An inter-laboratory comparison study of image quality of PET scanners using the NEMA NU 2-2001 procedure for assessment of image quality.

An inter-laboratory comparison study was conducted to assess the image quality of PET scanners in Austria. The survey included both dedicated PET scanners (D-PET, n = 8) and coincidence cameras (GC-PET, n = 7). Measurement of image quality was based on the NEMA (National Electrical Manufacturers Association) NU 2-2001 protocol and the IEC (International Electrotechnical Commission) body phantom. The latter contains six fillable spheres ranging in diameter from 37 mm down to 10 mm and a 'lung' insert. The two largest lesions L1-2 simulate cold lesions, the four smaller ones (L3-6) are filled with 18F and activity concentration ratios relative to background of 8:1 and 4:1, respectively. Acquisition and reconstruction in the study employed the participating institutes' standard oncological processing protocol. Calculation of contrast of the spheres was performed with a fully automated procedure. Contrast quality indices (CQIs) reflecting global performance were obtained by summing individual contrast values. Other image quality parameters calculated according to the NEMA protocol were background variability and relative error for correction of attenuation and scatter. Contrast values obtained were 61 +/- 16 and 37 +/- 14 for L1 (per cent contrast +/- SD for D-PET and GC-PET, respectively), 57 +/- 16 and 29 +/- 16 for L2, 46 +/- 10 and 26 +/- 6.3 for L3, 37 +/- 10 and 15 +/- 4.3 for L4, 26 +/- 11.5 and 6.1 +/- 2.5 for L5, 14 +/- 7.1 and 2.6 +/- 2.6 for L6, with D-PET systems consistently being superior to GC-PET systems. CQIs permitted ranking of the scanners, also demonstrating a clear distinction between D-PET and GC-PET systems. Background variability was largest for GC-PET systems; the relative error of attenuation and scatter correction was significantly correlated with image quality for D-PET systems only. The study demonstrated considerable differences in image quality not only between GC-PET and D-PET systems but also between individual D-PET systems with possible consequences for clinical interpretation of images and measurement of quantitative indices such as the standardized uptake value. The study provided valuable feedback to the participants as well as baseline data for improving interchangeability of PET images and of quantitative indices between different laboratories.