Vibration Analysis of MRI Scanner Mounting Points in a Semi-Trailer

JMP Medical is the manufacturer of high-end specialized mobile and relocatable medical units. It supplies worldwide healthcare providers by offering relocatable MRI/CT buildings, mobile X-ray and mammography trucks, mobile primary care units, and modular labs.

The advantages of such mobile medical solutions are to:

• bypass space shortage,

• improve patient throughput,

• create the possibility to offer local MRI/CT healthcare service,

• avoid healthcare service disruptions during facility renovation or system replacement,

• reach patients located distantly, and

• place auxiliary CT Scanner Unit dedicated to a distinct group of patients (e.g., infected).

The mobile MRI laboratory

JMP Medical’s R&D department is constantly testing and researching in response to market needs. This project is co-financed by the European Union from the European Regional Development Fund under the Intelligent Development Program. It is implemented as part of a competition of the National Center for Research and Development.

The product of the project will be an innovative magnetic resonance imaging laboratory on a semi-trailer. It aims to provide the possibility of temporary MRI examinations in a healthcare facility and to constitute a fully mobile diagnostic laboratory. The first trailer is in production and the prototype will be tested later this year. The MRI trailer will meet all the requirements for 1.5T MRI laboratories to ensure the highest standard of safety and quality of imaging.

Research and development works will be carried out in 4 stages. When implemented the project will ensure the possibility of performing magnetic resonance imaging at healthcare facilities where the installation of a stationary laboratory is impossible due to limitations in space, lack of adequate load-bearing capacity of ceilings, etc.

MRI noise and vibration

MRI scanners use powerful magnetic fields, magnetic field gradients, radio waves, and computers to generate images of internal human organs. The scanners employ fast switching of currents in the gradient coils to enhance the imaging quality and shorten scanning time. This, however, generates vibration and noise excited by the electromagnetic forces in the gradient coil.

Once the MRI is installed in a building or, as in this case, a trailer, vibration and noise are introduced due to several reasons:

• the structural properties of the location of the machinery mounts, 

• dynamic properties of the supporting structure, 

• the presence of other machinery, 

• etc.

The MRI noise is propagated through the structure and the air. It may excite other installations, such as heating, ventilation, and air conditioning (HVAC), to induce more noise, and affect other sensitive equipment. Vibration and noise isolation becomes even more challenging when the structure housing the MRI is not designed for it. 

Since the MRI scanners weigh up to thousands of kilograms, structural reinforcement of the floor supporting the MRI may be necessary. This reinforcement may introduce additional transmission paths for the vibration. And the vibration may then further propagate to new parts of the structure. 

In short, to prevent any annoyance and unwanted effects on performance a careful study of the MRI noise and vibration properties and the transfer paths is needed. Proper measures are taken accordingly.

ENVIBRA – a Dewesoft partner – is located in Poznan. They specialize in industrial testing machinery and equipment for the simulation, recording, and analysis of dynamic signals. The group of experienced engineers provides the Polish market with devices such as:

• vibration analysis systems, 

• motion simulators, 

• vibration and pressure sensors, 

• laser vibrometers, 

• signal recorders and analyzers,

• and dedicated test stands.

Measurement setup

Data Acquisition Hardware

• SIRIUSi 6xACC, 2xACC data acquisition system with DualCoreADC technology

• SIRIUSi Custom data acquisition system with DualCoreADC technology

• SIRIUS SBOX processing computer with built-in 10Hz GPS/GNSS receiver

• Single- and triaxial MEMS and piezoelectric (IEPE) accelerometers

• 10Hz GPS/GNSS receiver

• Non-contact, laser displacement sensor, temperature and humidity sensors

The Dewesoft SIRIUS high-dynamic USB and EtherCAT data acquisition slices offer a wide range of configuration possibilities. The SIRIUS DAQs can easily be daisy-chained to extend channel count.

The ultra-rugged SBOX computer and data logger works in tandem with the modular SIRIUS data acquisition systems. It will add SSD data logging and real-time data processing capabilities.

Data acquisition and analysis software

• DewesoftX data acquisition software (version X3 SP9)

• DewesoftX FFT analysis option

The DewesoftX data acquisition software suite offers advanced data recording, signal processing, data analysis, data visualization, and reporting features. 

The Dewesoft FFT analyzer (Fast Fourier transformation) option shows the frequency components of acquired signals in amplitude and frequency. The FFT analyzer in Dewesoft has advanced cursor functions, high freely selectable line resolution, flexible averaging as well as advanced functions for in-depth analysis.

Measurements

The purpose of the test was to perform a vibration analysis at the resonance attachment points on the floor inside the trailer. The aim is to check with the MRI manufacturer’s limits and to confirm simulation models experimentally.

Acceleration was measured during the test ride on a local road as well as in the parking position with the ignition on. Additional parameters were recorded thanks to the flexibility of the SIRIUS units.

Dewesoft SIRIUS signal analyzers with DualCoreADC technology offer excellent dynamic range (up to 160dB) and were used to perform the tests. The signal was recorded with a sampling frequency of 10kHz per channel.

SIRIUS devices offer amazing flexibility to select from many available amplifiers which allow for connecting different transducers. The measurements were made by mounting the accelerometers at two attachment points on both sides of the MRI device.  

A measuring system with the necessary cabling has been mounted at the rear of the semi-trailer. During the test, other signals were recorded: 

• GPS position of the truck

• Acceleration on the trailer axle

• Displacement (road profile) using a laser sensor

All measurements were synchronized over time.

According to the manufacturer’s requirements, recorded acceleration signals were filtered with a bandpass filter. We have shown a relationship between the truck’s velocity vs. time presenting the speed below and above 50km/h with a different colour.

Using the Math module the functionality of DewesoftX software we could add more information to the graph with all events for which the acceleration threshold was exceeded. This easily permitted the conclusion that for lower speeds the acceleration levels were within the manufacturer’s limits.

Additionally, recorded data such as the road profile allowed us to eliminate errors related to road unevenness. Furthermore, we researched the truck staying in the parking position. 

Conclusion

DewesoftX software allowed for fast processing and filtering of the sampled data. Road profile recorded with laser displacement sensor and GNSS data gave an additional input and allowed deeper data analysis and visualization.

The versatility of the proposed measurement solution combined with an intuitive software interface were key factors in the customer’s decision process.

Reference

• Khan, Imran: MRI Scanner’s Vibration Isolation: Experimental Measurements, Analysis Techniques, and Analytical Models, January 31, 2017

More information:

Vibration AnalysisVibration Analysis and Vibration Testing Solutions