Comparison of dedicated breast positron emission tomography and whole-body positron emission tomography/computed tomography images: a common phantom study

Objective: High-resolution dedicated breast positron emission tomography (dbPET) can visualize breast cancer more clearly than whole-body PET/computed tomography (CT). In Japan, the combined use of dbPET and whole-body PET/CT is necessary in indications for health insurance. Although several clinical studies have compared both devices, a physical evaluation by the phantom test has not been reported. The aim of this study was to compare the ability of ring-shaped dbPET and whole-body PET/CT using a common phantom with reference to the Japanese guideline for the oncology ¹⁸F-fluorodeoxyglucose (FDG)-PET/CT data acquisition protocol.

Methods: A cylindrical breast phantom with four spheres of different diameters (16, 10, 7.5, and 5 mm) filled an FDG solution at sphere-to-background radioactivity ratios (SBRs) of 2:1, 4:1, and 8:1 was prepared. Images were then acquired by whole-body PET/CT and subsequently by dbPET. The reconstructed images were visually evaluated and the coefficient of variation and uniformity of the background (CV_background and SD_ΔSUVmean), percentages of contrast and background variability (%Q_H,5mm and %N_5mm), and their ratio (%Q_H,5mm/N_5mm), and relative recovery coefficient were compared with the standards defined in the protocol for whole-body PET/CT.

Results: The parameters were calculated at an SBR of 8:1, which was the only SBR in which a 5-mm sphere was visible on both devices. The standards were defined as < 10% for CV_background, ≤ 0.025 for SD_ΔSUVmean, < 5.6% for %N_5mm, > 2.8 for %Q_H,5mm/N_5mm, and > 0.38 for the relative recovery coefficient of the smallest sphere (10 mm in diameter) in the protocol for whole-body PET/CT (the %Q_H,5mm was not determined for that protocol); the respective values were 6.14%, 0.024, 4.55%, 3.66, and 0.33 for dbPET and 2.21%, 0.021, 3.11%, 1.72, and 0.18 for PET/CT. The Q_H,5mm was 16.67% for dbPET and 5.34% for PET/CT. The human images also showed higher lesion-to-background contrast on dbPET than on PET/CT despite the noisier background observed with dbPET.

Conclusion: The common phantom study showed that the background was noisier and that the contrast was much higher in the dbPET image than in the PET/CT image. The acquisition protocol and standards for dbPET will need to be different from those used for whole-body PET/CT.