Kalender W A, Wolf H, Suess C, Gies M, Greess H, Bautz W A
Institute of Medical Physics, University of Erlangen, Germany.
Eur Radiol. 1999;9(2):323-28. doi: 10.1007/s003300050674.
We investigated approaches to reducing the dose in CT without impairing image quality. Dose can be reduced for non-circular object cross-sections without a significant increase in noise if X-ray tube current is reduced at angular tube positions where the X-ray attenuation by the patients is small. We investigated different schemes of current modulation during tube rotation by simulation and phantom measurements. Both pre-programmed sinusoidal modulation functions and attenuation-based on-line control of the tube current were evaluated. All relevant scan parameters were varied, including constraints such as the maximum modulation amplitude. A circular, an elliptical and two oval water phantoms were used. Results were validated on six cadavers. Dose reduction of 10-45% was obtained both in simulations and in measurements for the different non-circular phantom geometries and current modulation algorithms without an increase in pixel noise values. On-line attenuation-based control yielded higher reductions than modulation by a sinusoidal curve. The maximal dose reduction predicted any simulations could not be achieved due to limits in the modulation amplitude. In cadaver studies, a reduction of typically 20-40% was achieved for the body and about 10% for the head. Variations of our technique are possible; a slight increase in nominal tube current for high-attenuation projections combined with attenuation-based current modulation still yields significant dose reduction, but also a reduction in the structured noise that may obscure diagnostic details. We conclude that a significant reduction in dose can be achieved by tube current modulation without compromising image quality. Attenuation-based on-line control and a modulation amplitude of at least 90% should be employed.
我们研究了在不损害图像质量的情况下降低CT剂量的方法。对于非圆形物体横截面，如果在患者对X射线衰减较小的管角度位置降低X射线管电流，剂量可以降低而不会显著增加噪声。我们通过模拟和体模测量研究了管旋转过程中不同的电流调制方案。评估了预编程的正弦调制函数和基于衰减的管电流在线控制。所有相关扫描参数都有所变化，包括最大调制幅度等限制条件。使用了圆形、椭圆形和两个椭圆形水模。在六具尸体上验证了结果。对于不同的非圆形体模几何形状和电流调制算法，在模拟和测量中均实现了10%-45%的剂量降低，且像素噪声值没有增加。基于衰减的在线控制比正弦曲线调制实现了更高的剂量降低。由于调制幅度的限制，无法实现模拟预测的最大剂量降低。在尸体研究中，身体部位通常实现了20%-40%的剂量降低，头部约为10%。我们的技术可以有变化；对于高衰减投影，稍微增加标称管电流并结合基于衰减的电流调制，仍然可以显著降低剂量，同时也能减少可能掩盖诊断细节的结构噪声。我们得出结论，通过管电流调制可以在不影响图像质量的情况下显著降低剂量。应采用基于衰减的在线控制和至少90%的调制幅度。
