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Since 1994, PET - and later PET-CT - have gained significant clinical importance. Since 2002, PET-CT systems (PET + multislice CT) are available. The combination of high sensitivity PET images fused with high resolution CT images has gained widespread clinical acceptance for diagnosis, staging and re-staging as well as prediction of response to chemotherapy in oncology. Besides oncology, there are clear indications in diseases of the heart and the brain. The development of new systems in mainly based on multislice CT (64 slice). Radiopharmacology is advancing quickly, especially in the fields of oncology and neurological disorders. However, the limited reimbursement in Germany hampers this development.

Unlabelled: The National Electrical Manufacturers Association (NEMA) NU 2-2001 performance measurements were conducted on the Discovery RX, a whole-body PET/CT system under development by GE Healthcare. The PET scanner uses 4.2 x 6.3 x 30 mm lutetium yttrium orthosilicate (LYSO) crystals grouped in 9 x 6 blocks. There are 24 rings with 630 crystals per ring and the ring diameter is 88.6 cm. The transaxial and axial fields of view are 70.0 and 15.7 cm, respectively. The scanner has retractable septa and can operate in both 2-dimensional (2D) and 3-dimensional (3D) modes. 2D acquisitions use ring differences of +/-4 for direct and +/-5 for cross slices; 3D acquisitions use a ring difference of 23. The coincident window width is 6.5 ns and the energy window is 425-650 keV. Other than the detectors, the system uses the same hardware and software as a Discovery ST. The CT scanner is a 16-slice LightSpeed; the performance characteristics of the CT component are not included herein., Methods: Performance measurements of sensitivity, spatial resolution, image quality, scatter fraction and counting rate performance, and image quality were obtained using NEMA methodology., Results: The system sensitivity in 2D and 3D was measured as 1.7 cps/kBq and 7.3 cps/kBq, respectively. The transaxial resolution for 2D (3D) was 5.1 mm full width at half maximum (FWHM) (5.0 mm) at 1 cm from gantry center and the radial and tangential resolutions were 5.9 mm (5.9 mm) and 5.1 mm (5.2 mm) at 10 cm, respectively. The axial resolution for 2D (3D) was 4.8 mm FWHM (5.8 mm) and 6.3 mm (6.5 mm) at 1 cm and 10 cm from gantry center, respectively. The scatter fraction was 13.1% and 31.8% in 2D and 3D. The peak noise equivalent count rate (NECR) was 155 kcps at 92.1 kBq/mL in 2D and 117.7 kcps at 21.7 kBq/mL in 3D for a noise-free estimation of randoms. The contrast of the 22, 17, 13, and 10 mm hot spheres in the image quality phantom in 2D (3D) were 74.6% (72.4%), 56.7% (59.5%), 46.2% (44.6%), and 17.9% (18.0%), respectively., Conclusion: The Discovery RX is a scanner that possesses high NECR, low scatter fraction, and good spatial resolution characteristics.

Unlabelled: This study evaluates the 2-dimensional (2D) and 3-dimensional (3D) performance characteristics of a newly developed PET/CT scanner using the National Electrical Manufacturers Association (NEMA) NU 2-1994 (NU94) and NEMA NU 2-2001 (NU01) standards. The PET detector array consists of 10,080 individual bismuth germanate crystals arranged in 24 rings of 420 crystals each. The size of each crystal is 6.3 x 6.3 x 30 mm in the axial, transaxial, and radial dimensions, respectively. The PET detector ring diameter is 88.6 cm with axial and transaxial fields of view (FOVs) of 15.7 and 70 cm, respectively. The scanner has a uniform patient port of 70 cm throughout the PET and CT FOV, and the PET scanner is equipped with retractable septa to allow 2D and 3D imaging., Methods: Spatial resolution, scatter fraction, sensitivity, counting rate, image quality, and accuracy as defined by the NEMA protocols of NU94 and NU01 for 2D and 3D modes are evaluated. The 2D mode data were acquired with a maximum ring difference of 5, whereas the 3D mode acquisition used ring differences of 23. Both 2D and 3D mode data were acquired with an energy window of 375-650 keV. Random estimation from singles counting rate was applied to all relevant analysis. In addition, images from 2 clinical whole-body oncology studies acquired in 2D and 3D modes are shown to demonstrate the image quality obtained from this scanner., Results: The 2D NU94 transaxial resolution is 6.1-mm full width at half maximum (FWHM) 1 cm off center and increases to 6.9 mm tangential and 8.1 mm radial at a radius (R) of 20 cm. NU01 2D average transaxial (axial) FWHM resolution measured 6.1 (5.2) mm at R = 1 cm and 6.7 (6.1) mm at R = 10 cm. The NU94 scatter fraction for 2D (3D) was 13% (29%), whereas the NU01 scatter fraction gave 19% (45%). NU01 peak 2D (3D) noise equivalent counting rate (T(2)/[T + R + S]) was 90.2 (67.8) kilocount per second (kcps) at 52.5 (12) kBq/mL. Total 2D (3D) system sensitivity for true events is 8 (32.9) kcps/kBq/mL for NU94 and 1.95 (9.2) kcps/Bq for NU01., Conclusion: The results show excellent system sensitivity with relatively uniform resolution throughout the FOV, making this scanner highly suitable for whole-body studies.

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.