Logarithmic amplifier for computed tomography tasks using fluoroscopic projections

Abstract

The image intensifier (II)-based imaging systems, as radiotherapy simulators or C-arm X-ray units, have also been used for image acquisition in computed tomography. When analogue-to-digital conversion is performed on the output signal of the television camera, the accuracy for low-amplitude video signals, corresponding to X-ray pathways crossing high attenuation structures, is limited. To deal with this lack of accuracy, we investigated the benefits of using a logarithmic amplifier (LOGAMP) inserted between the television camera output and the analogue-to-digital converter (ADC) in the image acquisition chain. Such a device was intended to provide better use of the available ADCs of a given resolution and actually to reduce the quantization noise. Simulated data were used in this study, and cases with and without logarithmic amplifier were compared. Based on the simulation results, we formulate requirements for several signal and acquisition system parameters where the use of such a circuit is recommended.