SU-E-I-52: Noise Level and Contrast Dependent Behavior of MTF in Iterative Reconstruction CT Imaging

Iterative reconstruction (IR) technique is growingly used in clinical CT imaging due to its ability to provide improved image quality at lower patient doses. However, the nonlinear frequency response of IR technique, which may affect quantitative analysis, is rarely explored. This study evaluates noise level and contrast dependent behavior of MTF in IR CT imaging with a multi-contrast slit phantom scanned at different dose levels.

A multi-contrast slit phantom was created consisting of acrylic panel and aluminum foils of different thickness. Images were acquired on multi-detector CT (Discovery CT750 HD: GE) at two dose levels (10mAs and 200mAs), and were reconstructed using FBP and two IR technique (ASIR50 and VEO). Line spread functions were extracted across slits of two different thickness (80um and 144um) on images scanned at two dose levels, and were Fourier transformed to evaluate the MTFs of IR and FBP reconstruction techniques, producing a total of 12 MTF curves.

MTF of 200mAs scan showed clearly higher responses up to 28% than that of 100mAs scan in VEO, marginally higher values up to 5% in ASIR50, and were in good agreement in FBP. At same dose level, the MTFs with higher contrast slit (144um) showed marginally higher response than that of lower contrast slit (80um) in VEO and ASIR50.

Our study revealed that MTF of IR technique degrades depending on noise level at low dose scan. Therefore, we recommend that its characteristic should be considered in quantitative analysis such as lesion size measurement.