title: Critical factors in the measurement of tablet film coatings using terahertz pulsed imaging.
abstract: The present work gives an insight into some key measurement and signal processing considerations in terahertz pulsed imaging (TPI). TPI is increasingly used for the measurement of the spatial variation of coating thickness on coated solid dosage forms. The potential of TPI for the assessment of coating thickness distributions and the use in process development is described in recent literature. However, some critical factors need to be taken into account when working with this technique. These are (1) the signal processing of the raw data, (2) the influence of the composition of the sample matrix on the TPI signals and subsequent coating analysis, (3) signal distortions that can occur at tablet edges or areas with defects, and (4) the refractive index as a key parameter in the quantification of layer thickness. In this paper, we will highlight to what extent these factors impact on the qualitative and quantitative analysis of TPI data and how artifacts and misinterpretation of data can be avoided to ensure fully quantitative and robust measurements.
authors.affiliation: Institute of Pharmaceutics and Biopharmaceutics, Heinrich-Heine-University, Düsseldorf 40225, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Brock
authors.affiliation: Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB2 3RA, UK.
authors.forename: J Axel
authors.initials: JA
authors.lastname: Zeitler
authors.affiliation: Global Chemical and Pharmaceutical Development, Bayer Pharma AG, Berlin 13353, Germany.
authors.forename: Adrian
authors.initials: A
authors.lastname: Funke
authors.affiliation: Institute of Pharmaceutics and Biopharmaceutics, Heinrich-Heine-University, Düsseldorf 40225, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Knop
authors.affiliation: Institute of Pharmaceutics and Biopharmaceutics, Heinrich-Heine-University, Düsseldorf 40225, Germany. Electronic address: kleinebudde@hhu.de.
authors.forename: Peter
authors.initials: P
authors.lastname: Kleinebudde
mesh_terms: D003460:Crystallization; D010316:Particle Size; D012031:Refractometry; D013608:Tablets, Enteric-Coated / Q000737:chemistry*; D055069:Terahertz Imaging / Q000379:methods*
chemical_list: D013608:Tablets, Enteric-Coated