Nickoloff E L, Berman H L
Department of Radiology, College of Physicians and Surgeons, Columbia University and Columbia-Presbyterian Medical Center, New York, NY 10032.
Radiographics. 1993 Nov;13(6):1337-48. doi: 10.1148/radiographics.13.6.8290728.
The x-ray spectrum is defined as the energy distribution of the radiation produced in an x-ray exposure. The x-ray spectrum has a major impact on image quality and radiation dose delivered to patients. The authors explored the effects of three key factors on x-ray spectra: generator type, peak tube potential, and filtration. Different generator types are characterized by the amount of ripple in the kilovoltage waveform. Those with high (100%) ripple such as single-phase units produce less penetrating radiation than units with low (4%) ripple such as three-phase, 12-pulse generators. As peak tube potential increases, the half-value layer increases nearly linearly; radiation output increases by approximately the square of the tube potential. Filtration materials with atomic numbers less than 42, such as aluminum, titanium, copper, and niobium, produce similar spectra, with only slight variations in efficiency. Although aluminum has the lowest efficiency, this may be compensated for by increasing milliampere seconds. Filtration in addition to the inherent filtration provided by the tube reduces both skin surface dose and average depth-dose, with the optimal amount being approximately 2-3 mm or less of aluminum-equivalent material.
X射线谱被定义为在X射线曝光过程中产生的辐射的能量分布。X射线谱对图像质量和传递给患者的辐射剂量有重大影响。作者探讨了三个关键因素对X射线谱的影响：发生器类型、管电压峰值和滤过。不同的发生器类型以千伏波形中的纹波量为特征。纹波高（100%）的发生器，如单相装置，产生的穿透性辐射比纹波低（4%）的发生器，如三相12脉冲发生器少。随着管电压峰值的增加，半价层几乎呈线性增加；辐射输出大约按管电压的平方增加。原子序数小于42的滤过材料，如铝、钛、铜和铌，产生相似的能谱，只是效率略有差异。虽然铝的效率最低，但可以通过增加毫安秒来弥补。除了管本身提供的固有滤过外，额外的滤过可降低皮肤表面剂量和平均深度剂量，最佳的滤过量约为2 - 3毫米或更少的铝等效材料。
