Schmuck B D, Carey C M
J Res Natl Inst Stand Technol. 2010 Apr 1;115(2):75-83. doi: 10.6028/jres.115.006. Print 2010 Mar-Apr.
Contact X-ray microradiography is the current gold standard for measuring mineral densities of partially demineralized tooth specimens. The X-ray sensitive film specified in the last J Res NIST publication on the subject is no longer commercially available. OBJECTIVES: Develop a new microradiographic method by identifying a commercially available film with greater than 3000 lines per millimeter resolution, which is sensitive to X rays, and develop correct film processing for X-ray microradiographic application. METHODS: A holographic film was identified as a potential replacement film. Proper exposure was determined utilizing a thick nickel plate to create test-strips. Film development was bracketed around manufacturer suggestions. Film linearity was determined with aluminum step-wedges. Microradiographs of 100 µm thick tooth sections, before and after acidic challenges, were a final test for film. Magnified images were captured with a digital microscope camera with 0.305 micrometers per pixel resolution. RESULTS: The appropriate film exposure was 30 minutes at 80 kV(p) and 3 mA with a development time of 2 minutes. Step-wedge experiments show the system to be linear in terms of pixel intensities with respect to x-ray attenuation for normalized pixel intensity values that are 10% to 90% of full scale (r(2) = 0.997) which encompasses the full exposure region of tooth tissue. Enamel sections were analyzed and show distinctive differences between erosion and demineralization. The image capture device resolution of 0.305 micrometers per pixel limits the system resolution. CONCLUSION: Use of the identified holographic film when combined with the described processing modifications has resulted in an improved X-ray microradiographic method for the measurement of mineral density of dental hard tissues. The method described can be further improved by using a higher resolution digitization system. The method is appropriate for quantitatively measuring changes in mineral density and erosion.
接触式X射线显微放射成像术是测量部分脱矿牙齿标本矿物质密度的当前金标准。美国国家标准与技术研究院（NIST）上一次关于该主题的研究报告中指定的X射线敏感胶片已不再有商业供应。目的：通过识别一种分辨率大于每毫米3000线、对X射线敏感的商用胶片，开发一种新的显微放射成像方法，并开发适用于X射线显微放射成像应用的正确胶片处理方法。方法：一种全息胶片被确定为潜在的替代胶片。利用一块厚镍板制作测试条来确定合适的曝光量。胶片显影围绕制造商的建议进行调整。用铝制阶梯楔形块确定胶片的线性度。对100微米厚的牙齿切片在酸性侵蚀前后进行显微放射成像，作为对胶片的最终测试。用分辨率为每像素0.305微米的数字显微镜相机拍摄放大图像。结果：合适的胶片曝光条件是在80 kV（p）和3 mA下曝光30分钟，显影时间为2分钟。阶梯楔形块实验表明，对于归一化像素强度值为满量程的10%至90%（r² = 0.997）的情况，该系统在像素强度方面相对于X射线衰减呈线性，这涵盖了牙齿组织的整个曝光区域。对牙釉质切片进行了分析，显示出侵蚀和脱矿之间的明显差异。每像素0.305微米的图像采集设备分辨率限制了系统分辨率。结论：使用所确定的全息胶片并结合所述的处理改进方法，已产生一种改进的用于测量牙齿硬组织矿物质密度的X射线显微放射成像方法。通过使用更高分辨率的数字化系统，所描述的方法可以进一步改进。该方法适用于定量测量矿物质密度和侵蚀的变化。
