Construction Of Auricular Cartilage Models For 3D Bioprinting Based On Multimodal MRI Images

Background:Constructing a high-fidelity,structurally stable and safe auricular cartilage scaffold has always been the core of auricle reconstruction to repair congenital microtia.Construction methods of the ear cartilage scaffold have been continuously improved,including hand crafting of rib cartilage,cartilage tissue engineering and 3D bioprinting.Compared with the first two methods,3D bioprinting technology can accurately control the macroscopic and microscopic structure of ear cartilage scaffold through computer-aided design(CAD)without intercepting the patient's costal cartilage,reducing the injury to the patients.Therefore,it is the primary research direction of accurate construction of the ear cartilage scaffold model.Image acquisition is one of the major factors affecting the accuracy of 3D bioprinting structures.3D laser scanning,computer tomography(CT)and conventional magnetic resonance imaging(MRI)sequences have poor imaging effects on auricular cartilages,which are not suitable for the segmentation of ear cartilages,resulting some precision errors in the constructed models.This study aims to explore scanning protocols suitable for auricular cartilage and to construct a high-precise auricular cartilage scaffold providing the model basis for 3D bioprinting.Methods:MRI was performed on the unilateral auricles of 40 healthy volunteers with 3.0 T Philips(Achieva)rincluding UTE,3D-T2,PDW and PROSET.Firstly,the auricular cartilages were manually segmented by two experienced raters(Raterl and Rater2)with UTE and 3D-T2,and cartilage volume(Cg.V),surface area(Cg.S),and thickness(Cg.Th)were calculated.Then,based on the above morphological indexes,the paired t-test was performed on the intra-rater segmentation results,and the precision errors(PE),intraclass correlation coefficients(ICC),Pearson correlation coefficients and Dice similarity coefficients(DSC)of intra-rater and inter-rater segmentation were analyzed.PE and ICC were used to evaluate the segmentation reproducibility.ICC was one of the reliability coefficient indicators for evaluating the inter-observer reliability and test-retest reliability.DSC can further evaluate the similarity of segmentation results.Fine structure segmentation was then performed on the ear based on UTE,3D-T2 and PDW.Finally,the ear cartilage model was repaired and sliced to provide an ear cartilage scaffold model for 3D bioprinting.Results:This study discovered a scanning scheme suitable for the ear cartilage segmentation.UTE and 3D-T2 could be used to segment ear cartilages.There was no significant difference between Cg.V and Cg.Th in intra-rater.Inter-and intra-rater precision errors(PE%cv)of Cg.V,Cg.S and Cg.Th were less than 5%,intraclass correlation coefficients(ICC)were higher than 0.95,0.89,0.69,respectively,and Pearson's correlation coefficients were higher than 0.95,0.95,0.78.DSC could reach 80%.This study demonstrated that the scanning protocol could characterize the variation of ear cartilage morphology between individuals,and good inter-and intra-rater segmentation reproducibility of auricular cartilages were achieved.Besides,although Cg.Th had a low correlation,different raters could detect intact ear cartilage contours.A high-fidelity auricle cartilage scaffold model was constructed based on MRI sequences with specific imaging effects on the ear cartilage.In addition,based on UTE,3D-T2 and PDW,the external auricle was divided into thirteen fine structures.This study proposed the use of ear fine structures to assist in the surgical planning and postoperative evaluation of auricle reconstruction.Conclusions:This study demonstrated that the precision of the manual segmentation results based on UTE and 3D-T2 was sufficient to detect patient-specific variation in auricular cartilage shape,and the proposed scanning protocol could be used as an image acquisition strategy for the construction of auricular cartilage scaffold model in 3D bioprinting.Based on the individual-specific ear cartilage imaging sequences,this study constructed ear cartilage scaffold models for 3D bioprinting,and also provided a method for combining the fine structures of the ear to assist the clinician in developing a surgical plan and postoperative evaluation.