# Selected Applications of Terahertz Pulses in Medicine and Industry
## 2 Terahertz Imaging and Spectroscopy in Medicine and Biology
Following this proof of principle, in vivo measurements were performed on hospital patients, which clearly showed how the carcinoma increased in extent with increasing distance below the surface of the skin and reflecting the principal location of the basal cells. The advantage of terahertz imaging is shown in Figure 1, which is an example of basal cell carcinoma. A photograph of the skin is on the left and the corresponding terahertz image of the surface is in the centre. By contrast, the image on the right was taken at a depth corresponding to the stratum corneum-epidermis interface. The enhanced spreading of the cancer below the surface is clearly evident. The \"gold standard\" histo-pathology result is shown below the images, which is in agreement with the terahertz image. The field of view is approximately 8 mm square. A further guide to future uses of terahertz imaging is indicated, as the time dependent shape of the terahertz pulse has a positive contrast for basal cell carcinoma compared with normal tissue, where it is negative for inflammation and scar tissue. Many forms of cancer have been investigated by terahertz, such as colonic [9] and oral. Due to its prevalence, breast cancer has received the most attention, where the limited penetration of terahertz prevents use in mammographic screening. However, it has considerable success in the investigation of excised tissue, particularly the margins between healthy and cancerous regions. In this respect, it has an advantage over the \"gold standard\" of histology where analysis can take over a day in marked contrast to  
Figure 1: The above figure, (courtesy of TeraView), illustrates how basal cell carcinoma extends below the surface of skin in a patient. The left shows a photograph of the surface of the skin, a terahertz image of the surface is in the centre and the terahertz image of the stratum corneum–epidermis interface (not visible to the naked eye) shows that the cancer is widespread. See also reference [31]. terahertz, where determination of tissue type and margins can be performed in real time in an operating theatre. This in-theatre use of terahertz has both economic and psychological benefits. Economic benefits stem from the fact that at present, around 20% of patients are recalled for surgery, reflecting the surgeon's desire to conserve as much healthy tissue as possible and resulting in cancerous tissue remaining near the margins. There is a psychological benefit because the recall process for additional procedures, results in patient anxiety and distress and complete removal of the diseased tissue in a single operation has beneficial effects to them. Significantly, the enhanced sensitivity of terahertz imaging [5] was apparent by an image showing the existence of an early case of ductal carcinoma in situ, DCIS, which in the first stages is very difficult to directly observe with X-rays. First, measurements on excised cancerous tissue were sufficiently encouraging to stimulate comprehensive investigations. A detailed investigation of many excised samples of tissue containing breast cancer using a handheld terahertz imager, developed by TeraView, is discussed in references [32; 33]. Different statistical techniques were used, and the results showed good values of sensitivity, specificity and accuracy, SSA; however, the major cause of false positives was the presence of fibrous tissue, which reflected in a similar way to cancerous tissue. When the fibrous samples were excluded, the SSA values rose to over 90%, which was comparable with other diagnostic techniques. Reflections from adipose tissue were quite different from cancer reflections and did not present any particular problems. Pulsed terahertz is used in order to obtain a 3D image. However, CW investigations have revealed a strong frequency dependence of absorption, which has not been investigated in detail.