Acquisition protocols of quantitative 177Lu-Dotatate SPECT/CT imaging based on different energy windows and collimators / 中国医学影像技术

ABSTRACT

Objective: To explore the optimal acquisition protocols for 177Lu-Dotatate SPECT/CT imaging based on different energy windows and collimators. Methods 177Lu SPECT images of a NEMA IEC body phantom with known activity concentration ration (121) between filled hollow spheres and uniform background were acquired with 3 different collimators Low energy high resolution (LEHR), medium energy general purpose (MEGP) and high energy general purpose (HEGP). Main energy window was defined around the energy peak 113 keV, 208 keV and 113 keV+208 keV with 20% width. Scatter correction was performed with applying attenuation correction and triple energy window method. Thus 9 different acquisition protocols could be produced, including LEHR_113, LEHR_208, LEHR_113+208, MEGP_113, MEGP_208, MEGP_113+208, HEGP_113, HEGP_208 and HEGP_113+208 in short. The intensity ratio between spheres and background, relative error and conversion factor were measured and corrected for partial volume effect and used to compare the performance of different methods. Results: The contrast of MEGP_208 SPECT image was the worst, whereas better visual resolution images were achieved by MEGP_208 and MEGP_113+208. The measured average intensity ratios of 9 methods were all lower than the real ratio (F=2.659, P=0.040). The relative error of intensity ratio in MEGP_113+208 was the minimum ([-1.33±6.40]%), and in LEHR_208 was the maximum ([-58.34±14.42]%). All acquisition protocols showed significant difference in conversion factor (F=4.846, P=0.003). Conclusion: Different acquisition protocols have significant effect on the results of 177Lu-Dotatate SPECT/CT quantitative imaging. Image quality of MEGP collimator combined with 113 keV+208 keV is the best, and the intensity ratio is the closest to the real ratio.