This study aims to evaluate the application of 5.0 T ultra-high-field MRI in knee joint imaging and directly compare its performance to the widely used 3.0 T MRI to explore its primary advantages.

This prospective study recruited healthy volunteers and patients with chronic knee pain between December 2023 and August 2024. All subjects underwent both 3.0 T and 5.0 T knee joint MRI scans. The imaging sequences included T1WI, 2D FS_PDWI, and 3D FS_PDWI sequences. Three musculoskeletal radiologists independently evaluated the image quality. Quantitative analysis measured the signal-to-noise ratio (SNR) of muscles, cartilage, and bone, while semi-quantitative analysis assessed overall image quality, diagnostic confidence, artifacts, homogeneity of fat suppression, and the visualization of knee structures, including cartilage, ligaments, menisci, and bone marrow edema. Statistical analysis was conducted using the Wilcoxon signed-rank test, and inter-rater agreement was evaluated using the Fleiss kappa coefficient.

A total of 48 healthy volunteers and 55 patients with chronic knee pain were included. Quantitative analysis showed that the SNR of muscles, cartilage, and bone in all sequences was significantly higher with 5.0 T MRI compared to 3.0 T (mean difference range -1.1 to -7.7, P<0.05). Semi-quantitative analysis indicated that the image quality of 5.0 T in 2D sequences was superior to 3.0 T (mean difference -0.24 to -0.50, P<0.05), whereas no significant advantage was observed for 3D PDWI sagittal imaging (mean difference -0.12, P=0.054). There was no significant difference between 5.0 T and 3.0 T in terms of artifacts and homogeneity of fat suppression (P>0.05). Although 5.0 T did not show significant advantages in reading outcomes, it significantly improved diagnostic confidence (mean difference -0.14 to -0.37, P<0.001) and demonstrated superior imaging of various knee structures (mean difference -0.11 to-0.35, all P<0.05). The inter-rater agreement among the three radiologists ranged from moderate to high (kappa 0.486 to 0.969).

Compared with 3.0 T MRI, 5.0 T ultra-high-field MRI demonstrated significant advantages in knee joint imaging, particularly in the quality of muscle, cartilage, and bone imaging as well as in diagnostic confidence. Additionally, 5.0 T did not show any disadvantages in terms of artifact control and fat suppression uniformity. However, no significant advantage was noted in 3D PDWI image quality.