Non-Invasive Detection And Evaluation Of Auricular Cartilage In Vivo By UTE T₂^* Mapping

To explore the feasibility of non-invasive measurement of auricular cartilage in vivo using UTE sequences combined with T2*mapping technology.We used Ultra-short Echo Time(UTE)sequences with T2*mapping techniques for non-invasive measurement of auricular cartilage in vivo.The composites of rabbit auricular chondrocytes-silk fibroin scaffold were implanted into four rabbits,and the MRI images obtained were analyzed using the same method as volunteers to verify the feasibility of T2*mapping techniques.In 30 volunteers,we used UTE sequences to get MRI images of external ears.In order to evaluate the auricular cartilage separately from the external ear(containing not only auricular cartilage but also surrounding tissues,e.g.skin,fat,and other soft tissues),the manually delineated labels of auricular cartilage and external ear for each subject were applied for the component analysis to obtain both the T2*value of the segmented auricular cartilage and that of the external ear.Finally,the attenuation curves of signal intensity with UTE time were fitted.In the experiment of mono-component analysis of the 30 right-sided ears,the mean T2*value of external ear was 49.269±16.979 ms and the mean T2*value of segmented auricular cartilage was 23.799±9.629 ms.In the bi-component analysis,the mean short component T2*was 11.713±3.111 ms and the mean long component T2*was 65.128±13.132 ms for the external ear,while for the segmented auricular cartilage,the mean short component T2*was 5.577±1.830 ms and the mean long component T2*was 30.628±8.413 ms.There was a significant difference of short component T2*value between the external ear and the auricular cartilage(P<0.001)in the bi-component analysis.The model with bi-exponential fitting outperformed the one with mono-exponential fitting with better fitted curves,R2[bi]=0.999±0.001 vs.R2[mono]=0.905±0.014(P<0.001).In animal experiments,multi-short TE sequence images of the composite of rabbit auricular chondrocytes-silk fibroin scaffold were collected,and the T2 mapping analysis results of the MRI scanner workstation were saved.The T2*values of the complex were calculated using the same method as that of healthy volunteers and compared with the results from the workstation.In the mono-component analysis of animal,the results of T2*mapping of each implant are consistent with the T2 mapping results processed by the workstation,and the trend of the mono-component analysis of T2*mapping is more stable.In the bi-component analysis,the T2*s value and T2*1 value of each implant showed a trend of rising first and then falling.When the T2*s value reached the peak,it can be regarded as the bound water component(cartilage or cartilage-like tissue)of the composite of rabbit auricular cartilage chondrocytes-silk fibroin scaffold increased mostly.Using UTE sequences,MRI images of healthy human auricular cartilage can be collected,which can be used for T2*mapping analysis and fitting attenuation curves.In rabbits,T2*mapping technology accomplished noninvasive detection of rabbit auricular chondrocytes-silk fibroin scaffold complex.The proposed UTE T2*mapping has shown to be a feasible non-invasive means for quantifying the auricular cartilage in vivo and a potential tool used to monitor the development of auricular cartilage in reconstructive surgery for microtia using tissue engineering or 3D bioprinting technique in the future.