The Inveon small-animal PET scanner is characterized by a large, 127-mm axial length and a 161-mm crystal ring diameter. The associated high sensitivity is obtained by using all lines of response (LORs) up to the maximum ring difference (MRD) of 79, for which the most oblique LORs form acceptance angles of 38.3°with transaxial planes. The result is 2 phenomena that are normally not encountered in PET scanners: a parallax or depth-of-interaction effect in the axial direction and the breakdown of Fourier rebinning (FORE). Both effects cause a deterioration of axial spatial resolution. Limiting the MRD to smaller values reduces this axial blurring at the cost of sensitivity. Alternatively, 3-dimensional (3D) reconstruction techniques can be used in which the rebinning step is absent. The aim of this study was to experimentally determine the spatial resolution and sensitivity of the Inveon for its whole field of view (FOV). Methods: Spatial resolution and sensitivity were measured using filtered backprojection (FBP) with FORE, FBP with LOR angle-weighted adapted FORE (AFORE), and 3D ordered-subset expectation maximization followed by maximum a posteriori reconstruction (OSEM3D/ MAP). Results: Tangential and radial full width at half maximum (FWHM) showed almost no dependence on the MRD using FORE and FBP. Tangential FWHMs were 1.5 mm in the center of the FOV (CFOV) and 1.8 mm at the edge of the FOV (EFOV). Radial FWHMs were 1.5 and 3.0 mm in the CFOV and EFOV, respectively. In contrast, axial FWHMs increased with the MRD and ranged between 1.1 and 2.0 mm in the CFOV and between 1.5 and 2.7 mm in the EFOV for a MRD between 1 and 79. AFORE improved the axial resolution for a large part of the FOV, but image noise increased. OSEM3D/MAP yielded uniform spatial resolution in all directions, with an average FWHM of 1.65 6 0.06 mm. Sensitivity in the CFOV for the default energy and coincidence time window was 0.068; peak sensitivity was 0.111. Conclusion: The Inveon showed high spatial resolution and high sensitivity, both of which can be maintained using OSEM3D/MAP reconstruction instead of rebinning and 2D algorithms. The Inveon (Siemens) small-animal PET scanner differs from its predecessor, the microPET Focus 120 (F120; Siemens), by its larger lutetium orthosilicate (LSO) detector blocks, improved processing of high-speed events (1-4), and shorter, tapered light guides coupling the detector blocks to the photomultiplier tubes (5). The Inveon contains 4 rings of 16 blocks-20 · 20 detectors of 1.5 · 1.5 mm each, resulting in an axial length of 127 mm. The F120 consists of 4 rings of 24 blocks-12 · 12 detectors of the same size, leading to an axial length of 76 mm. Table 1 compares the geometric properties of the Inveon with several other commercial crystal-based small-animal PET scanners.The main advantage of the larger axial field of view (FOV) of the Inveon is the higher detection efficiency (or sensitivity), with a peak value as specified by the manufacturer of greater than 0.1 in the center of the FOV (CFOV) for the ...

The positron emitters 18 F, 68 Ga, 124 I, and 89 Zr are all relevant in small-animal PET. Each of these radionuclides has different positron energies and ranges and a different fraction of single photons emitted. Average positron ranges larger than the intrinsic spatial resolution of the scanner (for 124 I and 68 Ga) will deteriorate the effective spatial resolution and activity recovery coefficient (RC) for small lesions or phantom structures. The presence of single photons (for 124 I and 89 Zr) could increase image noise and spillover ratios (SORs). Methods: Image noise, expressed as percentage SD in a uniform region (%SD), RC, and SOR (in air and water) were determined using the NEMA NU 4 smallanimal image-quality phantom filled with 3.7 MBq of total activity of 18 F, 68 Ga, 124 I, or 89 Zr. Filtered backprojection (FBP), orderedsubset expectation maximization in 2 dimensions, and maximum a posteriori (MAP) reconstructions were compared. In addition to the NEMA NU 4 image-quality parameters, spatial resolutions were determined using small glass capillaries filled with these radionuclides in a water environment. Results: The %SD for 18 F, 68 Ga, 124 I, and 89 Zr using FBP was 6.27, 6.40, 6.74, and 5.83, respectively. The respective RCs were 0.21, 0.11, 0.12, and 0.19 for the 1-mm-diameter rod and 0.97, 0.65, 0.64, and 0.88 for the 5-mm-diameter rod. SORs in air were 0.01, 0.03, 0.04, and 0.01, respectively, and in water 0.02, 0.10, 0.13, and 0.02. Other reconstruction algorithms gave similar differences between the radionuclides. MAP produced the highest RCs. For the glass capillaries using FBP, the full widths at half maximum for 18 F, 68 Ga, 124 I, and 89 Zr were 1.81, 2.46, 2.38, and 1.99 mm, respectively. The corresponding full widths at tenth maximum were 3.57, 6.52, 5.87, and 4.01 mm. Conclusion: With the intrinsic spatial resolution (1.5 mm) of this latestgeneration small-animal PET scanner, the finite positron range has become the limiting factor for the overall spatial resolution and activity recovery in small structures imaged with 124 I and 68 Ga. The presence of single photons had only a limited effect on the image noise. MAP, as compared with the other reconstruction algorithms, increased RC and decreased %SD and SOR.

F-FDG for detecting tumors using a pretargeting procedure. Mice were implanted with carcinoembryonic antigen (CEA; CEACAM5)-expressing LS174T human colonic tumors and a CEA-negative tumor, or an inflammation was induced in thigh muscle. A bispecific monoclonal anti-CEA × anti-hapten antibody was given to mice, and 16 hours later, 5 MBq of 68 Ga-or 18 F-labeled hapten peptides were administered intravenously. Within 1 hour, tissues showed high and specific targeting of 68 Ga-IMP-288, with 10.7 ± 3.6% ID/g uptake in the tumor and very low uptake in normal tissues (e.g., tumor-to-blood ratio of 69.9 ± 32.3), in a CEA-negative tumor (0.35 ± 0.35% ID/g), and inflamed muscle (0.72 ± 0.20% ID/g). 18 F-FDG localized efficiently in the tumor (7.42 ± 0.20% ID/g) but also in the inflamed muscle (4.07 ± 1.13% ID/g) and in several normal tissues; thus, pretargeted 68 Ga-IMP-288 provided better specificity and sensitivity.Positron emission tomography (PET)/computed tomography images reinforced the improved specificity of the pretargeting method.18