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Thursday, 30 December, 1999, 15:46 GMT
Burn scanners will save skin
By BBC News Online's Damian Carrington
A new technique for assessing serious burns could save many thousands of people from long-term damage and severe pain.
The ultrasound scanner, which has just finished trials in California, enables doctors to make the crucial decision of whether to perform skin grafts or not with much greater accuracy.
In a double-blind trial, which looked at 500 burn sites in 100 patients, the scanner correctly diagnosed serious burns in every case. Doctors inspecting the burns got it right just 65% of the time.
The new device was created by Professor Joie Jones, from the Radiological Sciences Department at the University of California Irvine, working with Professor Bruce Achauer, Chief of the University's Burn Centre.
"The problem is that even when a really well-trained physician looks at a burn patient he only has his vision to make a diagnosis with," says Professor Jones. "What he would really like to find out is whether the capillary layer has been burned."
The capillary layer is where blood is supplied to the skin. If it has been destroyed then the body cannot 'import' the materials needed to repair the skin, and the wound will never heal. In this case a skin graft is essential.
"If the patient doesn't have a graft, the wound will get infections, it could spread and even lead to death," says Professor Jones.
"But grafts are very painful, very expensive and leave a patient hospitalised for months," he adds. So identifying the patients who do not require grafts is just as vital.
Dr Peter Shakespeare, Director of the Laing Laboratory for Burn Injury Investigation at Salisbury District Hospital, UK, says: "Also, grafts are not as good - there are no sweat glands, no hair follicles and it doesn't look as good.
"It's a very important decision for the surgeon to make and technology could add something in this area. Anything that improves the selection of wounds for surgery can be nothing but helpful."
Dr Keith Judkins, Director of the Burn Centre at Pinderfields Hospital, Yorkshire, UK, says: "In determining burn depth, nothing is foolproof, but a relatively easy one to determine is a superficial burn - you press it and the wound blanches as capillaries empty and then refill. Then you know capillaries are OK."
Dr Judkins says that 14,000 people are hospitalised with burn injuries every year in the UK.
Hitting a brick wall
The key to the new ultrasound technique is overcoming the differences in acoustical properties between the transponder that produces the ultrasound, the air and the patient's skin. If this is not done, then most of the energy of the sound waves is lost - "It's like hitting a brick wall," says Professor Jones.
Current ultrasound techniques, for imaging foetuses for example, require the transponder to be pressed against the skin.
For burns patients, says Professor Jones, "this has two major downsides: it's time consuming, but it's also extremely painful and is therefore just not used.
"But there is a trick you can use. You place what's called an acoustical matching layer between the transducer and the air or the body. This acts as a bridge and transfers acoustical energy across the difference.
"We have built one for the transponder-air difference - that's what's unique and clever about what we have done."
This means that ultrasound scanning of burns can be done with an air gap in between.
The plastic layer, which contains tiny air bubbles, is just a few tenths of a millimetre thick, but allows enough energy to pass for a high-resolution scan to be performed.
The scan produces an image of the vital few millimetres of skin from the comfortable distance of a few centimetres away. It should be possible to do this in real time, says Professor Jones, and will not require extensive training for doctors.
Other technologies have been tried before to solve the problem of burn diagnosis, including thermography, light reflectance and laser doppler, but none have been widely taken up.
But Professor Jones says: "In comparison to all other methods, the non-contact ultrasound seems easier to use. It certainly is more accurate and sensitive.
"The optical properties of soft tissue in burns only vary by about 0.5%. So using a laser, for example, will be difficult at best.
"In contrast, the acoustical properties of soft tissue vary over three orders of magnitude. Thus, any ultrasonic method has the sensitivity to detect even subtle changes in soft tissues."
Dr Shakespeare, whilst believing that the new technique is "very interesting", thinks the surgeon's visual skills should not be written off yet: "The surgeon may be less reliable, but he is on the spot and can walk around. He is also already equipped with the finest image analysis software available - the human brain."
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