Performance evaluation of the new whole-body PET/CT scanner: Discovery ST

Abstract

Characterisation of the physical performance of the new integrated PET/CT system Discovery ST (GE Medical Systems) has been performed following the NEMA NU 2-1994 (N-94) and the NEMA NU 2-2001 (N-01) standards in both 2D and 3D acquisition configuration. The Discovery ST combines a four or eight multi-slice helical CT scanner with a PET tomograph which consists of 10,080 BGO crystals arranged in 24 rings. The crystal dimensions are 6.3 x 6.3 x 30 mm(3) and they are organised in blocks of 6 x 6 crystals, coupled to a single photomultiplier tube with four anodes. The 24 rings of the PET system allow 47 images to be obtained, spaced by 3.27 mm, and covering an axial field of view of 157 mm. The low- and high-energy thresholds are set to 375 and 650 keV, respectively. The coincidence time window is set to 11.7 ns. Using the NEMA N-94 standard, the main results were: (1) the average (radial and tangential) transverse spatial resolution (FWHM) at 1, 10 and 20 cm off axis was 6.28 mm, 7.09 mm and 7.45 mm in 2D, and 6.68 mm, 7.72 mm and 8.13 mm in 3D; (2) the sensitivity for true events was 8,567 cps/kBq/cc in 2D and 36,649 cps/kBq/cc in 3D; (3) the scatter fraction was 15% in 2D and 30% in 3D; (4) the peak true events rate, the true events rate at 50% of the system dead-time and the true events rate when equal to the random events rate were 750 kcps at 189.81 kBq/cc, 744 kcps at 186.48 kBq/cc and 686 kcps at 150.59 kBq/cc, respectively, in 2D, and 922 kcps at 44.03 kBq/cc, 834 kcps at 53.28 kBq/cc and 921 kcps at 44.03 kBq/cc in 3D; (5) the noise equivalent count (NEC) peak rate was 270 kcps at 34.38 kBq/cc in 3D, with random coincidences estimated by delayed events. Using the NEMA N-01 standards the main results were: (1) the average transverse and axial spatial resolution (FWHM) at 1 cm and 10 cm off axis was 6.28 (4.56) mm and 6.88 (6.11) mm in 2D, and 6.29 (5.68) mm and 6.82 (6.05) mm in 3D; (2) the average sensitivity for the two radial positions (r=0 cm and r=10 cm) was 1.93 cps/kBq in 2D and 9.12 cps/kBq in 3D; (3) the scatter fraction was 19% in 2D and 45% in 3D; (4) the NEC peak rate was 54 kcps at 46.99 kBq/cc in 2D and 45.5 kcps at 10.84 kBq/cc in 3D, when random coincidences were estimated by using k=2 in the NEC formula, while the NEC peak rate was 81 kcps at 64.43 kBq/cc and 66 kcps at 14.86 kBq/cc in 2D and 3D, respectively, when random coincidences were estimated by using k=1 in the NEC formula. The new integrated PET-CT system Discovery ST has good overall performances in both 2D and 3D, with in particular a high sensitivity and a very good 3D NEC response.

PET/CT imaging: Effect of respiratory motion on apparent myocardial uptake

“…The PET/CT tomograph used in this study was a GE Discovery ST [9]. The CT device had 16 rows of detectors (pitch 1.375:1, helical thickness 3.75 mm, table speed 68.75 mm/s, with a rotation speed of 2.5 revolutions/s).…”

Primer on molecular imaging technology

“…The standard configuration for a PET detector utilizes inorganic scintillation crystals, which absorb the 511-keV photons and generate a flash of light. Most state-of-the-art PET systems use arrays of discrete scintillation crystals separated by reflectors [5][6][7][8][9][10]. 511-keV photons are highly penetrating and in order to stop them efficiently for good photon sensitivity, the array crystals must have high atomic number (Z) and density and be relatively thick (long).…”

“…For example, suppose a 370-MBq (10-mCi) radionuclide dose is injected into a subject that attenuates (absorbs) photons by an average factor of 10 and the subject is placed in a PET system with 100 detector modules providing a total of 1% coincidence photon detection efficiency (photon sensitivity). Then the average photon event rate per detector module is roughly 3.7×10 8 (radionuclide decays per second)×2(photons per event)×0.1(photon attenuation factor)×0.01(sensitivity)÷100(photon detector modules)= 3,700 counts per second. If each system detector module required 1 ms of processing time per event, there could be significant pile up of events.…”

18F-FDG PET/CT for the Prediction and Detection of Local Recurrence After Radiofrequency Ablation of Malignant Lung Lesions

“…During the uptake period, patients rested quietly in the injection room. All PET/CT studies were acquired on combined PET/CT tomographs, either Biograph (Siemens Medical Solutions, Inc.) (20), Discovery LS (GE Healthcare) (21), Discovery ST (GE Healthcare) (22), or Discovery STE (GE Healthcare) (23). After the topogram (scout view), a low-dose CT scan was obtained from the skull base to the inguinal region.…”