The use of PET respiratory gating in PET/CT results in lesion volumes closer to those assessed by CT and improved measurements of tracer uptake for lesions in the lungs, according to research published in the December issue of the American Journal of Roentgenology.

“Physiologic motion, particularly breathing, affects PET images because of the long acquisition time,” the authors noted.

A multinational research team from Beth Israel Deaconess Medical Center in Boston and Eberhard-Karls-University Medical Center in Tubingen, Germany, conducted a study on the effects of using respiratory gating during FDG PET/CT on the determination of lesion size and the measurement of tracer uptake in patients with pulmonary nodules in a clinical setting.

The scientists assembled a cohort of 18 patients with known pulmonary nodules that underwent conventional whole-body PET/CT followed by an additional gated PET acquisition over the chest. All imaging was conducted on a Discovery LS (GE Healthcare) PET system. Respiratory gating was conducted with Varian Real-Time Positioning Management from Varian Medical Systems.

The researchers noted that the respiratory-gating system added an extra 10 minutes of scanning duration and approximately 10 extra minutes of setup time per patient.

“The respiratory-gating method used in our investigations made it possible to observe the movement of lung lesions during PET/CT and to visually evaluate the extent of respiratory motion,” the authors wrote.

The researchers compared the data from the whole-body PET/CT, CT and gated PET/CT for lesion dimension and standardized uptake values (SUVs).

“Our data revealed that the difference between lesion size assessments on PET and CT was significantly lower for gated PET (mean lesion volume ± SE, 16.78 ± 9.44 cm³) than for ungated PET,” the authors wrote.

They found that measurements of the average lesion volume were highest on the ungated PET studies, significantly lower on the gated PET studies and lowest on the CT studies. However, the difference between measurements on gated PET and those based on CT was insignificant, the researchers reported.

“Although not always apparent by direct visual estimation, tumor volume, as seen on gated PET, was significantly lower, decreasing by 44.5 percent, and the extent of tumor was diminished along all three axes,” the authors wrote.

They observed that although respiratory gating was useful for PET imaging, applying respiratory gating to the CT acquisition (four-dimensional CT) could further bridge the gap between PET and CT but would add to the radiation dose and are unwarranted.

“Our findings show that respiratory gating improves PET/CT measurement of SUV and volume,” the authors wrote. “This improvement may be important—for example, in treatment planning before radiation therapy to define more precisely the irradiation target volume, especially when respiratory-gated radiation therapy is intended.”