| Cone Beam Computed Tomography has the principle advantages of lower radiation dose and higher spatial resolution than spiral CT.In oral cone-beam CT,image-guided radiotherapy,digital breast tomosynthesis,acral cranial,etc.have replaced or are expected to replace and surpass the corresponding functions of spiral CT.Specifically in the field of dental cone-beam CT,due to the advantages of high image detail resolution,low radiation dose,fast scanning speed,and dexterity in size,it is mostly used in dental diagnosis fields such as implants,maxillofacial surgery,and periodontal teeth.It is favored by more and more dental clinics.With the increase of the people’s disposable income,the willingness to go to a doctor due to oral diseases has also increased,and a number of dental cone-beam CT equipment manufacturers have emerged at home and abroad.Generally,different countries have different regulatory requirements for medical equipment from R&D to marketing.my country has a clear hierarchical registration access system for medical equipment,and dental cone-beam CT belongs to the third category of medical equipment.According to the existing national/industry standard requirements,manufacturers need to evaluate the quality of registered equipment including mechanical performance,software performance,image quality,etc.Among them,image quality evaluation is an indispensable part of the evaluation system.Evaluation parameters include spatial resolution,density resolution,image uniformity,etc.Through analysis,the quality of the image can be intuitively reflected,thereby evaluating the overall quality of the equipment.For manufacturers to meet the requirements of the evaluation system,the development and design of image quality evaluation phantoms that conform to the evaluation system is a crucial part.In order to complete this part,this article combines the existing spiral CT image quality evaluation system and refers to industry standards to design and produce a phantom that conforms to dental cone-beam CT image evaluation,and uses it to perform image denoising.the study.Based on the full consideration of image quality evaluation system parameters and portability,this research designed and produced a set of modules including spatial resolution,density resolution,uniformity,layer thickness,water model,and metal artifact correction modules.Evaluate the phantom.The main body of the phantom has a height of 150mm and a diameter of 100mm.The height of each module varies from 20-35mm.The main body material is PMMA(polymethyl methacrylate,1.18 g/cm3),embedded with different materials such as titanium rods,tungsten wires,water,Air,polyethylene(PE),etc.Based on the uniformity module,it is found that the dental cone-beam CT image is very noisy.To this end,this paper proposes an image denoising algorithm based on the combination of median filtering and prior images,which uses the advantages of median filtering for uniform area denoising and the prior image’s good retention of edge tissue information and weighted reconstruction.The result Achieve a good balance between denoising and edge information retention.To verify its effectiveness,two sets of phantom data and two sets of real data experiments were carried out.The results show that the image SNR of the algorithm in this paper is improved by 23%and 5%,respectively,compared with the median filter algorithm.The phantom and real head data designed in this paper are denoised by this method.Visual observation finds that the noise is effectively removed and the edge information of the image is well preserved.In this paper,a set of image quality evaluation system phantoms are designed,and in view of the serious problem of image noise in the uniformity module evaluation,an image denoising method is proposed,which significantly improves the image quality.Although the research content of this article has achieved preliminary results in image quality evaluation and image quality improvement,it still needs to be further explored for popularization and application. |
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