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'Smart needle' will aid tissue characterization

MIT researchers have developed a needle embedded with microchips that could replace several of the probes now used by doctors to characterize tissues such as tumors.

The novel needle could also be less expensive than current probes and is 30 percent smaller in diameter-a fact that patients will appreciate.

The researchers led by Kenneth S. Szajda, a research affiliate of the Harvard-MIT Division of Health Sciences and Technology (HST), have built a prototype of the device that measures temperature. The ultimate goal, however, is a needle that measures a variety of parameters in addition to temperature, such as pH, oxygen concentration and radiation dosage.

The needle was originally developed for use in the hyperthermic treatment of cancer, in which heat is used to improve the effectiveness of radiation and chemotherapies. This leads to shrinkage and frequently complete elimination of solid tumors. "Characterization of the tumor environment is essential to planning and evaluating hyperthermic treatments," Dr. Szajda said. Though conventional temperature probes for this purpose "work very well," he said, "they have limitations. Our idea was to build something that would work even better." The resulting device could be used in other procedures that require tissue characterization.

In addition to Dr. Szajda, MIT investigators involved in the work are Dr. H. Frederick Bowman, director of the MIT Hyperthermia Program, who holds appointments in HST, in radiation therapy at Harvard, and in the Department of Mechanical Engineering; Dr. Charles G. Sodini, a professor in the Department of Electrical Engineering and Computer Science (EECS) and associate director of the Microsystems Technology Laboratories, and Tracy E. Adams, a graduate student in EECS and in the HST medical engineering PhD program.

Dr. Szajda came up with the idea for the needle about six years ago when he was thinking about a topic for his doctorate. Though trained as an analog circuit designer-he received his SB and SM from MIT in that area-he also had an interest in biomedical applications of circuits. He had collaborated since 1985 with Dr. Bowman on issues related to hyperthermic treatments, first through the Undergraduate Research Opportunities Program, then through research for his SM and SB theses.

"I was talking with Professor Sodini, my undergraduate advisor, who had always expressed an interest in my work with Dr. Bowman," he remembers, "and suddenly a bulb went on in my head." Why not apply microelectronics to measuring the parameters important to hyperthermic treatments?

The idea appealed to both Professor Sodini and Dr. Bowman. "I like chip-design projects with applications in a variety of areas rather than justanother faster computer," said Professor Sodini, an integrated circuitdesigner.

In the resulting prototype device, eight microchips are embedded in a channel milled down the length of the needle. Each "smart" chip not only senses temperature, but also processes and digitizes the temperature signals so they can later be read by a computer. A separate chip near the head of the needle coordinates data flow between the microchip sensors and a personal computer. The needle is attached to the computer via a flexible microribbon cable.


The most important advantage of the needle over conventional probes is its potential for measuring a variety of parameters with the same device. This is possible because of a standard architecture for the overall system, or set of physical and electrical specifications that each smart sensor must satisfy.

"Think of it as analogous to an electrical plug," Dr. Szajda said. The plug itself must meet certain specifications or it won't fit into the wall, but the electric company doesn't care what appliance the plug is attached to. Similarly, each sensor must meet certain specifications for interacting with other parts of the system, but what each sensor does within its own borders can change.

The overall result? A clinician interested in, say, the temperature and oxygen concentration of a tissue could order a needle with sensors for only those parameters. "It makes the sensing game kind of like what they call a plug-and-play system," Dr. Szajda said. "I don't need to redesign the whole system every time I need a new sensor configuration."

To date the researchers have developed and tested temperature sensors for the system, but Dr. Szajda is currently working on radiation and oxygen sensors with Thermal Technologies of Cambridge. "We decided to focus on temperature first because it's a simple measurement to make relative to others," he said.

Other advantages of the needle include its size and potential cost. The use of microelectronic technology could reduce costs because, among other things, the sensors could be mass-produced. Further, "once we've optimized the process we should be able to put together custom-configured needles in a very short time," Dr. Szajda said.


In addition to the continuing development of radiation and oxygen sensors, the researchers are also working on the next generation of the temperature-sensor microchip. Ms. Adams recently succeeded in cutting the length of each chip in half to about 4mm. This means that the researchers will be able to fit more chips on each needle, which increases the spatial resolution of the system.

The group also continues to develop software that translates signals from the chips into usable data on a computer screen. When the overall system is more complete, researchers at the Dana-Farber Cancer Institute hope to use it in ongoing hyperthermia and radiation studies. "The microsensor technology will permit investigation of the interrelationships between temperature, tissue oxygenation, pH and blood flow-parameters that influence the results of cancer therapy," Dr. Bowman said.

The work has been supported in the past by the National Cancer Institute of the National Institutes of Health, but is currently unfunded. Partly as a result, Dr. Szajda holds a position at MIT, donates time to Thermal Technologies, and also works full-time at LSI Logic in Waltham (his position there is unrelated to the needle). Nevertheless, he remains very involved in the needle project. "The ultimate reward for me," he said, "is if this ends up in the clinic helping patients."

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