PT  - JOURNAL ARTICLE
AU  - Takayuki Shibutani
AU  - Masahisa Onoguchi
AU  - Takayuki Kanno
AU  - Takafumi Mochizuki
AU  - Kazuhiro Shiba
TI  - Development of a novel phantom to evaluate the characteristics of dual-isotope simultaneous acquisition in a small-animal SPECT-PET/CT system
DP  - 2021 May 01
TA  - Journal of Nuclear Medicine
PG  - 3032--3032
VI  - 62
IP  - supplement 1
4099  - http://jnm.snmjournals.org/content/62/supplement_1/3032.short
4100  - http://jnm.snmjournals.org/content/62/supplement_1/3032.full
SO  - J Nucl Med2021 May 01; 62
AB  - 3032Objectives: We developed a novel phantom that can evaluate image quality and quantitative indexes including partial volume effect in both hot and cold regions. The aim of this study was to demonstrate the image quality and quantitative indexes of hot and cold regions for dual-isotope simultaneous acquisition (DISA) compared with the single-isotope acquisition (SA) using the novel phantom. Methods: Data acquisition was performed using VECTor+/CT (MILabs, B.V., Netherlands) of a small-animal SPECT-PET/CT scanner equipped with a clustered multi-pinhole collimator of ultra-high-resolution type. A novel phantom composed by two cylindrical parts with 40 mm diameter, and a hot- or cold-rod phantom of 1 - 6 mm was inserted into one of the cylindrical parts. Hot-rod and two cylindrical parts were filled with 99mTc and/or 18F solution. The radioactive concentration of hot-rod and background (BG) was set at 4:1. Furthermore, the 18F/99mTc ratio was changed from 0.8 to 4 using radioactive decay. The energy window of 99mTc and 18F was set to 141 keV ± 10% and 511 keV ± 10%, and scatter energy windows were set at 7% lower and upper of the main photopeak with 99mTc and 18F. SPECT and PET images were reconstructed using a pixel-based OSEM method with Gaussian filter. In addition, scatter correction (SC) and attenuation correction (AC) were used in the TEW and CT-based AC. The ROI was drawn on the hot- or cold-rod and BG part to calculate the contrast and recovery coefficient. Moreover, we calculated the percentage of coefficient variation (%CV) and the relative error of Bq/mL corrected by cross-calibration factor using the circle ROI of 80% area and profile curve set in the uniform cylindrical part. Results: Contrast decreased with a smaller rod diameter in both hot and cold regions. Furthermore, the contrast of SA image with 99mTc was lower than that of DISA image with 99mTc. However, the contrast of DISA image with 99mTc was improved by SC. The recovery coefficients were lower for hot-rod and higher for cold-rod less than 4mm in diameter. When the 18F/99mTc ratio was 3 or more, the %CV gradually increased to more than 10%. The relative error of Bq/mL for 99mTc was underestimated by 23.4% - 41.2% with or without AC and SC. The relative error of Bq/mL for 18F was the lowest value in ACSC. Conclusions: We evaluated the image quality and quantitative indexes of hot- and cold-rod region using the novel phantom. VECTor+/CT SPECT-CT system is affected by the partial volume effect at less than 4 mm, and we demonstrated the excellent image quality when the 18F/99mTc ratio was less than 3.