Use of count-based image reconstruction to evaluate the variability and repeatability of measured standardised uptake values.

Standardized uptake values (SUVs) are the most widely used quantitative imaging biomarkers in PET. It is important to evaluate the variability and repeatability of measured SUVs. Phantom studies seem to be essential for this purpose; however, repetitive phantom scanning is not recommended due to the decay of radioactivity. In this study, we performed count-based image reconstruction to avoid the influence of decay using two different PET/CT scanners. By adjusting the ratio of 18F-fluorodeoxyglucose solution to tap water, a NEMA IEC body phantom was set for SUVs of 4.0 inside six hot spheres. The PET data were obtained using two scanners (Aquiduo and Celesteion; Toshiba Medical Systems, Tochigi, Japan). We set the start time for image reconstruction when the total radioactivity in the phantom was 2.53 kBq/cc, and employed the counts of the first 2-min acquisition as the standard. To maintain the number of counts for each image, we set the acquisition time for image reconstruction depending on the decay of radioactivity. We obtained 50 images, and calculated the SUVmax and SUVpeak of all six spheres in each image. The average values of the SUVmax were used to calculate the recovery coefficients to compare those measured by the two different scanners. Bland-Altman analyses of the SUVs measured by the two scanners were also performed. The measured SUVs using the two scanners exhibited a 10-30% difference, and the standard deviation (SD) of the measured SUVs was between 0.1-0.2. The Celesteion always exhibited higher values than the Aquiduo. The smaller sphere exhibited a larger SD, and the SUVpeak had a smaller SD than the SUVmax. The Bland-Altman analyses showed poor agreement between the SUVs measured by the two scanners. The recovery coefficient curves obtained from the two scanners were considerably different. The Celesteion exhibited higher recovery coefficients than the Aquiduo, especially at approximately 20-mm-diameter. Additionally, the curves were lower than those calculated from the standard 30-min acquisition images. We propound count-based image reconstruction to evaluate the variability and repeatability of measured SUVs. These results are also applicable for the standardization and harmonization of SUVs in multi-institutional studies

The Bland-Altman plots of count-based measured SUV_max and SUV_peak.

<p>The Bland-Altman plots of SUV_max (A-C) and SUV_peak (D-F) measured by the <i>Celesteion</i> and <i>Aquiduo</i>.</p

The measured SUV_max and SUV_peak of a 37-mm-diameter sphere with a 2-min acquisition over time.

<p>Standardized uptake values (SUVs) obtained from constant 2-min acquisition periods using the <i>Celesteion</i> scanner are shown over time to compare the resulting SUVs. The scatter plot depicts SUV_max (solid, black circle) and SUV_peak (empty/open circle) values. The solid and dotted trend lines correspond to SUV_max and SUV_peak, respectively.</p

The curves of the recovery coefficients.

<p>The curves of the recovery coefficients measured by the <i>Celesteion</i> (a) and <i>Aquiduo</i> (b) scanners. The solid line with black circles corresponds to the average of the count-based measurements. The dashed line with black squares corresponds to the standard 30-min acquisition measurements.</p

The distributions of count-based measured SUV_max and SUV_peak.

<p>The distribution of the SUV_max (A-C) and SUV_peak (D-F) of the representative three spheres. The 50 count-based measurements were performed using the <i>Celesteion</i> (solid, black circle) and <i>Aquiduo</i> (empty/open circle) scanners. The solid and dotted trend lines correspond to the <i>Celesteion</i> and <i>Aquiduo</i>, respectively.</p

Mean and standard deviation (SD) of measured SUVs.

<p>Mean and standard deviation (SD) of measured SUVs.</p

Time calculations for image reconstruction.

<p>Time calculations for image reconstruction.</p

The results of Bland-Altman analyses of the SUVs measured by the <i>Celesteion</i> and <i>Aquiduo</i> scanners.

<p>The results of Bland-Altman analyses of the SUVs measured by the <i>Celesteion</i> and <i>Aquiduo</i> scanners.</p