Attenuation and image noise level based online z-axis tube current modulation for CT scans independent with localizer radiograph: simulation study and results
2009
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.
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