Hayakawa Y, Farman A G, Kelly M S, Kuroyanagi K
Division of Radiology and Imaging Sciences, School of Dentistry, University of Louisville, Ky., USA.
Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1998 Nov;86(5):601-5. doi: 10.1016/s1079-2104(98)90354-7.
The DIGORA intraoral radiographic storage phosphor system needs to be calibrated before images are made. Calibration involves inputting of the maximum exposure to be used. This investigation studied the effects of different maximum exposure calibration settings on the mean pixel value for selected regions of interest and the signal-to-noise ratio for images of a test phantom.
A dental phantom containing a step wedge made of different thicknesses of homogeneously radiopaque bone-equivalent material was imaged at 70 kVp with exposures ranging from 12.8 to 105.2 microC.kg-1. Images were displayed through use of imaging software, and a region of interest was set for each bone-step. The mean pixel values and their standard deviations were measured.
Except for very low exposures (< 10% of the calibrated maximum), there was a linear relationship between exposure and the pixel values within the regions of interest irrespective of the calibrated maximum exposure. Low exposures resulted in underexposed low-contrast images. Low calibrated maximum exposures (< 54.5 microC.kg-1) resulted in low-density images with poor signal-to-noise ratios.
Because of the very wide image latitude of the DIGORA system, loss of image quality was not observed as a result of adjustments in the calibration setting over the range of exposure commonly used in dental practice. The highest accepted exposure was limited by prior calibration; hence, if diligence is applied, patient exposure can be minimized without detriment to image quality.
在使用DIGORA口腔内射线照相存储磷光体系统进行成像之前，需要对其进行校准。校准包括输入要使用的最大曝光量。本研究调查了不同最大曝光校准设置对选定感兴趣区域的平均像素值以及测试体模图像信噪比的影响。
使用包含由不同厚度的均匀射线不透光骨等效材料制成的阶梯楔形块的牙科体模，在70 kVp下进行成像，曝光量范围为12.8至105.2 μC·kg⁻¹。通过成像软件显示图像，并为每个骨阶梯设置一个感兴趣区域。测量平均像素值及其标准差。
除了极低的曝光量（<校准最大曝光量的10%）外，无论校准的最大曝光量如何，曝光量与感兴趣区域内的像素值之间都存在线性关系。低曝光量导致图像曝光不足且对比度低。校准的最大曝光量较低（<54.5 μC·kg⁻¹）会导致图像密度低且信噪比差。
由于DIGORA系统具有非常宽的图像宽容度，在牙科实践中常用的曝光范围内调整校准设置不会导致图像质量下降。最高允许曝光量受先前校准的限制；因此，如果谨慎操作，可以在不损害图像质量的情况下将患者的曝光量降至最低。
