Impact of patient body habitus on image quality and quantitative value in bone SPECT/CT.

Abstract

The first edition of guidelines for standardization of bone single photon emission computed tomography (SPECT) imaging was published in 2017, and the optimization and standardization are widely promoted. To the purpose, clarification of the factors related to image quality and quantitative values and their influence are required. The present study aimed to clarify and optimize the influence of patient body habitus on image quality and quantitative values in bone SPECT/CT. National Electrical Manufacturers Association body phantom (S-size) and custom-made large body phantoms (M-size and L-size) that simulate the abdomens of Japanese patients weighing 60, 80, and 100kg, were used. Each phantom was filled with 99mTc-solutions of 108 and 18kBq/mL for the hot spheres and background, respectively. Dynamic SPECT acquisition was performed for 6000s (150s /rotation × 40 rotation). The data were divided into six projection data and reconstructed each acquisition time (150, 300, 450, 600, 750, 900s, and single projection 6000s). Image quality was evaluated for contrast (QH, 17mm), background noise (NB, 17mm), contrast-to-noise ratio (CNR), maximum standardized uptake value (SUVmax, 17mm), and visual assessment for a 17mm hot sphere. Image quality in the 300s acquisition showed that values of QH, 17mm, CNR, and SUVmax, 17mm decreased (-16.7%, -11.8%, and -11.3%) for M-size and (-28.2%, -30.1%, and -21.7%) for L-size compared with S-size, respectively. No significant difference was observed in NB, 17mm values. M-size and L-size required 1.2 and 2.3 times longer acquisition, to achieve same CNR as S-size. In visual assessment, 17mm hot sphere could not be detected only in the L-size. When the Japanese bone SPECT guidelines criteria were applied in 600s, the sphere could be detected between all phantoms. Patient body habitus significantly affects image quality and decreases the quantitative value in bone SPECT/CT. For the optimization, extend acquisition time according to the patient body habitus is effective for image quality. And for the standardization, it is important to achieve imaging conditions that meet the Japanese bone SPECT guidelines criteria to ensure adequate detectability.