Optimization of scanning time of ¹⁸F-FDG whole body PET/CT imaging in obese patients using quadratic dose protocol

¹⁸F-FDG imaging of overweight and obese patients is often challenging due to higher scattering and attenuation. Degradation of positron emission tomography (PET) image quality as the body weight increases is best overcome by using the quadratic dose protocol. Previously the implementation of this protocol on a Bismuth Germanium Oxide (BGO) scintillation crystal-based PET/CT system at Institut Kanser Negara (IKN), Malaysia practices using the linear dose protocol (T_min=2.5 minutes). Hence, this study aims to optimize the T_min of the quadratic dose protocol for ¹⁸F-FDG PET/CT.

This study was conducted based on the guideline published by the European Association of Nuclear Medicine (EANM) version 2.0 FDG-PET/CT and conducted in two phases. Firstly, 100 whole-body scan ¹⁸FFDG PET/CT images were selected for the average coefficient of variation (COV) analysis in the liver region. Second, a NEMA 2012/IEC2008 phantom was used to obtain the relationship between the COV_phantom and the scanning time. Finally, the images acquired using the two T_min were quantitatively compared using contrast recovery coefficient (Q_H), signal to noise ratio (SNR), and visibility (V_H). Independent t-test between each image quality parameter performed with p-value <0.05 considered significant.

The average COV of the liver was 17.7%. Currently, this value was clinically accepted to produce appropriate image quality at IKN. Interpolation at COV=17.7% gave a T_min value of 2.9 minutes. Comparisons show that the two T_min yielded equivalent PET/CT image quality (p-value of Q_H=0.774, SNR=0.780 and V_H=0.915).

The optimal T_min defined in this study was 2.9 minutes, 27.6% shorter than the Tmin previously defined based on COV=15%. Despite the higher average COV, the shorter T_min beneficial in the lower total ¹⁸F-FDG activity administered, reduce the internal dose to the patient while producing equivalent image quality.