PT  - JOURNAL ARTICLE
AU  - Akira Maebatake
AU  - Keishin Morita
AU  - Go Akamatsu
AU  - Yuji Tsutsui
AU  - Kazuhiko Himuro
AU  - Shingo Baba
AU  - Masayuki Sasaki
TI  - The Influence of Minimal Misalignment on the Repeatability of PET Images Examined by the Repositioning of Point Sources
AID  - 10.2967/jnmt.118.208835
DP  - 2019 Mar 01
TA  - Journal of Nuclear Medicine Technology
PG  - 55--59
VI  - 47
IP  - 1
4099  - http://tech.snmjournals.org/content/47/1/55.short
4100  - http://tech.snmjournals.org/content/47/1/55.full
SO  - J. Nucl. Med. Technol.2019 Mar 01; 47
AB  - We aimed to evaluate the influence of minimal misalignment of a hot spot on the repeatability of PET images using repositioning of point sources. Methods: Point sources with an inner diameter of 1 mm were made with 1 μL 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 min each with the point sources placed at 0, ±0.5, and ±1.0 mm in the x-axis direction. The data were reconstructed using ordered-subsets expectation maximization (OSEM) and OSEM plus point-spread function (PSF). The image matrix was 128 × 128, 200 × 200, 256 × 256, 400 × 400, and 512 × 512 pixels. The normalized maximum count (rMax), the coefficient of variance (CVmax), and the full width at half maximum were analyzed. Results: The hot spots on OSEM images far from the center became faint and broad, whereas those on OSEM+PSF images became small and dense. Although rMax was overestimated at the 5-cm position on OSEM images, rMax at other positions was overestimated on OSEM+PSF images with a matrix of at least 256 × 256. rMax showed a similar pattern in fixed- and variable-position images. CVmax in fixed-position OSEM images was less than 2%, irrespective of matrix size. In contrast, CVmax in variable-position images was higher than in fixed-position images. CVmax was higher for OSEM+PSF images than for OSEM images. The full width at half maximum increased at positions far from the center on OSEM images but 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 OSEM+PSF images. Precise positioning is necessary if PET is to be used as a biomarker. Professionals should recognize that PSF correction worsens the repeatability of the small hot spot although improving the spatial resolution of PET images.