Tuesday, November 18, 2008

Developments in Terahertz Imaging and its
Applications to Industry

Presented by
Philip F Taday, Ph.D.
Teraview Limited

The exceptional properties of terahertz radiation, such as ability to penetrate most non-polar materials that can be opaque for visible light or low contrast for x-rays and very importantly, low photon non-ionizing energies, make this radiation very attractive tool for aiding understanding of materials and products.

The coating of tablets that are of great importance to both the consumer and the pharmaceutical manufacturer. By controlling the release of the active pharmaceutical ingredient (API) tablet coatings ensure bioavailability, minimize harmful effects and the waste of the drug by delivering it at the specific site and at the optimum level. These functions may be compromised if a coating is non-uniform or has defects.  Until recently, the analysis of coating thickness relied on indirect techniques and it was usually determined by the weight gain of the coated tablet compared to the uncoated tablet core. Near-infrared and Raman spectroscopic and imaging techniques developed in recent years to yield information about the quality and integrity of the coatings are usually restricted to the outer surface of the tablet. In order to test the coating for uniformity or to analyze buried structures or even multiple layers within the tablet, the tablet has to be cut and spectroscopic images to be acquired for each layer. However, in contrast to the near-infrared and mid-infrared regions of the electromagnetic spectrum, many of the excipients used for coating solid dosage forms are transparent or semi-transparent to terahertz radiation. Moreover, terahertz radiation can easily penetrate commonly used coating polymers. This in turn means that, unlike aforementioned techniques, terahertz pulsed imaging non-destructively provides spatially resolved information from below the surface of the tablet. Consequently, terahertz measurements are arguably more suited to monitor key quality attributes of the pharmaceutical solid dosage forms during the manufacturing.

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