Evaluation of PET quantitation accuracy among multiple discovery IQ PET/CT systems via NEMA image quality test

Abstract

Introduction: Quantitative imaging biomarkers are becoming usual in oncology for assessing therapy response. The harmonization of image quantitation reporting has become of utmost importance due to the multi-center trials increase. The NEMA image quality test is often considered for the evaluation of quantitation and is more accurate with a radioactive solid phantom that reduces variability. The goal of this project is to determine the level of variability among imaging centers if acquisition and imaging protocol parameters are left to the center's preference while all other parameters are fixed including the scanner type. Methods: A NEMA-IQ phantom filled with radioactive 68 Ge solid resin was imaged in five clinical sites throughout Europe. Sites reconstructed data with OSEM and BSREM algorithms applying the sites' clinical parameters. Images were analyzed according with the NEMA-NU2-2012 standard using the manufacturerprovided NEMA tools to calculate contrast recovery (CR) and background variability (BV) for each sphere and the lung error (LE) estimation. In addition, a 18 F-filled NEMA-IQ phantom was also evaluated to obtain a gauge for variability among centers when the sites were provided with identical specific instructions for acquisition and reconstruction protocol (the aggregate of data from 12 additional sites is presented). Results: The data using the 68 Ge solid phantom showed no statistical differences among different sites, proving a very good reproducibility among the PET center models even if dispersion of data is higher with OSEM compared to BSREM. Furthermore, BSREM shows better CR and comparable BV, while LE is slightly reduced. Two centers exhibit significant differences in CR and BV values for the 18 F NEMA NU2-2012 experiments; these outlier results are explained.

Evaluation of a Method Combining Physical Experiment and Data Insertion For the Assessment of PET-CT Systems

“…However, replication of these tests is limited in terms of reproducibility and repeatability, due to the introduction of uncertainties during preparation and acquisition. Hence, similar experiments repeated at different times show variations, which can impact their results [4]. An example of such variations can be observed in the measurements of activity concentrations (kBq/mL) inside the compartments of the phantom related to the experimental series in Table 1.…”

“…These procedures involve experiments performed on phantoms that generally consist of relatively simple geometrical objects, fillable with radioactive aqueous solutions. Phantom tests are useful for controlling experimental parameters but, on the other hand, are limited by the operator's contribution in terms of reproducibility and repeatability [4]. In addition, some parameters do not vary during the acquisition, such as the activity ratio between two compartments.…”

Impact of the Q.Clear reconstruction algorithm on the interpretation of PET/CT images in patients with lymphoma

“…The OSEM reconstruction was performed with a 70-cm dual field of view (DFOV) into a 256 × 256 matrix with 4 iterations, 12 subsets and 6.4 mm of full width at half maximum (FWHM). Reconstruction with Q.Clear was performed with a β parameter of 350, which was selected basing on our own phantom studies [ 16 ]. Both PET results after different reconstructions were fused within the same CT image with the following parameters: 1.25-mm layer thickness, 1.375:1 pitch, 50-cm DFOV 50 and 512 × 512 matrix.…”

Impact of the Q.Clear reconstruction algorithm on the interpretation of PET/CT images in patients with lymphoma

“…The OSEM reconstruction was performed with a 70-cm dual eld of view (DFOV) into a 256x256 matrix with 4 iterations, 12 subsets and 6.4-mm of full width at half maximum (FWHM). Reconstruction with Q.Clear was performed with a β parameter of 350, which was selected basing on our own phantom studies [16]. Both PET results after different reconstructions were fused within the same CT image with the following parameters: 1.25 mm layer thickness,1.375:1 pitch, 50 cm DFOV 50, and 512x512 matrix.…”