SU-FF-J-20: How to Explore Alternative 4D CT Image Binning

Abstract

Purpose: Most 4D CT datasets use some external respiratory monitor as a surrogate for respiratory‐induced motion. The present work demonstrates the correlation between CTimage acquisition times, times reported in the file of a respiratory monitor and how this information can be used to resort the 4D images.Method and Materials: 4D data sets of a motion phantom and of a patient were acquired using two scanners(GE Discovery ST, GEMS; MX8000‐IDT, Philips Medical Systems), sorted and imported into a radiation treatment planning system (Pinnacle3, Philips Medical Systems). Displacements of a fiducial (RPM™, Varian Medical Systems) placed on the phantom were determined using the treatment planning system tools and recorded. These displacements were then correlated with displacements reported in the respiratory trace file. Software has been developed to generate 4D datasets based on phase or displacement. In this example the mid‐scan time (GE) or content time (Philips), as reported in the DICOM header in the CTimagedata sets, are used to correlate axial slices with fiducial displacement times. Results: The mid‐scan time does not directly correlate with the time of fiducial displacement over repeated beam‐on cycles. The mid‐scan time does correlate within each individual beam‐on cycle. Once the image times were correlated to those in the RPM files we extracted magnitude of fiducial displacement to effect displacement‐based binning of CTimages enabling the study of an alternative image‐sorting scheme. The content time requires a correlation of unequally spaced tags sent to the CTscanner. This technology is under development and requires more complexity in implementation. Conclusion: Alternative retrospective techniques of CTimage binning can be pursued. The present system of phase‐based binning demarked solely by the beginning cycle is effective, but can be improved by including more fiducial information. Conflict of Interest: MJF is supported by a Philips SRA.