<title>Abstract</title><sec>
<title>Background</title>
The amount of signal decreases when the acquisition duration is shortened. However, it is not clear how this affects the quantitative values. This study aims to clarify the effect of acquisition time shortening in brain tumor PET/CT using ¹¹C-methionine on the quantitative values.


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<title>Method</title>
This study was a retrospective analysis of 30 patients who underwent clinical ¹¹C-methionine PET/CT examination. PET images were acquired in list mode for 10 min. PET images of acquisition duration from 1 to 10 min with 1-min step were reconstructed. We examined the effect on the quantitative values of acquisition duration. We placed a volume of interest to include the entire tumor and regions of interest in the shape of a large crescent in the contralateral hemisphere in 5 contiguous axial slices as normal tissue. Quantitative values examined were maximum, peak, and mean standardized uptake values (SUVmax, SUVpeak, SUVmean), metabolic tumor volume (MTV), and maximum tumor to normal tissue ratio (TNRmax), with each duration compared to that with 10 min.


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<title>Results</title>
SUVmax, MTV, and TNRmax showed the highest values due to the effects of statistical noise when the acquisition time was 1 min. These values were stable when the acquisition duration was &gt; 6 min. SUVpeak and SUVmean showed mostly consistent values regardless of duration.


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<title>Conclusions</title>
SUVmax, MTV, and TNRmax are affected by acquisition time. If the acquisition duration was &gt; 6 min, the fluctuation could be suppressed within 5% in these quantitative values. However, SUVpeak was suggested to be a robust index regardless of the acquisition duration.


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