Scatter radiation in multi-slice CT system nowadays is playing a more and more important role, as the slice number is getting larger and larger, e.g. from 16 to 64 and even more. Scatter radiation may downgrade image quality e.g. create inhomogeneity and decrease the image contrast. Although in current multi-slice CT, anti-scatter collimation is widely used to reduce the scatter radiation received, as the detector is getting wider, its efficiency is getting weaker. Although beam hardening correction can somehow guarantee image homogeneity, as beam hardening effect and scatter radiation have different physical origin, a delegated scatter correction algorithm is desired. In this paper, we would like to propose a scatter correction algorithm working during data pre-processing before image reconstruction. After we implemented this algorithm in Siemens latest released Somatom Go. CT system, we obtain good image quality especially under certain clinical cases.
With the online z-axis tube current modulation (OZTCM) technique proposed by this work, full automatic exposure
control (AEC) for CT systems could be realized with online feedback not only for angular tube current modulation
(TCM) but also for z-axis TCM either. Then the localizer radiograph was not required for TCM any more. OZTCM
could be implemented with 2 schemes as attenuation based μ-OZTCM and image noise level based μ-OZTCM.
Respectively the maximum attenuation of projection readings and standard deviation of reconstructed images can be
used to modulate the tube current level in z-axis adaptively for each half (180 degree) or full (360 degree) rotation.
Simulation results showed that OZTCM achieved better noise level than constant tube current scan case by using same
total dose in mAs. The OZTCM can provide optimized base tube current level for angular TCM to realize an effective
auto exposure control when localizer radiograph is not available or need to be skipped for simplified scan protocol in
case of emergency procedure or children scan, etc.