Reliability of CEUS and MRI for grading knee-joint inflammation in juvenile idiopathic arthritis

OBJECTIVE: To examine the reliability of contrast-enhanced MRI (CEMRI) and contrast-enhanced ultrasound (CEUS) for grading arthritis. MATERIALS AND METHODS: Prospective study on 1-18-year-olds with juvenile idiopathic arthritis (JIA), performed during 2023/2024. All had CEUS and CEMRI of the knee on the same day. Two observers independently scored the US-video-clip for inflammation (0-3 scale), with a second reading after 6 weeks. Using VueBox®, peak enhancement (PE), time to peak (TTP) and wash-in area under the curve (WiAUC) were measured by both observers, separately. The MRIs were scored for inflammation (0-3 scale) twice by two observers. Peak enhancement intensity (PEI), TTP and initial area under the curve (iAUC) (Syngo.via®) were measured. RESULTS: Fifty-two patients (35 females), median age 12.4 years (IQR 8.9-15.6 years), were included. CEUS showed almost perfect intra/interreader agreement for the degree of overall inflammation (intrareader kappa 0.90 [0.83-0.98], interreader kappa 0.85 [0.76-0.93]). Interreader PE and WiAUC agreement was excellent (ICC 0.99 [95% CI 0.99-1.00] and 0.97 [95% CI 0.95-0.98], respectively), while TTP performed moderately (ICC 0.66 [95% CI 0.40-0.80]). On CEMRI, intra/interreader agreement for overall synovial inflammation was almost perfect (intrareader kappa 0.94 [95% CI 0.88-1.00]; interreader kappa 0.92 [95% CI 0.85-1.00]). Interreader PEI and iAUC agreement was excellent (ICC 0.99 [95% CI 0.98-0.99] and 0.98 [95% CI 0.97-0.99], respectively), while TTP had good agreement (ICC 0.76 [95% CI 0.59-0.86]). CONCLUSION: Subjective grading of synovial inflammation on a 0-3 scale demonstrated high reliability for both CEUS and CEMRI. Both methods have excellent relative reliability (ICC) for quantitative measurements; however, their absolute precision (LoA) is poor. KEY POINTS: Question Are CEUS and CEMRI reliable tools to grade the activity of knee-joint arthritis in children with juvenile idiopathic arthritis? Findings Subjective grading of arthritis performed well within and between observers for both CEUS and CEMRI. Both methods provide reliable dynamic measurements; however, their precision is poor. Clinical relevance CEUS offers high-precision, real-time imaging for grading active knee-joint inflammation in children with juvenile idiopathic arthritis, with future potential to replace the current standard of CEMRI.