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. 2015 Aug 21;49(3):227-33.
doi: 10.1515/raon-2015-0014. eCollection 2015 Sep.

The impact of reconstruction algorithms and time of flight information on PET/CT image quality

Alen Suljic  1 , Petra Tomse  2 , Luka Jensterle  2 , Damijan Skrk  3
Affiliations

The impact of reconstruction algorithms and time of flight information on PET/CT image quality

Alen Suljic et al. Radiol Oncol. .

Abstract

Background: The aim of the study was to explore the influence of various time-of-flight (TOF) and non-TOF reconstruction algorithms on positron emission tomography/computer tomography (PET/CT) image quality.

Materials and methods: Measurements were performed with a triple line source phantom, consisting of capillaries with internal diameter of ∼ 1 mm and standard Jaszczak phantom. Each of the data sets was reconstructed using analytical filtered back projection (FBP) algorithm, iterative ordered subsets expectation maximization (OSEM) algorithm (4 iterations, 24 subsets) and iterative True-X algorithm incorporating a specific point spread function (PSF) correction (4 iterations, 21 subsets). Baseline OSEM (2 iterations, 8 subsets) was included for comparison. Procedures were undertaken following the National Electrical Manufacturers Association (NEMA) NU-2-2001 protocol.

Results: Measurement of spatial resolution in full width at half maximum (FWHM) was 5.2 mm, 4.5 mm and 2.9 mm for FBP, OSEM and True-X; and 5.1 mm, 4.5 mm and 2.9 mm for FBP+TOF, OSEM+TOF and True-X+TOF respectively. Assessment of reconstructed Jaszczak images at different concentration ratios showed that incorporation of TOF information improves cold contrast, while hot contrast only slightly, however the most prominent improvement could be seen in background variability - noise reduction.

Conclusions: On the basis of the results of investigation we concluded, that incorporation of TOF information in reconstruction algorithm mostly affects reduction of the background variability (levels of noise in the image), while the improvement of spatial resolution due to incorporation of TOF information is negligible. Comparison of traditional and modern reconstruction algorithms showed that analytical FBP yields comparable results in some parameter measurements, such as cold contrast and relative count error. Iterative methods show highest levels of hot contrast, when TOF and PSF corrections were applied simultaneously.

Keywords: PET/CT; image quality; point spread function; reconstruction algorithm; time of flight.

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Figures

FIGURE 1.
FIGURE 1.
Triple line insert for spatial resolution measurements and Jaszczak phantom for measurements of described image quality parameters.
FIGURE 2.
FIGURE 2.
Hot contrast in relation with cylinder diameter and reconstruction method (activity concentration ratio 8:1).
FIGURE 3.
FIGURE 3.
Cold contrast in relation with sphere diameter and reconstruction method (activity concentration ratio 1:8).
FIGURE 4.
FIGURE 4.
Background variability in relation with cylinder diameter and reconstruction method (activity concentration ratio 2:1).
FIGURE 5.
FIGURE 5.
Background variability in relation with sphere diameter and reconstruction method (activity concentration ratio 1:2).
FIGURE 6.
FIGURE 6.
Visual assessment of image quality according to the reconstruction method and activity concentration ratio. FBP = filtered back projection; FBP+TOF = filtered back projection with incorporated time of flight information; OSEM = ordered subsets expectation maximization; OSEM+TOF = ordered subsets expectation maximization with incorporated time of flight information; True-X = iterative reconstruction method which incorporates point spread function (PSF) correction; True-X+TOF = iterative reconstruction method which incorporates point spread function (PSF) correction with incorporated time of flight information
See this image and copyright information in PMC

References

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