Scatter Correction of Septal Penetration for 123I-IMP Cerebral Blood Flow SPECT Adding Radioactivity from the Outside of Field of View-Comparison between Simulation-based and Multi-window Scatter Corrections

[Improvement of Standardized Uptake Value Accuracy in the 99mTc Body SPECT and SPECT/CT: Optimization of the Phantom for Calculating Becquerel Calibration Factor and Correction Method]

PURPOSE

The purpose of this study was to evaluate the best phantom for calculating the becquerel calibration factor (BCF) and correction method to obtain the improvement of standardized uptake value (SUV) accuracy in both single photon emission computed tomography (SPECT) and SPECT/CT.

METHOD

A SPECT/CT scanner was used in this study. BCFs were calculated using four phantoms with different cross sections including National Electrical Manufacturers Association International Electrotechnical Commission body phantom (NEMA IEC body phantom) filled with ^99mTcO₄^-, and five correction methods were used for reconstruction. SUVs were calculated by the NEMA IEC body phantom and pediatric phantom in house with these BCFs. We then measured SUV_mean in the background region of the NEMA IEC body phantom, SUV_max and SUV_peak of the 37-mm-diameter sphere.

RESULTS

In the SPECT scanner, SUV_mean and SUV_max measured 1.04 and 4.02, respectively, in the case of BCF calculation and SUV measurement using NEMA IEC body phantoms without corrections. In the SPECT/CT scanner, SUV_mean with CT attenuation correction (AC) was in agreement with the theoretical values using each phantom. SUV_max showed the same trend.

CONCLUSION

In the SPECT scanner, it is possible to obtain a highly accurate SUV by using a phantom that matches the size of the subject for BCF calculation and without correction. In the SPECT/CT scanner, highly accurate SUVs can be obtained by using CT-based attenuation correction, and these values do not depend on the size of the BCF calculation phantom.

Examination of cross-calibration and concentration linearity with quantitative gallium-67 single-photon emission computed tomography: phantom experiment

We evaluated whether scattered radiation should be considered for cross-calibration and concentration linearity with quantitative gallium-67 (⁶⁷Ga) single-photon emission computed tomography (SPECT). The scanned data from cylinder and spherical phantoms were used. They were reconstructed using ordered subset expectation maximization with resolution recovery, scatter, and computed tomography (CT)-based attenuation correction. The standardized uptake values (SUVs) of the cylinder phantom SPECT/CT images were calculated using system planar sensitivity with and without scatter correction, and the results were compared with the theoretical value. To determine concentration linearity, the relationship between the measured SUVs in three different spherical phantoms was evaluated. SUVs calculated by system planar sensitivity without scatter correction were closer to the theoretical values. Furthermore, the 37-mm sphere showed proper radioactive linearity. Our study suggests the utility of the SUV for ⁶⁷Ga SEPCT/CT. Nevertheless, additional studies are required.