Table 2. Advantages and limitations/drawbacks of THz imaging.

Advantages	Drawbacks/limitations
Non-ionising radiation; is considered safe for biological imaging.	Limited penetration depth and THz waves cannot penetrate into the human body due to high water component.
Sensitive to water component. Biological molecules' characteristic energies lie in the THz region (the energy of vibrational and rotational molecules correspond to that of the THz photons).	Difficulties in the development of appropriate THz sources • Measuring speeds and scanning times require improvement. • Bulky systems due to their components, like the use of fs lasers. • System costs are relatively high (mainly due to the use of fs lasers). • Problems in transferring THz waves and difficulties in achieving distance sensing in air over several metres. • Need to improving systems with a large signal-to-noise ratio. • Some THz sources cannot be used at room temperature.
It can perform non-destructive testing and contact-free imaging or characterisation of the sample.
Compared with microwaves, THz waves possess shorter wavelength and consequently greater spatial resolution can be achieved.
The long wavelength of the THz photons enables the THz radiation to penetrate many materials.
THz radiation is not heavily affected by Rayleiyh scattering.	Limited imaging resolution due to long wavelength.
Fills the ‘gap’ in medical imaging modalities.	Applications still in research.
Can perform spectroscopy. Medical imaging can be combined with spectroscopy information. Biochemical and morphological features can be provided simultaneously.	Low contrast between healthy and pathological tissues.