Summary
Fiber optic sensors have become the key technology driving the latest feature suite upgrades for MRI and the design of new MRI equipment. In this article, we present three MRI-based motion control applications, demonstrating the operation and use of a recently developed, commercially available MRI-based safety fiber optic feedback sensor.
case study
- Case Study #1 MRI-Safe Patient Footrest System Used to Validate MRI Technology
Functional magnetic resonance imaging (fMRI) is a technology based on brain blood flow and oxygen metabolism imaging, using magnetic resonance imaging to observe brain function. One area of fMRI research is the study of brain damage caused by injury or stroke and the subsequent evaluation of the effectiveness of various therapeutic and rehabilitation techniques. Marquette University designed a footrest device for fMRI patients, as shown in Figure 4A. Using MICRONOR MR318 fiber optic incremental encoder outputs to monitor pedal velocity and angular position, the experiments successfully correlated locomotor activity with corresponding observed cortical brain activity. Some of the results are shown in Figure 4B, which depicts functional images correlating three motor activities (pedaling, light footing, and finger tapping) with specific cortical active regions in the brain. This initial study is the first to accurately record pedaling-related human brain activity and correlate it with fMRI imaging.
- Case Study #2 MRI Safety Device for Studying Traumatic Brain Injury (TBI) Mechanics
Military and civilian scientists are collaborating with the Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc. (HJF) through the National Institutes of Health A funding award to study the mechanisms of traumatic brain injury. As shown in Figure 5, the MRI safety device applies a slight angular acceleration to the skull of a human volunteer within the MRI scanner. During the experiments, an MRI-compatible fiber optic absolute position sensor was used to measure angular position as well as capture instantaneous velocity and acceleration. As shown in Figure 6, this data is then correlated in real-time with the MRI imaging. The simulated traumatic event occurred within approximately 400 ms. The sensor system controller provides hardware functionality to output real-time trigger signals to synchronize MRI imaging with head position within 0.04°. The fiber optic sensor has a high resolution of 8192 and a fast update rate of 850µs, and can record 500 data points for an event. With this amount of fine-grained data, the research team was able to extract velocity and acceleration information from the recorded data.
- Case Study #3 MRI-Safe Treadmill for Advanced Cardiac Stress Testing
Heart disease is the leading cause of death in the United States. EXCMR, Inc. has developed an MRI safe treadmill for advanced cardiac stress testing and cardiac imaging. MRI cardiac imaging offers imaging assessment and patient safety superior to conventional nuclear or ultrasound techniques. By placing the treadmill in the MRI suite, EXCMR enables imaging of the heart immediately after exercise (within 30 seconds) before stress-induced cardiac abnormalities disappear. If the treadmill is located far from the imaging system, these images cannot be acquired quickly enough. The MRI-safe treadmill is shown in Figure 7. It operates in close proximity to the MRI scanner (Zone 4) and can use certain approved metallic materials. However, active electronic devices are not permitted. The motors that run the treadmill belt are hydraulically driven, and all feedback sensors must be electronically passive. Patient Emergency Stop (MR380), Treadmill Incline (MR340) and Speed (MR382) are specially designed MRI safety sensors based on Micronor Incorporated's commercial fiber optic sensors. Three fiber optic sensors are connected to an integrated controller located in the monitoring room (Zone 3) via a 50-foot six-core fiber optic cable.
in conclusion
In conclusion, fiber optic sensor technology is a key enabler in the development of MRI-safe motion control systems required for advanced medical research . Fiber optic sensors are passive in nature and are not affected by magnetic fields . Fiber optics provide an ideal all-dielectric transmission medium between the MRI scanner (Zone 4) and the MRI control/equipment room (Zone 3) . Made of suitable materials, MRI-safe fiber optic sensors provide electromagnetic transparency for safe use in and around the extreme electromagnetic field strength range of MRI scanners . They are robust, easy to install , and do not produce artifacts or affect imaging results even when used inside MRI bores .
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