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A new combined lutetium oxyorthosilicate (LSO) PET/CT scanner with an extended axial field-of-view (FOV) of 21.8 cm has been developed (Biograph TruePoint PET/CT with TrueV; Siemens Molecular Imaging) and introduced into clinical practice. The scanner includes the recently announced point spread function (PSF) reconstruction algorithm. The PET components incorporate four rings of 48 detector blocks, 5.4 cm x 5.4 cm in cross-section. Each block comprises a 13 x 13 matrix of 4 x 4 x 20 [mm.sup.3] elements. Data are acquired with a 4.5 ns coincidence time window and an energy window of 425-650 keV. The physical performance of the new scanner has been evaluated according to the recently revised National Electrical Manufacturers Association (NEMA) NU 2-2007 standard and the results have been compared with a previous PET/CT design that incorporates three rings of block detectors with an axial coverage of 16.2 cm (Biograph TruePoint PET/CT; Siemens Molecular Imaging). In addition to the phantom measurements, patient Noise Equivalent Count Rates (NECRs) have been estimated for a range of patients with different body weights (42-154 kg). The average spatial resolution is the same for both scanners: 4.4 mm (FWHM) and 5.0 mm (FWHM) at 1 cm and 10 cm respectively from the center of the transverse FOV. The scatter fractions of the Biograph TruePoint and Biograph TruePoint TrueV are comparable at 32%. Compared to the three ring design, the system sensitivity and peak NECR with smoothed randoms correction (1R) increase by 82% and 73%, respectively. The increase in sensitivity from the extended axial coverage of the Biograph TruePoint PET/CT with TrueV should allow a decrease in either scan time or injected dose without compromising diagnostic image quality. The contrast improvement with the PSF reconstruction potentially offers enhanced detectability for small lesions. Index Terms--Extended FOV, NEMA measurements, PET/CT, PSF reconstruction.

The combination of PET and SPECT in one device may have clinical and economic advantages. The PET/SPECT camera developed as a joint venture between CPS Innovations, Knoxville, TN, and Siemens Medical Systems, Hoffmann Estates, IL, is a fully 3-D system with 511 keV transmission sources. The detector is based on a NaI-LSO phoswich scintillator. The individual LSO and NaI crystals have a size of 4.3 x 4.3 10 [mm.sup.3]. The 12 x 12 crystal blocks are read out by 2 x 2 in photomultiplier tubes, arranged in a low cost quadrant sharing system. The purpose of this paper is to illustrate phoswich detector setup and to evaluate the detector performance for both modes, PET, and SPECT. The quadrant sharing method and the two crystal layers require special algorithms to find the individual crystal regions and distinguish them from light cross talk caused by adjacent blocks. The base for this procedure is a position profile acquired with a flood source. The mean energy resolution for the NaI(TI) crystal layer was 13.1% (FWHM) at 140 keV and 15.7% (FWHM) at 511 keV for the LSO crystal layer. For the PET setup the average time resolution was 3.4 ns (FWHM). A daily quality check showed a very stable detector condition. Peak shifts due to room temperature changes were very little for both modes and both crystal layers. Index Terms--NaI-LSO detector, PET/SPECT, quadrant-sharing.

Quantitation in Emission Tomography (PET and SPECT) requires that several physical factors are taken into account. Attenuation, which can be determined on SPECT and PET devices, can be corrected using transmission tomography. Here we quantitatively compared the relative performance of transmission scans in SPECT and PET using a calibrated liquid solution with a linear attenuation coefficient ([Mu]) nearly equivalent to that of skeletal cranium bone over the range of energies 50 to 600 keV. We showed that contrast recovery are similar in PET and SPECT for large structures (> 30 mm), but higher in PET as object size decreases.

The influence of the collimator on the contrast recovery of hyperfixation was studied using a dual-headed single photon emission computed tomography (SPECT) system with standard clinical acquisition parameters. Three parallel collimator sets and two fan beam collimator sets were tested with a Jaszczak phantom. The six spheres of the phantom were filled with 99mTc, and four background levels were progressively obtained by adding radioactivity to the cylinder of the phantom, providing four hyperfixation levels. The effects of angular sampling and reconstruction filters have been tested. The statistical analysis was performed with analysis of variance (ANOVA). This study demonstrates the advantage of ultra-high resolution fan beam collimators for contrast recovery of hyperfixation with SPECT when using 64 projections over 360 [degrees], in particular when the contrast is low. We also demonstrate that fan beam collimators permit smaller size hyperfixation detection. Index Terms - Fan beam collimators, hyperfixation detectability, SPECT.

Abstract. Longitudinal positron emission tomography (PET) studies of 6-[sup 18]F-L-dopa uptake in the striatum are used to assess the progression of Parkinson's disease or the survival of neuronal cells grafted in parkinsonian patients. These studies are performed over several years, and data analysis may suffer from the change from old tomographs to new machines with better sensitivity and spatial resolution. Furthermore, such studies on parkinsonian patients may be accomplished in either 2D or 3D acquisition mode. The aforementioned improvements offer great benefits for the study of neurodegenerative diseases, especially those affecting the striatum. However, direct comparison of data is not straightforward owing to variation in scanner characteristics. In this study, we assessed the feasibility of comparing the 6-[sup 18]F-L-dopa striatal uptake values (K[sub c]) measured in two groups of healthy subjects using two tomographs of different generations. We re-studied and compared acquisitions performed on 14 healthy subjects using 6-[sup 18]F-L-dopa. Half of these studies had been performed in 2D acquisition mode using an ECAT 953B. The other half had been performed in 3D acquisition mode using an ECAT EXACT HR+. Different reconstruction protocols were used and the K[sub c] values obtained were statistically compared. The results showed that lowering the transverse spatial resolution of images obtained with the scanner having the better spatial resolution, so that it more closely matched that of the other... [ABSTRACT FROM AUTHOR]