This synopsis outlines the Japanese guideline Version 1.0 for the data acquisition protocol of oncology FDG-PET/CT scans that was created by a joint task force of the Japanese Society of Nuclear Medicine Technology (JSNMT) and the Japanese Council of PET Imaging, and published in Kakuigaku-Gijutsu 29(2):195–235, 2009, in Japanese. The guideline aims at standardizing the PET image quality among facilities and different PET/CT scanner models by determining and/or evaluating the data acquisition condition in experiments using an IEC body phantom, as well as by proposing the criteria for human image quality evaluation using patient noise equivalent count (NEC), NEC density, and liver signal-to-noise ratio.
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Appendix: Physical indicators of image quality
Appendix: Physical indicators of image quality
Indicators of phantom image quality
In this guideline, NECphantom (noise equivalent count for phantom), percentage of contrast (Q H,10 mm), and percentage of background variability (N 10 mm) are used as indicators of body phantom image quality.
The NECphantom is calculated using the formula in Eq. 1:
where T, S, and R represent true, scatter, and random coincidences acquired within the scanning period, and P and D represent prompt and delayed coincidences. SF, k, and f represent scatter fraction, random scaling factor, and ratio of object size to sinogram. S a and r represent the cross-sectional area of the phantom and the radius of the detector ring diameter, respectively.
The phantom image is reconstructed with all available corrections applied, using the standard reconstruction algorithm and usual parameters for whole-body studies.
A transverse image centered on the hot sphere(s) is used in the analysis. A circular region of interest (ROI) with a 10-mm diameter is drawn on the 10-mm hot sphere. The ROI analysis tool should take partial pixels into account and also permit movement of the ROI in increments of 1 mm or smaller.
Twelve ROIs of the same size are drawn throughout the background at a distance of 15 mm from the edge of the phantom, but not closer than 15 mm to any sphere. The ROIs are also drawn on the slices as close as possible to ±1 cm and ±2 cm on either side of the central slice, resulting in a total of 60 background ROIs, twelve on each of the five slices. The locations of all ROIs should be fixed between successive measurements. The measured activity in each background ROI is recorded. The percent contrast for the 10-mm hot sphere (Q H,10 mm) is calculated as follows:
where C H,10 mm and C B,10 mm are the average measured activity in the ROI for the 10-mm sphere and the average measured activity in all the background 10-mm diameter ROIs, respectively. a H /a H is the activity concentration ratio for the hot sphere to the background.
The percentage of background variability N 10 mm for the 10-mm sphere is calculated as follows:
where SD10 mm is the standard deviation of the background ROI counts for the 10-mm sphere, calculated as follows:
Indicators of human image quality
Noise equivalent count per patient height (NECpatient) and noise equivalent count per volume (NECdensity) are evaluated as potential physical indicators of image quality.
The NECpatient is defined to allow for patient height normalization. In this guideline, since the axial scanning range is variable, NECpatient is defined as shown in Eq. 5:
where NEC i and x represent NEC for each bed position (i) and the length (cm) of the axial field of view to be evaluated (i = 1–I), which extends from the neck to the abdomen in this guideline, respectively.
NECi is calculated using the formula in Eq. 6,
where P i and D i represent prompt and delayed coincidences for each bed position. SF represents the scatter fraction measured within the NEMA NU 2-2001 Standard , and k is set to 0 or 1 depending on whether you use variance reduction techniques for estimating a smooth random distribution or using direct random subtraction.
NECdensity is defined as shown in Eq. 7:
The NECdensity reflects normalized effective counts distributed within the subject body and represents count statistics per subject volume including lung area. The NEC i is calculated as shown in Eq. 6, and V (cm3) represents the subject volume within the axial extent to be evaluated (i = 1–I), i.e., from the neck to the abdomen in this guideline.
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Fukukita, H., Senda, M., Terauchi, T. et al. Japanese guideline for the oncology FDG-PET/CT data acquisition protocol: synopsis of Version 1.0. Ann Nucl Med 24, 325–334 (2010). https://doi.org/10.1007/s12149-010-0377-7