Effect of variation in relaxation parameter value on LOR-RAMLA reconstruction of 18F-FDG PET studies.
OBJECTIVE
We tested the impact of different values of the relaxation parameter lambda (lambda) 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 lambda 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 lambda increased. The best noise-versus-resolution trade-off was obtained with lambda in the 0.04-0.06 range. For LOR-RAMLA reconstruction, the manufacturer allows a possible lambda choice from 0.025 to 0.1. We would not advise too small (0.025) or too large (0.1) lambda values which result in too smooth or too noisy images.


CONCLUSIONS
We determined optimal lambda values in LOR-RAMLA on a Gemini XL PET/CT scanner. Caution is needed when using lambda values out of that range.
Groheux
David
D
Department of Nuclear Medicine, Saint-Louis Hospital, University of Paris VII, Paris, France. dgroheux@yahoo.fr
Martineau
Antoine
A
Vrigneaud
Jean-Marc
JM
Hindie
Elif
E
Baillet
Georges
G
Moretti
Jean-Luc
JL
D000465:Algorithms; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D016013:Likelihood Functions; D008175:Lung Neoplasms / Q000000981:diagnostic imaging; D008198:Lymph Nodes / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D011786:Quality Control; D019275:Radiopharmaceuticals
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18