The terahertz (THz) region of the electromagnetic (EM) spectrum has several advantages for skin cancer detection, dental imaging, and pharmaceutical applications. Continuous wave (CW) and pulsed THz transmission-mode and reflection-mode imaging with non-ionizing and noninvasive properties for tooth imaging are considered an alternative modality to X-ray imaging. Dental imaging application of THz imaging exploits the change in the refractive index between dental caries and enamel and/or dentine tissues. Dental caries or tooth decay is the most common human disease, and there is currently no sensitive or accurate means for detecting it using X-rays in its early stages, when tissue damage can be minimized or even reversed. The shortfalls of existing clinical tools are compounded by the fact that some dentists do not regularly assess patients for caries with X-rays owing to fears associated with exposure to ionizing radiation. One needs to go the dentist every six month to reduce exposure to ionizing radiation.These fears are even more serious when it comes to children.
Terahertz rays used for tooth imaging have been in the news for more than a decade. Terahertz rays are a viable option for in vivo imaging of dental carries. Interest in biomedical applications has been increasing since the first introduction of THz pulsed imaging (TPI) in 1995 by Hu and Nuss. Their THz images of porcine tissue demonstrated a contrast between muscle and fats. This initial study promoted later research on the application of THz imaging to other biological samples. THz pulsed imaging actually can be viewed as an extension of the THz-Time domain spectroscopy (TDS) method. T-rays have longer wavelength than X-rays resulting in less scattering when passing through tooth samples.Terahertz imaging offers a non-invasive non-ionising alternative to x-rays and additionally provides higher contrast in clinical diagnosis.
THz imaging involves in vivo imaging of the tooth to examine surface features and employs reflection geometry THz probe used for THz reflection from the outer layer of enamel. Terahertz Pulsed Imaging system is one such system that distinguishes between the different types of tissue in a human tooth; detect caries at an early stage in the enamel layers of human teeth and monitor early erosion of the enamel at the surface of the tooth . Caries are a result of mineral loss from enamel, and this causes a change in refractive index within the enamel. The change in refractive index means that small lesions, smaller than those detected by the naked eye, can be detected.