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. 2018 Winter;6(1):15-23.
doi: 10.22038/aojnmb.2017.26684.1186.

Characteristics of Smoothing Filters to Achieve the Guideline Recommended Positron Emission Tomography Image without Harmonization

Yuji Tsutsui  1   2 , Shinichi Awamoto  1 , Kazuhiko Himuro  1 , Yoshiyuki Umezu  1 , Shingo Baba  3 , Masayuki Sasaki  4
Affiliations

Characteristics of Smoothing Filters to Achieve the Guideline Recommended Positron Emission Tomography Image without Harmonization

Yuji Tsutsui et al. Asia Ocean J Nucl Med Biol. 2018 Winter.

Abstract

Objectives: The aim of this study is to examine the effect of different smoothing filters on the image quality and SUVmax to achieve the guideline recommended positron emission tomography (PET) image without harmonization.

Methods: We used a Biograph mCT PET scanner. A National Electrical Manufacturers Association (NEMA) the International Electrotechnical Commission (IEC) body phantom was filled with 18F solution with a background activity of 2.65 kBq/mL and a sphere-to-background ratio of 4. PET images obtained with the Biograph mCT PET scanner were reconstructed using the ordered subsets-expectation maximization (OSEM) algorithm with time-of-flight (TOF) models (iteration, 2; subset, 21); smoothing filters including the Gaussian, Butterworth, Hamming, Hann, Parzen, and Shepp-Logan filters with various full width at half maximum (FWHM) values (1-15 mm) were applied. The image quality was physically assessed according to the percent contrast (QH,10), background variability (N10), standardized uptake value (SUV), and recovery coefficient (RC). The results were compared with the guideline recommended range proposed by the Japanese Society of Nuclear Medicine and the Japanese Society of Nuclear Medicine Technology. The PET digital phantom was developed from the digital reference object (DRO) of the NEMA IEC body phantom smoothed using a Gaussian filter with a 10-mm FWHM and defined as the reference image. The difference in the SUV between the PET image and the reference image was evaluated according to the root mean squared error (RMSE).

Results: The FWHMs of the Gaussian, Butterworth, Hamming, Hann, Parzen, and Shepp-Logan filters that satisfied the image quality of the FDG-PET/CT standardization guideline criteria were 8-12 mm, 9-11 mm, 9-13 mm, 10-13 mm, 9-11 mm, and 12-15 mm, respectively. The FWHMs of the Gaussian, Butterworth, Hamming, Hann, Parzen, and Shepp-Logan filters that provided the smallest RMSE between the PET images and the 3D digital phantom were 7 mm, 8 mm, 8 mm, 8 mm, 7 mm, and 11 mm, respectively.

Conclusion: The suitable FWHM for image quality or SUVmax depends on the type of smoothing filter that is applied.

Keywords: FDG PET; SUV; Smoothing filter.

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Figures

Figure 1
Figure 1
Flow chart for the evaluation of the image quality and harmonization for different smoothing filters and FWHMs.
Figure 2
Figure 2
PET images of the NEMA IEC Body phantom using different smoothing filters and FWHMs.
Figure 3
Figure 3
The image quality in relation to the different smoothing filters and FWHMs: (a) background variability; (b) Contrast noise ratio.
Figure 4
Figure 4
Recovery coefficients in relation to the different smoothing filters and FWHMs.
Figure 5
Figure 5
RMSE between the PET images with different smoothing filters and the digital phantom.
Figure 6
Figure 6
Frequency amplitude in relation to the frequency of the different smoothing filters.
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