Optimization of acquisition parameters for reduced-dose thoracic CT: A phantom study - 04/05/20
Highlights |
• | Favoring high tube voltage is the best option for reduced-dose CT protocols. |
• | Lowest scores for subjective image quality are reached with low pitch factor. |
• | Decrease of SNR does not necessarily go along with reduced subjective image quality. |
Abstract |
Purpose |
The purpose of this study was to analyze the impact of different options for reduced-dose computed tomography (CT) on image noise and visibility of pulmonary structures in order to define the best choice of parameters when performing ultra-low dose acquisitions of the chest in clinical routine.
Materials and methods |
Using an anthropomorphic chest phantom, CT images were acquired at four defined low dose levels (computed tomography dose index [CTDIvol]=0.15, 0.20, 0.30 and 0.40mGy), by changing tube voltage, pitch factor, or rotation time and adapting tube current to reach the predefined CTDIvol-values. Images were reconstructed using two different levels of iteration (adaptive statistical iterative reconstruction [ASIR®]-v70% and ASIR®-v100%). Signal-to-noise ratio (SNR) as well as contrast-to-noise ratio (CNR) was calculated. Visibility of pulmonary structures (bronchi/vessels) were assessed by two readers on a 5-point-Likert scale.
Results |
Best visual image assessments and CNR/SNR were obtained with high tube voltage, while lowest scores were reached with lower pitch factor followed by high tube current. Protocols favoring lower pitch factor resulted in decreased visibility of bronchi/vessels, especially in the periphery. Decreasing radiation dose from 0.40 to 0.30mGy was not associated with a significant decrease in visual scores (P<0.05), however decreasing radiation dose from 0.30mGy to 0.15mGy was associated with a lower visibility of most of the evaluated structures (P<0.001). While image noise could be significantly reduced when ASIR®-v100% instead of ASIR®-v70% was used, the visibility-scores of pulmonary structures did not change significantly.
Conclusion |
Favoring high tube voltage is the best option for reduced-dose protocols. A decrease of SNR and CNR does not necessarily go along with reduced visibility of pulmonary structures.
Le texte complet de cet article est disponible en PDF.Keywords : Radiation dosage, Tomography, X-ray computed, Thorax, Phantoms
Plan
Vol 101 - N° 5
P. 269-279 - mai 2020 Retour au numéroBienvenue sur EM-consulte, la référence des professionnels de santé.