Aim of this work was the implementation and alidation, for the Discovery-ST PET/CT (GE Medical Systems) ystem, of the acquisition-specific noise equivalent counts AS-NEC) method to establish the amount of tracer to be injected n 3D 18F-FDG whole body (WB) PET studies to achieve the peak of the NEC (NEC-p) at the acquisition time. The AS-NEC method ses prompts, delayed events and detector dead-time of a single eference PET scan to calculate the full shape of the NEC curve. The method was implemented using a 3D decay series of the 70 cm EMA 2001 (line source in a 20 cm diameter solid polyethylene ylinder) phantom and validated with the cylindrical NEMA 994 (diameter, 20 cm; length, 20 cm) and NEMA 2001 IEC body hantoms. The NEC curves generated by the single frames of the hantom series, using the AS-NEC method, well correlated with the experimental NEC curves proving the validity of the method nd the possible application to clinical studies. The AS-NEC model as then retrospectively applied on 40 3D 18F-FDG WB studies n a range of body mass index (BMI) between 16 and 30 (kg/m2) 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 possibility 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.
Danna, M., Lecchi, M., Bettinardi, V., Gilardi, M., Stearns, C., Lucignani, G., et al. (2006). Generation of the acquisition-specific NEC (AS-NEC) curves to optimize the injected dose in 3D 18F-FDG whole body PET studies. IEEE TRANSACTIONS ON NUCLEAR SCIENCE, 53, 86-92 [10.1109/TNS.2005.862966].
Generation of the acquisition-specific NEC (AS-NEC) curves to optimize the injected dose in 3D 18F-FDG whole body PET studies
GILARDI, MARIA CARLA;FAZIO, FERRUCCIO
2006
Abstract
Aim of this work was the implementation and alidation, for the Discovery-ST PET/CT (GE Medical Systems) ystem, of the acquisition-specific noise equivalent counts AS-NEC) method to establish the amount of tracer to be injected n 3D 18F-FDG whole body (WB) PET studies to achieve the peak of the NEC (NEC-p) at the acquisition time. The AS-NEC method ses prompts, delayed events and detector dead-time of a single eference PET scan to calculate the full shape of the NEC curve. The method was implemented using a 3D decay series of the 70 cm EMA 2001 (line source in a 20 cm diameter solid polyethylene ylinder) phantom and validated with the cylindrical NEMA 994 (diameter, 20 cm; length, 20 cm) and NEMA 2001 IEC body hantoms. The NEC curves generated by the single frames of the hantom series, using the AS-NEC method, well correlated with the experimental NEC curves proving the validity of the method nd the possible application to clinical studies. The AS-NEC model as then retrospectively applied on 40 3D 18F-FDG WB studies n a range of body mass index (BMI) between 16 and 30 (kg/m2) 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 possibility 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.
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