An MRI image of a tarantula colored to highlight the heart in the posterior part of the body. Credit: Gavin Merrifield

By putting a live tarantula into a special MRI scanner designed for rodents and other small animals, researchers discovered that the spider appears to have a unique heart beat.

"In the videos you can see the blood flowing through the heart and tantalisingly it looks as though there might be 'double beating' occurring, a distinct type of contraction which has never been considered before. This shows the extra value of using a non-invasive technique like MRI," said researcher Gavin Merrifield, in a press release from the Society for Experimental Biology. Merrifield presented the research today at the society's annual conference in Glasgow.

Researchers say that using this technology to study live animals could bring greater insight into their physiology and behavior. "One potential practical use of this research is to ascertain the chemical composition of spider venom," says Mr. Merrifield. "Venom has applications in agriculture as a potential natural pesticide. On the more academic side of things if we can link MRI brain scans with a spider's behavior, and combine this with similar data from vertebrates, we may clarify how intelligence evolved."

Living laser: This live cell, which makes a large amount of green fluorescent protein, is the core of a new laser design. Credit: Malte Gather.

A laser based on living cells has been created by researchers at Harvard Medical School and the Massachusetts General Hospital in Boston. They were motivated to overcome one of the fundamental limitations on biological imaging: it's very difficult to get visible and infrared light in and out of the body.

Living lasers have a few basic parts that are drawn from the same list as any laser. First, the researchers genetically modified human liver cells so that they produce large amounts of green fluorescent proteins that are scattered throughout the cell. A cell carrying these proteins acts as the "gain medium"—the part of the laser that amplifies light energy. '

Like any laser, the cell laser needs an energy source to "pump" it and increase the power of the light it can emit. The researchers pumped the living lasers by pulsing the cells with light through a microscope. As light bounces around inside the cell and is re-emitted by the fluorescent proteins, it's amplified, increasing in power before being emitted in a coherent beam. To keep the light bouncing around as long as possible, to gain as much power as possible, the Boston group placed these cells inside a biocompatible optical cavity—essentially a tiny, highly reflective, cell-shaped hole.

In a paper in Nature Photonics, the Boston researchers suggest that living lasers would help get light-encoded information into and out of the body. These living lasers are fundamentally different from cells that simply make fluorescent proteins: by definition, a laser emits a strong, coherent beam of light. Laser light is great for carrying information over distances, whether that's from country-to-country in the optical fibers that make up the backbone of the internet.

Optical imaging labels can report on the molecular workings of tissues and cells in the body. Fluorescent protein tags that emit visible or infrared light are now common tools for studying cell biology in test tubes. But getting such light in and out of the body is difficult because light diffuses as it passes through biological tissues. Living lasers, if they're made into practical systems, have the potential to change that. One can imagine having a hybrid living-nonliving medical implant under the skin that would beam out a stream of information about biomarkers in the blood, for example.

The main challenge with any new kind of laser is figuring out how to pump it in a practical way. Using a microscope to pump the living lasers is a good way to prove that they work but it's not that practical for applications. Lasers can either be pumped with electricity or light, but how would that be accomplished inside the body?

Perhaps this work can dovetail with other projects directed at developing implantable electronics. Other groups have already developed implantable light sources and electrical diodes that might pump a living laser. A group at the University of Illinois and Tufts University, for example, have made biocompatible and high quality LEDs, transistors, electrodes, and other electronics, and have shown they work when implanted in living animals.

Illuminating Alzheimer's: Physicians can detect signs of Alzheimer's in the living human brain thanks to a new imaging tool. High levels of amyloid plaques, a hallmark of the disease, are marked in red. Credit: Avid Radiopharmaceuticals.

An advisory panel for the U.S. Food and Drug Administration gave conditional approval on Thursday for a new imaging agent that could aid in early detection of Alzheimer's. If the FDA follows the panel's recommendation, as it usually does, it will be the first such tool available to physicians to detect amyloid plaques, the neurological hallmark of the disease, in the living human brain.

As I noted in a story we posted yesterday on the technology, experts say the tracer will be especially useful in future research studies testing drugs designed to prevent the brain damage that causes Alzheimer's, as well as in diagnosing difficult and atypical cases of the disease.

The tracer, developed by Avid Radiopharmaceuticals (recently acquired by Eli Lilly) binds to amyloid plaques in the brain and is detected via position emission tomography (PET) scans. Previously, the only definitive way to detect amyloid in the brain, and hence definitely diagnose the disease, was via an autopsy.

The approval is conditional on the development of standards that make reading the scans consistent between radiologists and a doctor-training program. According to a report from the New York Times,

The question about interpreting the scans arose because in the Avid study, radiologists did not establish a firm cutoff point that would say whether a person had significant amounts of plaque. Instead they did a graded analysis. What is needed in practice is a set level that would say yes or no, and distinguish significant plaque accumulation from insignificant amounts. And the company must show that its cutoff points are accurate and that different radiologists assess the same scan in the same way.

Some people have plaque without having Alzheimer's, so if a scan shows plaque, doctors will have to use their clinical judgment, taking into account a patient's symptoms, in deciding what the scan results mean, noted Dr. P. Murali Doraiswamy, an Alzheimer's researcher at Duke University and a clinical investigator in the Avid trial. But if a scan shows no plaque, the situation is simpler, Dr. Doraiswamy said. It means the doctor should focus on other causes for the symptoms.