Metal artifact reduction for small metal implants on CT: Which image reconstruction algorithm performs better?

PURPOSE

To compare the performance of different image reconstruction algorithms in the presence of small metal objects of different sizes and at different dose levels.

METHOD

A fresh bone of bovine femur was drilled with seven drill bits of increasing diameter. CT images with eight different dose levels were acquired and reconstructed with three algorithms: hybrid iterative reconstruction - HIR, Full model-based iterative reconstruction - full MBIR and a single energy metal artifact reduction - SEMAR. Trabecular distortion adjacent to metal was evaluated subjectively with a four-point scale. Edge profile artifacts were evaluated quantitatively by measuring drill bit diameter overestimation and the width of the low-density halo surrounding the drill bit.

RESULTS

Trabecular distortion was higher with full MBIR compared to HIR and SEMAR (P < 0.0001) and increased with drill bits larger than 1.2 mm and with doses lower than 18.1 mGy.cm. Low-density halos size and drill bit diameter overestimation decreased with full MBIR compared to the other two reconstruction algorithms and with SEMAR compared to HIR (P < 0.0001). There was a mean drill bit overestimation of 0.56 ± 0.25 mm for full MBIR versus 0.68 ± 0.09 mm for SEMAR and mean low-density halo diameters of 0.03 mm ± 0.08 for full MBIR versus 0.42 mm ± 0.09 for SEMAR.

CONCLUSION

Algorithm performance is influenced by dose levels and metal object size and no individual algorithm provides the best overall performance. Full MBIR is better in reducing edge artifacts and SEMAR is the best option for larger metal implants and low dose protocols.