Improving breast cancer detection
A simple technique for looking for breast cancer involves feeling the breasts for an unusual lump which could be a tumour, but this is like feeling for a small marble in a wrapped present. In hospitals, mammography is used to screen for tumours. An X-ray of the breast is taken and specialists look for changes in the density of the tissue. Mammograms can be uncomfortable, because the breast is pressed firmly between two plates to get a good X-ray, and the results are not always conclusive.
Mammogram showing breast cancer
A mammogram showing breast cancer. The arrow on the mammogram points to the cancerous tissue. As a mammogram is a ‘screening tool’, a further biopsy was needed to confirm this was a cancerous mass.
Dr Eli Van Houten and his team at the University of Canterbury are researching different non-invasive methods to detect and diagnose breast cancer that are more accurate and less painful.
Digital image-based elasto-tomography (DIET)
Other researchers have shown that cancerous tissue is stiffer (less elastic) than healthy tissue because it has a denser cell structure, so Eli's team are testing to see if they can detect the stiffer cancer tissue by vibrating breasts very rapidly and looking at the change in motion of reference points on the breast surface.
What is the DIET project?
Dr Eli van Houten at the University of Canterbury talks about the DIET project, which is an exciting new breast cancer screening technique being developed.
The DIET project uses digital cameras to take images at high speed of moving breast tissue. It’s known that cancer tissue is much stiffer, or less elastic, than normal tissue. The idea behind the DIET project is to capture surface data, or surface motion, and use it to determine the internal elasticity of breast tissue.
Eli’s team use cylinders of silicon, which they call ‘phantoms’, as models to test how well surface movement predicts the elasticity of underlying tissues. Some phantoms have stiffer objects inserted in them, to act as tumours. The team puts dots on the outside of the phantoms as reference points to measure for movement.
They vibrate the phantom and use standard digital cameras that are wired up to computers to take photos.
Using surface motion to find stiffness
Dr Ashton Peters from the University of Canterbury talks about how they can use the surface motion of a breast to determine what the internal stiffness is like.
Ashton’s role on the DIET project is to take surface motion information and convert this, using software he has written, into a description of the stiffness within the breast. Hotspots of increased stiffness on the images they produce could point to abnormalities, such as tumours.
Normal digital cameras cannot take pictures quickly enough, so strobe light flashes at the same rate as the silicon model is vibrating. This means that, even though the phantom is moving really fast, the pictures appear still.
About twenty photographs are put together into a slow motion video – the dots on the surface actually move in an elliptical path.
The DIET process
Dr Eli Van Houten from the University of Canterbury describes how the DIET project relies on taking multiple still images of a moving object to get information about the surface and surface motion.
The DIET process involves taking many still images of the surface of a phantom or real breast. They need lots of images because the breasts are moving and they need to not only capture the surface, but the moving surface. This means they need a sequence of images so they can see the change in the surface over time.
The video information is compared to simulated computer models. An image is produced with different colours showing varying stiffness in the phantom. The images of a normal phantom and one with a ‘tumour’ can then be compared and differences can be investigated.
Once the method is refined, Eli and his team will start imaging the surface of breasts with the cameras and look at their motion.
When Eli and his team change from using phantoms to using people, they will have some new challenges. One of the first is trying to model the boundary of the breast tissue and the muscle and ribs in the chest wall. (This is even harder to do in men.) The team also need their computer models to allow for the fact that breasts come in many shapes and sizes, but still be able to indicate possible cancer tissue.
Challenges for the DIET project
Dr Ashton Peters from the University of Canterbury talks about one of the major challenges in imaging breast cancer – the chest wall.
Tumours that are located deep within the breast tissue near the boundary between the breast and the chest have always presented a challenge. These tumours have always been very difficult to detect, using either mammograms or by manual examination. The DIET team hopes that this is where their new method will have an advantage over existing techniques.
This technique can only be used to detect the presence of tumours. Other techniques are needed to diagnose what kind of tumours are there.
Magnetic resonance elastography (MRE)
Where DIET looks at the breast surface, this method looks at movement of tissue inside the breast and is more accurate, rather than inferring from the movement on the breast surface. However, it is expensive – instead of using digital camera imaging, it uses magnetic resonance imaging (MRI) and the equipment needed to do this is far from cheap. One picture costs approximately $4,500, and several are needed to get an accurate diagnosis.
Eli's team wants to provide a more accurate diagnosis of the type and location of the cancer within the breast. They started by building a special container that shakes the silicon gel phantoms in a very regular and precise way. The motion data from the MRI is turned into stiffness data – unhealthy tissue is about 10% stiffer than healthy tissue. The tissue’s varying stiffness can be calculated and made into an image.
Developing medical imaging techniques
Dr Eli Van Houten and Dr Ashton Peters at the University of Canterbury talk about how they’ve gone about developing a new technique to screen for breast cancer.
There are a number of challenges involved in developing new medical imaging techniques. The process usually starts with proving you can do it in theory, using pen and paper or computer simulations, and then it moves to phantom studies. In this case, the phantoms are ‘breasts’ made of silicon. Once they can accurately work out the internal structure of the phantom breasts, which have fake tumours in them, they can then move to imaging real breasts, with the associated challenges of working with real tissue and real people.
Eli’s team is now using this technique on patients with suspected tumours.
Healthy and unhealthy tissue can be very difficult to detect using current medical imaging techniques such as mammography and ultrasound. In an MRI, the different tissue shows up much more clearly. Eli's team is taking this one step further by looking at the movement of the tissue in the MRI – with very promising results.
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Useful link
The University of Waikato's Yifan Chen is investigating the use of microwave signals, similar to a mobile phone, to detect breast cancer. Read more in this New Zealand Herald news article .
