Design and evaluation of a laboratory prototype system for 3D photoacoustic full breast tomography.


Photoacoustic imaging can visualize vascularization-driven optical absorption contrast with great potential for breast cancer detection and diagnosis. State-of-the-art photoacoustic breast imaging systems are promising but are limited either by only a 2D imaging capability or by an insufficient imaging field-of-view (FOV). We present a laboratory prototype system designed for 3D photoacoustic full breast tomography, and comprehensively characterize it and evaluate its performance in imaging phantoms. The heart of the system is an ultrasound detector array specifically developed for breast imaging and optimized for high sensitivity. Each detector element has an acoustic lens to enlarge the acceptance angle of the large surface area detector elements to ensure a wide system FOV. We characterized the ultrasound detector array performance in terms of frequency response, directional sensitivity, minimum detectable pressure and inter-element electrical and mechanical cross-talk. Further we evaluated the system performance of the laboratory prototype imager using well-defined breast mimicking phantoms. The system possesses a 2 mm XY plane resolution and a 6 mm vertical resolution. A vasculature mimicking object was successfully visualized down to a depth of 40 mm in the breast phantom. Further, tumor mimicking spherical objects with 5 and 10 mm diameter at 20 mm and 40 mm depths are recovered, indicating high system sensitivity. The system has a 170 × 170 × 170 mm3 FOV, which is well suited for full breast imaging. Various recommendations are provided for performance improvement and to guide this laboratory prototype to a clinical version in future.

Source: http://www.opticsinfobase.org

Imaging Breast Cancer with Light.


Breast cancer is one of the most common forms of cancer and cancer deaths among women worldwide. Routine screening can increase breast cancer survival by detecting the disease early and allowing doctors to address it at this critical stage. A team of researchers at the University of Twente in the Netherlands have developed a prototype of a new imaging tool that may one day help to detect breast cancer early, when it is most treatable.

If effective, the new device, called a photoacoustic mammoscope, would represent an entirely new way of imaging the breast and detecting cancer. Instead of X-rays, which are used in traditional mammography, the photoacoustic breast mammoscope uses a combination of infrared light and ultrasound to create a 3-D map of the breast. The researchers describe their device in a paper published today in The Optical Society’s (OSA) open-access journal Biomedical Optics Express.

A 3-D Map of the Breast

In the new technique, infrared light is delivered in billionth-of-a-second pulses to tissue, where it is scattered and absorbed. The high absorption of blood increases the temperature of blood vessels slightly, and this causes them to undergo a slight but rapid expansion. While imperceptible to the patient, this expansion generates detectable ultrasound waves that are used to form a 3-D map of the breast vasculature. Since cancer tumors have more blood vessels than the surrounding tissue, they are distinguishable in this image.

Currently the resolution of the images is not as fine as what can be obtained with existing breast imaging techniques like X-ray mammography and MRI. In future versions, Srirang Manohar, an assistant professor at the University of Twente who led the research, Wenfeng Xia, a graduate student at the University of Twente who is the first author on the new paper, and their colleagues expect to improve the resolution as well as add the capability to image using several different wavelengths of light at once, which is expected to improve detectability.

The Twente researchers, who belong to the Biomedical Photonic Imaging group run by Professor Wiendelt Steenbergen, have tested their prototype in the laboratory using phantoms – objects made of gels and other materials that mimic human tissue. Last year, in a small clinical trial they showed that an earlier version of the technology could successfully image breast cancer in women.

Manohar and his colleagues added that if the instrument were commercialized, it would likely cost less than MRI and X-ray mammography.

“We feel that the cost could be brought down to be not much more expensive than an ultrasound machine when it goes to industry,” said Xia.

The next step, they say, will be to prepare for larger clinical trials. Several existing technologies are already widely used for breast cancer screening and diagnosis, including mammography, MRI, and ultrasound. Before becoming routinely used, the photoacoustic mammoscope would have to prove at least as effective as those other techniques in large, multicenter clinical trials.

“We are developing a clinical prototype that improves various aspects of the current version of the device,” said Manohar. “The final prototype will be ready for first clinical testing next year.”

Scientists unveil energy-generating window.


Scientists in China said Thursday they had designed a “smart” window that can both save and generate energy, and may ultimately reduce heating and cooling costs for buildings.

Scientists unveil energy-generating window

While allowing us to feel close to the outside world, windows cause heat to escape from buildings in winter and let the Sun‘s unwanted rays enter in summer.

This has sparked a quest for “smart” windows that can adapt to weather conditions outside.

Today’s  are limited to regulating light and heat from the sun, allowing a lot of potential  to escape, study co-author Yanfeng Gao of the Chinese Academy of Sciences told AFP.

“The main innovation of this work is that it developed a concept smart window device for simultaneous generation and saving of energy.”

Engineers have long battled to incorporate energy-generating solar cells into window panes without affecting their transparency.

Gao’s team discovered that a material called  (VO2) can be used as a transparent coating to regulate infrared radiation from the Sun.

VO2 changes its properties based on temperature. Below a certain level it is insulating and lets through infrared light, while at another temperature it becomes reflective.

A window in which VO2 was used could regulate the amount of Sun energy entering a building, but also scatter light to  the team had placed around their glass panels, where it was used to generate energy with which to light a lamp, for example.

“This smart window combines energy-saving and generation in one device, and offers potential to intelligently regulate and utilise solar radiation in an efficient manner,” the study authors wrote in the journal Nature Scientific Reports.



Chameleon in lab: Looking cooler when heated, thin coating tricks infrared cameras.


Active camouflage has taken a step forward at the Harvard School of Engineering and Applied Sciences (SEAS), with a new coating that intrinsically conceals its own temperature to thermal cameras.

A chameleon in the physics lab

In a laboratory test, a team of applied physicists placed the device on a hot plate and watched it through an  as the  rose. Initially, it behaved as expected, giving off more infrared light as the sample was heated: at 60 degrees Celsius it appeared blue-green to the camera; by 70 degrees it was red and yellow. At 74 degrees it turned a deep red—and then something strange happened. The  plummeted. At 80 degrees it looked blue, as if it could be 60 degrees, and at 85 it looked even colder. Moreover, the effect was reversible and repeatable, many times over.

These surprising results, published today in the journal Physical Review X (an open-access publication of the American Physical Society), illustrate the potential for a new class of engineered materials to contribute to a range of new military and everyday applications.

Principal investigator Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at Harvard SEAS, predicts that with only small adjustments the coating could be used as a new type of thermal camouflage or as a kind of encrypted beacon to allow soldiers to covertly communicate their locations in the field.

The secret to the technology lies within a very thin film of vanadium oxide, an unusual material that undergoes dramatic electronic changes when it reaches a particular temperature. At , for example, pure vanadium oxide is electrically insulating, but at slightly higher temperatures it transitions to a metallic, electrically conductive state. During that transition, the optical properties change, too, which means special temperature-dependent effects—like infrared camouflage—can also be achieved.

The insulator-metal transition has been recognized in vanadium oxide since 1959. However, it is a difficult material to work with: in bulk crystals, the stress of the transition often causes cracks to develop and can shatter the sample. Recent advances in  synthesis and characterization—especially those by coauthor Shriram Ramanathan, Associate Professor of Materials Science at Harvard SEAS—have allowed the creation of extremely pure samples of thin-film vanadium oxide, enabling a burst of new science and engineering to take off in just the last few years.

“Thanks to these very stable samples that we’re getting from Prof. Ramanathan’s lab, we now know that if we introduce small changes to the material, we can dramatically change the optical phenomena we observe,” explains lead author Mikhail Kats, a graduate student in Capasso’s group at Harvard SEAS. “By introducing impurities or defects in a controlled way via processes known as doping, modifying, or straining the material, it is possible to create a wide range of interesting, important, and predictable behaviors.”

By doping vanadium oxide with tungsten, for example, the transition temperature can be brought down to room temperature, and the range of temperatures over which the strange thermal radiation effect occurs can be widened. Tailoring the material properties like this, with specific outcomes in mind, may enable engineering to advance in new directions.

The researchers say a vehicle coated in vanadium oxide tiles could mimic its environment like a chameleon, appearing invisible to an infrared camera with only very slight adjustments to the tiles’ actual temperature—a far more efficient system than the approaches in use today.

Tuned differently, the material could become a component of a secret beacon, displaying a particular thermal signature on cue to an infrared surveillance camera. Capasso’s team suggests that the material could be engineered to operate at specific wavelengths, enabling simultaneous use by many individually identifiable soldiers.

And, because thermal radiation carries heat, the researchers believe a similar effect could be employed to deliberately speed up or slow down the cooling of structures ranging from houses to satellites.

The Harvard team’s most significant contribution is the discovery that nanoscale structures that appear naturally in the transition region of  can be used to provide a special level of tunability, which can be used to suppress thermal radiation as the temperature rises. The researchers refer to such a spontaneously structured material as a “natural, disordered metamaterial.”

“To artificially create such a useful three-dimensional structure within a material is extremely difficult,” says Capasso. “Here, nature is giving us what we want for free. By taking these natural metamaterials and manipulating them to have all the properties we want, we are opening up a new area of research, a completely new direction of work. We can engineer new devices from the bottom up.”






Gold-plated nano-bits find, destroy cancer cells.


Carl Batt

Batt
Dickson Kirui

Kirui

Comparable to nano-scale Navy Seals, Cornell scientists have merged tiny gold and iron oxide particles to work as a team, then added antibody guides to steer the team through the bloodstream toward colorectal cancer cells. And in a nanosecond, the alloyed allies then kill the bad guys – cancer cells – with absorbed infrared heat.

This scenario is not science fiction – welcome to a medical reality.

“It’s a simple concept. It’s colloidal chemistry. By themselves, gold and iron-oxide alloys are benign and inert, and the infrared light is low-power heating,” said Carl Batt, Cornell’s Liberty Hyde Bailey Professor of Food Science and the senior author on the paper. “But put these inert alloys together, attach an antibody to guide it to the right target, zap it with infrared light and the cancer cells die. The cells only need to be heated up a few degrees to die.”

Batt and his colleagues – Dickson K. Kirui, Ph.D. ’11, a postdoctoral fellow at Houston Methodist Research Institute and the paper’s first author; Ildar Khalidov, radiology, Weill Cornell Medical College; and Yi Wang, biomedical engineering, Cornell – published their study in Nanomedicine (print edition, July 2013).

For cancer therapy, current hyperthermic techniques – applying heat to the whole body – heat up cancer cells and healthy tissue, alike. Thus, healthy tissue tends to get damaged. This study shows that by using gold nanoparticles, which amplify the low energy heat source efficiently, cancer cells can be targeted better and heat damage to healthy tissues can be mitigated. By adding the magnetic iron oxide particles to the gold, doctors watching MRI and CT scanners can follow along the trail of this nano-sized crew to its target.

When a near-infrared laser is used, the light penetrates deep into the tissue, heating the nanoparticle to about 120 degrees Fahrenheit – an ample temperature to kill many targeted cancer cells. This results in a threefold increase in killing cancer cells and a substantial tumor reduction within 30 days, according to Kirui. “It’s not a complete reduction in the tumor, but doctors can employ other aggressive strategies with success. It also reduces the dosage of highly toxic chemicals and radiation – leading to a better quality of life,” he explained.

Team develops compact, high-power terahertz source at room temperature


Terahertz (THz) radiation—radiation in the wavelength range of 30 to 300 microns—is gaining attention due to its applications in security screening, medical and industrial imaging, agricultural inspection, astronomical research, and other areas. Traditional methods of generating terahertz radiation, however, usually involve large and expensive instruments, some of which also require cryogenic cooling. A compact terahertz source—similar to the laser diode found in a DVD player —operating at room temperature with high power has been a dream device in the terahertz community for decades.

Manijeh Razeghi, Walter P. Murphy Professor of Electrical Engineering and Computer Science at Northwestern University‘s McCormick School of Engineering and Applied Science, and her group has brought this dream device closer to reality by developing a compact, room-temperature source with an of 215 microwatts.

Razeghi presented the research October 7 at the International Conference and Exhibition on Lasers, Optics & Photonics in San Antonio, and will also present at the European Cooperation in Science and Technology conference in Sheffield, England on October 10. The findings were published July 1 in the journal Applied Physics Letters and was presented at the SPIE Optics + Photonics conference in August in San Diego.

Razeghi’s group is a world leader in developing quantum cascade lasers (QCL), compact semiconductor lasers typically emitting in the mid-infrared spectrum ( of 3 to 16 microns).

Terahertz radiation is generated through nonlinear mixing of two mid-infrared wavelengths at 9.3 microns and 10.4 microns inside a single quantum cascade laser. By stacking two different QCL emitters in a single laser, the researchers created a monolithic nonlinear mixer to convert the mid-infrared signals into , using a process called difference frequency generation. The size is similar to standard , and a wide spectral range has already been demonstrated (1 to 4.6 THz).

“Using a room-temperature mid-infrared laser to generate terahertz light bypasses the temperature barrier, and all we need to do is to make the output power high enough for practical applications,” said Razeghi, who leads Northwestern’s Center for Quantum Devices (CQD). “Most applications require a minimum of microwatt power levels, but, of course, the higher the better.”

The achieved output power, 215 microwatts, is more than three times higher than earlier demonstrations. This dramatic boost is due to a number of novelties, including Cherenkov phase matching, epilayer down mounting, symmetric current injection, and anti-reflection coating.