Transthoracic impedance based respiratory gating in PET imaging: A feasibility study

Respiratory motion is an image degradation factor in thoracic Position Emission Tomography (PET) imaging. A primary step in the majority of motion compensation approaches is gating. Unfortunately, gating usually requires an extra hardware device, which usually is unfamiliar to the medical staff making the procedure complex and error prone, and therefore, uncommon clinical practice. The primary objective of this work is to investigate the feasibility of transthoracic impedance measured using ECG electrodes in their normal positions as respiratory signal source in PET gating. A high frequency, 56 kHz, small current was delivered to the subject and the variation on the voltage due to impedance change with respiration was measured through ECG electrodes. The obtained signal was then processed to remove the noise and baseline wandering. Animal experiments were conducted in mice, rats, and Tibet mini pig to evaluate impedance measurement capturing respiration. The respiratory signal was synchronized with a preclinical small animal PET scanner developed at HUST University, China. An 18F-FDG PET scan was preformed on Tibet mini pig to evaluate the gating system. An amplitude-based gating was performed on PET data. The resultant impedance measurements were promising in terms of respiratory signal quality, and the image resolution was improved in gated images compared to the non-gated images. In conclusion, the proposed transthoracic impedance measurement proves to be a practical, cheap, and clinically friendly gating system. Moreover, the system facilitates cardiac gating without an extra setup in the patient side and it is also applicable to other imaging modalities.