DOCTORS will soon be able to spot cancers in parts of the body where other imaging methods have failed. The technique, which uses a type of radiation known as T-rays, has just been tested on humans for the first time, with striking results.
T-rays penetrate a few millimetres of the skin, a region that other techniques cannot 鈥渟ee鈥�. Optical imaging reveals mainly surface features, while X-rays and MRI scans show deeper tissue. And because T-rays are not ionising, they do not carry the same health risks as X-rays.
Terahertz radiation, as T-rays are properly known, has a frequency between infrared and radio waves and is generated by firing a laser at a semiconductor crystal (see Graphic). Until this method was developed by a team at the Toshiba Cambridge Research Laboratory there was no efficient way of producing the rays.
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Hopes that T-rays could be used to detect cancer were raised by experiments carried out in tissue samples by a company called TeraView, also based in Cambridge (快猫短视频, 14 September 2002, p 34). The company is now presenting the first T-ray images from humans. They reveal the extent of skin cancers beneath the surface, something that cannot otherwise be seen until the tissue is removed.
Medical physicists at TeraView took images from 10 patients at the nearby Addenbrooke鈥檚 Hospital who were about to have skin cancers surgically removed. After surgery, the cells were analysed to see which ones were cancerous, and the information compared with the T-ray images. In every case, the area that showed positive in the images exactly matched the region that was found to be cancerous.
The team is not sure why cancer looks different from healthy tissue when exposed to T-rays. One possible explanation is that cancerous regions contain more fluid because the tumour sucks in nutrients as it grows. Since T-rays are absorbed strongly by water, the tumour appears darker.
Whatever the explanation, the data confirms that T-ray imaging could give valuable information to surgeons before they operate. 鈥淲e want to provide them with a tool so that when they cut this thing out, they know they are getting the whole of the tumour,鈥� says Tony Fitzgerald, a medical physicist with TeraView.
Fitzgerald will unveil the results at the World Congress on Medical Physics and Biomedical Engineering in Sydney, Australia, this week. He will also announce the first pre-clinical trial of the technology at St Thomas鈥� Hospital in London, to start later this year. The trial will collect data from around 50 patients to see if the technique is sensitive enough for surgeons to start using.
Although the first application of T-rays will be to image skin cancers such as basal cell carcinomas and melanomas, Fitzgerald points out that around 85 per cent of cancers occur in the surface layers of organs, including the skin, colon and oesophagus. TeraView hopes to develop a probe that can be used inside the body, to scan for even more kinds of cancer.
T-rays could also be used for real-time imaging during surgery, to highlight tumour cells the surgeon has missed. At the moment, patients face a recurrence of the disease and further surgery if any of the cancer cells are overlooked, so surgeons often remove more tissue than necessary.
Cancer specialist Lynda Bobrow, who examines excised breast tissue at Addenbrooke鈥檚, is working with TeraView on this application. 鈥淚t鈥檚 early days,鈥� she says, 鈥淏ut it looks very promising.鈥�