From New Scientist, 12 June 1999
by Rob Edwards
ULTRASOUND SCANS can stop cells from dividing and make them commit suicide.
A research team in Ireland say this is the first evidence that routine scans, which have let doctors peek at fetuses and internal organs for the past 40 years, affect the normal cell cycle.
A team led by Patrick Brennan of University College Dublin gave 12 mice an 8-megahertz scan lasting for 15 minutes. Hospital scans, which reflect inaudible sound waves off soft tissue to produce images on a monitor, use frequencies of between 3 and 10 megahertz and can last for up to an hour
The researchers detected two significant changes in the cells of the small intestine in scanned mice compared to the mice that hadn't been scanned. Four and a half hours after exposure, there was a 22 per cent reduction in the rate of cell division, while the rate of programmed cell death or "apoptosis" had approximately doubled.
Brennan believes there will be similar effects in humans. "It has been assumed for a long time that ultrasound has no effect on cells," he says. "We now have grounds to question that assumption."
Brennan stresses, however, that the implications for human health are uncertain. "There are changes happening, but we couldn't say whether they are harmful or harmless," he explains. The intestine is a very adaptable organ that can compensate for alterations in the cell cycle, says Brennan.
It is possible that the sound waves damage the DNA in cells, delaying cell division and repair. Brennan suggests that ultrasound might be switching on the p53 gene which controls cell deaths. This gene, dubbed "the guardian of the genome", produces a protein that helps cells recognise DNA damage and then either self-destruct or stop dividing.
Studies in the early 1990s by researchers at the University of Rochester in New York and the Batelle Pacific Northwest Laboratories in Richland, Washington, showed that tissue heating due to ultrasound can cause bleeding in mouse intestines. Ultrasonographers now tune the power of scans to reduce such heating.
But Brennan's work is the first evidence that scans create changes in cells. "Our results are preliminary and need further investigation," he says. The team presented their results at the Radiology 1999 conference in Birmingham last month and are now preparing them for submission to a peer-reviewed journal.
Alex Elliott, a researcher in clinical physics at the University of Glasgow, thinks that Brennan's results are important and should be followed with further studies. "If the conditions of his experiments really compare to the clinical use of ultrasound," he says, "we may have to review the current safety limits."
