Huda W, Scalzetti E M, Levin G
Department of Radiology, SUNY Upstate Medical University, 750 E Adams St, Syracuse, NY 13210, USA.
Radiology. 2000 Nov;217(2):430-5. doi: 10.1148/radiology.217.2.r00nv35430.
To investigate how changes in kilovolt peak and milliampere second settings, and patient weight affect transmitted x-ray energy fluence and the image contrast-to-noise ratio (CNR) at abdominal computed tomography (CT).
Cylinders of water were used as patient models, and x-ray spectra, including x-ray tube potentials of 80-140 kVp, were investigated. The mean photon energy and energy fluence transmitted through water cylinders with varying diameters and the image contrast for fat, muscle, bone, and iodine relative to water were determined. The effect of changing the x-ray tube potential on CNR also was investigated.
At a constant kVp, increasing patient weight from 10 kg to 120 kg reduced the transmitted energy fluence by two orders of magnitude. Changing the x-ray tube potential from 80 kVp to 140 kVp increased the mean photon energy from approximately 52 keV to approximately 72 keV and thus reduced the image contrast relative to water by 12% for muscle, 21% for fat, 39% for bone, and 50% for iodine (approximate reduction values). Increasing the x-ray tube potential from 80 kVp to 140 kVp increased the CNR by a factor of 2.6 for muscle and by a factor of 1. 4 for iodine.
With changes in patient weight at abdominal CT, x-ray tube potentials must be varied to maintain a constant detector energy fluence. Increasing the x-ray tube potential generally improves CNR.
研究千伏峰值和毫安秒设置的变化以及患者体重如何影响腹部计算机断层扫描（CT）时的透射X射线能量注量和图像对比噪声比（CNR）。
使用水圆柱体作为患者模型，研究包括80 - 140 kVp X射线管电位在内的X射线光谱。测定通过不同直径水圆柱体透射的平均光子能量和能量注量，以及脂肪、肌肉、骨骼和碘相对于水的图像对比度。还研究了改变X射线管电位对CNR的影响。
在恒定千伏峰值下，患者体重从10 kg增加到120 kg使透射能量注量降低了两个数量级。将X射线管电位从80 kVp改变为140 kVp，使平均光子能量从约52 keV增加到约72 keV，从而使肌肉相对于水的图像对比度降低12%，脂肪降低21%，骨骼降低39%，碘降低50%（近似降低值）。将X射线管电位从80 kVp增加到140 kVp，肌肉的CNR增加了2.6倍，碘的CNR增加了1.4倍。
在腹部CT检查中，随着患者体重的变化，必须改变X射线管电位以保持探测器能量注量恒定。增加X射线管电位通常会提高CNR。
