Generation of the Acquisition-Specific NEC (AS-NEC) Curves to Optimize the Injected Dose in 3D F-FDG Whole Body PET Studies

• Published in: IEEE transactions on nuclear science Vol. 53; no. 1; p. 86
• Main Authors: Danna, M, Lecchi, M, Bettinardi, V, Gilardi, M, Stearns, C, Lucignani, G, Fazio, F
• Format: Journal Article
• Language: English
• Published: New York The Institute of Electrical and Electronics Engineers, Inc. (IEEE) 01.02.2006
• Subjects: Acquisitions; Bismaleimides; Body mass index; Body size (biology); Cylinders; Marketing; Mathematical models; Polyethylene terephthalates; Reduction; Three dimensional
• DOI: 10.1109/TNS.2005.862966
• ISSN: 0018-9499

Aim of this work was the implementation and validation, for the Discovery-ST PET/CT (GE Medical Systems) system, of the acquisition-specific noise equivalent counts (AS-NEC) method to establish the amount of tracer to be injected in 3D 18 F-FDG whole body (WB) PET studies to achieve the peak of the NEC (NEC-p) at the acquisition time. The AS-NEC method uses prompts, delayed events and detector dead-time of a single reference PET scan to calculate the full shape of the NEC curve. The method was implemented using a 3D decay series of the 70 cm NEMA 2001 (line source in a 20 cm diameter solid polyethylene cylinder) phantom and validated with the cylindrical NEMA 1994 (diameter, 20 cm; length, 20 cm) and NEMA 2001 IEC body phantoms. The NEC curves generated by the single frames of the phantom series, using the AS-NEC method, well correlated with the experimental NEC curves proving the validity of the method and the possible application to clinical studies. The AS-NEC model was then retrospectively applied on 40 3D 18 F-FDG WB studies in a range of body mass index (BMI) between 16 and 30 (kg/m 2 ) (6 under-weight (uw), 18 normal-weight (nw), 16 over-weight (ow)). For each acquisition frame of each patient study, the activity at the acquisition time, corresponding to the NEC-p was identified on the NEC curves. Furthermore, as the NEC curves show a region around the NEC-p with small variations (nearly a plateau), the values of radioactivity corresponding to a reduction of 1%, 3% and 5% with respect to NEC-p were also calculated to assess a possible reduction of the doses to be injected in clinical studies. The results show that the average activities at the acquisition time corresponding to the NEC-p were comparable for the three BMI classes: 336.7 MBq ( sd = 22.2 ) , 329.3 MBq ( sd = 33.3 ) , 344.1 MBq ( sd = 48.1 ) for uw, nw and ow, respectively. Therefore, the total average NEC-p activity for the three BMI classes was 336.7 MBq ( sd = 40.7 ) . The mean values of the radioactivity at a reduction of 1%, 3% and 5% with respect to the NEC-p were: 284.9 MBq ( sd = 40.7 ) , 247.9 MBq ( sd = 33.3 ) and 225.7 MBq ( sd = 29.6 ) respectively. These results indicate the possibi- lity to use, for the Discovery-ST, a single injection protocol of 448 MBq (for the range of BMI here considered) to have an activity at the acquisition time (after 45 min of uptake) of 336.7 MBq (NEC-p). Nevertheless, the plateau near the NEC-p suggests the possibility to reduce significantly the dose to be injected in clinical studies down to about 330 MBq, while preserving suitable NEC performance ( - 3 %) with respect to the NEC-p. This result was supported by image quality assessment performed on reconstructed images of the NEMA 2001 IEC body phantom.