The aim of the present study was to evaluate the effect of postinjection transmission scanning (Post-Tx) on both the qualitative interpretation and the quantitative analysis of cardiac 18F-FDG PET images. Furthermore, the accuracy of 2 different methods to correct for emission contamination was studied. An additional aim of this study was to compare images reconstructed with both standard filtered backprojection (FBP) and an iterative reconstruction algorithm (ordered-subset maximization expectation [OSEM]). Methods: Sixteen patients underwent dynamic 18F-FDG imaging. Both before injection of 18F-FDG and after completing the emission scan, a 10-min transmission scan was performed (Pre-Tx and Post-Tx, respectively). Images were reconstructed using both FBP and OSEM. The emission study reconstructed with Pre-Tx was considered to be the gold standard. Emission studies were also reconstructed with Post-Tx, with and without correction for emission contamination. Correction for emission contamination was performed with either transmission image segmentation (TIS) or by estimating the emission bias from the last emission frame (dwell profile [DP] method). All images were then compared by calculating ratios of 18F-FDG activity between corresponding myocardial segments in each patient. Furthermore, qualitative grading of 18F-FDG uptake was compared between the studies. Results: The mean ratio of 18F-FDG activity between segments from FBP-Post and FBP-Pre was 0.78 ± 0.08. When TIS and DP were used, the mean ratios were 0.80 ± 0.07 and 0.94 ± 0.06, respectively. The use of OSEM resulted in, on average, 2% lower values for 18F-FDG activity as compared with FBP. The mean normalized 18F-FDG uptake was higher in FBP-Post, especially in segments with decreased 18F-FDG activity. Only in the case of DP were no significant differences observed as compared with FBP-Pre. In general, qualitative analysis of the images showed that the agreement between the reconstruction methods was comparable with the reproducibility of FBP-Pre. Conclusion: Post-Tx for attenuation correction in cardiac 18F-FDG PET scans resulted in substantial underestimation of 18F-FDG activity. More accurate results were obtained with correction for emission contamination using DP. Differences in visual assessment of 18F-FDG images were small. Finally, iterative reconstruction could be used as an alternative to FBP in static 18F-FDG imaging of the heart.
|Number of pages||7|
|Journal||Journal of nuclear medicine|
|Publication status||Published - 1 Feb 2004|
- Iterative reconstruction
- Postinjection transmission scanning