Lipophilicity can be used to estimate blood-brain barrier permeability in PET (brain) biomarker development.

"Relationship between lipophilicity and brain extraction of C-11-labeled radiopharmaceuticals" J Nucl Med 1983, 24, 1030-8.

"Halogenated 4-(Phenoxymethyl)piperidines as Potential Radiolabeled Probes for σ-1 Receptors:  In Vivo Evaluation of [123I]-1-(Iodopropen-2-yl)-4-[(4-cyanophenoxy)methyl]piperidine" J Med Chem 1997, 40, 1657-67 and references therein.  (Lipophilicity estimation: LogP 7.5 value is determined by reverse-phase HPLC with non-radioactive 'cold' compounds)

"An admonition when measuring the lipophilicity of radiotracers using counting techniques" Appl Radiat Isot 2001, 54, 203-8.  (also known as, "Pre-washing Shake flask" method; A radiolabeled compound is necessary for the determination of lipophilicity.)

"Determination of lipophilicity and its use as a predictor of blood-brain barrier penetration of molecular imaging agents" Mol Imaging Biol 2003, 5, 376-89. (Review)

Lipophilicity prediction