A comparison of smooth and sharp kernel CT reconstructions in the detection of unilateral sacral fractures

Objective The goal of this study is to determine whether smooth kernel reconstructions are more sensitive than sharp kernel ones for the detection of sacral stress fractures (SF) using MRI as the reference standard. Materials and methods This retrospective study included 100 subjects in whom CT and MR of the pelvis were performed for a clinical suspicion of SF from January 2014 to May 2020 in our institution. MR was used as the reference standard for the presence of SF. Smooth and sharp kernel CT datasets of the 100 patients were pooled and analyzed randomly. Three readers of various experiences in MSK imaging independently evaluated the axial CT images for the presence of a SF. Results SF was present on MR in 31 patients (22 women, 9 men; mean age 73.6 ± 19.6) and absent in 69 (48 women, 21 men; mean age 68.8 ± 19.0). Depending on readers, sensitivities ranged from 58 to 77% for the smooth kernel and from 52 to 74% for the sharp kernel reconstructions. For each reader, sensitivities (as well as negative predictive values) of CT were slightly greater on the smooth kernel reconstructions. Conclusion The use of smooth kernel reconstructions improved the sensitivity of CT for the detection of SF compared to the sharp kernel reconstructions usually used and regardless of the experience of the radiologist. Smooth kernel reconstructions should, therefore, be scrutinized in patients with suspicion of SF.