A Device-Free Respiratory Gating Technique for Dynamic CT Using Time-Density Curve Analysis: A Technical Report With Clinical Applications.

Respiratory motion remains a major challenge in thoracic and cardiac CT. Conventional respiratory gating techniques often rely on external monitoring devices or dedicated software, which may complicate workflow and limit clinical availability. We developed a simple, device-free respiratory gating technique based on time-density curve (TDC) analysis derived directly from routinely acquired dynamic CT data. By placing a region of interest (ROI) on the chest wall, attenuation changes over time were analyzed to generate an intrinsic surrogate respiratory waveform, enabling retrospective identification of respiratory phases without additional hardware. The novelty of this approach lies in its use of intrinsic image data to generate a surrogate respiratory waveform, thereby eliminating the complexity and synchronization uncertainty associated with external monitoring devices. The proposed workflow was implemented using standard dynamic CT protocols and applied to representative clinical applications, including lung tumor motion assessment for radiotherapy planning and free-breathing coronary CT angiography (FB-CCTA) in a patient unable to perform reliable breath-holding. This image-based approach provides a practical method for respiratory phase estimation and may expand the clinical applicability of dynamic CT imaging in situations where conventional respiratory control is impractical.