Dose reduction in CT by on-line tube current control: principles and validation on phantoms and cadavers

We investigated approaches to reducing the dose in CT without impairing ima ge quality. Dose can be reduced for non-circular object cross-sections with out a significant increase in noise if X-ray tube current is reduced at ang ular tube positions where the X-ray attenuation by the patients is small. W e investigated different schemes of current modulation during tube rotation by simulation and phantom measurements. Both pre-programmed sinusoidal mod ulation functions and attenuation-based on-line control of the tube current were evaluated. All relevant scan parameters were varied, including constr aints such as the maximum modulation amplitude. A circular, an elliptical a nd two oval water phantoms were used. Results were validated on six cadaver s. Dose reduction of 10-45% was obtained both in simulations and in measure ments for the different non-circular phantom geometries and current modulat ion algorithms without an increase increase in pixel noise values. On-line attenuation-based control yielded higher reductions than modulation by a si nusoidal curve. The maximal dose reduction predicted by simulations could n ot be achieved due to limits in the modulation amplitude. In cadaver studie s, 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 normal tube current for high-attenuation projections combined with atten uation-based current modulation still yields significant dose reduction, bu t also a reduction in the structured noise that may obscure diagnostic deta ils. We conclude that a significant reduction in dose can be achieved by tu be current modulation without compromising image quality. Attenuation-based on-line control and a modulation amplitude of at least 90 % should be empl oyed.