The effect of cartilage dehydration and rehydration on quantitative ultrashort echo time biomarkers

Background: The effect of dehydration of ex vivo cartilage samples and rehydration with native synovial fluid or normal saline on quantitative ultrashort echo time (UTE) biomarkers are unkonwn. We aimed to investigate the effect of cartilage dehydration-rehydration on UTE biomarkers and to compare the rehydration capabilities of native synovial fluid and normal saline.Methods: A total of 37 cartilage samples were harvested from patients (n=5) who underwent total knee replacement. Fresh cartilage samples were exposed to air to dehydrate for 2 hours after baseline magnetic resonance (MR) scanning, then randomly divided into two groups: one soaking in native synovial fluid (n=17) and the other in normal saline (n=20) to rehydrate for 4 hours. UTE-based biomarkers [T-1, adiabatic T-1? (AdiabT(1?)), macromolecular proton fraction (MMF), magnetization transfer ratio (MTR), and T2*] and sample weights were evaluated for fresh, dehydrated, and rehydrated cartilage samples. Differences and agreements between groups were assessed using the values of fresh cartilage samples as reference standard. Results: Dehydrating in air for 2 hours resulted in significant weight loss (P=0.000). T-1, AdiabT(1?), and T-2* decreased significantly while MMF and MTR increased significantly (all P<0.02). Non-significant differences were observed in cartilage weights after rehydrating in both synovial fluid and normal saline, with P values being 0.204 and 0.769, respectively. There were no significant differences in T-1, AdiabT(1?), MMF, and MTR after rehydrating in synovial fluid (P>0.0167, with Bonferroni correction) while T-2* (P=0.001) still had significant differences compared with fresh samples. However, no significant differences were detected for any of the evaluated UTE biomarkers after rehydrating in normal saline (all P>0.05). No differences were detected in the agreement of UTE biomarker measurements between fresh samples and samples rehydrated with synovial fluid and normal saline.Conclusions: Cartilage dehydration resulted in significant changes in UTE biomarkers. Rehydrating with synovial fluid or normal saline had non-significant effect on all the evaluated UTE biomarkers except T-2* values, which still had significant differences compared with fresh samples after rehydrating with synovial fluid. No significant difference was observed in the rehydration capabilities of native synovial fluid and normal saline.