摘要： Objective: We aimed to evaluate the influence of the minimal misalignment of the hot spot on the repeatability of PET images using the repositioning of point sources. Methods: Point sources with an inner-diameter of 1 mm were made with 1μL of 18F solution. Seven point sources were placed on the x-axis in the field-of-view. For fixed position imaging, PET data were acquired for 10 min 5 times serially. For variable position imaging, PET data were acquired for 10 minutes each with the point sources placed at 0 mm, ±0.5 mm, and ±1.0 mm in the x-axis direction. The data were reconstructed using ordered-subsets expectation maximization (OSEM) and OSEM with point-spread function (OSEM+PSF) algorithms. The image matrix was 128×128, 200×200, 256×256, 400×400, and 512×512 pixels. The normalized maximum count (rMax), the variation of rMax (CVmax) and full width at half maximum (FWHM) were analyzed. Results: The hot spots on OSEM images far from the center became faint and broad, while those on the OSEM+PSF images became small and dense. Although the rMax was overestimated at the 5 cm position on OSEM image, those at other positions were overestimated on OSEM+PSF images with a matrix size of ≥256×256. The rMax showed a similar pattern in fixed and variable position images. The CVmax in fixed position OSEM images were <2%, irrespective of the matrix size. In contrast, the CVmax in variable position images were higher in comparison to fixed position images. The CVmax of the OSEM+PSF images were higher in comparison to OSEM images. The FWHM increased at positions far from the center on OSEM image, while that was stable at all positions on OSEM+PSF images. Conclusion: The repeatability of the small hot spot was affected by the minimal misalignment, especially on the OSEM+PSF images. Precise positioning is necessary if PET is to be used as a biomarker. Professions should recognize that the PSF correction deteriorates the repeatability of the small hot spot although it improves the spatial resolution of PET images.