Elastography shows promise for detecting cancers without biopsy
18 February 2013
Researchers from the University of Oslo and Beaujon University
Hospital in Paris are to start clinical trials of a new method for
detecting cancer that measures the elasticity of body tissue.
Elasticity in body tissue is related to the density of blood
vessels. Tumours have more blood vessels than healthy tissue and
malignant tumours usually have even more blood vessels and a greater
blood flow than benign tumours.
"We still don't know a lot about elastography, but the method
looks promising. If elastography is the technique we are hoping for,
this can become an important examination in the future. This would
allow us to use elastography to characterize different types of
tumours, such as cancer of the liver", says Anne Cathrine Martinsen,
Section Manager of Diagnostic Physics at the Intervention Centre and
Associate Professor in the Department of Physics at the University
The examination is simple: the doctor places a vibrator on the
location that is to be examined. The vibrator has a pulse of up to
200 oscillations per second and the pressure wave from the vibrator
goes through the organ. This allows doctors to study the elasticity
of the healthy and diseased parts.
Researchers at the Beaujon University Hospital in Paris are
already testing elastography on patients with liver fibrosis, an
illness in which the liver has become stiff due to hepatitis or
alcohol damage. The Intervention Centre in Oslo is now planning to
test the method on Norwegian patients with liver fibrosis to replace
a biopsy, which means that patients do not have to have a needle
inserted into their liver to take a sample of tissue.
"Elastography-ultrasound is completely different from the current
use of ultrasound. Traditional ultrasound sends out a signal that
returns as an echo. The problem is that it is impossible to
distinguish between malignant and benign tumours with regular
ultrasound," said Professor Sverre Holm of the Department of
Informatics at the University of Oslo, Norway, to the research
Ultrasound creates two types of waves; the most common type is a
pressure wave, which penetrates the tissue. The second type, called
shear wave, is created by the radiation pressure from the pressure
wave and runs horizontally. While pressure waves are mostly affected
by fluids, shear waves capture the characteristics of the other 30%
of the body that does not consist of water.
Shear waves are created when pressure waves are sent to specific
points. From there, the special diagonal energy waves are created.
The trick is to use the regular ultrasound waves to measure the
diagonal energy pulse.
Ultrasound shear waves can be used to measure
elasticity in soft tissue and distinguish between healthy tissue and
tumours, as shown by the colouring.
"We must reconstruct what happens. We must discard all
information from the pressure waves and only retain the information
from the shear waves," said Professor Holm.
The pressure wave has a speed of 1,500 metres a second, while the
shear wave has a speed of one to ten metres a second. "A regular
ultrasound scanner takes a hundred images a second. The speed must
be increased to a thousand images a second in order to capture shear
waves. To manage this speed, we must sacrifice some of the image
quality," said Postdoctoral Fellow Peter Näsholm of the Department
of Informatics at Oslo University.
If the frequency changes, the speed of the waves will change. It
turns out that the more dangerous a tumour is, the the higher the
speed of the waves is. A large calculation capacity is required to
interpret these waves and the mathematics is complicated.
"If elastography is to replace breast cancer screening, it must
be able to see smaller tumours and to see the tumours better than it
does currently. In mammography, it is difficult to detect small
tumours. There is hope that elastography can also be used to see
small tumours, but there is still quite a way to go", notes
radiologist Per Kristian Hol of the Intervention Centre in Oslo.