Respiratory Gating
491
Temporal Resolution
Temporal resolution, also called time resolution, repre-
sents the time window of the data that is used for
image reconstruction. It is essential for respiratory CT
imaging. The higher the temporal resolution, the
fewer the motion artifacts. A temporal resolution of a
half of the Rotation Time can be achieved.
Technical Principles
Basically, there are two different technical approaches
for respiration correlated CT acquisition:
• Prospectively respiratory-triggered sequential scan-
ning.
• Retrospectively respiratory-gated spiral scanning.
In both cases, the respiration signal is recorded and
used to either initiate prospective image acquisition
(triggering), or to perform retrospective image recon-
struction (gating). Only scan data acquired in a user-
selectable phase of the respiration cycle is used for
image reconstruction.
Respiratory Triggering
Sequential scans are triggered by respiration signal
during a predefined amplitude of inhalation or exhala-
tion.
Triggering is based on the maximum and minimum of
the predicted respiration amplitude of the next 100%
inspiration.