Improved image quality of FDG whole body PET/CT by time-of-flight reconstruction: A human study

Objectives Time-of-flight (TOF) reconstruction improves image quality in phantom studies. We aimed to investigate the impact of TOF on image quality by evaluating the coefficient of variation (CV) of physiological tracer distribution in organ structures of a group of normal patients.

Methods FDG whole body PET/CT (Siemens Biograph mCT) was performed from skull base to upper thigh at 2 minutes/bed for 25 patients (BMI range 16.4 to 48.9, mean 24.6±6.2, average injected dose 427MBq). Using point spread function, TOF (parameters: 2 iterations, 21 subsets, 5mm at FWHM, matrix size 200x200) and non-TOF (parameters: 3 iterations, 24 subsets, 5mm at FWHM, matrix size 200x200) images were reconstructed. In each patient, spherical volume of interest (VOI) of different sizes was centrally placed within 12 organ structures on CT (diameter 10mm: parotid gland, thyroid, lumen of the aortic arch, myocardium; 15mm: body of pancreas, marrow in body of L5, psoas muscle and gluteus maximus; 20mm: spleen; 35mm: lung apex and base; 40mm: liver) and they were copied to the TOF and non-TOF PET images for SUV measurements. CV was calculated by dividing the standard deviation with SUVmean. CV for each organ structure on TOF and non-TOF images were compared using paired student t-test.

Results Significant improvement of CV was detected in spleen (22%), liver (15%), and body of pancreas (12%) [all p values<0.001]; parotid gland (17%), lumen of the aortic arch (16%), marrow in the body of L5 (10%) and psoas muscle (10%) [all p values<0.05]. Improvement was also observed in myocardium (13%), thyroid (9%), gluteus maximus (8%) and lung base (7%). However, deterioration was observed in lung apex (10%) [p<0.05].

Conclusions The use of TOF generally enhances image quality of normal organ structures in FDG whole body PET/CT, particularly the solid organs in the abdomen