Abstract
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Objectives In cardiac SPECT, we observe more than 2 cm displacements of internal organs caused by respiration. A key aspect of motion correction is monitoring requiring belts or markers attached to the patient. Markers are monitored with special external detectors. We introduce a new method of patient motion monitoring in SPECT using low power microwave radar.
Methods An patient experiment was performed using a dual-head GE Hawkeye SPECT/CT system. A standard air-pressure belt device was attached to the patient for respiratory monitoring. Signals were acquired from the air-pressure belt and a radar device during a simulated cardiac SPECT study. The radar device produced micropower frequency modulated radar (MFMR) signals which were analyzed to separate signals with different repetition periods: gantry rotation, respiration and cardiac. Aperiodic changes in the radar reflection magnitudes correspond to involuntary body motions, and were used to evaluate data integrity over the entire scan.
Results MFMR with unique combinations of spatial resolution, sensitivity and range selectivity enables independent monitoring of targets separated by 15 cm or more and provides sufficient sensitivity to distinguish respiration and cardiac motion from motion of extremities. Comparison of MFMR to the standard air-pressure belt signal confirmed its ability of real-time respiration monitoring. Time-series analysis of MFMR signals for a patient inside a moving scanner showed that gantry and respiratory motion were separated.
Conclusions Several radar types have been used previously to monitor breathing and heart rate in patients, but their operation is disrupted by the presence of large moving objects in the field of view of radar antennae. MFMR solves this problem by combination of its target resolution ability and new data analysis methods. MFMR motion monitoring enables straightforward monitoring of cardiac and respiratory motion in continuously-rotating-camera cardiac SPECT.
Research Support NIH R01-EB00121 and DOE Contract DE-AC02-05CH11231