Imaging technology is becoming increasingly prevalent in our society. X-ray scanners are routinely used to examine luggage at airports, for example, and most hospitals are equipped with ultrasound scanners and magnetic resonance imaging machines. There is also a wealth of other less well known applications throughout industry. For instance, X-rays are used for package inspection, while the defects or voids in materials on production lines are often probed using microwaves or ultrasound.
In spite of their considerable success, X-rays, magnetic resonance imaging and ultrasound all have shortcomings. Many clinicians and non-medical users feel that fundamentally different physical principles are needed to provide safer and more cost-effective imaging techniques. And physicists are turning to other regions of the electromagnetic spectrum to address these issues.
Indeed, a cursory examination reveals that conventional imaging techniques only use the extreme ends of the electromagnetic spectrum: photons with energies greater than 30 keV for X-rays, and around 0.4 µeV for magnetic resonance imaging. The radiation between these extremes falls largely into the visible, infrared and millimetre or microwave regions.
In the April issue of Physics World magazine, Don Arnone, Craig Ciesla and Michael Pepper at Toshiba Research Europe, Cambridge, UK, describe the advantages of Terahertz imaging.