title: A short-scan method for k(3) estimation with moderately reversible PET ligands: application of irreversible model to early-phase PET data.
abstract: Long dynamic scans (60-120 min) are often required for estimating the k(3) value, an index of receptor density, by positron emission tomography (PET). However, the precision of k(3) is usually low in kinetic analyses for reversible PET ligands compared with irreversible ligands. That is largely due to unstable estimation of the dissociation rate constant, k(4). We propose a novel '3P+' method for estimating k(3) of moderately reversible ligands, where a 3-parameter model without k(4) is applied to early-phase PET data to obtain a good model-fit of k(3) estimation. By using [(11)C] Pittsburgh compound B (PIB) (k(4) = 0.018/min) as an example of a moderately reversible ligand, the 3P+ method simulation with a 28 min PET scan yielded less than 3% k(3) relative bias with a +100% k(3) change. In [(11)C]PIB PET scans of 15 normal controls (NC) and nine patients with Alzheimer's disease (AD), the 3P+ method provided a precise k(3) estimate (mean SE of 13.6% in parietal cortex; covariance matrix method). The results revealed linear correlations (r = 0.964) of parietal k(3) values in 24 subjects between 28minute 3P+ method and conventional 90 minute 4-parameter method. A good separation of k(3) between NC and AD groups (P < 0.001; t-test) was replicated in 28 minute 3P+ method. The short-scan 3P+ method may be a practical alternative method for analyzing reversible ligands.
authors.affiliation: Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 260-8555, Japan. ksatok@med.teikyo-u.ac.jp
authors.forename: Koichi
authors.initials: K
authors.lastname: Sato
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Fukushi
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Shinotoh
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Shimada
authors.forename: Noriko
authors.initials: N
authors.lastname: Tanaka
authors.forename: Shigeki
authors.initials: S
authors.lastname: Hirano
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Irie
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000814:Aniline Compounds; D052160:Benzothiazoles / Q000493:pharmacokinetics*; D001921:Brain / Q000378:metabolism*; D002250:Carbon Radioisotopes / Q000493:pharmacokinetics*; D006801:Humans; D008024:Ligands; D008875:Middle Aged; D008954:Models, Biological; D049268:Positron-Emission Tomography / Q000379:methods*; D013844:Thiazoles
chemical_list: C475519:2-(4'-(methylamino)phenyl)-6-hydroxybenzothiazole; D000814:Aniline Compounds; D052160:Benzothiazoles; D002250:Carbon Radioisotopes; D008024:Ligands; D013844:Thiazoles