3D Printing Technology Of Personalized Mastoid Air Cells Based On HRCT Data

BackgroundSuppurative otitis media and cholesteatoma are common middle ear diseases,which cause pus flow,hearing loss,tinnitus and other discomfort,and can even cause intracranial and external complications,which seriously affect the quality of life of the patients,there is a risk of disability,life-threatening.Operation is the main effective measure to treat suppurative otitis media and cholesteatoma.With the continuous optimization of surgical equipment,instruments and new materials,as well as the continuous improvement of the pursuit of auditory function reconstruction,surgical procedures are diversified.However,no matter what kind of surgical procedures,there are still cases of failed treatment such as fluid pus,granulation residue and recurrence of cholesteatoma.How to effectively control suppurative otitis media and the recurrence of cholesteatoma is an urgent problem in ear microsurgery.It was found that the mastoid air cells and the eustachian tube played an important role in maintaining the pressure balance in the middle ear,and the negative pressure in the middle ear caused by poor mastoid gasification and poor eustachian tube function may be the main reason for postoperative recurrence.On this basis,we put forward the theory of"balance of middle ear pressure",that is,the mastoid,middle ear and eustachian tube are classified as a"balance"system.The middle ear part is the fulcrum,and the mastoid and eustachian tube are the ends of the fulcrum respectively.When either end is out of balance,the whole system is out of balance.Improving the function of eustachian tube and reconstructing the function of good air cells are important ways to reduce the negative pressure in the middle ear.In recent years,a large number of researchers have made good progress in exploring effective treatment methods to improve the function of eustachian tube,but few studies have been reported on the reconstruction of mastoid air cells function.The application of effective mastoid air cells reconstruction method in mastoid surgery of the middle ear is a blank chapter in the field of ear microsurgery.In the reconstruction and repair of human tissue defects,individuation and precision are important directions in the development of modern medicine.As one of the important signs of the third industrial revolution,the technology of three dimensions print（TDP）,which was developed in the 1980s,can realize the personalized repair of the damaged tissue according to the medical image data,and is an important way for personalized and accurate treatment.TDP technology has been very mature to realize personalized medical model,surgical auxiliary instruments,orthodontic appliances and implant manufacturing,which is widely used in bone and joint,oral and maxillofacial,plastic surgery,cardiothoracic,neurosurgery and other clinical disciplines,and is an effective way to achieve complete personalized accurate pathological resection and defect repair treatment.Based on the application of TDP technology in the field of medicine,it is expected to realize the reconstruction of the mastoid air cells.This study aims to explore the technique of establishing a 3D digital model of personalized mastoid air cells based on high resolution computer tomography（HRCT）data,Materialise’s interactive medical image control system（MIMICS）and computer aided design（CAD）,and using the corresponding materials to make rapid prototyping（RP）by 3D printing equipment.In order to realize the personalized structure reconstruction of mastoid air cells,and provide the foundation for further functional reconstruction research and the application in middle ear mastoid surgery.Part Ⅰ:Surface Area and Volume Measurement of Mastoid Air Cells by 3D Reconstruction Based on HRCTObjective Based on healthy pneumatic mastoid adult temporal bone HRCT,3D reconstruct mastoid air cells by medical image control system,and measure surface area（SA）,volume（volume,V）and surface-to-volume ratio（SA/V）of mastoid air cells.To reveal reference value range and characteristics of SA,V,SA/V in mastoid of pneumatic type.Material and Methods The temporal bone HRCT data of 108（216 ears）adult patients with mastoid of pneumatic type in our hospital from January 2016to June 2017 were retrospectively analyzed.All patients were excluded from middle ear disease.Mimics 21.0 medical imaging control system was used to reconstruct the temporal bone HRCT mastoid air cells and measure its SA,V,SA/V.SPSS 25.0 software was used to determine the reference value range,to compare the difference of mentioned above measurements between the sexes by mann-whitney U test,to compare the difference of SA and V between the left and right ears by paired Wilcoxon test,to compare the difference of SA/V between the left and right ears by paired t test.Results In 108 cases（216 ears）,the pneumatic mastoid air cells SA showed a skewed distribution,with the median value of 9220.20（6837.42-12472.07）mm²（M（Q₁-Q₃）,similarly hereinafter）,and the 95%reference value range was 3105.70～21218.66mm².V was skewed,with the median of 7255.86（5178.03-9796.77）mm³,and the 95%reference value range was 2185.78～19297.57mm³.SA/V is normally distributed,with an average（1.3098±0.2444）mm^-1（±s）,and the 95%reference value range was 0.8308～1.7888mm^-1.Male SA and V of mastoid air cells were all larger than female,and the difference was statistically significant（P<0.05）,while male SA/V was less than female,and the difference was statistically significant（P<0.05）.There was no significant difference between left ear and right ear in SA and SA/V of mastoid air cells（P>0.05）,while left V was larger than right,and the difference was statistically significant（P<0.05）.Conclusion In adults with healthy mastoid of pneumatic type,95%reference value range of SA,V and SA/V were 3105.70～21218.66mm²,2185.78～19297.57mm³and 0.8308～1.7888mm^-1,respectively.The SA and V is significantly different among individuals,and the SA/V has little difference among individuals.Part Ⅱ:3D Modeling and Rapid Prototyping of Personalized Mastoid Air Cells Based on Temporal Bone HRCTObjective Based on the reference value ranges of SA,V and SA/V of healthy pneumatic mastoid air cells and preoperative temporal bone HRCT,to explore the feasibility of 3D printing technology to reconstruct the personalized mastoid air cells structure.Material and Methods One patient with chronic suppurative otitis media who underwent middle ear mastoid surgery in our hospital from January 2018to June 2019 was selected.Importing patient preoperative temporal bone HRCT data into Mimics 21.0,3D reconstruct the mastoid air cells range,vertical facial nerve bone tube,semicircular canals,middle cranial bone plate,sigmoid sulcus bone plate,double abdominal muscle crest and outer ear canal.Then,the mastoid air cells range of 3D reconstruction and other important anatomical structures were conducted by Boolean logic"non-"operation,and the 3D model of the simulate mastoid contour cavity was obtained.The 3d model of the mastoid cavity is imported into the 3-matic12.0 computer aided design forward engineering software,which turns its design into a grid support for SA、V and SA/V reache reference value range.In mimics 21.0,the temporal bone of the patient was reconstructed,and the mastoid cortex was extracted that the upper boundary is the temporal line,the anterior boundary is the bone outer ear wall,the posterior boundary is the front of the cusp of the mastoid and parietal notch.The operation of the Boolean logic"and"operation of the mastoid cortex and the grid support is obtained,and the reconstructed model of the the personalized mastoid with the cortical bone and the air cells is obtained.Finally,enter it to 3D printing equipment using related materials for rapid prototyping.Results 1.In the reconstructed mastoid air cells supports designed according to the simulate mastoid contour cavity 3D model with pore sizes of 0.5 mm,1.0 mm,1.5 mm,2.0 mm,2.5 mm,3.0 mm,all the supports SA and V are in the 95%reference value range.The SA/V of supports with pore sizes of 1.0 mm,1.5 mm,2.0 mm was within 95%reference value range.The SA/V of support with pore sizes of 0.5mm beyond the upper limit of the95%reference value range,1.7888mm^-1.The SA/V of supports with pore sizes of 2.5mm and 3.0mm failed to reach the lower limit of 95%reference value range,0.8050mm^-1.The SA/V of support with pore sizes of 1.0mm was 1.3856mm^-1,which was closest to the average value,1.3098 mm^-1,of results in experiment 1 among all the supports with different pore sizes.2.The personalized reconstruction of mastoid air cells formed by Resin Light Processing molding are well restored.The hardness of the reconstruction of cortical bone plate and air cells support are well restored.Conclusion Based on the temporal bone HRCT of the patient and the reference value range of SA,V and SA/V of the healthy pneumatic mastoid air cells,the model was constructed by the medical image control system and the computer aided design software,shape through the 3D printing equipment of rapid prototyping technology of TDP is a feasible way to realize the personalized structure reconstruction of mastoid air cells.