The Clinical Value of the MAR + Metal Artifact Reduction Algorithm for Postoperative Assessment of Lumbar Internal Fixation.

Background: With the widespread use of lumbar pedicle screws for internal fixation, the morphology of the screws and the surrounding tissues should be evaluated. The metal artifact reduction (MAR) technique can reduce the artifacts caused by pedicle screws, improve the quality of computed tomography (CT) images after pedicle fixation, and provide more imaging information to the clinic.

Purpose: To explore whether the MAR + method, a projection-based algorithm for correcting metal artifacts through multiple iterative operations, can reduce metal artifacts and have an impact on the structure of the surrounding metal.

Materials and methods: A total of 57 patients who underwent lumbar spine CT examination after lumbar internal fixation from January to December 2023 in our hospital were retrospectively enrolled. The CT images were reconstructed using MAR + and non-MAR + techniques and were subdivided into MAR + and non-MAR + groups. The CT number (in Hounsfield units) and the SD noise values of the spinal canal, vertebral body, psoas major muscle, and adjacent fat were measured in the 2 groups of CT images, and the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. The subjective score was evaluated by two diagnostic radiologists using a double-blind method for image quality evaluation of the MAR + group and the non-MAR + group, and the image quality was classified on a 5-point scale. The rank-sum test was utilized to compare the subjective and objective scores of the 2 groups.

Results: The SD values of the spinal canal ( Z =-4.12, P <0.01), vertebral body ( Z =-3.81, P <0.01), and psoas major muscle ( Z =-3.87, P <0.01) in the MAR + group were significantly lower than those in the non-MAR + group ( P <0.05). However, the SD values of the adjacent fat ( Z =-2.03, P =0.42) in the MAR + group, although smaller than those in the non-MAR + group, were not statistically significant. The CNR values of vertebral canal ( Z =-2.67, P =0.008) and fat ( Z =-2.60, P =0.009) were higher in the MAR + group than in the non-MAR + group, whereas the CNR values of the vertebral body ( Z =-6.74, P <0.01) in the MAR + group were smaller than those in the non-MAR + group, and the difference of all of them was statistically significant ( P <0.05). Furthermore, for both CT and SNR values, the MAR group's values were all less than those of the non-MAR group and were statistically significant ( P <0.05). The subjective scores of the measurement points were all higher in the MAR + group than in the non-MAR + group.

Conclusions: The MAR + technique has a noise reduction effect on different tissues and artifacts are significantly reduced. Although the artifacts caused by metal screws were not completely eliminated, the MAR + technique was able to reduce the interference of artifacts in the diagnosis of CT images, thus improving their diagnostic quality.