Norwegian and French scientists are assessing a completely new way to detect cancer by measuring the elasticity of tumors. Called elastography, in a few years, the new modality may be as common as X-ray imaging.
“Elastography gives oncologists yet another method for detecting tumors. Elastography may be especially suitable for determining how serious the illness is,” remarked radiologist and clinical consultant Dr. Per Kristian Hol at the Intervention Center at Oslo University Hospital, Rikshospitalet (Norway).
To detect cancer, determine how the cancer is developing and how lethal it is, hospitals must frequently employ large and costly methods such as X-rays, magnetic resonance imaging (MRI), positron emission tomography (PET) or computed tomography (CT). Some of these modalities use a lot of radiation and others are very expensive to run.
Every year, it is estimated by experts in Norway that nearly 100 Norwegians get cancer from X-ray radiation. This is what radiologist Dr. Lars Borgen found in his dissertation in clinical medicine in 2012. The radiation from a round in a CT machine is 10 times higher than the average background radiation during an entire year, according to particle physicist Dr. Erlend Bolle. For PET scans, the patient is injected with radioactive tracers. “We want the best possible diagnostics with the least possible radiation. Elastography is completely safe,” said Dr. Hol.
Elastography can be combined with either MRI or ultrasound. MR machines are expensive. “Ultrasound is cheap, but the result depends a lot on how good the ultrasound examination is. In the future, we envision that elastography will be performed at a regular doctor’s office,” said Dr. Hol.
The University Hospital is now planning to test the method on patients. “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 tumors, such as cancer of the liver,” said Dr. Anne Cathrine T. Martinsen, who is the section manager of diagnostic physics at the Intervention Centre and associate professor in the department of physics at the University of Oslo.
Tumors do not have the same elasticity as healthy tissue. Elasticity is related to the density of blood vessels. Tumors have more blood vessels than healthy tissue. Malignant tumors typically have even more blood vessels and a greater blood flow than benign tumors. Different tumors at different stages of the development of the cancer have different elasticity. Tumors may be less or more elastic than healthy tissue. Some tumors may metastasize, whereas others do not. According to the research, the investigators can get a completely new map of organs and tumors by measuring elasticity.
The examination is simple. The clinician positions a vibrator on the location that is to be examined. The vibrator has a pulse of up to 200 oscillations per second. The pressure wave from the vibrator goes through the organ. This allows doctors to study the elasticity of the healthy and diseased parts.
Researchers from the Hôpital Beaujon University Hospital (Paris, France) are now evaluating elastography on patients with liver fibrosis, a disorder in which the liver has become stiff caused by alcohol damage or hepatitis. The Intervention Centre in Oslo is now planning to test the method on Norwegian patients with liver fibrosis. The method can replace biopsy. This means that patients do not have to have a needle inserted into their liver.
In the last four years, Prof. Sverre Holm in the department of informatics at the University of Oslo, has collaborated closely with the French researchers. Prof. Holm has researched ultrasound for 20 years and is also adjunct professor in the department of circulation and medical imaging at the Norwegian University of Science and Technology.
Ultrasound creates two types of waves. The most common type is pressure waves. Pressure waves go down into the tissue. The other waves are created by the radiation pressure from pressure waves and run horizontally and are called shear waves. Whereas pressure waves are mostly affected by fluids, the shear waves capture the characteristics of the other 30% of the body that does not consist of water. Until now, it has not been possible to measure shear waves. “We study how the shear waves behave in the tissue, and look at viscosity [studies how liquid the fluid is], attenuation, and velocity,” said Dr. Holm.
The pressure wave has a speed of 1,500 meters per second. The shear wave has a speed of 1-10 meters per 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,” stated postdoctoral fellow Peter Näsholm, from the department of informatics.
If the frequency changes, the speed of the waves will change. It appears that the more dangerous a tumor is, the higher is the speed of the waves. A large calculation capacity is required to interpret these waves. The mathematics, however, is quite complicated.
French researchers believe that in the future, elastography may replace mammography. Mammography employs X-rays to image breasts and any dose of radiation is undesirable. “Elastography can be an important supplementary examination in the diagnosis of breast cancer. Large clinical trials will be carried out in the near future to see if we can replace mammography with elastography,” said Prof. Mickael Tanter at ESPCI, the Technical University College for Industrial Physics and Chemistry (Paris, France), which is behind the technology used by the French ultrasound company Supersonic Image.
The Intervention Center in Oslo is less certain, however, than the French professor. “If elastography is to replace breast cancer screening, it must be able to see smaller tumors and to see the tumors better than it does currently. In mammography, it is difficult to detect small tumors. There is hope that elastography can also be used to see small tumors, but there is still quite a way to go,” remarked radiologist Per Kristian Hol.
Oslo University Hospital, Rikshospitalet
ESPCI, the Technical University College for Industrial Physics and Chemistry