Quantifying Auricular Cartilage in Vivo Using Ultra-Short Echo Time (UTE) T2* Mapping

In this paper, UTE (Ultra-short Echo Time) T2* mapping is proposed to non-invasively evaluate auricular cartilage in 30 volunteers. The mono- and bi-exponential models were used for mono- and bi-component analysis (short component T2* and long component T2*) respectively. 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 are applied for the computed component analysis to obtain both the T2* value of the segmented auricular cartilage and that of the external ear. In the experiment of mono-component analysis of 30 right-sided ears, the mean T2* value of external ear was 41.451 ± 13.332ms and the mean T2* value of segmented auricular cartilage was 34.107 ± 11.820ms. In the bi-component analysis, the mean short component T2* was 9.594 ± 2.482ms and the mean long component T2* was 53.042 ± 10.439ms for the external ear, while for the segmented auricular cartilage, the mean short component T2* was 8.096 ± 2.172ms and the mean long component T2* was 44.907 ± 9.179ms. There was a significant difference of short component T2* value between the external ear and the auricular cartilage (9.594 ± 2.482ms vs. 8.096 ± 2.172ms, 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] = 0.892 ± 0.031. Our preliminary results demonstrated that the T2* mapping values computed from both mono- and bi-component analyses were significantly different between the external ear and the auricular cartilage. The proposed UTE T2* mapping has shown to be a feasible non-invasive means for quantifying the auricular cartilage in vivo and could be used to monitor the development of auricular cartilage in reconstructive surgery for microtia using tissue engineering or 3D bioprinting technique in the future.