Question

Describe the process of acquiring a 4D computed tomography scan.

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Answer 1

4D CT scan is basically 3D scans at multiple phases. Over-sampling images are captured at all positions of interest along the axis(long) of the patient. All images are tagged with breathing signals(each signal is tagged with breathing signal). Images are sorted with respect to their breathing signals. Many 3D CT scans are obtained and each scan has its corresponding breathing phase. This all constitutes the 4D CT which covers the whole breathing cycle.

The Image acquisition can be performed by either Cine mode or Helical mode. In Cine mode, images are acquired repeatedly at each couch position. A helical mode has a single-slice CT and multiple-slice CT. An Image is obtained with a small pitch. In a single slice, the pitch is the ratio of table travel per rotation(mm) to X-ray beam width (mm) or the ratio of table travel per rotation(mm) to slice thickness (mm). In a mutiple slice, the factor of the number of simultaneous channels comes into consideration while calculating the pitch. Breathing signals are obtained using monitors like RPM or from the variation of the CT scans of patient's front surface like chest.