Discrete Decreased Activity in the Lower Thoracic Spine on FDG PET/CT

Purpose We observed that the diaphragmatic motion causing the well-known, so-called banana artifact on PET/CT images may additionally cause decreased FDG activity involving 1 or 2 lower thoracic vertebrae. The aim of this study was (1) to formally evaluate if this observation is indeed true and, if so, (2) to assess its frequency. Patients and Methods One hundred fifty-four PET/CT scans (81 males and 73 females, age 61 ± 13 years) were analyzed. On the coronal CT images, the vertebra above where the hemi-diaphragmatic surfaces abut the vertebral column was defined as the target vertebra (TV). On sagittal PET images, FDG activity in TV was visually and quantitatively assessed. Then, the severity of banana artifact on coronal PET images was graded from 0 to 2: 0 if there was no artifact, 1 if a thin photopenic stripe, and 2 if a thick banana-shaped photopenic artifact in the vicinity of diaphragm. Results Visually decreased activity in TV was present in 0% (0/93), 3% (1/34), and 59% (16/27) of scans graded as 0, 1, and 2, respectively (grade 0 and/or 1 vs. grade 2, P < 0.001). The SUV ratio of TV to reference vertebrae were 0.99 ± 0.14, 0.99 ± 0.15, and 0.84 ± 0.19 in grade 0, 1, and 2 scans, respectively (P < 0.001). Conclusion Error of attenuation correction from respiratory motion can lead to underestimation of FDG activity in the lower thoracic spine, and this should not be interpreted as possible marrow replacement process requiring further imaging if there is coexisting banana artifact.