Image-Quality Assessment for Several Positron Emitters Using the NEMA NU 4-2008 Standards in the Siemens Inveon Small-Animal PET Scanner

Abstract

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.

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Bone Marrow Stromal Cell Transplantation Enhances Recovery of Local Glucose Metabolism After Cerebral Infarction in Rats: A Serial 18F-FDG PET Study

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Routine Production of 89Zr Using an Automated Module

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