Melanoma is one of the less common types of skin cancer but it accounts for the majority of the skin cancer deaths (about 75 percent).
The five-year survival rate for early stage melanoma is very high (98 percent), but the rate drops precipitously if the cancer is detected late or there is recurrence.
So a great deal rides on the accuracy of the initial surgery, where the goal is to remove as little tissue as possible while obtaining “clean margins” all around the tumor.
So far no imaging technique has been up to the task of defining the melanoma's boundaries accurately enough to guide surgery.
Instead surgeons tend to cut well beyond the visible margins of the lesion in order to be certain they remove all the malignant tissue.
Two scientists at Washington University in St. Louis have developed technologies that together promise to solve this difficult problem.
Their solution, described in the July issue of ACS Nano, combines an imaging technique developed by Lihong Wang, PhD, the Gene K. Beare Distinguished Professor of Biomedical Engineering, and a contrast agent developed by Younan Xia, PhD, the James M. McKelvey Professor of Biomedical Engineering.
Together the imaging technique and contrast agent produce images of startling three-dimensional clarity.VIDEO NEWS RELEASE
The imaging technique is based on the photoacoustic effect discovered by Alexander Graham Bell 100 years ago. Bell exploited the effect in what he considered his greatest invention ever, the photophone, which converted sound to light, transmitted the light and then converted it back to sound at the receiver.
(The public preferred the telephone to the photophone, by some facetious accounts because they just didn’t believe wireless transmission was really possible.)
In Bell’s effect, the absorption of light heats a material slightly, typically by a matter of millikelvins, and the temperature rise causes thermoelastic expansion.
“Much the same thing happens,” says Wang “when you heat a balloon and it expands.”
If the light is pulsed at the right frequency, the material will expand and contract, generating a sound wave.
“We detect the sound signal outside the tissue, and from there on, it’s a mathematical problem,” says Wang. “We use a computer to reconstruct an image.”
“We’re essentially listening to a structure instead of looking at it,” says Wang.
“Using pure optical imaging, it is hard to look deep into tissues because light is absorbed and scattered,” Wang explains. “The useful photons run out of juice within one millimeter.”
Lihong Wang with the photoacoustic imaging system built in his lab. The photoacoustic technique had been used in the 1980s to test non-biological materials for cracks, but in 2003. Wang and his colleagues published startling photoacoustic images of a rat brain, taken through the skin and skull, that showed how the brain responded when the rat’s whiskers were touched. Today more papers are published about photoacoustic imaging than any other type of optical imaging, says Wang.
Photoacoustic tomography (PAT) can detect deep structures that strongly absorb light because sound scatters much less than light in tissue.
“PAT improves tissue transparency by two to three orders of magnitude,” says Wang.
Moreover, it’s a lot safer than other means of deep imaging. It uses photons whose energy is only a couple of electron-volts, whereas X-rays have energies in the thousands of electron-volts. Positron emission tomography (PET) also requires high-energy photons, Wang says.A smart contrast agent
Still, photoacoustic images of melanomas are fuzzy and vague around the edges. To improve the contrast between the malignant and normal tissue, Xia loads the malignant tissue with gold.
“Gold is much better at scattering and absorbing light than biological materials,” Xia says. “One gold nanocage absorbs as much light as a million melanin molecules,” says Xia.
Xia’s contrast agent consists of hollow gold cages, so tiny they can only be seen through the color they collectively lend to the liquid in which they float.
By altering the size and geometry of the particles, they can be tuned to absorb or scatter light over a wide range of wavelengths.
In this way the nanoparticles behave quite differently than bulk gold.
For photoacoustic imaging, Xia’s team tunes the nanocages to absorb strongly at 780 nanometers, a wavelength that falls within a narrow window of tissue transparency in the near-infrared.
Light in this sweet spot can penetrate as deep as several inches in the body.
Once injected, the gold particles naturally tend to accumulate in tumors because the cells that line a tumor’s blood vessels are disorganized and leaky.
But Xia has dramatically increased the uptake rate by decorating the nanoparticles with a hormone that binds to hormone receptors on the melanoma’s cells.
The molecule is alpha-melanocyte-stimulating hormone, slightly altered to make it more stable in the body. This hormone normally stimulates the production and release of the brown pigment melanin in the skin and hair.
As is true in many types of cancers, this hormone seems to stimulate the growth of cancerous cells, which produce more hormone receptors than normal cells.
In experiments with mice, melanomas took up four times as many “functionalized” nanocages than nanocages coated with an inert chemical. With the contrast agent, the photoacoustic signal from the melanoma was 36 percent stronger.
But seeing is believing. Subcutaneous mouse melanomas barely visible to the unaided eye show up clearly in the photoacoustic images, their subterranean peninsulas and islands of malignancy starkly revealed.
Biocompatible 3-D tracking system has potential to improve robot-assisted surgery
17.02.2017 | Children's National Health System
Real-time MRI analysis powered by supercomputers
17.02.2017 | University of Texas at Austin, Texas Advanced Computing Center
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".
Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
17.02.2017 | Medical Engineering
17.02.2017 | Medical Engineering
17.02.2017 | Health and Medicine