Impact of filter convolution and displayed field of view on estimation of coronary Agatston scores in low-dose lung computed tomography

Abstract

Background: Coronary artery calcification (CAC) may be quantified on low-dose computed tomography (CT) of the lung (LDCT). This study aims to evaluate the effects of filter convolution (FC) and displayed field of view (dFOV) in a Toshiba 320-row CT scanner in quantifying CAC, and to compare the CAC scores obtained by LDCT with standard cardiac CT.

Methods: Fifty subjects (52 to 85years, mean 68.5, 36 males) with visible CAC underwent both standard cardiac CT and LDCT. CAC scores were obtained from standard cardiac CT using conventional FC12(22) (FC12 with 22-cm dFOV) and four different LDCT protocols: FC02(22), FC02(40), FC08(22), and FC08(40). CAC scores obtained by each LDCT protocol were compared with those obtained by standard cardiac CT.

Results: CAC scores obtained by all four LDCT protocols were well correlated with those by standard protocol (Pearson's coefficient=0.978 to 0.987, p<0.001; kappa=0.731 to 0.836, p<0.001). CAC scores obtained by FC08(22) showed the best agreement with standard cardiac CT (kappa=0.836, p<0.001). Under fixed dFOV, CAC scores in FC08 were significantly higher than in FC02 (p<0.001). Under fixed FC, CAC scores were significantly higher in 22-cm dFOV than in 40-cm dFOV (p≤0.006).

Conclusions: Both FC and dFOV have significant impact on CAC scoring. To obtain reliable data, consistent parameters should be employed when quantifying CAC using LDCT. In a Toshiba 320-row CT scanner, CAC scores obtained by FC08(22) agree well with standard cardiac CT.

Keywords: Computed tomography; Coronary calcification; Displayed field of view; Filter convolution; Low-dose lung CT.