Human (13)N-ammonia PET studies: the importance of measuring (13)N-ammonia metabolites in blood.
Dynamic (13)N-ammonia PET is used to assess ammonia metabolism in brain, liver and muscle based on kinetic modeling of metabolic pathways, using arterial blood (13)N-ammonia as input function. Rosenspire et al. (1990) introduced a solid phase extraction procedure for fractionation of (13)N-content in blood into (13)N-ammonia, (13)N-urea, (13)N-glutamine and (13)N-glutamate. Due to a radioactive half-life for (13)N 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 (13)N-ammonia injections with a 60-min interval. Blood data from a (13)N-ammonia brain PET study (from Keiding et al. 2006) showed: (1) time courses of (13)N-ammonia fractions could be described adequately by double exponential functions; (2) metabolic conversion of (13)N-ammonia to (13)N-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 (13)N-concentration in blood as input function, whereas assessment of metabolic processes requires (13)N-ammonia measurements.
Keiding
Susanne
S
PET Centre, Aarhus University Hospital, Aarhus, 8000, Denmark. susanne@pet.auh.dk
Sørensen
Michael
M
Munk
Ole Lajord
OL
Bender
Dirk
D
D000641:Ammonia / Q000032:analysis* / Q000097:blood*; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism / Q000503:physiopathology; D001923:Brain Chemistry / Q000502:physiology; D002851:Chromatography, High Pressure Liquid; D006501:Hepatic Encephalopathy / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000503:physiopathology; D006801:Humans; D022124:Hyperammonemia / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000503:physiopathology; D007700:Kinetics; D009448:Neurochemistry / Q000379:methods; D009590:Nitrogen Radioisotopes; D049268:Positron-Emission Tomography / Q000379:methods*; D011237:Predictive Value of Tests; D013997:Time Factors
D009590:Nitrogen Radioisotopes; D000641:Ammonia