Dose reduction in CT by anatomically adapted tube current modulation. 1. Simulation studies

Tube current modulation governed by x-ray attenuation during CT (computed t omography) acquisition can lead to noise reduction which in turn can be use d to achieve patient dose reduction without loss in image quality. The pote ntial of this technique was investigated in simulation studies calculating both noise amplitude levels and noise distribution in CT images. The depend ence of noise on the modulation function, amplitude of modulation, shape an d size of the object, and possible phase shift between attenuation and modu lation function were examined. Both sinusoidal and attenuation-based contro l functions were used to modulate tube current. Noise reduction was calcula ted for both ideal systems and for real systems with limited modulation amp litude, Dose reductions up to 50% can be achieved depending on the phantom geometry and tube current modulation function. Attenuation-based tube curre nt modulation yields substantially higher reduction than fixed-shape modula tion functions. Optimal results are obtained when the current is modulated as a function of the square root of attenuation. A modulation amplitude of at least 90% should be available to exploit the potential of these techniqu es. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99 )03011-4].