Optimized dose regimen for whole-body FDG-PET imaging

Abstract

BackgroundThe European Association of Nuclear Medicine procedure guidelines for whole-body fluorodeoxyglucose positron-emission tomography (FDG-PET) scanning prescribe a dose proportional to the patient’s body mass. However, clinical practice shows degraded image quality in obese patients indicating that using an FDG dose proportional to body mass does not overcome size-related degradation of the image quality. The aim of this study was to optimize the administered FDG dose as a function of the patient’s body mass or a different patient-dependent parameter, providing whole-body FDG-PET images of a more constant quality.MethodsUsing a linear relation between administered dose and body mass, FDG-PET imaging was performed on two PET/computed tomography scanners (Biograph TruePoint and Biograph mCT, Siemens). Image quality was assessed by the signal-to-noise ratio (SNR) in the liver in 102 patients with a body mass of 46 to 130 kg. Moreover, the best correlating patient-dependent parameter was derived, and an optimized FDG dose regimen was determined. This optimized dose regimen was validated on the Biograph TruePoint system in 42 new patients. Furthermore, this relation was verified by a simulation study, in which patients with different body masses were simulated with cylindrical phantoms.ResultsAs expected, both PET systems showed a significant decrease in SNR with increasing patient’s body mass when using a linear dosage. When image quality was fitted to the patient-dependent parameters, the fit with the patient’s body mass had the highest R2. The optimized dose regimen was found to be Anew= c/t × m2, where m is the body mass, t is the acquisition time per bed position and c is a constant (depending on scanner type). Using this relation, SNR no longer varied with the patient’s body mass. This quadratic relation between dose and body mass was confirmed by the simulation study.ConclusionA quadratic relation between FDG dose and the patient’s body mass is recommended. Both simulations and clinical observations confirm that image quality remains constant across patients when this quadratic dose regimen is used.

Improving the Detection of Small Lesions Using a State-of-the-Art Time-of-Flight PET/CT System and Small-Voxel Reconstructions

“…Thirty-nine consecutive patients with lung cancer, who underwent 18 F-FDG PET/CT, were analyzed. Patients signed a written informed consent form, and this study was approved by the local ethical committee of our institution.…”

“…Results: For phantom spheres 13 mm or less, we found higher contrast-recovery coefficients and SNRs using small-voxel reconstructions. For 66 included 18 F-FDG PET-positive lesions, the average increase in SUV mean and SUV max using the small-voxel images was 17% and 32%, respectively (P , 0.01). For lesions less than 0.75 mL (21 in total), the average increase was 21% and 44%, respectively.…”

“…1 MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands; 2 Department of Nuclear Medicine, Isala Hospital, Zwolle, The Netherlands; and 3 Department of Medical Physics, Isala Hospital, Zwolle, The Netherlands A major disadvantage of 18 F-FDG PET involves poor detection of small lesions and lesions with low metabolism, caused by limited spatial resolution and relatively large image voxel size. As spatial resolution and sensitivity are better in new PET systems, it is expected that small-lesion detection could be improved using smaller voxels.…”

“…For the phantom study, we determined contrast-recovery coefficients and signal-to-noise ratios (SNRs). For the patient study, 18 F-FDG PET-positive lesions in the chest and upper abdomen with a volume less than 3.0 mL (diameter, ,18 mm) were included. Lesion mean and maximum standardized uptake values (SUV mean and SUV max , respectively) were determined in both image sets.…”

Connections Between Noise Equivalent Count Rate and Image Noise in Pet Medical Imaging

“…In clinical practice, administered activity is limited by radiation safety factors instead of scanner count rate performance. PET/CT studies in normal weight patients are usually operated in the linear part of the NECR curve, where the contributions of deadtime and random coincidences have a much smaller effect on NECR than at higher FDG activities where the NECR curve becomes flat [10].…”