Emission segmented attenuation correction method without transmission scan can accurately measure tissue tracer concentration on small animal PET

Abstract

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Objectives: Small animal PET is a useful tool to study rodent biology and metabolism in vivo. However, a transmission scan (Ts) for accurate attenuation correction require a long scan time due to limited activity in external transmission source. To reduce PET scan time for quantitative studies, accuracy of the emission segmented attenuation correction (ESAC) method was evaluated.

Methods: PET data were acquired with a dedicated small animal PET (Hamamatsu SHR-41000). For the phantom study, a cylinder phantom filled with 18F solution was scanned to acquire emission data. Ts method was performed using a 68Ge/68Ga rod source one day after the emission scan. For the animal study, six rats were studied (male, 280-330 g). Ts method was performed for 60 min, followed by a 30 min emission scan which was started 45 min after the injection of 8 MBq of 18F-FDG. These images were reconstructed with Ts, ESAC, and no attenuation correction (nAc) using the same reconstruction parameters. Regional PET values were obtained from regions of interest drawn on each image. Quantitative values obtained by the ESAC and nAc were compared with those with Ts using a paired t test.

Results: The nAc significantly underestimated tissue tracer activity as compared with the Ts (P<0.01) both in the phantom and rat study. However, there was no significant difference between ESAC and Ts both in the phantom and rat study. The ESAC showed closer results to Ts than nAc although the ESAC tended to underestimate the rat brain concentration compared with Ts (y=0.75x+16.2).

Conclusions: The ESAC method without the Ts method can provide simple and accurate way to measure tissue tracer concentration with reducing PET scan time.