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. 2022 Oct;23(10):e13751.
doi: 10.1002/acm2.13751. Epub 2022 Aug 17.

Characterization of time of flight and resolution modeling on image quality in positron emission tomography

Terrance J Moretti  1 , Stephanie M Leon  1 , Colin J Schaeffer  1 , Manuel Arreola  1
Affiliations

Characterization of time of flight and resolution modeling on image quality in positron emission tomography

Terrance J Moretti et al. J Appl Clin Med Phys. 2022 Oct.

Abstract

Time-of-flight (TOF) and resolution modeling (RM) algorithms are frequently used in clinical PET images, and inclusion of these corrections should measurably improve image quality. We quantified the effects of these correction algorithms on reconstructed images via the following metrics: recovery coefficients (RCs), contrast-to-noise ratio (CNR), noise-power spectrum (NPS), modulation transfer function (MTF), and the full width at half maximum (FWHM) of a point source. The goal of this experiment was to assess the effects of the correction algorithms when applied singly or together. Two different phantom tests were performed and analyzed by custom software. FWHM and MTF were measured using capillary tube point sources, while RCs, CNR, and NPS were measured using an image quality body phantom. Images were reconstructed with both TOF and RM, only TOF, only RM, or neither correction. The remaining reconstruction parameters used the standard clinical protocol. RM improved RCs, FWHM, and MTF, without increasing overall noise significantly. TOF improves CNR for small objects FWHM or MTF but did not decrease noise. RCs were not statistically improved by enabling these algorithms. Inclusion of both correction algorithms in image reconstruction provides an overall improvement to all metrics relative to the uncorrected image, but not by a significant margin in multiple aspects.

Keywords: image quality; positron emission tomography (PET); resolution modelling; time of flight.

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Conflict of interest statement

The authors have no conflict of interest to disclose.

Figures

FIGURE 1
FIGURE 1
Example ROI map created when performing the National Electrical Manufacturer's Association (NEMA) image quality test. The smaller red circles indicate the six hot spheres; the larger blue circles indicate the background ROIs. Each of the 37‐mm diameter blue ROIs contains five smaller concentric ROIs with sizes matching the red ROIs, which are not shown.
FIGURE 2
FIGURE 2
Recovery coefficents for (a) 4:1 sphere‐to‐background activity ratio and (b) 8:1 sphere‐to‐background activity ratio. Error bars represent standard deviations. Enabling both resolution modeling (RM) and Time‐of‐flight (TOF) appears to provide the best recovery coefficient (RC) value for all object sizes, but this difference was not significant.
FIGURE 3
FIGURE 3
Noise‐power spectrum (NPS) curves obtained for the (a) 4:1 and (b) 8:1 activity ratios. Curves have been normalized to the activity present at scan time. Error bars represent standard deviations.
FIGURE 4
FIGURE 4
Contrast‐to‐noise ratio (CNR) plots for (a) 4:1 sphere to background ratio and (b) 8:1 sphere to background ratio. Error bars represent standard deviations.
FIGURE 5
FIGURE 5
Modulation transfer function (MTF) curves obtained from the point source images. Error bars represent standard deviations. Improvements in MTF when using resolution modeling (RM) are shown, and the independence from Time‐of‐flight (TOF) is illustrated.
See this image and copyright information in PMC

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