadidi M, Båth M, Nyrén S. Dependency of image quality on acquisition protocol and image processing in chest tomosynthesis - a visual grading study based on clinical data. Br J Radiol. 2018; 91(1087):20170683.
https://doi.org/10.1259/bjr.20170683