The influence of iterative reconstruction level on image quality and radiation dose in CT pulmonary angiography examinations

Computed Tomography Pulmonary Angiography (CTPA) examination is one of the essential imaging procedures to detect pulmonary embolism (PE). Despite its advantages, it may contribute high dose exposure to the patients if unoptimized parameters were applied. Numbers of optimization techniques have been introduced to reduce dose while preserving the diagnostic quality of the procedure. Hence, this study aimed to evaluate the effects of using iterative reconstruction (IR) algorithm with adoption of different tube potentials and establish the Figure of Merit (FOM) in the relationship between radiation exposure and image quality. Thirty adult patients (n = 30) were retrospectively recruited. Data, such as patient demography, scanning protocols and radiation dose information, were collected and analyzed. Each CT image was reconstructed with different levels of IR algorithm. A 150 mm(2)-wide circular region of interest (ROI) was drawn inside five consecutive areas surrounding the pulmonary artery in each reconstructed image. Diagnostic performance was evaluated based on signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). Meanwhile, FOM was evaluated in four different indicators, which were SNR2/C-vol, SNR2/SSDE, CNR2/C-vol and CNR2/SSDE. Volume weighted CT Dose Index (C-vol) and Size-specific Dose Estimate (SSDE) were estimated for each subject and utilized for the denominator in calculating FOM. C-vol and SSDE increased up to 170% and 154%, respectively, with higher tube voltage. They also increased up to 33% and 16%, respectively, as the patients' effective diameter increased. SNR, CNR and FOM values were comparable with different IR levels, tube voltage and effective diameter. In conclusion, CTPA would yield better results with increasing IR levels, decreasing tube voltage and on patients with small body size.