Science 1663

Spotlight

Better Breast Cancer Detection and Diagnostics, Getting inside a Fly's Head, The Sound of One Star Falling, Exploits with Superbright Light

Better Breast Cancer Detection and Diagnosis

Women may eventually have access to safer, more-comfortable, and more-accurate breast cancer scans. Currently, the only routine breast-screening technology is mammography, which uses low-dose x-rays to scan through tissue and capture on film a two-dimensional (2D) projection of the breast.

Los Alamos scientist Lianjie Huang, in collaboration with researchers from Karmanos Cancer Institute (KCI), London's Imperial College, and Stanford University, has developed a better way, producing a three-dimensional (3D) image, using not x-rays, but sound waves.

This view of a 3D ultrasound CT image was obtained, from a patient, using KCI’s prototype device. It shows a cross section of the breast near the chest wall (top of image) and a vertical cross section through the remainder of the breast. A tumor (red) is visible near the chest wall.

The technique, called ultrasound computed tomography (ultrasound CT), uses a prototype scanning device built at KCI. A woman's breast is immersed in water and surrounded by a ring-shaped array of hundreds of ultrasound elements. Each element emits ultrasound waves and then receives waves that are scattered from the soft tissue. The array is moved incrementally down the entire breast, gathering data at each step.

A suite of newly developed computer algorithms converts the stepwise ultrasound data into a series of high-resolution, 2D images and then turns the series into a single 3D image. The technology actually obtains three kinds of images, corresponding to the speed, attenuation, and reflectivity of the waves. The wealth of information allows ultrasound CT to single out cancerous lesions more accurately than can today's mammography.

Ultrasound CT has the potential to detect cancer in its earliest stages. And since it is both safer (no ionizing radiation) and more comfortable (there is no need to compress tissue as there is in mammography), it should prove an attractive alternative for future breast cancer screening.

Getting inside a Fly's Head

Why in the world would anyone care about a fly's head?

A team of researchers at Los Alamos (Ilya Nemenman), Princeton, and Indiana University has looked into one and learned something new about neurons, the electrically charged cells that transmit information in the nervous system. They've disproved the current view of how neurons transmit data in the part of a fly's brain that processes visual information.

Information is passed between neurons in a series of voltage "spikes." Because the spikes all have the same shape, they can convey information only through their placement in time. Scientists have long debated whether information is transmitted in the lengths of the time intervals between spikes or in the average number of spikes in much larger windows of time. The latter model has generally prevailed and has been used in the development of artificial neural networks— electrical circuits or software designed to mimic how biological nerve systems process sensory input.

A fly’s visual system can help us design better artificial neural networks. IMAGE courtesy of Dennis Kunkel Microscopy, Inc

This team found instead that a fly's visual system conveys information by controlling the intervals between successive spikes, to a precision of 200 millionths of a second. The finding sheds light not only on how these and possibly other types of neurons actually work but also suggests a reason why existing artificial neural networks designed to, for example, recognize faces do not work very well.

The scientists developed a new mathematical technique to analyze the timing of the spikes produced by a neuron sensitive to horizontal motion in a fly's field of view. The fly was immobilized on a small programmable turntable spinning fast enough to simulate the horizontal-rotation component of the insect's aerial acrobatics. To provide extra realism, team members placed the apparatus outdoors, where the visual background was far more natural and complex than it could be in a laboratory and where the fly's reactions to natural fluctuations in light—caused by passing clouds, for example—could also be recorded and analyzed.

The team believes the laboratory settings of previous studies were too monotonous and predictable to allow access to accurate data about how the fly's visual system responds in the natural environment.

The Sound of One Star Falling

In 1908, a meteor several hundred meters in diameter exploded when it entered Earth's atmosphere over Russia. The blast wave flattened forests and jiggled the pens of newly invented barographs far away in Britain.

On a vastly smaller scale, a meteor with a diameter less than 10 centimeters (about the size of a softball) can also produce atmospheric disturbances at the ground. A small meteor, frictionally heated by the air rushing past it, produces its own "blast wave," a pulse of low-frequency sound waves (infrasound). The frequency is 0.02 to 20 hertz—too low for humans to hear. In a collaborative project, the Laboratory's Doug ReVelle and students and faculty at the University of Western Ontario are using infrasound to detect small meteors and estimate their energy, location, and duration.

A sensor used to detect small meteors.

The researchers are using an array of infrasonic sensors, as well as radar, video cameras, and seismic and radio sensors. The equipment is located in Ontario. Every month the scientists observe at least one meteor that can produce infrasound detectable at the ground—a flux at least 100 times higher than earlier observations had suggested. They have also found that meteor-infrasound theory—developed by ReVelle more than 30 years ago—agrees well with the measurements. The theory had been untestable until now because only a handful of infrasonic observations of small meteors had been made.

"Infrasound can also be used to observe large manmade chemical and nuclear explosions," ReVelle says. "Although such explosions can be intentionally hidden from satellites, their ‘sound effects' can still give them away." In fact, the Department of Energy supports the infrasound monitoring program at Los Alamos, the only such program in the United States. The program operates six infrasonic-sensor arrays in western states. The arrays are routinely used to monitor White Sands Missile Range test explosions, NASA Space Shuttle launches and reentries, smaller missile launches, earthquakes, volcanic eruptions, and gas-fire explosions, among other events

Exploits with Superbright Light

Amazing things can be done when the small amount of energy needed to light a 100-watt bulb for one second is packed into a tiny pulse of laser light lasting but a trillionth of a second and having a spot size about 100 times smaller than the period at the end of this sentence. That's what Los Alamos scientists have demonstrated with the new ultra-short, highly-focused, ultra-intense pulses available from the newly enhanced Trident laser, now delivering power at one-tenth of a petawatt (a petawatt equals a million-billion watts).

Shine one of those tiny pulses on a thin foil target and it produces an intense pulse of x-rays with the right energies (18–35 thousand volts—kilovolts) to make high-precision images of imploding fusion capsules, just what will be needed to diagnose fusion experiments at the National Ignition Facility at Lawrence Livermore National Laboratory. Prepare that foil target in a slightly different way, and the Trident laser pulse will produce a beam of 50-million-electronvolt protons, a beam with 10 times more energy content than found in proton beams from similar lasers for the same laser intensity.

Sandrine Gaillard, a Laboratory affiliate, stares into Trident’s north target chamber where ultra-short laser pulses create high-energy-density plasmas as well as monoenergetic ion pulses for cancer research applications.

At this energy and intensity the proton beam has a host of potential uses, from making images (proton radiographs) of dense objects to making radioisotopes for medical applications or performing tabletop nuclear physics experiments. Slightly higher energies make possible other applications, like treating cancers or screening containers for the presence of plutonium or uranium. The laser itself might even be used to divert lightning from power lines and buildings.

With all these applications in sight, Kirk Flippo, one of the Trident physicists, is excited about the future. "Short-pulse technology could revolutionize many aspects of our lives, and Trident is one of a handful of systems leading the way."

Other scientists emphasize Trident's basic research potential. It can re-create states of matter seen only around black holes and inside gamma-ray bursts, thereby expanding the field of laboratory astrophysics. It can also produce ultra-short x-ray pulses to image the gyrations of proteins as they fold and can even be used to observe such bizarre phenomena as "Unruh radiation," the theoretical radiation emitted by a particle subjected to massive acceleration.

Trident has just become a national user facility, opening its doors to scientists everywhere and giving all a chance to channel their ideas into real experiments.