Will Help Detect Breast Cancer
by Michael Insana*
Most of us think of NDT in terms of engineering materials, however, the scope of potential applications is much broader. This month's article gives insight to an interesting application in the medical field. The article describes how a new technique called elastography using ultrasound and other technologies was developed to provide and NDT solution for detecting tumors in breast tissues.
G.P. Singh
Associate Contributing Editor
A team of researchers is developing a new NDT technology using ultrasound, signal processing, and finite element modeling. The new technology, called elastography, is being developed as a cheaper, faster, and more accurate method for detecting tumors in breast tissue. The technology is of great interest as doctors agree that the majority of deaths from breast cancer can be eliminated by early detection. The current methods to detect breast tumors have drawbacks. Mammograms are expensive and expose patients to radiation, a factor that can actually cause cancer. The physical breast exams, performed either by doctors or women themselves, are subjective and leave room for a large margin of error. Furthermore, this type of exam is not effective in identifying tumors that are not close to the surface of the skin.
The principal investigator, Dr. Jonathan Ophir of the University of Texas Medical School (UTMS) in Houston, leads a team of researchers working to develop techology that will ovecome some of the shortcoming of the current methods. The research team is made up of researchers at UTMS, the University of Kansas Medical Center (KUMC), and Ecole Polytechnique in Montreal. Elastography, a new type of medical imaging, uses ultrasound and other technologies to create an image that describes the elastic properties of certain tissues. The basis of elastography is that the way in which something moves can tell researchers about what type of tissue it is.
Applied to breast cancer, an elastogram gives an image of how a lesion looks when pressure is applied. Malignant tumors are 10 to 100 times stiffer than other breast tissues. The way in which a malignant tumor moves is thus far different from the way a harmless cyst does.
Applied to breast cancer, an elastogram gives an image of how a lesion looks when pressure is applied.
To test the elastography technology, researchers need to create thousands of samples based on varying conditions such as a malignant tumor near the chest cavity or a cyst near glandular tissue. Because it is impossible to find human subjects to meet each criteria the team wants to test, they are using an engineering software developed by Algor, Inc., to run tests on various hypothetical tissue arrangements to see how different types of tissues move when pressure is applied. The software does this by applying mathematical formulas that represent movement in the real world.
Engineering software tests how objects will respond under real world conditions, and engineers typically use it for mechanical and civil engineering problems. For example, it can predict if an engine part will weaken if it is heated too much or how a bridge will react during an earthquake.
For the breast cancer research project, researchers began by tailoring the software to meet their specific needs. It came equipped with data about how metal alloys and other materials respond in various situations; they had to supply data about malignant tumors and other breast tissues. Then it could use this data to tell how, for example, a benign tumor near glandular tissue would move.
To create an elastogram, physicians scan a tissue region with ultrasound twice, once before compressing the tissue and once after. Signal processing then takes over to create and display the image. First, the postcompression data are compressed and expanded (companded) to roughly match the position of ultrasound echoes to those in the precompression data. Second, correlation techniques are used to match the two data sets on a fine scale. Together, the coarse and fine scale motion detectors estimate how far each point in the tissue has moved - its displacement. (Sonar and radar signals are examined in a similar way to find the range, bearing, and speed of ships and airplanes.) Finally, the elastogram can be formed. The image is the strain in the tissue, which is found by calculating the rate that displacement changes with respect to position.
The quality of the image depends entirely on the signal processing, which is based on knowing how tissues move when compressed. The elastogram gives a visual image of how various tissues move when compressed, and based on that information, physicians can draw better conclusions about the type of tissue they’re dealing with. However, for this method to be effective, it is essential to test a variety of scenarios, not just those immediately available. Computer modeling makes is possible to create samples which represent the gamut of possible tissue arrangements.
For each hypothetical placement of tissues, the research team creates a computer model of the tissue in its normal state. Next, the computer is told to compress the tissue one percent. The proprietary linear stress analysis software tests this compressed model to see how the tissue moves.
The resulting analysis image indicates if a particular tissue arrangement is difficult to detect, and if that is the case, the researchers perform a real life test using gelatinous materials that imitate the various lesions and breast tissues.
Setting up a lab test takes about a week to create the gelatinous form to the research team’s exact specifications. Besides the higher cost, signal processing done on the gelatinous forms is time consuming. It only takes the software about a half an hour to run an analysis, and real life tests of the gelatinous materials have been in close agreement with the software’s analyses.
Although it may be a few years before elastography is used, researchers are hopeful that it will offer new solutions to providing a cost effective, accurate, and safe method for detecting breast and other types of tumors. Until a cure for breast cancer is found, elastography may provide more effective early detection at a low cost, thereby saving thousands of lives.
Figure 1 - A modeled strain field. Targets, simulating breast lesions at different depths, are placed on the diagonal of a gelatin block. When compressed from above, the vertical strain field is predicted by the software.
Figure 2a
Figure 2b An elastogram of the block is measures (2a) without and (2b) with companding, a noise-reducing process that signal processors use.
Figure 3 - Combining proprietary software with an ultrasound simulator, an elastogram is simulated and found to be very similar to the original measured test.
- * University of Kansas Medical Center, Dept. of Radiology, 3901 Rainbow Blvd., Kansas City, KS 66160; (913) 588-6893; fax (913) 588-7876.
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