by John Newell
Former Science Editor, BBC World Service
The world's smallest ultrasound camera has been developed by British doctors and engineers to scan the insides of coronary arteries. It works on the same principle as those used to examine unborn babies but is less than one millimetre in diameter.
The detailed scans provided by the camera will improve the treatment of coronary thromboses. By revealing the exact nature of thickening in the arterial wall the device will help to ensure that the best treatment is given and that ultrasound scans will avoid the need for a lot of unnecessary surgery.
Although it is extremely small, the device contains 64 crystals transducers that convert electric current into vibrations. Each transducer vibrates in turn to produce a beam of soundwaves - vibrations pitched too high for the human ear to hear. These bounce off the walls of the artery and are picked up by the transducers working in reverse, converting the soundwaves into electrical signals that are fed down a fine wire to the outside of the body, where a computer converts them into detailed 3D moving pictures of the inside of the artery.
The space inside the coronary artery is only about three millimetres in diameter. As seen by the ultrasonic eye it looks like the inside of a pipe, a new clean pipe if the person being scanned is young and healthy; a corroded old pipe with lumps of matter sticking to its walls if the artery belongs to someone threatened by heart disease.
The mini ultrasound camera is the brainchild of Dr. Martin Rothman, a consultant cardiologist at the London Hospital and the medical director of Intravascular Research, the British company now making the device. He chose ultrasound rather than light as a means of imaging partly because even the finest fibre-optic cable is too thick to squeeze into the coronary artery, and partly, as Dr. Rothman points out, because sound can "see through" the murky surroundings.
"It can pass through a blood-filled environment and it can also pass through the tissue of the artery wall," he says. "If you use light you have to get rid of the blood and replace it with a clear liquid while you are .taking pictures. And the heart doesn't like that over a long period; it can only stand it for five to ten seconds, whereas with ultrasound you can work inside the blood with no problems for the patient "
X-ray pictures of arteries are taken by injecting a soluble substance that makes the blood opaque to X-rays into the circulation. The whole artery shows up black in the picture and any narrowing is clearly visible, but there is no detail at all of what's inside. Dr. Rob Dickinson, technical director of Intravascular Research, had the job of making Martin Rothman's dreams of what he'd like to see come true.
Dr. Dickinson says, "You can now see the inside of the artery as if you had sliced it in half and were looking at each half. You can see any of the artery's blockages, which of course are the main medical problem, and you can see their extent. And because the ultrasound can slice through the arterial wall you can see the detail actually inside the arterial wall.
"This enables us to tell if the artery is normal or if it has abnormalities such as fatty deposits or if it's hardened with calcium, another common problem. And that tells us how to treat the artery on the spot. We can then put in some other catheters fine flexible tubes that we use to treat the particular problem we've just seen."
The ultrasound camera is inserted into the coronary artery by first inserting a catheter into an artery near the groin and gently pushing and guiding it up till it gets to the entry to a coronary artery. Then a fine wire with the camera on the tip is pushed up inside the catheter and down the artery taking pictures as it goes.
If an artery needs to be opened up in the standard way, then the whole procedure has to be repeated with another catheter carrying a tiny balloon on its tip, which is pushed into a point where the artery is dangerously narrow and then inflated to expand the artery and clear the blockage.
This is called balloon angioplasty and is much the most common treatment for narrowed arteries. Alternatively, a small metal cage may be fitted in the artery to keep its walls apart. Martin Rothman and Rob Dickinson are already working on a Mark 2 version of their device which will carry balloon and cage on the same catheter as the camera, so that as soon as the camera has located and diagnosed the problem the treatment can follow immediately. That is a few years away, but a slightly larger version of the sound camera is already undergoing clinical trials
For more information contact:
Intravascular Research Ltd.
Unit 12, Alice Court, 116 Putney Bridge Road, London, United Kingdom, SW15 2NQ
Tel: +44 181 877 9604 | Fax: +44 181 877 9879