An operator-passive thoracic impedance approach for Respiratory motion gating in myocardial perfusion SPECT

Respiratory motion gating (R-Gating) in SPECT myocardial perfusion imaging (MPI) usually requires external devices and extra work of the technologist for patient setup. In this paper, we developed an operator-passive R-Gating technique without external devices. Method: Using the thoracic impedance approach, the respiratory motion signal was obtained simultaneously with the ECG signal from the same ECG leads. With list-mode acquisition, the respiratory motion signal was tagged to the SPECT data and was used to rebin the list-mode data into R-Gating data. Forty consecutive patients were scanned to evaluate and establish the R-Gating approach. Both the conventional data and the list-mode data were saved. Then forty eight consecutive patients were scanned for respiratory motion assessment using the established approach. Results: The summed R-Gating images were different from the summed ECG-gating images in only three of the forty patients (7.5%) and equivalent in the rest of the patients (92.5%). R-Gating with six respiratory phases showed optimal motion detection and image quality compromise. The R-Gating images illustrated different types of motion of the heart during respiratory cycles, including 3-D translation, apparent rotation of the heart along the long axis, and pivoting at the base. The observed motion of the heart in R-Gating images correlated well with the detected respiratory motion signal. For the motion assessment studies, 28/48 (58.3%) showed no motion or small motion, 20/48 (41.7%) of stress and 18/48 (37.3%) of rest studies showed medium motion, and 2/48 (4.2%) of rest studies showed large motion. In conclusion, we developed an effective operator-passive approach for respiratory motion gating for SPECT MPI.