Boston Hospital Uses Ultrasound to Track Patients

By Evan Schuman  |  Posted 2006-03-11

Boston Hospital Uses Ultrasound to Track Patients

When Brigham and Womens Hospital in Boston needed to find a better way to track emergency room patients, they wanted to use RFID. But they ran into a wall. Literally.

It seems that the radio frequency approach was able to triangulate the position of patients by distance, but not by room. It wouldnt recognize walls so it couldnt identify rooms.

Working with a grant from the National Library of Medicine, hospital officials started experimenting with a technology their maternity wards were already quite familiar with: ultrasound.

A modified version of the same technology that lets first-trimester parents see their yet-to-be-born baby is being used to address the hospitals need for a patient-tracking system.

That need was initially envisioned for catastrophic situations—a Katrina-level natural disaster or a 9/11-level terrorist attack—where a hospital would quickly get flooded with patients on little notice.

As patients are moved from waiting rooms to various triage centers to makeshift patient rooms and operating rooms, its easy for a hectic hospital to lose track of some.

But Dr. Tom Stair, an attending physician in Brigham and Womens emergency department and one of the physicians in charge of the patient-tracking project (called SMART, standing for Scalable Medical Alert and Response Technology), quickly concluded that such capabilities need not be limited to large-scale disasters.

"This happens on a smaller scale almost every afternoon," he said, pointing out that the hospitals emergency room has space for 44 patients. "Almost every single day, we go beyond that and start losing medical records and losing track of patients."

For practical business issues, giving the emergency room more space is not a likely option. The emergency room "doesnt generate that much money for the hospital, so they dont want us to grow that much," Stair said.

The need for creative approaches for tracking patients quickly is exacerbated by the realities of 21st century hospital management.

"The surge capacity that used to be here [in Boston] is gone," Stair said. "There used to be lots of empty hospital beds sitting around" but hospital closings have changed much of that.

"In the interest of economy, we have made it all go away."

Indeed, for potential emergencies, Stairs team has been looking at those closed hospitals as emergency overflow locations.

The hospitals experimental system consists of a small fannypack with a Hewlett-Packard iPAQ handheld running Linux. Four cables come out of the pack and are attached to the patient: three are glued to the patients chest and one is clipped to the finger.

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This allows the hospital to both monitor the patients exact location—using a tracking device that Stair describes as looking like "a fat ballpoint pen"—as well as watch some vital signs, specifically cardiac rhythm and oxygen saturation.

The systems intent is to start tracking patient location and condition immediately at the site of the emergency and continue ambulance transportation, triage and movement through multiple medical sites and eventually between rooms at the final facility.

SMART, which is a collaboration between Brigham, the neighboring Harvard Medical School and the Massachusetts Institute of Technology, coordinates all of that data and shares it across an 802.11b wireless network to the network server.

Other iPAQs are used by hospital staff to monitor the results from the patient devices. "The PDA screen for the caregivers, it looks like a spreadsheet" and allows personnel to zoom in on any patient.

When medical readings go beyond set limits, "it shows a color change and the thing will buzz and vibrate," Stair said. "When somebody develops an abnormal heart rhythm, theres going to be an alarm."

Next Page: Ultrasound versus RFID.

Ultrasound Versus RFID

But the most challenging part was finding a way for precise patient location. "Most people use RFID for tracking like this, but ultrasound is very sensitive to walls, which is important for us," Stair said.

"If you use a radio-frequency transmitter and then a bunch of detectors that triangulate where something is, you can detect [the patient] a floor above or below. It cant detect if youre on one side of the wall."

The tracking device that Brigham is using comes from a Norway company called Sonitor Technologies.

The system places specially-designed microphone detectors throughout rooms and hallways, said Sonitor CEO Terry Aasen. The detectors can detect and identify patient signals from a distance of 100 feet.

The signals is at a frequency too high to be heard by humans and is similar to the sonar system used by bats. The signals use MFSK (Multiple Frequency Shift Keying) to differentiate the sounds emitted to identify different patients.

The shorter the distance, the more precise the system will be, Aasen said, but 100 feet is a safe distance. "At that length, youre depending on echos and other things in the room," he said.

The system can detect whether there is even slight movement from a patient and it responds by sending out a tone that is detected by the nearest microphone.

"Within the tag, there is an extremely sensitive motion detector. Movement wakes up the item," Aasen said.

Brigham has been testing the system on "healthy volunteers" for about three months with ten of the kits, Stair said.

"Right now, we only have [tracking] beacons halfway around the lobby. We can tell if they went to the coffee shop," he said.

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Stair said it was difficult to project the eventual cost of such a system when deployed. Initial costs include about $800 for each iPAQ (one stays with the patient while others are used by staff to see the monitoring results), $10 for each lead, $30 for each position sensor and about $60 for each of five Wi-Fi access points.

"But the cost of putting it all together and creating the homegrown software, that I cant calculate," Stair said, but added that the grant-funded three years of development cost "about a million dollars. Theres a lot of engineering time and a lot of expensive professionals."

The ER physician said he saw a particularly effective use for the SMART system when he volunteered in New Orleans to help with Katrina emergency medical care.

"They turned the basketball arena at LSU [Louisiana State University] into a field hospital. There were stretchers set all around," he said. The potential of losing track of the many patients flowing in and out of that makeshift medical center was huge, he said.

Retail Center Editor Evan Schuman can be reached at

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