Respiratory-gated positron emission tomography and breath-hold computed tomography coupling to reduce the influence of respiratory motion: methodology and feasibility

BACKGROUND

Respiratory motion causes uptake in positron emission tomography (PET) images of chest and abdominal structures to be blurred and reduced in intensity.

PURPOSE

To compare two respiratory-gated PET binning methods (based on frequency and amplitude analyses of the respiratory signal) and to propose a "BH-based" method based on an additional breath-hold computed tomography (CT) acquisition.

MATERIAL AND METHODS

Respiratory-gated PET consists in list-mode (LM) acquisition with simultaneous respiratory signal recording. A phantom study featured rectilinear movement of a 0.5-ml sphere filled with (18)F-fluorodeoxyglucose ((18)F-FDG) solution, placed in a radioactive background (sphere-to-background contrast 6:1). Two patients were also examined. Three figures of merit were calculated: the target-to-background ratio profile (TBRP) in the axial direction through the uptake (i.e., the sphere or lesion), full-width-at-half-maximum (FWHM) values, and maximized standard uptake values (SUV(max)).

RESULTS

In the phantom study, the peak TBRP was 0.9 for non-gated volume, 1.83 for BH-based volume, and varied between 1.13 and 1.73 for Freq-based volumes and between 1.34 and 1.66 for Amp-based volumes. A reference volume (REF-static) was also acquired for the phantom (in a static, "expiratory" state), with a peak TBRP at 1.88. TBRPs were computed for patient data, with higher peak values for all gated volumes than for non-gated volumes.

CONCLUSION

Respiratory-gated PET acquisition reduces the blurring effect and increases image contrast. However, Freq-based and Amp-based volumes are still influenced by inappropriate attenuation correction and misregistration of mobile lesions on CT images. The proposed BH-based method both reduces motion artifacts and improves PET-CT registration.

An easy-to-use phantom and protocol for weekly PET quality assessment: a multicenter study

The authors have developed a simple phantom and dedicated software for the quality assessment of positron emission tomography (PET) scanners. The phantom is a parallelepiped box filled with a relatively low activity 18FDG solution and in which simple test objects are placed. Various image quality parameters are checked, including signal-to-noise ratio, image uniformity, slice thickness, slice sensitivity profile, spatial resolution, and dose calibration accuracy. Automatic image analysis consists in detecting surfaces and objects, defining regions of interest, acquiring reference point coordinates, and establishing gray-scale profiles. The total time needed for quality assessment (preparation and image acquisition) is less than 15 min with 37 MBq (1 mCi) 18FDG. The system's ease of use encourages frequent image quality assessment-for example, the comparison of PET scanners in interdepartment studies and the monitoring and evaluation of possible drifts over time. By way of an example, the authors present weekly quality assessment results obtained over up to 7 months at four PET facilities.