Purpose: To develop a self‐sorting four‐dimensional CT (4D‐CT) technique that uses body volume as the respiratory surrogate. Method and Materials: Respiratory signals are determined by the changes in body volume at each slice location as a function of image acquisition time. Respiratory phases were then calculated for each image and used in 4D‐CT retrospective sorting. The technique was validated on an in‐house built motion phantom and tested on a lung cancer patient and a liver cancer patient. Self‐sorted 4D‐CT images were compared to the 4D‐CT images generated using Varian's RPM system. Results: Both phantom and patient study revealed excellent agreement in image quality between the self‐sorted 4D‐CT and the Vairan's RPM‐sorted 4D‐CT. Mean difference in amplitude in phantom study is 0.1±0.1mm. Breathing cycles can be clearly seen in all image sets by observing the position changes of tumors and organs (liver, stomach, and kidneys). The fact that the self‐sorted 4D‐CT technique worked well for the tumor in the upper lung region (which typically moves much less than the abdomen regions during the breathing) suggested that the body volume is a sensitive marker of respiration. Small discrepancies do exist between the two sorting methods on the phase‐by‐phase basis. It is difficult, however, to conclude which method has the better image quality. Conclusions: Self‐sorted 4D‐CT using body volume alone as the respiratory surrogate is feasible. Its image quality is comparable to that using Varian's RPM system. This new technique has the potential in reducing 4D‐CT simulation time and increasing patients' comfort while maintaining the same image quality.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging