A PET gating system for respiratory motion compensation of lung lesions

Abstract

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Objectives: Respiratory motion during PET imaging of the chest degrades image quality and reduces the ability to determine accurately the location, size, shape and activity concentration of lung lesions. The aim of this research is to develop and validate a system that can extract and process in real time the patient’s respiratory signal in order to gate the acquisition of PET images and reduce the effects of respiratory motion. Methods: The respiratory gating system is based on a high-resolution CCD laser displacement sensor (Keyence Corp.), which monitors the breathing movement by projecting a visible red light on the patient’s chest or abdomen. A LabVIEW program converts the displacement information to the respiratory signal, calculates its magnitude and frequency, and performs thresholding in order to generate trigger pulses to gate the PET scanner. The laser device is attached to a custom built mechanical assembly enabling height and angular adjustments. The respiratory gating system performed gated acquisitions in 8-bin frame mode and variable bin list mode with a C-PET and a Gemini PET/CT (Philips Medical Systems) but can be practically interfaced to any manufacturer’s PET scanner. Two phantoms were developed for testing the gating system: a motorized oscillating device and a ventilator supplied lung simulator. Positron emitting sources were attached to the phantoms and variable speeds of oscillation and amplitudes of motion were simulated. Results: Phantom experiments with Na-22 point sources demonstrated significantly reduced blurring and more accurate recovery of the actual counts in gated versus non-gated images. A simulated lung acquisition at 12 breaths per minute with up to 4cm displacement of a 5mm lesion phantom resulted in 5% overestimation of the actual size with respiratory gating versus 65% without gating. Imaging of two patients with lung lesions verified the reliable performance of the respiratory gating system. Conclusions: A respiratory gating system was developed using a high-resolution laser displacement sensor that can reliably perform gated acquisition of PET images. Phantom experiments demonstrated more accurate spatiotemporal definition of simulated lesions. Imaging of additional patients is ongoing.

Research Support (if any): SNM 2006 Pilot Research Grant