  Purpose: Siemens has developed several iterative reconstruction (IR)
algorithms on their CT scanners. SAFIRE is available on most of their CT
scanners. The latest algorithm, ADMIRE, is available on their newest high-end
CT scanners. The aim of our study was to compare the noise reduction properties
of the two IR algorithms using objective methods. Methods and Materials: The
homogeneous module of the Catphan phantom was scanned on a Siemens AS+ and a
Siemens Flash CT scanner using an axial abdomen protocol with fixed tube
current at two dose levels. The images were reconstructed with an abdomen
filter (B30) using filtered back projection (FBP) and a low, medium, and high
level of SAFIRE or ADMIRE. Noise Power Spectrum (NPS) curves were calculated
using these images. Then, an anthropomorphic abdomen phantom (Kyoto Kagaku
PH-5) was scanned using the same setup and exposure parameters. Fifty axial
images at the same slice location were used to calculate inter-image standard
deviation maps. Results: At full dose, the median values of the NPS curves were
similar for both scanners at all IR levels. At low dose the median values of
the NPS curves were generally shifted towards lower spatial frequencies,
usually resulting in a more blotchy image texture. This shift was more
prominent for ADMIRE compared to SAFIRE for all IR levels. Based on the
inter-image standard deviation maps of the anthropomorphic phantom, ADMIRE
removed noise near edges more efficiently than SAFIRE. Conclusion: No
significant improvement in maintaining noise structure were found for the
ADMIRE algorithm. Based on the inter-image standard deviation maps, ADMIRE
removed noise near edges more efficiently than SAFIRE.
