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Fiber Optics Sensors for Patient Monitoring during MRI examination

posted by Rugged Monitoring on 2020-07-14

Fiber Optics Sensors for Patient Monitoring during MRI examination

Magnetic Resonance Imaging (MRI) is a medical imaging technique used to examine the anatomy and physiological processes of the body. To form the images, MRIs utilize strong magnetic fields, magnetic field gradients, and radio waves.  The MRI environment has high levels of magnetic induction density, typically in the range of 1.5 T to 3 T, systems with 9.4 T to 21 T also exist in the market. In such an environment, conventional temperature sensors like thermocouples, RTD’s or any metal sensing elements are not designed to function. The metal sensing elements distort the field distribution and thereby affect the output image quality.

Fiber optic sensors (FOS) are ideal for such a high Electro Magnetic (EM) field Radio Frequency (RF) environment as they are inherently immune to both RF and EM field. Additionally, FOS can be easily integrated to MR patient monitor to read temperature during the MRI examination. FOS are widely used in the many MRI applications and we will explore them below :


Superconductor Magnet

MRI field is generated by the superconductor magnet which consists of many coils and windings through which electricity passes, leading to the creation of a magnetic field.  The below schematic shows the placement of the coils in a typical MRI machine.  As mentioned earlier, the magnetic density is in the order 1.5 T to 3T and in some systems stronger fields in the 9.4 T to 21 T exist. To maintain such a strong field superconductivity is uses and for superconductivity to be used, the wires connecting the coils must be bathed in helium at –265 degrees C. Hence , it is crucial to monitor the temperature of the helium to prevent the wires from overheating. If the wires were to overheat, it would result in sub-optimal pictures/images. So, to monitor the temperature traditional sensors cannot be used because of the cryogenic temperatures and strong EM/RF fields. FOS probes are ideal as they have a wide temperature range, which goes from -270 to +270 C and accurate down to +/- 0.2 C

Internal schematic of MRI

Internal schematic of MRI


MRI Coils

A coil consists of one or more loops of conductive fiber looped around the core. These coils are used to create the magnetic field as well as detect a changing magnetic field by voltage induced in the wire. These coils need precise temperature monitoring because an overheating of them can cause a change in the quality of the images produced. Due to the coils being a part of the hardware for the MRI, big temperature sensors are not ideal.  FOS probes are ultrathin with diameters from 100 to 500 µm. They can be easily integrated into existing devices with no or minimum modification.

MRI coils wrapped around a patient

MRI coils wrapped around a patient


Patient Temperature Monitoring

MRI examinations take place in a narrow cylindrical tube for about 10-15 mins, which sometime may induce panic attacks or claustrophobia. Additionally, in some brain scans the patient is restrained with collars and belts to avoid any movement when inside the machine. With some high-risk patients, this may induce some undesirable anxiety or stress. Patient’s temperature increases rapidly showing signs of stress. FOS probes can be safely placed on the patient skin or nasal area to capture these temperature changes and the patient can be continuously monitored for any signs of stress. FOS inherent immunity to EM/RF fields and their bio safety makes them ideal for this application. Below picture is an example of how the FOS can be placed on the patient and the temperature readout can be obtained to monitor. 

Probe placement on a patient with readout to monitor

Probe placement on a patient with readout to monitor


Baby Incubators during MRI

Babies, especially those born prematurely cannot properly regulate their own temperature, so it is essential for a machine to be doing it for them. For many premature babies, an MRI is done to make sure that their anatomy is normal, and that proper development is occurring. For the temperatures to be monitored during the transport to the MRI and during the MRI, temperature sensors compatible with MRIs are necessary to get accurate reading. FOS probes lends itself well for this application as they are bio safe and immune to EM/ RF fields. 

 Baby Incubator station for MRI

 Baby Incubator station for MRI


Rugged Monitoring LSENS

Rugged Monitoring (RM) has extensive experience in designing custom FOS probes for MRI applications. The probes are specifically developed with fast response time ~30ms for harsh environments like MRI machines and there are several LSENS sensors already in the market used by research institutions, surgeons, and equipment manufacturers. RM is a pioneer in making custom fibers that would easily integrate into existing equipment. To learn more about LSENSB, please visit the medical solutions page. 

Source:

1. Superconductor magnet

2. MRI coils

3. Neonatal pic

4. Patient monitoring