Purpose: In clinical computed tomography (CT), the image data is acquired during continuous
rotation. If the time during which the signal is integrated (the frame time) is too long, the data
is blurred in the view direction. This can be overcome by having a high angular sampling rate,
but for systems with limited bandwidth, the increased amount of data can be a problem. In this
paper, we evaluate the benefit of maintaining a high angular sampling rate on the CT gantry
and performing a decimation (digital low-pass filtration followed by a downsampling) in the view
direction before the bottleneck of the data transfer chain.
Methods: A theoretical evaluation of the effects of the decimation is presented and the
implementation of the digital filter is discussed. The compression scheme is evaluated on image
data of a CATPHANR 504 phantom.
Results: From a resolution point-of-view, it is beneficial to sample at more than twice the
Nyquist frequency (the minimum rate required for not introducing aliasing). At this sampling
rate, a decimation step can reduce the amount of data by a factor of two without loosing any of
the signal. It is demonstrated that a 2:1 compression can be achieved without compromising the
spatial resolution or increasing the noise.
Conclusions: In continuous rotation CT, the angular sampling rate must be high in order
not to suffer from blur in the view direction. From a sampling point-of-view, the sampling rate
is higher than necessary and the signal can be decimated (low-pass filtered and downsampled)
without losing any signal. The proposed compression scheme can be implemented on the CT
gantry and thus reduce the bandwidth requirements on the data transfer.