Hardness and density distributions of pharmaceutical tablets measured by terahertz pulsed imaging

Robert K. May, Ke Su, Lianghao Han, Shuncong Zhong, James A. Elliott, Lynn F. Gladden, Mike Evans, Yaochun Shen, J. Axel Zeitler

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We present terahertz pulsed imaging (TPI) as a novel tool to quantify the hardness and surface density distribution of pharmaceutical tablets. Good agreement between the surface refractive index (SRI) measured by TPI and the crushing force measured from diametral compression tests was found using a set of tablets that were compacted at various compression forces. We also found a strong correlation between TPI results and tablet bulk density, and how these relate to tablet hardness. Numerical simulations of tablet surface density distribution by finite element analysis exhibit excellent agreement with the TPI measured SRI maps. These results show that TPI has an advantage over traditional diametral compression and is more suitable for nondestructive hardness and density distribution monitoring and control of pharmaceutical manufacturing processes.
Original languageEnglish
Pages (from-to)2179-2186
Number of pages8
JournalJournal of Pharmaceutical Sciences
Issue number7
Early online date22 Apr 2013
Publication statusPublished - Jul 2013
Externally publishedYes


  • mechanical properties
  • compaction
  • tableting
  • imaging methods
  • processing
  • terahertz pulsed imaging (TPI)
  • tablet hardness testing
  • density distribution
  • finite element analysis (FEA)
  • diametral compression test (DCT)

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