Positron Emission Tomography of the Liver

Sørensen, Michael; Keiding, Susanne

doi:10.1002/9780470691861.ch5h

Cited by 3 publications

(1 citation statement)

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“…Hyperammonemia is considered a major causative factor because most patients with HE have elevated blood concentrations of ammonia, which in high concentrations is neurotoxic (Cooper and Plum 1987;Jones and Basile 1998;Cooper 2001;Butterworth 2002: Johansen et al 2007Iversen et al 2009). Dynamic 13 N-ammonia PET has been used in humans to assess ammonia metabolism in brain (Lockwood et al 1979(Lockwood et al , 1984(Lockwood et al , 1991Ahl et al 2004;Weissenborn et al 2004;Keiding et al 2006;Sørensen and Keiding 2007a;Sørensen et al 2009;Berding et al 2009), liver (Keiding et al 2001(Keiding et al , 2005Sørensen and Keiding 2007b) and muscle (Nishiguchi et al 2003). The PET procedure encompasses intravenous injection of 13 N-ammonia tracer followed by dynamic measurements of radioactivity concentrations in arterial blood (samples) and tissue (PET camera).…”

Section: Introductionmentioning

confidence: 99%

539 Human 13n-Ammonia Pet Studies: The Importance of Measuring 13n-Ammonia Metabolites in Blood

Sørensen¹,

Keiding²,

Munk³

et al. 2010

Journal of Hepatology

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Section: Introductionmentioning

confidence: 99%

539 Human 13n-Ammonia Pet Studies: The Importance of Measuring 13n-Ammonia Metabolites in Blood

Sørensen¹,

Keiding²,

Munk³

et al. 2010

Journal of Hepatology

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New findings on cerebral ammonia uptake in HE using functional 13N-ammonia PET

Sørensen

Keiding

2007

Metab Brain Dis

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PET is a functional imaging technique suitable for studies of brain ammonia metabolism. Dynamic (13)N-ammonia PET yields time-courses of radioactivity concentrations in brain (PET camera) and blood (samples). Ahl et al. (Hepatology 40:73-79, 2004) and Keiding et al. (Hepatology 43:42-50, 2006) analysed such data in patients with HE by a kinetic model accounting for transfer of (13)N-ammonia across the blood-brain barrier (BBB) and intracellular formation of (13)N-glutamine. Initial unidirectional (13)N-ammonia transfer across BBB was characterized by the permeability-surface area product PS(BBB) (ml blood min(-1) ml(-1) tissue). There was a tendency to lower PS(BBB) values in patients with cirrhosis and HE than in patients with cirrhosis without HE and healthy controls but the differences were not statistically significant. Keiding et al. (Hepatology 43:42-50, 2006) also calculated PS(met) (ml blood min(-1) ml(-1) tissue) as a measure of the combined transfer of (13)N-ammonia across BBB and subsequent intracellular metabolism of (13)N-ammonia; neither did this PS-value show significant difference between the groups of subjects. Net flux of ammonia from blood into intracellular metabolites was linearly correlated to arterial ammonia. In conclusion, basic brain ammonia kinetics was not changed significantly in patients with cirrhosis +/- HE compared to healthy controls. Blood ammonia seems to be the more important factor for increased brain ammonia uptake in HE.

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Human 13N-ammonia PET studies: the importance of measuring 13N-ammonia metabolites in blood

et al. 2010

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Dynamic 13N-ammonia PET is used to assess ammonia metabolism in brain, liver and muscle based on kinetic modeling of metabolic pathways, using arterial blood 13N-ammonia as input function. Rosenspire et al. (1990) introduced a solid phase extraction procedure for fractionation of 13N-content in blood into 13N-ammonia, 13N-urea, 13N-glutamine and 13N-glutamate. Due to a radioactive half-life for 13N of 10 min, the procedure is not suitable for blood samples taken beyond 5–7 min after tracer injection. By modifying Rosenspire’s method, we established a method enabling analysis of up to 10 blood samples in the course of 30 min. The modified procedure was validated by HPLC and by 30-min reproducibility studies in humans examined by duplicate 13N-ammonia injections with a 60-min interval. Blood data from a 13N-ammonia brain PET study (from Keiding et al. 2006) showed: (1) time courses of 13N-ammonia fractions could be described adequately by double exponential functions; (2) metabolic conversion of 13N-ammonia to 13N-metabolites were in the order: healthy subjects > cirrhotic patients without HE > cirrhotic patients with HE; (3) kinetics of initial tracer distribution in tissue can be assessed by using total 13N-concentration in blood as input function, whereas assessment of metabolic processes requires 13N-ammonia measurements.

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Positron Emission Tomography of the Liver

Cited by 3 publications

References 39 publications

539 Human 13n-Ammonia Pet Studies: The Importance of Measuring 13n-Ammonia Metabolites in Blood

539 Human 13n-Ammonia Pet Studies: The Importance of Measuring 13n-Ammonia Metabolites in Blood

New findings on cerebral ammonia uptake in HE using functional 13N-ammonia PET

Human 13N-ammonia PET studies: the importance of measuring 13N-ammonia metabolites in blood

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