MRI of Total Hip Arthroplasty: Successful Ripple Artifact Reduction Using Wavelet Domain Filtering

Slice encoding for metal artifact correction (SEMAC) is used in MRI for total hip arthroplasties for metal artifact reduction. However, ripple artifacts often arise near the implant, impairing diagnosis in affected regions.

Applying a wavelet domain filter (WD-Filter) might reduce ripple artifacts and improve image quality.

Retrospective.

100 patients with primary total hip arthroplasty (female: 51, mean age: (64 ± 13) years; male: 49, mean age: (65 ± 13) years) who underwent clinically indicated MRI using compressed sensing SEMAC.

1.5 T; compressed sensing-accelerated turbo spin-echo (TSE)-based SEMAC sequence.

Three readers rated 250 ripple artifacts before and after applying the WD-filter. 4-point Likert scales were used for the intensity of ripple artifacts (Likert-RA, "none": 1, "mild": 2, "moderate": 3, "severe": 4) and the image quality (Likert-IQ, "poor": 1, "moderate": 2, "good": 3, "excellent": 4). The relative reduction of the signal intensity standard deviation ( $\Delta S{D}_{\mathrm{ROI}}$ ) was measured in a region of interest (ROI) containing the ripple artifact.

Inter-reader agreement was assessed with Fleiss' kappa, with 95% confidence intervals. Differences between pre- and post-filter ratings (Likert-RA and Likert-IQ) were evaluated using the Wilcoxon signed-rank test, while $\Delta S{D}_{\mathrm{ROI}}$ was compared using a two-sided paired t-test. A p value of less than 0.05 indicated statistical significance.

Prior to WD-Filter application, $\left(122\pm 2\right)$ ripple artifacts were rated as "severe", $\left(95\pm 3\right)$ as "moderate", and $\left(32\pm 1\right)$ as "mild". After filtering, $\left(168\pm 4\right)$ artifacts were rated as "none", and $\left(82\pm 4\right)$ as "mild". Upon filter application, Likert-RA and Likert-IQ significantly improved from $\left(3.4\pm 0.7\right)$ to $\left(1.3\pm 0.5\right)$ and $\left(1.4\pm 0.5\right)$ to $\left(3.4\pm 0.6\right)$ , respectively, with a large effect size (r > 0.89) and "almost perfect" inter-rater agreement (kappa range: 0.86-0.96). The filtered images showed a significantly reduced $\Delta {\mathrm{SD}}_{\mathrm{ROI}}$ compared to the unfiltered images (relative change: $\left(19\%\pm 10\%\right)$ ).

The WD-Filter effectively reduced ripple artifacts in MRI of total hip arthroplasty and improved image quality.

3.

Stage 3.