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The position of an object defines its location relative to a convenient frame of reference at any particular time. A frame of reference is an arbitrary set of axes from which the position and motion of an object are described. Earth is often used as a frame of reference, and we often describe the position of an object as it relates to stationary objects on Earth. For example, a rocket launch could be described in terms of the position of the rocket with respect to Earth as a whole. On the other...
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To describe the motion of an object, one should first be able to describe its position (where it is at any particular time). More precisely, the position needs to be specified relative to a convenient frame of reference. A frame of reference is an arbitrary set of axes from which the position and motion of an object are described. Earth is often used as a frame of reference to describe the position of an object in relation to stationary objects on Earth.
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Prospective displacement and velocity-based cine 4D CT.

U W Langner1, P J Keall

  • 1Department of Radiation Oncology, Radiation Physics Division, Stanford University Cancer Center, 875 Blake Wilbur Drive, Stanford, California 94305-5847, USA. ulangner@stanford.edu

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A new prospective method for four-dimensional computed tomography (4D CT) image sorting reduces artifacts and patient dose. This prospective respiratory displacement and velocity-based cine 4D CT (PDV CT) method improves accuracy and efficiency compared to retrospective approaches.

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Area of Science:

  • Medical Imaging
  • Radiology
  • Radiation Oncology

Background:

  • Four-dimensional computed tomography (4D CT) image sorting is retrospective, leading to artifacts and increased patient dose.
  • Artifacts in 4D CT arise from mismatches in respiratory signal displacement and phase, causing errors in contouring and dose calculations.
  • Higher radiation doses in 4D CT compared to 3D CT are a significant concern.

Purpose of the Study:

  • To develop and evaluate a prospective respiratory displacement and velocity-based cine 4D CT (PDV CT) method.
  • To minimize artifacts and potentially reduce radiation dose in 4D CT imaging.
  • To compare the accuracy and efficiency of PDV CT with retrospective 4D CT acquisition methods.

Main Methods:

  • Developed a PDV CT method triggering image acquisition based on simultaneous displacement and velocity tolerances of the respiratory signal.
  • Compared PDV CT with retrospective 4D CT methods using respiratory signals from 24 lung cancer patients (103 sessions).
  • Simulated image acquisition and calculated root mean square (RMS) differences in displacement and velocity to evaluate sorting accuracy.

Main Results:

  • Patient dose reductions ranged from 22% to 50% with PDV CT.
  • PDV CT showed similar overall accuracy to retrospective displacement sorting, with up to 20% RMS difference improvement.
  • Velocity RMS differences improved by 30-45% compared to retrospective phase sorting.
  • Acquisition efficiency varied from 10% to 93% depending on chosen tolerances.

Conclusions:

  • PDV CT is a valuable tool for reducing artifacts in 4D CT images and lowering patient dose.
  • The method offers improved accuracy in velocity sorting and significant dose reduction.
  • Potential drawbacks include increased acquisition time and cost, requiring careful parameter selection.