Melanoma, though a less common type of skin cancer, accounts for about 75% of skin cancer deaths. The five-year survival rate for melanoma, if caught early, is 98 percent. That number drops drastically if the cancer is detected late or if it returns.
Because of this, it is important that the initial surgery to remove cancerous cells is accurate enough while leaving healthy tissue in tact.
Up until now, there has been no imaging technique that adequately defines the boundaries of the malignant tissue. Because of this, doctors usually remove excessive tissue around the cancerous cells to ensure a minimal chance of recurrence. Two scientists from Washington University in St. Louis have engineered technologies that promise to alleviate this problem.
The solution combines an imaging technique and a contrast agent that were developed by Lihong Wang, PhD, and Younan Xia, PhD, respectively. The combination of technologies provides an accurate three-dimensional rendering of the cancerous cells.
The technique, which is based on the photoacoustic effect discovered by Alexander Graham Bell, uses light and sounds waves for imaging purposes. Basically, when light pulses through tissue at the right frequency, the tissue generates sound waves as it expands and contracts. A computer then uses a mathematical problem to reconstruct an image from the sound waves.
The use of sounds waves in imaging works a lot better than light because light scatters much more often in tissue, creating a distorted image. The technology is called photoacoustic tomography (PAT).
“PAT improves tissue transparency by two to three orders of magnitude,” says Wang.
Not only that, PAT is a lot safer than other deep imaging technologies, like X-rays, because it uses up to 100 times less voltage output. In addition, photoacoustic images to no require patients consume contrasting agents for the image to be seen.
Although the technology is a vast improvement on other imaging resources, the images still come out fuzzy around the edges of the malignant tissue. In order to improve the image, Xia loads the tissue with gold.
“Gold is much better at scattering and absorbing light than biological materials. One gold nanocage absorbs as much light as a million melanin molecules,” says Xia.
The gold nanocages can be tuned to absorb and scatter light at many different wavelengths. In addition, gold particles that are injected into the body naturally accumulate in tumors because the malignant cells are disorganized and leaky.
In experiments in mice, the photacoustic signal with the addition of the gold agent was 36% stronger. Subcutaneous melanomas that are barely visible show up clearly, and in great depth, on photoacoustic images.
This advancement in melanoma imaging is not only important in the early detection of skin cancer; however, it can assist surgeons in accurately removing advancement malignant tissue. This means that patients who are diagnosed at a later stage may have a higher survival rate than in the past.
