Improvement in PET/CT Image Quality with a Combination of Point-Spread Function and Time-of-Flight in Relation to Reconstruction Parameters

Abstract

The aim of this study was to investigate the effects of the pointspread function (PSF) and time-of-flight (TOF) on improving 18 F-FDG PET/CT images in relation to reconstruction parameters and noise-equivalent counts (NEC). Methods: This study consisted of a phantom study and a retrospective analysis of 39 consecutive patients who underwent clinical 18 F-FDG PET/CT. The body phantom of the National Electrical Manufacturers Association and International Electrotechnical Commission with a 10-mm-diameter sphere was filled with an 18 F-FDG solution with a 4:1 radioactivity ratio compared with the background. The PET data were reconstructed with the baseline orderedsubsets expectation maximization (OSEM) algorithm, with the OSEM1PSF model, with the OSEM1TOF model, and with the OSEM1PSF1TOF model. We evaluated image quality by visual assessment, the signal-to-noise ratio of the 10-mm sphere (SNR 10 mm ), the contrast of the 10-mm sphere, and the coefficient of variance in the phantom study and then determined the optimal reconstruction parameters. We also examined the effects of PSF and TOF on the quality of clinical images using the signal-to-noise ratio in the liver (SNR liver ) in relation to the NEC in the liver (NEC liver ). Results: In the phantom study, the SNR 10 mm was the highest for the OSEM1PSF1TOF model, and the highest value was obtained at iteration 2 for algorithms with the TOF and at iteration 3 for those without the TOF. In terms of a postsmoothing filter full width at half maximum (FWHM), the high SNR 10 mm was obtained with no filtering or was smaller than 2 mm for algorithms with PSF and was 4-6 mm for those without PSF. The balance between the contrast recovery and noise is different for algorithms with either PSF or TOF. A combination of PSF and TOF improved SNR 10 mm , contrast, and coefficient of variance, especially with a small-FWHM gaussian filter. In the clinical study, the SNR liver of the low-NEC liver group in the OSEM1PSF1TOF model was compared with that of the high-NEC liver group in conventional OSEM. The PSF1TOF improved the SNR liver by about 24.9% 6 9.81%. Conclusion: A combination of PSF and TOF clearly improves image quality, whereas optimization of the reconstruction parameters is necessary to obtain the best performance for PSF or TOF. Furthermore, this combination has the potential to provide good image quality with either lower activity or shorter acquisition time, thus improving patient comfort and reducing the radiation burden. PET/ CT with 18 F-FDG is useful for the detection and staging of various malignant tumors, monitoring of their response to therapy, and prognostic stratification (1-6). High image quality is required for an accurate diagnosis, although the spatial resolution of PET is relatively low in comparison to other imaging modalities (7). Recently, the information provided by the point-spread function (PSF) and time-of-flight (TOF) has been expected to improve the spatial resolution and signal-to-noise ratio (SNR), respectively, of PET images (8-10).A PET sca...

Impact of Image Reconstruction Settings on Texture Features in 18F-FDG PET

“…The delineated lesion is also shown in green in the figure. Consistent with the previous findings (22)(23)(24)(25)(26), OSEM 1 TOF 1 PSF produced visually the best image among the chosen 4 reconstruction algorithms with their default settings. In addition, quantitative assessment supported the fact that OSEM 1 TOF 1 PSF produced the best image with an SNR of 9.1 in the liver, whereas the SNR of OSEM, OSEM 1 PSF, and OSEM 1 TOF were 5.2, 5.5, and 8.5, respectively.…”

“…Thus, the impact of the partial-volume effect can be neglected. Previous studies (22)(23)(24)(25)(26) demonstrated that OSEM 1 PSF 1 TOF produced better image quality than other methods in terms of SNR, contrast, and lesion detectability. Therefore, in this study, the tumor VOIs were delineated on the image reconstructed by OSEM 1 PSF 1 TOF with default settings and then applied to the other methods.…”

“…However, only filtered backprojection and ordered-subset expectation maximization (OSEM) were investigated. The techniques of time-of-flight (TOF) and point-spread function (PSF) modeling have been shown to clearly improve image quality in terms of signal-to-noise ratio (SNR), lesion contrast, and coefficient of variation (COV) on background and are now standard in most scanners (22)(23)(24)(25)(26). TOF improves SNR and thus reduces heterogeneity due to noise.…”

Effect of Reconstruction Parameters in High-Definition PET/CT on Assessment of Lymph Node Metastases in Head and Neck Squamous Cell Carcinoma

“…Diagnostic visualization of large necrotic lymph node metastases at level II on left side of neck patient with cancer of unknown primary (CUP; thick straight arrow) did not differ in any postfiltered images despite increased image blurring with 6 mm in FWHM. (23), in which the use of a 3-mm gaussian filter was recommended for algorithms not based on a point-spread function.…”

Status of cardiovascular PET radiation exposure and strategies for reduction: An Information Statement from the Cardiovascular PET Task Force

“…More recently time-of-flight and resolution recovery reconstruction algorithms have been investigated as techniques for improving image quality. 36,37 Further study is needed before they can be used routinely for dose reduction. Recommendation: Use iterative reconstruction to improve image quality of emission datasets.…”