Terahertz pulsed imaging identifies counterfeit products
Terahertz technology has the advantages of being non ionizing, non destructive, and able to image at depth. The technique's ability to act as both an analytical tool as well as for monitoring or inspection applications has fuelled interest in many markets including security, military, medical, and pharmaceuticals. Though counterfeiting is a key issue facing many industries, provision of pharmaceuticals is one of the few where counterfeit products can lead to serious illness, injury, and potentially death. A recent report by the World Health Organisation has shown that counterfeit medication can account for up to 30% of product sales in some countries. Worse than that, a key route of these fake medicines to the public is via the internet: here, counterfeit product can account for 50% of all medical transactions.
To counter this, we at TeraView have developed Terahertz Pulsed Imaging (TPI™) technology to non-destructively image solid dosage forms in three dimensions. Operating at wavelengths between microwave and infrared, our technology can provide information that is not obtainable at other wavelengths. The system provides information on tablet and coating integrity and structure, and it also has the ability to monitor internal changes, such as moisture ingress, over time: specifically, this means it can detect changes in the polymorphic or hydrate state of a drug substance within a tablet or capsule. Because the method is not destructive, the dosage structure, or changes within it, can give insight in to any variations that are seen in the drug release profile from the tablet or capsules.
The unique spectral and/or structural fingerprints obtained using terahertz imaging are sensitive to small variances in a product, and every tablet manufactured has a fingerprint that is specific to its physical structure and chemical composition. The acquired spectra can even show up differences in the manufacturing methods used, even though outwardly the products may look the same. It is this capability that makes TeraView imaging technology useful in counterfeit detection.
How it works
TPI combines refractive index measurements with terahertz spectroscopic measurements to build complete three-dimensional maps of the internal structures of samples in a non destructive manner.1–4 The concept behind it is similar to that of a radar system. The terahertz beam, consisting of a train of pulses, is scanned across the sample (see Figure 1) and reflections are received from various layers or interfaces within. The delay of the reflected pulse across the transient electric field is measured in the time domain, obtaining both the amplitude and phase of the pulse to give depth information within the sample. Multiple return pulses occur wherever there is a refractive index change due to chemical or physical differences (see Figure 2). In some circumstances, the waveforms can then be mathematically transformed to produce an absorption spectrum for the sample to determine its composition and structural features.
Absorptions observed in the terahertz region are commonly associated with the fundamental intermolecular hydrogen bonding vibrations and crystalline-structure lattice vibrations. Although most common organic and inorganic materials are semi-transparent to terahertz frequencies, they usually generate distinctive spectra that enable them to be imaged, identified, and analysed using terahertz light, giving both qualitative and quantitative capability.
