Holograms — 3-D images created by lasers — have been around for about 30 years. But it is only recently that scientists, including an MU physicist, have started to think about using the technology to photograph live tissues as a way to detect diseases.
Though his work is still in initial laboratory stages, Sunder Balasubramanian, a post-doctoral fellow in the MU Department of Physics and Astronomy, hopes it could lead to one of the first noninvasive methods to screen for skin cancer, the most common form of cancer in the United States.
“In the absence of competing technologies, this would be the only fast, reusable and most importantly noninvasive way for skin cancer screening,” he said.
The technique, known as optical coherence imaging, uses light beams of very low wavelength — instead of tissue-damaging X-rays — and a special kind of semiconductor film to develop the holographic image.
The technique was initially developed in a laboratory at Purdue University, where Balasubramanian did his graduate studies.
Currently, skin cancer screening methods are almost entirely dependent on the visual expertise of dermatologists. If a problem is detected, that initial visual screening is followed by a biopsy, which involves taking a tissue sample and testing it for the presence of disease.
According to the National Cancer Institute, such visual screening can result in false-positive results, where harmless skin conditions are mistaken for cancer. And unnecessary biopsies are costly and can expose patients to new risks of scarring and infection.
The most common rate of suspected melanoma — the most dangerous form of skin cancer — ranges between one and three per 100 people screened. But the rate of confirmed melanoma cases is between one and four per 1,000 people screened.
Given the large gap between diagnoses and detection, Balasubramanian’s work, if successful, could lead to a form of screening that is as objective as a biopsy but relatively inexpensive and not invasive.
How it works
OCI uses light in the far infrared region of the light spectrum. A beam of light is first split into two. One of the resulting beams, known as the reference beam, is allowed to fall directly on the semiconductor film without passing through the object to be imaged.
The other beam, the object beam, is projected on the object, gets reflected and falls on the film. The light reflected off the object produces a complicated pattern of waves that is representative of the shape and size of the object. The reflected beam and the reference beam interfere with each other, producing a complicated interference pattern that represents the detailed structure of the object.
This method can be used to get a detailed structure of the cells of skin tissue. Individual beams can be used to make a detailed point-by-point scan of the skin, giving details of individual cells.
Because cancerous cells form clumps of rapidly multiplying cells, this imaging technique can easily distinguish between cancerous and noncancerous skin. The advantage of using far infrared light is that this light is not absorbed by water in the cells, increasing its accuracy.
An older and related method that uses holograms for imaging live tissue is optical interference tomography (OCT), which unlike OCI does not employ the use of a semiconductor film.
OCT is an established procedure in health imaging, including screening for retinal problems. However, there are limitations with the tomography method that the imaging technique overcomes.
“The depth that you can get with tomography is not as much as with the imaging technique,” Balasubramanian said. “Also, tomography uses complicated algorithms to interpret the results, whereas our technique is a direct imaging technique. The interference is picked up by a camera, and so you have a direct and immediate picture.”
Although various tissue imaging techniques have been developing rapidly, the development of OCI has been limited, because semiconductors have only become available for use as film in the past 10 years, he said.
Balasubramanian is trying to obtain better resolution with this imaging technique in order to produce the most detailed image possible. This is done by moving the object beam through very short distances, while still interfering with the reference beam.
“The reason it is taking so long, is because we have to find the shortest distance that one light beam can be moved, so that it still interferes with the other beam,” he said. “And by moving the beam through very short distance you get better depth.”
Balasubramanian has been able to successfully use the imaging technique in the laboratory with mouse tumors. He is collaborating with researchers in MU’s health sciences department to move the study into its developmental phase.
However, Balasubramanian thinks there are many more detailed studies yet to be done with imaging real tumors, before the technique can become available to the public.
“As a doctor you’re not looking at probability, you want certainty when it comes to using the technique on real people,” he said. “I think we are looking at another 10 to 15 years.”
Searching for cancer
While OCI remains in development, cancer patients continue to rely on visual screening methods for initial tests for skin cancer.
Earlier this month, eight medical residents from the University Hospital’s dermatology department offered free skin cancer screenings at the Oakland Plaza Senior Center.
One of the clues the doctors-in-training were looking for was a scaly or crusty bump formed on the surface of the skin from over-exposure to sunlight.
One of the forms of skin cancer that often proves life threatening is melanoma, which causes about 74 percent of skin cancer deaths in America. Melanoma is highly malignant and can easily spread to other parts of the body.
“The worst case that I have seen is in a patient whose melanoma had grown through the ribs and the digestive system,” said David Lane, University Hospital’s chief dermatology resident. “So as they get bigger, melanomas eat through anything in its way, by causing necrosis of other normal cells.”
Columbia resident Roy Sublett, 76, survived melanoma. He worked for more than 50 years as a welder until he retired several years ago.
About 15 years ago, he discovered some patches on his ear lobes, hands and on the top of his head that crusted and bled.
He was successfully treated for the cancer, but he is not free of the fear of its reappearance. He made sure he used the opportunity to get a free screening at the senior center event.
“I still have it pop up now and then,” Sublett said. “But I tested okay this time. I really appreciate it very much that they are doing this, and I hope they will reach more people through this. More people should be aware of this, since it can cause death.”