Purpose: We tested the impact of different values of the relaxation parameter lambda (λ) on contrast and noise in line-of-response row-action maximum likelihood algorithm (LOR-RAMLA) in 18F-fluorodeoxyglucose positron emission tomography (PET)/computed tomography (CT) imaging.
Methods: Phantom studies were performed on a Gemini XL PET/CT scanner. The NEMA/IEC (National Electrical Manufacturers Association/International Electro technical Commission) torso phantom was used and acquisition data were reconstructed with λ values ranging from 0.025 to 0.1. Quality of the reconstructed images was evaluated by contrast recovery coefficients and background variability values according to the NEMA NU 2-2001 procedures.
Results: Contrast recovery coefficients and background variability increased significantly when λ increased. The best noise-versus-resolution trade-off was obtained with λ in the 0.04–0.06 range. For LOR-RAMLA reconstruction, the manufacturer allows a possible λ choice from 0.025 to 0.1. We would not advise too small (0.025) or too large (0.1) λ values which result in too smooth or too noisy images.
Conclusion: We determined optimal λ values in LOR-RAMLA on a Gemini XL PET/CT scanner. Caution is needed when using λ values out of that range.
aDepartment of Nuclear Medicine, Saint-Louis Hospital
bEAD Imagerie Moléculaire Diagnostique et Ciblage Thérapeutique, IUH, University of Paris VII
cDepartment of Nuclear Medicine, Bichat Hospital, Paris, France
Correspondence to Dr David Groheux, MD, Department of Nuclear Medicine, Saint-Louis Hospital, Assistance publique-Hopitaux de Paris, 1 avenue Claude Vellefaux, 75475 Paris Cedex 10, France
Tel: +33 1 42 49 94 11; fax: +33 1 42 49 94 05; e-mail: firstname.lastname@example.org
Received 6 February 2009 Revised 17 May 2009 Accepted 31 May 2009