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Scientists develop new technologies for Blast Pressure Sensors and protection from traumatic brain injury

Some 1 million people suffer traumatic brain injuries annually. Concussion can cause inner ear damage that can cause dizziness, anxiety, depression, moodiness, balance problems and irritability, said Elizabeth Kirkpatrick, the physical therapist for the Fort Drum Traumatic Brain Injury Clinic. The three different forms of TBI—severe, moderate, and mild—all manifest in different ways ranging from memory loss and extended unconsciousness to a simple headache. Mild TBI tends to go unnoticed. In the most severe cases, internal bleeding increases pressure on the brain, which chokes off blood circulation and can be debilitating or fatal. The cost of treating traumatic brain injury (TBI) is estimated to run into billions of dollars in the future.


To date, the majority of research targeted at understanding and mitigating TBI has focused on impact (blunt trauma), where the duration and magnitude of the acceleration imparted by the impact are typically used to predict damage. However, in some environments, blasts can be a significant contributor to TBI. Recent research has shown that multiple exposures to explosions, even from a safe distance from flying shrapnel, may damage the brain.


One blast may not cause effects like memory loss or slurred speech, the telltale signs of brain trauma, and, especially while in theatre, there’s really no easy way to diagnose the condition, says Alex Balbir, director of Warrior Care Network and Independence Services at the Wounded Warriors Project.


Now, researchers are working on advancing new technology that can accurately measure blast strength, and whether or not it causes an mTBI. New understanding of how blast can contribute to brain trauma provides a pathway for improving helmet systems and other protective equipment, and designing vehicles or structures to enhance the protection of their occupants from blast. Better designs for protective equipment and vehicles would result in fewer casualties from TBI, improved operational effectiveness, and reduced costs associated with veterans’ treatment. There is also the potential to provide criteria, or even sensing devices, for identifying when blast victims might require immediate medical intervention, independent of what they self-report, and therefore save lives.


A group of U.S. Navy scientists have created a new and improved way to detect traumatic brain injuries. The sensor, which uses a specialized crystal and amplifier in order to measure the high-frequency energies of a strong blast, can be easily mounted to a helmet or body armor, making it perfect for military or potential athletic applications.


By combining electrical impedance sensing with a conventional pressure sensor, Dartmouth College engineer Ryan Halter is creating an early warning system that may help doctors treat traumatic brain injuries before they permanently damage the brain.

Predicting blast loads

Using LLNL modeling methods a new mechanism was discovered that may contribute significantly to the generation of blast-induced traumatic brain injury. Current protection systems, e.g., helmets, are designed primarily to protect against various forms of debris and shrapnel, not blast. Leveraging LLNL modeling methods and understanding of this new mechanism could contribute to the design of protective equipment that better protects against blast without sacrificing its effectiveness against other threats.


LLNL’s high fidelity hydrocode is capable of predicting blast loads and directly coupling those loads to structures to predict a mechanical response. By combining this code and our expertise in modeling blast-structure interaction and damage, along with our access to experimental data and testing facilities, we can contribute to the design of protective equipment that can better mitigate the biological effects of blast.


LLNL has investigated two types of sensors to quantify the blast environment, which will help medical personnel diagnose the severity of injuries and triage patients. Both sensor designs are small and lightweight. One new sensor uses a tiny microelectromechanical gauge and the other is an inexpensive, disposable, and easily replaceable plastic cylinder. Each sensor contains a paper that changes color when exposed to specific levels of pressure.


Navy scientists develop state-of-the-art sensor for detecting blast-injured brains

The cutting-edge technology, a very small but highly sensitive blast sensor, can operate at extremely high frequencies, allowing it to measure rapid changes in force and therefore predict and analyze traumatic forces more accurately than current tools.


The Navy filed for a patent the technology in April, listing Drs. Peter Finkel and Margo Staruch of the Naval Research Laboratory’s Materials Science & Technology Division, and Dr. Timothy Bentley, an expert in traumatic brain injuries at the Office of Naval Research as the inventors.


“With exposure of an individual to a blast event, mild traumatic brain injury (mTBI) may occur that can cause lasting damage and that poses a greater threat if the individual is exposed to a second event shortly thereafter,” the scientists wrote in the application. “To correlate the motion of the head to any potential injury…it is desirable to measure the acceleration of the head as well as the profile of the blast wave.”


There is a strong need, they concluded, for an “improved blast sensor” to measure these types of waves and potentially better and more quickly diagnose brain injury in the field.


Current Department of Defense rules requires everyone within 165 feet of an explosion to “stand down” for 24 hours and undergo a mandatory medical checkup. According to Bentley, this approach presents two major challenges. Some forward operating bases are only 300 or so feet across, so half of the personnel would need to stand down after an explosion. Furthermore, 24 hours isn’t enough time for a regular medical exam to detect signs of even mild TBI.


However, using the blast-proof, coin-sized sensors field doctors can, with help from a special algorithm to convert data into a “go or no-go” injury threshold, almost immediately determine if exposed warfighters can stay in the fight, or need a TBI-focused medical exam.


The Navy built prototype sensors uses PMN-PT Piezoelectric Single Crystals purchased from CTG Advanced Materials. The primary component of the pressure sensor is an aluminum cylinder with two windows allowing for positioning of the crystal and to allow for wiring. The center of the cylinder has been bored out to hold the active piezoelectric crystal and other components. The crystal is positioned between two ceramic cylinders that have a layer of tape on the side in contact for the crystal for additional compliance and electrical insulation. A strain transfer rod is directly connected to a diaphragm to convert a pressure wave (e.g., a blast wave) into a force on the piezo crystal.


Early Warning System May Prevent Brain Damage

In healthy adults, intracranial pressure never rises above 20 millimeters of mercury. If it does, doctors must intervene. Since patients with severe traumatic brain injuries are prone to internal bleeding, clinicians must monitor pressure inside their skull.


Current procedures call for neurosurgeons to drill a small hole into the skull and insert an intercranial pressure sensor directly into the brain tissue. If the brain starts to leak blood, it swells and causes pressure inside the skull to rise. The sensor alerts physicians, who try to reduce the swelling with either medication or a decompressive craniectomy, removing a section of the skull so the brain has room to expand, Halter said.


Pressure inside the skull can spike very quickly. The brain contains a reserve space that resembles an empty balloon. Just as water enters an empty balloon without increasing pressure, blood seeps into the empty space without any resistance. But once the balloon—or brain—has filled that space, the addition of any more fluid boosts pressure immediately.


It can happen at any time. Physicians typically scan patients with severe traumatic brain injuries using computed tomography (CT) to image the brain. Yet injuries often evolve after the scan, worsening or developing new hemorrhages that then go undetected.


When intercranial pressure rises above 20 mmHg, patients have much poorer outcomes. If it reaches 40 mmHg, they usually suffer permanent neurological damage. Halter’s invention seeks to monitor how blood fills the space around the brain before it fills up and pressure spikes. In animal trials, he does this by using scalp electrodes and a conventional intracranial pressure sensor with an electrode attached to it to map changes in impedance linked to the amount of blood in the cranium. Halter’s invention seeks to monitor how blood fills the space around the brain before it fills up and pressure spikes


Halter places eight electrodes, similar to those used for electrocardiograms, around the skull at 12 o’clock, 3 o’clock, 6 o’clock, and 9 o’clock and the four points halfway between them. He then injects small, imperceptible currents between two electrodes at a time.


He then measures the voltage between the two electrodes. This is directly related to the impedance of the brain tissue and blood between them, Halter says. This enables him to determine whether blood is leaking into the cranium earlier than using a pressure monitor alone. Impedance sensors also indicate where the buildup is occurring.


Halter’s system also takes advantage of the conventional intracranial pressure sensor placed within the brain. He couples the sensor’s catheter to a very thin electrode that is similar to FDA-approved electrodes for deep brain stimulation and monitoring.


The combined sensor monitors both pressure and impedance within the brain. This is more difficult than it appears, since, in a healthy brain, small cyclic changes in intercranial pressure and voltage occur during each heartbeat. “Ordinarily, when blood is pumped into the [healthy] brain during each heartbeat, you get a small change in fluid volume in the brain,” Halter said. In this case, the correlation between pressure and voltage is low, and there is less chance of an injury.


“When you have a large injury, small changes in volume lead to very large changes in pressure,” he says. This increases the correlation between pressure and voltage, indicating a likely problem. Together, the brain and scalp electrodes provide a system for continuous monitoring before bleeding causes additional damage.




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