Path Found to a Combined MRI and CT Scanner

Omni-tomography could add together the advantages of several medical imaging technologies

Image: Mehau Kulyk/Science Photo Library/Getty Images

A technology that better targets an X-ray imager’s field of view could allow various medical imaging technologies to be integrated into one. This could produce sharper, real-time pictures from inside the human body, says a researcher who hopes to one day build such a unified imager.


Ge Wang, the director of Rensselaer Polytechnic Institute’s Biomedical Imaging Cluster, in Troy, N.Y., calls his vision omni-tomography. Mixing and matching imaging techniques, such as computed tomography, magnetic resonance imaging, and single-photon emission computed tomography, could improve biomedical research and facilitate personalized medicine, says Wang, an IEEE Fellow.


To fit these imaging methods together, Wang and his collaborators have been developing a technology called interior tomography. In standard CT, X‑rays pass through two-dimensional slices of the body, and then a computer processes the data to build up a picture. If the scanner is trying to image the aorta, for instance, it will X-ray a whole section of the chest, including the points where the body ends and the open air begins. That boundary provides the image-building algorithm with defined edges and the background information it needs to operate. But interior tomography focuses only on structures inside the body, which reduces the patient’s radiation exposure. “If you’re only interested in the heart, why bother to cover your whole chest with X-rays?” says Wang. 


Narrowing the view, however, eliminates the usual reference points needed to create an image conventionally. Interior tomography relies on a different set of hints. The new technique uses information about how substances within the body (such as blood) and air pockets alter X-rays to provide the algorithm with a base for reconstructing the image. It can even use old X-ray images of the same patient to help out. 


Focusing on a specific region has advantages, particularly with patients too big for conventional scanners. “If an object is wider than the X-ray beam width, classic theory says you cannot do an accurate reconstruction,” says Wang. That’s not a concern with interior tomography, he says. 


Images: Hao Gao & Ge Wang

Seeing Both Sides: A CT scanner’s X-rays [left side] provide good structural detail; MRI images [right] are good for seeing functional flaws. Omni-tomography could combine the two technologies in the same machine.

What’s more, Wang’s team has shown that this concept can be generalized for use in imaging methods other than CT scanning, including MRI. And that could lead to a true fusion of major medical imaging techniques. In part that’s because the technique allows the use of smaller X-ray detectors, which in turn makes it possible to fit more scanners into the same machine. 


There are already systems that combine two imaging methods—PET and CT or SPECT and CT, for instance. But those systems usually apply different methods in sequence rather than simultaneously, making it harder to see biological processes in action. The combination of CT and MRI has never been attempted before, but Wang says it’s possible now.


In fact, he and his collaborators in Australia, China, and the United States recently came up with a top-level engineering design for a CT-MRI scanner. They hope to present their design in June at the International Meeting on Fully Three-Dimensional Image Reconstruction in Radiology and Nuclear Medicine, in California. Applying interior tomography to MRI imaging allows the use of a weaker magnetic field, which is one way the design compensates for the incompatibility between powerful magnets in the MRI and rotating metal parts in the CT scanner. 


Wang’s team does not yet have the funding to build a combination CT-MRI scanner, but putting the two technologies together could prove useful. MRI gives high contrast and allows doctors to measure functional and even molecular changes; CT provides greater structural detail. Together, they might allow doctors to get a superior picture of processes in action, such as changes during a heart attack, or serve as a guide to a surgical procedure. The technology would be ideal for imaging vulnerable plaques, suggests Michael Vannier, one of Wang’s collaborators and a radiology professor at the University of Chicago. Vulnerable plaques are buildups on artery walls that are particularly unstable and prone to causing heart attack or stroke. A combination of structural, functional, and molecular information is needed to tell just how dangerous the plaque may be. “In the long run, we think putting many imaging modes together will give you more information,” Wang says.


Interior tomography “is certainly an interesting concept that takes the interest in combining modalities to the ‘ultimate’ level of a single device,” says Simon Cherry, director of the Center for Molecular and Genomic Imaging at the University of California, Davis. While omni-tomography is technically feasible, Cherry wonders whether it will make sense from a clinical and economic perspective. “There are some that say too many of our health-care dollars are spent on imaging, especially in the pursuit of defensive medicine. This will be an expensive machine,” he says. “These are the issues that may well determine whether this approach is successful.” 


About the Author

Neil Savage describes IEEE Fellow Ge Wang’s research on interior tomography, which he first came across while reporting on how medical device firms were trying to reduce the X-ray dosage produced by their imagers. Savage, a longtime Spectrum contributor, says, “With the growing popularity of scanning, finding ways to limit radiation exposure is important.”

The World's Most Powerful MRI Takes Shape

• Biomedical
• Imaging
• News

Medical researchers expect unprecedented resolution from 11.75-Tesla imager

•  

 

Illustration: Emily Cooper

This one goes to 11: The main superconducting coil for the INUMAC imager is made from 170 kilometers of niobium-titanium. When bathed in liquid helium and charged, it produces a magnetic field of 11.75 teslas.

An MRI scanner equipped with a superconducting magnet strong enough to lift a 60-metric-ton battle tank will offer unprecedented images of the human brain when it comes on line a little more than a year from now, say its builders.

The imager’s superconducting electromagnet is designed to produce a field of 11.75 teslas, making it the world’s most powerful whole-body scanner. Most standard hospital MRIs produce 1.5 or 3 T. A few institutions, including the University of Illinois at Chicago and Maastricht University, in the Netherlands, have recently installed human scanners that can reach 9.4 T. Superconducting magnets used in the Large Hadron Collider, which last year was used in the discovery of the Higgs boson, produce a field of 8.4 T.

The development of the scanner, known as INUMAC (for Imaging of Neuro disease Using high-field MR And Contrastophores), has been in progress since 2006 and is expected to cost €200 million, or about US $270 million. The project reached a key milestone this summer with delivery of more than 200 kilometers of superconducting cable, which is now being wound into coils that will produce the scanner’s magnetic field.

“We’re pretty proud of having met all the requirements, plus given them a little extra,” says Hem Kanithi, vice president of business development atLuvata, in Waterbury, Conn., which built the superconductor.

Standard hospital scanners have a spatial resolution of about 1 millimeter, covering about 10 000 neurons, and a time resolution of about a second. The INUMAC will be able to image an area of about 0.1 mm, or 1000 neurons, and see changes occurring as fast as one-tenth of a second, according to Pierre Védrine, director of the project at the French Alternative Energies and Atomic Energy Commission, in Paris. With this type of resolution, MRIs could detect early indications of brain diseases such as Alzheimer’s or Parkinson’s and perhaps measure the effects of any methods developed to treat those illnesses. It would also allow much more precise functional imaging of the brain at work than is currently available. “You cannot really discriminate today what is happening inside your brain at the level of a few hundred neurons,” Védrine says.

High-field MRI could also allow scientists to explore different methods of imaging. Most MRI machines rely on imaging the nuclei of hydrogen atoms, but stronger scanners might gain useful physiological information by looking for weaker signals from sodium or potassium nuclei.

Improved superconducting wire is key to making such a powerful machine. The wire in the INUMAC magnet is made from niobium-titanium, a common superconductor alloy. But it will experience some uncommon conditions as part of INUMAC. To reach the required field strength, the electromagnet must be able to carry 1500 amperes at 12 T and be cooled by superfluid liquid helium to 1.8 kelvins. That requires specialized manufacturing and precise control of the dimensions of the wire, allowing it to be coiled so the cables are aligned to within a few micrometers of precision. “We are pushing the superconducting material niobium-titanium very close to its limits,” Védrine says.

Another material, niobium-tin, can produce magnetic fields stronger than 20 T, but it was passed over for the job because it’s more expensive than niobium-titanium and very brittle, making it difficult to wind.

Ultimately, Luvata produced 170 km of wire for the main superconducting coil. The company made another 58 km for two secondary coils, which will produce an opposing magnetic field to shield the area outside the machine from stray magnetic fields.

Instead of winding the wire into one long coil, as is standard in systems with lower fields, engineers are using a “double pancake” design, in which the wire is coiled into two reels that are spliced together, one on top of the other. The whole magnet will consist of 170 of these double pancakes connected in series. Védrine explains that this reduces the chances for error: Making a mistake in the winding phase using a single helical coil could ruin the whole magnet. However, a miswound pancake can simply be swapped out for a new one. The design provides space for the liquid helium bath to reach all of the coil and keep the temperature low, and it also allows engineers to place the best-performing coils at the center of the system, which improves the precision of the magnetic field.

The inner diameter of the magnet will be 90 centimeters, wide enough for a human body. Patients getting scanned will lie entirely inside the machine, but the region where the field is precise enough to get maximum resolution will be only 22 cm long. “The very good field region is only in the middle of the magnet,” Védrine says. While patients could be situated so that other body parts would fit inside that region, “first we are concentrating on the brain,” he says. It would take an even more massive machine to enlarge the high-resolution area.

Védrine expects to deliver the fully assembled magnet by September of next year. Other parts of the imaging system will then be added in and around the magnet, followed by about three months of testing. “Probably we’ll have the first images by the beginning of 2015,” he says.

New Pacemakers Prove MRI-Proof

With some precautions, modern models are immune to scanner's deadly influence

According to both medical wisdom and regulatory decree, magnetic resonance imaging (MRI) scans and implanted heart devices such as pacemakers do not mix. Henry Halperin, an associate professor of medicine, radiology, and biomedical engineering at Johns Hopkins University School of Medicine in Baltimore, bluntly sums up the problem: "It is feared that the electromagnetic fields of the MRI may heat up metal components or pull on and dislodge the device, causing tissue damage, device malfunction, or possibly death."

Still, forgetful or comatose patients have inadvertently gotten scans, with more than two dozen deaths thought to be associated with the procedure. How many deaths were really due to the scan is anybody's guess; then again, nobody knows how many lives might be saved if patients with implants could get diagnostic MRI scans, which are regarded as the best imaging technology for the diagnosis of many cancers; diseases of the brain, head, and neck; and many cardiovascular conditions. It is estimated that half of patients with pacemakers become candidates for scanning at some point in their lives [see photo, " Safe Inside"].

For those who need it most, an option is now at hand. As part of an industry-supported study published in the 3 August issue of Circulation, Halperin and his colleagues reported that pacemakers made after 2000 can go through MRI machines safely if a team of specialists, including a cardiologist, supervises, following a specific safety protocol.

In a typical MRI, a 1.5-tesla magnet strings the body's protons tautly along the magnet's lines of force. Then radio frequency waves twang the protons out of alignment; when they snap back, they produce an RF signal from which an image of the body's organs is constructed. With all those electromagnetic fields, an electronic device that has an antenna-like electrode lead running into a human heart would seem, on the face of it, a dangerous thing.

The evolution of pacemaker technology and the way that new implants interact with an MRI is what makes scanning possible now, according to the researchers. At about 40 grams, modern pacemakers are, on average, just a fifth the weight of their ancestors, and the pull they're subjected to from a 1.5-T machine is only about the weight of two golf balls--hardly enough to dislodge the device.

But more striking was the discovery, in both animal and human subjects, that when the electrodes absorbed energy from the scanner's RF field, their temperature rose just 5 degrees C--hardly the flesh-cooking inferno doctors feared. According to the Johns Hopkins study, the lead, which runs from the pacemaker to the heart, is too short to couple well with the RF field, and capacitors in the device filter out a good deal of the energy that would cause heating.

All this good news isn't exactly welcome at Biophan Technologies Inc., a West Henrietta, N.Y., company founded in the late 1990s with the sole purpose of developing technologies that can make implants MRI-friendly. Michael Weiner, the company's chief executive officer, finds fault with the Johns Hopkins study, saying the heating result depends on where and when you measure the temperature. The researchers took the temperature at the pacemaker's electrode tip, which is metal and "works like a heat sink," Weiner says. "It's the tissue a few millimeters away that heats up." Because the study's subjects had gotten their implants just four weeks previously, he adds, not enough fibrous scar tissue had formed around the tip to furnish a potential hot spot.

Besides heat and the pull of the magnet, there are at least two other potential problems with the scanning of pacemakers. First, the RF wave front that sweeps over the body 200 to 300 times per second can set up a heart-quickening voltage gradient along the lead to the heart. Second, the current the RF field induces in the device could also, in principle, reset the pacemaker's rate. The Hopkins researchers found no evidence of either problem but acknowledged that they examined pacemakers in only 24 volunteer patients.

The safety protocol outlined for the Johns Hopkins study begins with the conventional remote testing of the implanted device--a pacemaker or a defibrillator. Next, doctors explain the potential risks to the patient and then turn off the device or put it in safe mode, using the device's built-in wireless link. They then scan the patient with an MRI machine in the presence of a cardiologist. Finally, the cardiologist uses the wireless link to check the implant, to make sure it still functions properly.

Johns Hopkins's Halperin says his group's study doesn't threaten Biophan's business. "We tested existing models, but the problem isn't solved, because each new device that comes out would have to be tested separately," he notes. "Besides, the monitoring protocol we use is fairly involved, and with what Biophan is talking about, you wouldn't have to do any of it. Everybody who needed an MRI could get one anywhere, instead of having to go to a special center that can take precautions."

Biophan's safety technologies include an in-lead RF filter--developed, by the way, at Johns Hopkins and licensed exclusively to Biophan--that reduces heating of the electrode in the heart by more than 95 percent. It also has what the company calls an anti-antenna. Normally, the pacemaker's lead makes a circuit, called the primary loop, by conduction from the electrode in the heart, through the patient, and back to the pacemaker. The anti-antenna, a structure in the lead, provides a reverse loop to cancel out any voltage gradient that might build up along the primary loop.

Other companies are working on similar technologies. Minneapolis-based Medtronic Inc., the leading pacemaker company and a backer of the Johns Hopkins research, says its pacemakers and defibrillators will be fully safe for MRI scanning by next year.

RFID Systems May Disrupt the Function of Medical Devices

• Computing
• Embedded Systems
• Article

Researchers ask whether hospitals should adopt new guidelines for medical electronics' interoperability

PHOTO: Andrei Malov/istockphoto

24 June 2008—The use of radio-frequency identification (RFID) systems in hospitals may not be entirely safe, new research suggests. According to a study published this week in the Journal of the American Medical Association, RFID tags and the devices they communicate with can disrupt the performance of medical equipment, including pacemakers and dialysis machines, potentially endangering the patients who depend on those devices.

Erik Jan van Lieshout and Remko van der Togt, along with their colleagues at the University of Amsterdam’s Academic Medical Center, tested whether the presence of RFID transponders and the readers they transmit to could interfere with the function of 41 different electronic medical devices. The team examined both an active RFID system, in which the tags have batteries that allow them to transmit continuously, and a passive system, whose tags are powered only when in the range of a transmitter’s electromagnetic field. In 123 tests, they found 34 incidences of interference.

Of those, the researchers categorized 22 cases as hazardous, meaning that the interference caused an equipment fault that could have direct physical impact on a patient. For example, in two such incidences, a mechanical ventilator and a syringe pump switched off when the RFID system was transmitting near them. The passive RFID tag they used, which had a higher energy output and operated at a frequency of 868 megahertz, induced three times as many disruptions as the active system, which operated at 125 kilohertz.

None of the tests involved patients—just equipment—and no real-life cases have yet been reported of RFID transponders causing a device to malfunction, according to the Dutch research.

The health-care market for RFID systems, according to IDTechEx, a consultancy that focuses on RFID, is about US $121 million, and the tags are increasingly becoming integrated into the hospital environment. They are used, for instance, to track the location of surgical sponges so they are not inadvertently left inside patients. RFID tags are also embedded in bracelets given to newborn babies to prevent kidnapping.

For van Lieshout, who works in his hospital’s intensive care unit, the question of RFID interference arose after he had conducted some similar experiments on the use of cellphones in hospitals. Noticing the growing presence of RFID transponders in the ICU, van Lieshout decided to consult the medical literature and ask his colleagues for guidance on whether the tags’ transmissions could affect the health of his patients. ”They told me, ’Oh yeah, it’s pretty safe.’ But I wanted to know, ’Well, how safe?’ And no one knew,” van Lieshout recalls.

He and his colleagues set out to gain a qualitative sense of their safety: rather than exhaustively testing all the configurations of each available RFID tag and reader, they chose two systems already used in retail and drug-supply chains. They placed a transmitting reader and tag near each medical device and observed the distances at which an electromagnetic field caused disturbances in the devices’ performance. They found that the median distance at which interference occurred was 30 centimeters, with a range extending to 600 cm for several of the devices. ”For a critical-care physician, it was astonishing to find out,” says van Lieshout.

Donald Berwick, president of the Cambridge, Mass.–based Institute for Healthcare Improvement, notes in an editorial accompanying the study that the impact of hospital electronics on patient care has been largely positive but poorly understood. ”Health care is full of tightly coupled, hard-to-see systems, and the naive introduction of a change as apparently isolated as RFID tags…might cause remote and dire consequences far away in space and time,” he writes. Berwick suggests that hospitals look into routinely checking for electromagnetic interference and that regulatory agencies consider updating safety standards for electronic medical equipment.

Setting meaningful standards for testing every existing RFID system with all electronic medical equipment might be a near-impossible task, however. ”RFID means a lot of different things—a lot of different frequency bands, and a lot of ways to use it,” says Ralph Herkert, a senior researcher at Georgia Tech Research Institute’s Medical Device Test Center. As Herkert explains it, tags can operate with readers from different manufacturers at the same carrier frequency, but each signal may be modulated at a different rate. In some cases, the interference might be due to the modulation rather than the carrier frequency or the energy output.

For years, hospital staff has questioned whether the transmitters in cellphones are dangerously disruptive to medical equipment, and bans have been both imposed and then lifted in hospitals across the developed world. This latest batch of evidence—the first to document the influence of RFID technology on medical devices—is unlikely to revive the contentious debate about the hazards of using transmitting technologies in hospitals, says Marlin Mickle, an electrical engineering professor at the University of Pittsburgh and executive director of its RFID Center of Excellence. ”Cellphones are uncontrolled because visitors with cellphones wander all over the place. But RFID readers are installed by the hospital staff,” Mickle says. ”They just have to be smart about where they put them.”

The question remains of how often those interactions between life-saving devices and RFID transponders would arise in the day-to-day operations of a hospital. ”I’m not hoping there will be a frenetic ban on RFID in health care,” van Lieshout says. ”We just have to know what we’re dealing with.”

Mickle compares the study’s relevance to the warnings that accompany implanted devices and pharmaceutical drugs. ”When companies advertise drugs on television, they also tell you all the things that could go wrong,” Mickle says. ”Many electronic devices have those same kinds of warnings. It doesn’t mean we can’t use them.”

Smartphones: The Pocketable PC

Is Your Phone Smarter Than a Fifth Grader?

Illustration: Frank Chimero

This is part of IEEE Spectrum's special report: Top 11 Technologies of the Decade

Douglas Adams's Hitchhiker's Guide to the Galaxyseries is named after a pocketable device that contains everything worth knowing. But that seems almost quaint today, when you can carry the full contents of the Web in your pocket, as well as a telephone, a camera, a radio, a television, and a navigation system. Today's smartphones are marvels of engineering, crammed with more features than the average PC. They've become the prime driver of innovation for both software and hardware.

It took half a century to shrink the mainframe from the size of a living room to that of a suitcase. It took another decade to make it smaller than a wallet. The smartphone has swallowed and assimilated functionality from music players, remote controls, gaming consoles, even printed maps and news publications. And now that smartphones are serving as Wi-Fi hot spots, they can replace wireless routers and modems, too. Smartphones are becoming as essential as keys or a wallet, and they'll soon replace those as well.

This has some real consequences. Unlike its predecessors, the smartphone is an inherently personal device: Not only is it always on, it's always somewhere on us. Without realizing it, we've let smartphones usher us into an age of ubiquitous, pervasive computing that technologists, as well as science-fiction authors, have been dreaming about for years [PDF].

"Smartphones help users stay connected to information at any given time, any given location," says Dilip Krishnaswamy, a Qualcomm engineer and associate editor in chief of IEEE Wireless Communications. "The information is just there when you need it."

We've come to rely on such connectivity. There's no need to pack a map or directions when an app can guide you in real time, nor to consult a restaurant guide before leaving the house. In these and a thousand other ways, the smartphone, more than any other technology to have emerged in the past decade, is the one that has most changed our lives.

To be sure, back in 1973, Motorola's Martin Cooper didn't set out to build an always-connected, portable computing device. He was simply trying to shrink the car phone down to the size and weight of a luggable brick. But once the cellphone had earned a permanent place in our pockets, it became an unavoidable platform for innovation, upstaging the PC. If Starbucks wants to make it quicker and easier to pay for a cup of coffee, why not do it through the phone? If The New York Times wants to get away from paper, well, everyone's already carrying around a perfectly readable screen.

Smartphones are more than just bells and whistles—they actually change behavior. With a traditional mobile phone, users spend most of their time making calls and sending text messages. On a smartphone, basic communication takes a back seat to Internet browsing, e-mail, entertainment, and games. This difference is due to three key ingredients, each of which has seen tremendous advances in the last decade: hardware, software, and network infrastructure.

The hardware is the most obvious. Thanks to high-resolution displays with touch screens or QWERTY keyboards and tiny camera lenses on the outside and gigahertz processors, radio antennas, and image sensors on the inside, the phones hardly resemble their modest predecessors.

But at least as important is the software. "The operating system is the foundation for everything else in a smartphone," says Donna Dubinsky, a cofounder of Palm, the company that first succeeded in cramming computer functionality into a pocketable device. Every major smartphone operating system now supports third-party applications that extend the phone's capabilities far beyond what any one manufacturer can do.

And in addition to using the resources of the phone itself, these apps can off-load data storage and processing to the cloud [see "It's Always Sunny in the Cloud"] in the form of server farms around the world, thanks to ever increasing wireless bandwidth—the third key development behind the smartphone. "People naturally want to focus on the device itself," says Dubinsky, "but what's important is the complete system, including hardware, software, and application development environment."

Current smartphones quietly shift between Wi-Fi and 3G so that users are always connected to the best available network. Remember that the iPhone, still less than four years old, didn't even access 3G networks when it launched. By October of last year, you could get a 3G signal at the top of Mount Everest, and now the first 4G networks are emerging.

Today we're seeing only hints of how a smartphone world will be different. With their numerous sensors, they will form nodes in a vast and unprecedented data collection network. Researchers have already used phones' accelerometers to follow basic health indicators (such as a patient's gait), their GPS to monitor crowd and pedestrian traffic patterns, and their microphones to track bird migrations. Several app developers have created the first useful examples of augmented reality—letting you point your phone at a restaurant and see a bunch of customer reviews, for example.

These capabilities come with strings attached, notably the addictive effects of always-on connectivity. BlackBerries are rightly nicknamed "CrackBerries" for the way they feed a workaholic's addiction. Krishnaswamy notes that we're training ourselves to always be ready for the next e-mail or status update, and we're disappointed when one doesn't arrive. And not everyone likes it when people interrupt dinner to surf the Web to fact-check the conversation.

Some experts even worry about a new digital divide between those who can afford smartphones and data plans and those who can afford only basic mobile phones. In fact, many smartphones cost more than low-end computers, once you take away the subsidized prices that wireless carriers offer for them. Yet in rural and impoverished areas, they represent a much better investment because they're self-contained, needing neither additional network infrastructure nor even reliable power.

In any case, many high-end features will inexorably filter down to low-end phones, as they have in the camera market, and what begins as a luxury will quickly become a necessity. In 2007, sales of smartphones surpassed sales of laptops, and some predict that by 2014 more people will browse the Internet by phone than from traditional computers [PDF].

The drive to communicate on ever-wider scales has shaped many of our technological advances, and these in turn have shaped how we communicate. Moving from text messages to Twitter updates, from voice to video chat seems to be part of our evolution. "The interesting thing is how it's changing human behavior itself," says Krishnaswamy. "Smartphones will become a sixth sense for the user, gathering information from wireless sensors in the user's environment and from the network, interpreting the information, and providing valuable feedback to the user."

This article originally appeared in print as "Smartphones."

For all of IEEE Spectrum's Top 11 Technologies of the Decade, visit the special report.

A Foucault Pendulum on a Chip

A MEMS microgyroscope mimics a 19th-century instrument's mechanism to boost abilities of inertial guidance systems

Photo: Alexander Trusov/University of California, Irvine

1 February 2011—A new type of microscopic gyroscope could lead to better inertial guidance systems for missiles, better rollover protection in automobiles, and balance-restoring implants for the elderly.

Researchers from the MicroSystems Laboratory at the University of California, Irvine (UCI), described what they’re calling a Foucault pendulum on a chip at last week’s IEEE 2011 conference on microelectromechanical systems (MEMS) in Cancun, Mexico. A Foucault pendulum is a large but simple mechanism used to demonstrate Earth’s rotation. The device the UCI engineers built is a MEMS gyroscope made of silicon that is capable of directly measuring angles faster and more accurately than current MEMS-based gyroscopes.

”Historically it has been very pie-in-the-sky to do something like this,” says Andrei Shkel, professor of mechanical and aerospace engineering at UCI.

Today’s MEMS gyroscopes don’t measure angles directly. Instead, they measure angular velocity, then perform a calculation to figure out the actual angle. When something is in motion, such as a spinning missile, keeping track of its orientation requires many measurements and calculations, and each new calculation introduces more error. Shkel says his gyroscope is more accurate because it measures the angle directly and skips the calculation. ”You’re pretty much eliminating one step,” he says.

The gyroscope works on the same principle as does the Foucault’s pendulum you’d find in many museums, demonstrating Earth’s spin. The plane on which the pendulum oscillates stays in one position relative to the fixed stars in the sky, but its path over the floor gradually rotates as the world turns. Similarly, the oscillation of a mass in the gyroscope stays the same with respect to the universe at large, while the gyroscope spins around it.

Of course, the pendulum in Shkel’s two-dimensional device is not a bob on a string. Instead, four small masses of silicon a few hundred micrometers wide sit at the meeting point of two silicon springs that are at right angles to each other. A small electric current starts the mass vibrating in unison. As the gyroscope spins, the direction of the vibrational energy precesses the same way a swinging pendulum would.

The gyroscope operates with a bandwidth of 100 hertz and has a dynamic range of 450 degrees per second, meaning it detects as much as a rotation and a quarter in that time. Many conventional microgyroscopes (at least those of the ”mode matching” variety) operate at only 1 to 10 Hz and have a range of only 10 degrees per second. But inertial guidance systems—such as those that stabilize an SUV when it hits a curb or keep a rapidly spinning missile on track—require both high dynamic range and high-measurement bandwidth to accurately and quickly measure directional changes in such moving objects.

Shkel described and patented the concept for a chip-scale Foucault pendulum back in 2002, but the device’s architecture requires such precise balance among its elements that it is too hard to manufacture, even nine years later. But last week, Shkel’s colleague Alexander Trusov presented a new design, which Shkel says is more complicated in concept but easier to make, requiring standard silicon processes and only a single photolithographic mask.

But it’s just one possible design. Shkel is on leave from his academic post and currently working with the U.S. Defense Advanced Research Projects Agency (DARPA), which has launched a program to create angle-measuring gyroscopes for better inertial guidance systems. Three-dimensional designs that use concepts other than the one behind his 2-D device might be preferable for DARPA’s needs because they’ll take up less space, Shkel says. He hopes the DARPA program will also improve manufacturing processes in general, giving conventional microgyroscopes higher precision for applications that don’t require the bandwidth and dynamic range of a chip-scale Foucault pendulum.

”We will have a new class of devices,” he says, ”but we will also help existing devices.”

About the Author

Neil Savage writes about nanotech, optoelectronics, and other technology from Lowell, Mass. In the February 2011 issue he wrote about efforts to develop rechargeable lithium-air batteries.

ISSCC 2011: Silicon Gets Personal

The 1950s pacemaker: a box that patients had to wheel around on a cart and keep plugged into a wall. Clearly a problem if you wanted to go outside, or if you lost power. This morning, Tim Denison, director of neuroengineering for implant maker Medtronic, asked engineers at the 2011International Solid-State Circuits Conference (ISSCC) to remember that device as he described the ongoing challenge for electrical engineers to make medical devices tinier, more efficient, and capable of treating more ailments. Denison was the first plenary speaker Monday morning at ISSCC which began this week in San Francisco. The theme of this year's conference is "electronics for healthy living."

Denison started his talk with the tale about pacemakers' early days and Medtronics founder Earl Bakken, who invented a battery-operated wearable pacemaker, after adapting a design for a metronome circuit that he saw in a popular science magazine. The device needed manual tuning to adjust the heartbeat's frequency (it's hard to sleep or to go for a jog when your heart rate never changes) and early designs had knobs for self tuning.

Today's pacemakers, thankfully, have come a long way. Completely implantable, they have leads that go into the heart through the patient's veins, and can monitor blood temperature and patient's breathing to adjust the rate. Denison questioned what was next in the pacemaker's evolution and showed a graphic of what looked like a hybrid between a pill and a fishing lure, a future device that could be implanted completely inside of someone's heart. He said that even that device was not the smallest we might see, and that other tiny gadgets could treat a wide range of problems.

In the Sunday tutorial "Interfacing Silicon with the Human Body" that he instructed, he outlined a variety of devices that are commercially available or in development to correct stray electrical signals that mess with our nervous system. These include gadgets for treating obsessive compulsive disorder, Parkinson's disease, dystonia (he showed a video of a patient before and after for this one), depression, migraine headaches, and fecal incontinence. The number of problems isn't limited to those where engineers can detect electrical signals either, he said in the tutorial, noting that small devices can now detect chemical signals and accelerations. He gave a nod to the menagerie of MEMS devices that we've seen wheeled out recently, specifically the Foucault pendulum turned accelerometer on a chip. 

Once we have all of those mini-devices that can correct what ails us, we might need to network them--so that doctors can know of any hitches. Denison mentioned that heart problems can start days before a patient needs to be rushed to the emergency room and a networked device could inform a doctor.

That idea fit well with the talk that followed by Imec Senior VP, Jo De Boeck on wireless personal healthcare. He described a "smart patch" that one day might monitor a variety of general health stats, and specifics depending on the patient. He gave examples including devices that could determine iron levels in a pregnant woman and when a patient has swallowed his pills (a means to improve medication compliance). He noted that one important development has been the proliferation of the smartphone and also pointed to a future need for cheap plastic circuits (such as the plastic microprocessor that his company will unveil later this week). He said that he believed that such circuit design would become increasingly important, pointing to the crowd of 3000 engineers gathered before him and noting that, in the future, half of the room might be working on plastics and half silicon.

A panel discussion this evening will get into some of the details of "Body Area Networks"--including security and protocols to make sure the future's smarter implants don't interfere with one another.