Pauwels R, Silkosessak O, Jacobs R, Bogaerts R, Bosmans H, Panmekiate S
Department of Radiology, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand.
Dentomaxillofac Radiol. 2014;43(5):20140059. doi: 10.1259/dmfr.20140059. Epub 2014 Apr 8.
To determine the optimal kVp setting for a particular cone beam CT (CBCT) device by maximizing technical image quality at a fixed radiation dose.
The 3D Accuitomo 170 (J. Morita Mfg. Corp., Kyoto, Japan) CBCT was used. The radiation dose as a function of kVp was measured in a cylindrical polymethyl methacrylate (PMMA) phantom using a small-volume ion chamber. Contrast-to-noise ratio (CNR) was measured using a PMMA phantom containing four materials (air, aluminium, polytetrafluoroethylene and low-density polyethylene), which was scanned using 180 combinations of kVp/mA, ranging from 60/1 to 90/8. The CNR was measured for each material using PMMA as background material. The pure effect of kVp and mAs on the CNR values was analysed. Using a polynomial fit for CNR as a function of mA for each kVp value, the optimal kVp was determined at five dose levels.
Absorbed doses ranged between 0.034 mGy mAs(-1) (14 × 10 cm, 60 kVp) and 0.108 mGy mAs(-1) (14 × 10 cm, 90 kVp). The relation between kVp and dose was quasilinear (R(2) > 0.99). The effect of mA and kVp on CNR could be modelled using a second-degree polynomial. At a fixed dose, there was a tendency for higher CNR values at increasing kVp values, especially at low dose levels. A dose reduction through mA was more efficient than an equivalent reduction through kVp in terms of image quality deterioration.
For the investigated CBCT model, the most optimal contrast at a fixed dose was found at the highest available kVp setting. There is great potential for dose reduction through mA with a minimal loss in image quality.
通过在固定辐射剂量下最大化技术图像质量，确定特定锥形束CT（CBCT）设备的最佳千伏峰值（kVp）设置。
使用3D Accuitomo 170（日本京都森田制造公司）CBCT。使用小体积电离室在圆柱形聚甲基丙烯酸甲酯（PMMA）体模中测量作为kVp函数的辐射剂量。使用包含四种材料（空气、铝、聚四氟乙烯和低密度聚乙烯）的PMMA体模测量对比度噪声比（CNR），该体模使用60/1至90/8的180种kVp/毫安（mA）组合进行扫描。以PMMA作为背景材料，测量每种材料的CNR。分析kVp和mAs对CNR值的纯效应。对于每个kVp值，使用CNR作为mA函数的多项式拟合，在五个剂量水平下确定最佳kVp。
吸收剂量范围为0.034毫戈瑞每毫安（mGy mAs⁻¹）（14×10厘米，60 kVp）至0.108毫戈瑞每毫安（mGy mAs⁻¹）（14×10厘米，90 kVp）。kVp与剂量之间的关系近似线性（R²>0.99）。mA和kVp对CNR的影响可以用二次多项式建模。在固定剂量下，随着kVp值增加，CNR值有升高趋势，尤其是在低剂量水平。就图像质量恶化而言，通过降低mA来降低剂量比通过降低kVp等效降低剂量更有效。
对于所研究的CBCT模型，在固定剂量下，在最高可用kVp设置下发现了最佳对比度。通过降低mA来降低剂量具有很大潜力，且图像质量损失最小。
