More Bang for the Ouch

Doctors tracking the progress of a disease for research or treatment must often gather detailed information from inside the body. They may need, for example, to take the temperature of a malignant tumor at several spots or check the blood flow and oxygen levels in a diabetic’s limb threatened with amputation.

One way of taking these measurements is with needlelike probes. Ideally, a single probe could collect several types of information, eliminating the need for multiple instruments and, for the patient, multiple pinpricks. While only single-purpose devices have been available, a needle that has been under development by MIT researchers could someday fit the bill.

Led by Kenneth S. Szajda, a research affiliate in the Harvard-MIT Division of Health Sciences and Technology, the MIT team has been developing a prototype device over the last six years. The designers-including H. Frederick Bowman, who heads the MIT Cancer Hyperthermia Program and is a lecturer in radiation therapy at Harvard Medical School, and Charles G. Sodini, a professor of electrical engineering and computer science at MIT-have so far outfitted their instrument only with multiple temperature sensors, the first kind of sensor they have created. But the probe should be able to handle different kinds of measurements at the same time because it can work with any sensor that fits its electronic specifications.

Along the length of the probe runs a thread-sized groove in which eight microchips lie tightly packed. Each chip in the prototype both senses the temperature at its location and processes the information into a form a computer can read and analyze. A ninth chip near the end of the needle opposite the tip coordinates the information flow to a personal computer, which is linked to the probe by a flexible cable.

According to Szajda, the linkage between sensor and processing electronics in each chip practically eliminates electrical noise that could otherwise corrupt sensors’ signals. And the probe’s diameter is 30 percent smaller than that of conventional probes, which translates into less pain for patients.

Monitoring Cancer Treatment

Szajda came up with the idea of an electronic, multipurpose medical probe while doing undergraduate and graduate research with Bowman. The original idea was to create a tool to monitor a cancer treatment that uses heat to boost the effectiveness of radiation and chemotherapy. In this therapy, as heat is applied, blood rushes to the tissue to cool it down. The rush of blood brings additional oxygen, which is thought to enhance the anti-cancer action of the toxic agents. To understand how best to take advantage of these effects, researchers need information concerning several questions, Bowman explains. The probe could provide the answers.

For instance, he says, “For any given temperature rise, how much will the blood flow increase? How long will that increase in blood flow persist after you’re no longer heating?” A tool that measures both blood flow and temperature at the same time could tell clinicians whether blood flow-and therefore oxygen level-remains elevated long enough to allow them to, say, do the heating in one room, then move the patient to another room for radiation treatment.

Bowman sees a host of other medical uses for the multipurpose needle as well. Organ transplants, for example, sometimes fail because blood vessels are not properly reconnected or the connection becomes blocked, cutting off the flow of blood to the new organ. A device that tracks blood flow could help transplant teams correct any such problem. In this case, the probe’s advantage is not its potential use with different sensors but with multiple sensors of one kind. The more sensors on the device, the more accurate the picture of blood flow to the organ.

Hoping to privately commercialize some of his work, Szajda is now independently designing electronic oxygen and radiation sensors for his probe, as well as evaluating the development of a blood-flow sensor. The challenges involved with these tasks are mostly mechanical, focusing, he says, on “how to build the structure you need and at the same time not disrupt the circuitry.”

An instrument that can measure both oxygen levels and blood flow might help diagnose conditions such as angina-severe chest pain that occurs when the heart is starved for oxygen because of insufficient blood flow. And in connection with cancer treatment, a probe including a radiation sensor would let researchers measure how much radiation is delivered to a tumor at a given time, as well as the total amount of radiation received. No technique is “available right now to make a direct measurement of that sort,” says David Gladstone, chief of clinical physics in radiation oncology at Dartmouth Hitchcock Medical Center in Hanover, N.H. Moreover, if a dose of radiation failed to kill as many tumor cells as expected, a multisensor probe could help researchers understand whether inadequate blood flow or oxygen supply were to blame. Then doctors could manipulate blood flow and oxygen levels before delivering further doses of radiation. Szajda’s probe, says Gladstone, would determine what’s happening inside a tumor in a way that nothing does today.