评估移动胸部计算机X线摄影的影像学参数：模体、图像质量和有效剂量。

Rill Lynn N, Brateman Libby, Arreola Manuel

Department of Radiology, University of Florida, Gainesville, Florida 32610, USA.

Med Phys. 2003 Oct;30(10):2727-35. doi: 10.1118/1.1611291.

Conventional chest radiography is technically difficult because of wide variations in tissue attenuations in the chest and limitations of screen-film systems. Mobile chest radiography, performed bedside on hospital inpatients, presents additional difficulties due to geometric and equipment limitations inherent in mobile x-ray procedures and the severity of illness in the patients. Computed radiography (CR) offers a different approach for mobile chest radiography by utilizing a photostimulable phosphor. Photostimulable phosphors overcome some image quality limitations of mobile chest imaging, particularly because of the inherent latitude. Because they are more efficient in absorbing lower-energy x-rays than rare-earth intensifying screens, this study evaluated changes in kVp for improving mobile chest CR. Three commercially available systems were tested, with the goal of implementing the findings clinically. Exposure conditions (kVp and grid use) were assessed with two acrylic-and-aluminum chest phantoms which simulated x-ray attenuation for average-sized and large-sized adult chests. These phantoms contained regions representing the lungs, heart and subdiaphragm to allow proper CR processing. Signal-to-noise ratio (SNR) measurements using different techniques were obtained for acrylic and aluminum disks (1.9 cm diameter) superimposed in the lung and heart regions of the phantoms, where the disk thicknesses (contrast) were determined from disk visibility. Effective doses to the phantoms were also measured for these techniques. The results indicated that using an 8:1, 33 lines/cm antiscatter grid improved the SNR by 60-300 % compared with nongrid images, depending on phantom and region; however, the dose to the phantom also increased by 400-600%. Lowering x-ray tube potential from 80 to 60 kVp improved the SNR by 30-40%, with a corresponding increase in phantom dose of 40-50%. Increasing the potential from 80 to 100 kVp reduced both the SNR and the phantom dose by approximately 10%. The most promising changes in technique for trial in clinical implementation include using an antiscatter grid, especially for large patients, and potentially increasing kVp.

传统的胸部X线摄影在技术上存在困难，这是由于胸部组织衰减差异很大以及屏-片系统存在局限性。床边对住院患者进行的移动胸部X线摄影，由于移动X线检查固有的几何和设备限制以及患者病情的严重程度，带来了额外的困难。计算机X线摄影（CR）通过使用光激励荧光体为移动胸部X线摄影提供了一种不同的方法。光激励荧光体克服了移动胸部成像的一些图像质量限制，特别是由于其固有的宽容度。因为它们在吸收低能X线方面比稀土增感屏更有效，本研究评估了改变管电压峰值（kVp）以改善移动胸部CR成像。测试了三种市售系统，目的是将研究结果应用于临床。使用两个丙烯酸和铝制胸部模型评估曝光条件（kVp和滤线栅使用情况），这两个模型模拟了平均体型和大体型成年胸部的X线衰减。这些模型包含代表肺、心脏和膈下区域，以允许进行适当的CR处理。对叠加在模型肺和心脏区域的丙烯酸和铝制圆盘（直径1.9 cm），使用不同技术获得信噪比（SNR）测量值，圆盘厚度（对比度）由圆盘可见度确定。还测量了这些技术对模型的有效剂量。结果表明，使用8:1、33线/cm的反散射滤线栅，与无滤线栅图像相比，信噪比提高了60%-300%，这取决于模型和区域；然而，模型的剂量也增加了400%-6(此处原文可能有误，推测为600%)。将X线管电压从80 kVp降低到60 kVp，信噪比提高了30%-40%，模型剂量相应增加了40%-50%。将管电压从80 kVp提高到100 kVp，信噪比和模型剂量都降低了约10%。在临床应用中最有前景的技术改变包括使用反散射滤线栅，特别是对体型较大的患者，以及可能增加管电压峰值。