Abstract
Image quality of CT scans suffers when objects undergo motion. Respiratory motion causes artifacts, which prevents adequate visualization of anatomy. Four-dimensional CT (4D-CT) is a method in which image reconstruction of moving objects is retrospectively gated according to the recorded phase information of the monitored motion pattern. Although several groups have investigated the use of 4D-CT in radiotherapy, little has been detailed with regard to the sorting method. We present a new retrospective gating technique with sorting based on the amplitude of the motion trace. This method is compared to previously developed methods that sort based on phase. A 16-slice CT scanner (Sensation 16, Siemens Medical Solutions, Erlangen, Germany) was used to acquire images of two phantoms on a motion platform moving in two dimensions. The motion was monitored using a strain gauge inserted inside an adjustable belt. A 180° interpolation was used for reconstruction after gating. Significant improvement using the amplitude-sorting technique was observed, particularly when testing nonperiodic motion functions. PACS numbers: 87.59.Fm, 87.53.Kn, 87.57.Ce
Highlights
Motion due to respiration causes artifacts in CT scanning, which results in a skewed size, shape, and density of objects in the image.[1,2,3,4] In diagnostic imaging, patients are often instructed to hold their breath for the duration of the scan to alleviate these problems
A long breath-hold places increased burden on patients, many of whom are unable to do so for an extended length of time.[5]. Second, the position of anatomical structures in the lung and diaphragm region changes with respiration, and it is different during a full inspiration breath-hold than it is during normal respiration
The y-axis represents the relative amplitude of the monitored motion pattern
Summary
Motion due to respiration causes artifacts in CT scanning, which results in a skewed size, shape, and density of objects in the image.[1,2,3,4] In diagnostic imaging, patients are often instructed to hold their breath for the duration of the scan to alleviate these problems. In four-dimensional CT (4D-CT), the patient is allowed to breathe freely while the respiration trace is recorded for the duration of the CT scan.[5,6,7,8,9,10] The time of image acquisition is recorded along with the respiration trace for subsequent correlation of image data with respiratory phase. This correlation allows images that were acquired at the same phase of respiration for all Z positions (the superior/inferior patient axis) to be combined into a phase-specific volume. Doing this for all phases of the respiratory cycle yields complete information about the respiratory motion pattern of the entire volume
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