Figure 12a: Terahertz imaging. (a) In vivo terahertz image of volunteer's forearm acquired by using a handheld terahertz imaging system. The image shows a 15 x 15-mm region; a scar running from left to right can be seen in the top half of the image. The image was generated by plotting the electric field value reflected from beneath the skin surface. Dark circular regions are hair follicles of normal skin, which are not present at the scar. (b) Axial terahertz image (b scan) of edge of volunteer's hand. Gray scale indicates signal amplitude, which is plotted against optical delay (y-axis) and position across the scanned area (x-axis). Decrease in stratum corneum thickness across the x-axis, from the palm-side (30 mm on x-axis) to the backside (70 mm) of the hand, is evident. (Image courtesy of Vincent Wallace, PhD, TeraView, Cambridge, England)